TY - JOUR AB - The plant hormone auxin is a key regulator of plant growth and development. Auxin levels are sensed and interpreted by distinct receptor systems that activate a broad range of cellular responses. The Auxin-Binding Protein1 (ABP1) that has been identified based on its ability to bind auxin with high affinity is a prime candidate for the extracellular receptor responsible for mediating a range of auxin effects, in particular, the fast non-transcriptional ones. Contradictory genetic studies suggested prominent or no importance of ABP1 in many developmental processes. However, how crucial the role of auxin binding to ABP1 is for its functions has not been addressed. Here, we show that the auxin-binding pocket of ABP1 is essential for its gain-of-function cellular and developmental roles. In total, 16 different abp1 mutants were prepared that possessed substitutions in the metal core or in the hydrophobic amino acids of the auxin-binding pocket as well as neutral mutations. Their analysis revealed that an intact auxin-binding pocket is a prerequisite for ABP1 to activate downstream components of the ABP1 signalling pathway, such as Rho of Plants (ROPs) and to mediate the clathrin association with membranes for endocytosis regulation. In planta analyses demonstrated the importance of the auxin binding pocket for all known ABP1-mediated postembryonic developmental processes, including morphology of leaf epidermal cells, root growth and root meristem activity, and vascular tissue differentiation. Taken together, these findings suggest that auxin binding to ABP1 is central to its function, supporting the role of ABP1 as auxin receptor. AU - Grones, Peter AU - Chen, Xu AU - Simon, Sibu AU - Kaufmann, Walter AU - De Rycke, Riet AU - Nodzyński, Tomasz AU - Zažímalová, Eva AU - Friml, Jirí ID - 1562 IS - 16 JF - Journal of Experimental Botany TI - Auxin-binding pocket of ABP1 is crucial for its gain-of-function cellular and developmental roles VL - 66 ER - TY - JOUR AB - Multiple plant developmental processes, such as lateral root development, depend on auxin distribution patterns that are in part generated by the PIN-formed family of auxin-efflux transporters. Here we propose that AUXIN RESPONSE FACTOR7 (ARF7) and the ARF7-regulated FOUR LIPS/MYB124 (FLP) transcription factors jointly form a coherent feed-forward motif that mediates the auxin-responsive PIN3 transcription in planta to steer the early steps of lateral root formation. This regulatory mechanism might endow the PIN3 circuitry with a temporal 'memory' of auxin stimuli, potentially maintaining and enhancing the robustness of the auxin flux directionality during lateral root development. The cooperative action between canonical auxin signalling and other transcription factors might constitute a general mechanism by which transcriptional auxin-sensitivity can be regulated at a tissue-specific level. AU - Chen, Qian AU - Liu, Yang AU - Maere, Steven AU - Lee, Eunkyoung AU - Van Isterdael, Gert AU - Xie, Zidian AU - Xuan, Wei AU - Lucas, Jessica AU - Vassileva, Valya AU - Kitakura, Saeko AU - Marhavy, Peter AU - Wabnik, Krzysztof T AU - Geldner, Niko AU - Benková, Eva AU - Le, Jie AU - Fukaki, Hidehiro AU - Grotewold, Erich AU - Li, Chuanyou AU - Friml, Jirí AU - Sack, Fred AU - Beeckman, Tom AU - Vanneste, Steffen ID - 1574 JF - Nature Communications TI - A coherent transcriptional feed-forward motif model for mediating auxin-sensitive PIN3 expression during lateral root development VL - 6 ER - TY - JOUR AB - Spatial regulation of the plant hormone indole-3-acetic acid (IAA, or auxin) is essential for plant development. Auxin gradient establishment is mediated by polarly localized auxin transporters, including PIN-FORMED (PIN) proteins. Their localization and abundance at the plasma membrane are tightly regulated by endomembrane machinery, especially the endocytic and recycling pathways mediated by the ADP ribosylation factor guanine nucleotide exchange factor (ARF-GEF) GNOM. We assessed the role of the early secretory pathway in establishing PIN1 polarity in Arabidopsis thaliana by pharmacological and genetic approaches. We identified the compound endosidin 8 (ES8), which selectively interferes with PIN1 basal polarity without altering the polarity of apical proteins. ES8 alters the auxin distribution pattern in the root and induces a strong developmental phenotype, including reduced root length. The ARF-GEF- defective mutants gnom-like 1 ( gnl1-1) and gnom ( van7) are significantly resistant to ES8. The compound does not affect recycling or vacuolar trafficking of PIN1 but leads to its intracellular accumulation, resulting in loss of PIN1 basal polarity at the plasma membrane. Our data confirm a role for GNOM in endoplasmic reticulum (ER) - Golgi trafficking and reveal that a GNL1/GNOM-mediated early secretory pathway selectively regulates PIN1 basal polarity establishment in a manner essential for normal plant development. AU - Doyle, Siamsa AU - Haegera, Ash AU - Vain, Thomas AU - Rigala, Adeline AU - Viotti, Corrado AU - Łangowskaa, Małgorzata AU - Maa, Qian AU - Friml, Jirí AU - Raikhel, Natasha AU - Hickse, Glenn AU - Robert, Stéphanie ID - 1569 IS - 7 JF - PNAS TI - An early secretory pathway mediated by gnom-like 1 and gnom is essential for basal polarity establishment in Arabidopsis thaliana VL - 112 ER - TY - JOUR AB - Auxin and cytokinin are key endogenous regulators of plant development. Although cytokinin-mediated modulation of auxin distribution is a developmentally crucial hormonal interaction, its molecular basis is largely unknown. Here we show a direct regulatory link between cytokinin signalling and the auxin transport machinery uncovering a mechanistic framework for cytokinin-auxin cross-talk. We show that the CYTOKININ RESPONSE FACTORS (CRFs), transcription factors downstream of cytokinin perception, transcriptionally control genes encoding PIN-FORMED (PIN) auxin transporters at a specific PIN CYTOKININ RESPONSE ELEMENT (PCRE) domain. Removal of this cis-regulatory element effectively uncouples PIN transcription from the CRF-mediated cytokinin regulation and attenuates plant cytokinin sensitivity. We propose that CRFs represent a missing cross-talk component that fine-tunes auxin transport capacity downstream of cytokinin signalling to control plant development. AU - Šimášková, Mária AU - O'Brien, José AU - Khan-Djamei, Mamoona AU - Van Noorden, Giel AU - Ötvös, Krisztina AU - Vieten, Anne AU - De Clercq, Inge AU - Van Haperen, Johanna AU - Cuesta, Candela AU - Hoyerová, Klára AU - Vanneste, Steffen AU - Marhavy, Peter AU - Wabnik, Krzysztof T AU - Van Breusegem, Frank AU - Nowack, Moritz AU - Murphy, Angus AU - Friml, Jiřĺ AU - Weijers, Dolf AU - Beeckman, Tom AU - Benková, Eva ID - 1640 JF - Nature Communications TI - Cytokinin response factors regulate PIN-FORMED auxin transporters VL - 6 ER - TY - JOUR AB - The sessile life style of plants creates the need to deal with an often adverse environment, in which water availability can change on a daily basis, challenging the cellular physiology and integrity. Changes in osmotic conditions disrupt the equilibrium of the plasma membrane: hypoosmotic conditions increase and hyperosmotic environment decrease the cell volume. Here, we show that short-term extracellular osmotic treatments are closely followed by a shift in the balance between endocytosis and exocytosis in root meristem cells. Acute hyperosmotic treatments (ionic and nonionic) enhance clathrin-mediated endocytosis simultaneously attenuating exocytosis, whereas hypoosmotic treatments have the opposite effects. In addition to clathrin recruitment to the plasma membrane, components of early endocytic trafficking are essential during hyperosmotic stress responses. Consequently, growth of seedlings defective in elements of clathrin or early endocytic machinery is more sensitive to hyperosmotic treatments. We also found that the endocytotic response to a change of osmotic status in the environment is dominant over the presumably evolutionary more recent regulatory effect of plant hormones, such as auxin. These results imply that osmotic perturbation influences the balance between endocytosis and exocytosis acting through clathrin-mediated endocytosis. We propose that tension on the plasma membrane determines the addition or removal of membranes at the cell surface, thus preserving cell integrity. AU - Zwiewka, Marta AU - Nodzyński, Tomasz AU - Robert, Stéphanie AU - Vanneste, Steffen AU - Friml, Jiřĺ ID - 1819 IS - 8 JF - Molecular Plant TI - Osmotic stress modulates the balance between exocytosis and clathrin mediated endocytosis in Arabidopsis thaliana VL - 8 ER - TY - JOUR AB - Cell polarity is a fundamental property of pro- and eukaryotic cells. It is necessary for coordination of cell division, cell morphogenesis and signaling processes. How polarity is generated and maintained is a complex issue governed by interconnected feed-back regulations between small GTPase signaling and membrane tension-based signaling that controls membrane trafficking, and cytoskeleton organization and dynamics. Here, we will review the potential role for calcium as a crucial signal that connects and coordinates the respective processes during polarization processes in plants. This article is part of a Special Issue entitled: 13th European Symposium on Calcium. AU - Himschoot, Ellie AU - Beeckman, Tom AU - Friml, Jiřĺ AU - Vanneste, Steffen ID - 1849 IS - 9 JF - Biochimica et Biophysica Acta - Molecular Cell Research TI - Calcium is an organizer of cell polarity in plants VL - 1853 ER - TY - JOUR AU - Grones, Peter AU - Friml, Jiřĺ ID - 1847 IS - 3 JF - Molecular Plant TI - ABP1: Finally docking VL - 8 ER - TY - JOUR AB - The plant hormone auxin and its directional transport are known to play a crucial role in defining the embryonic axis and subsequent development of the body plan. Although the role of PIN auxin efflux transporters has been clearly assigned during embryonic shoot and root specification, the role of the auxin influx carriers AUX1 and LIKE-AUX1 (LAX) proteins is not well established. Here, we used chemical and genetic tools on Brassica napus microspore-derived embryos and Arabidopsis thaliana zygotic embryos, and demonstrate that AUX1, LAX1 and LAX2 are required for both shoot and root pole formation, in concert with PIN efflux carriers. Furthermore, we uncovered a positive-feedback loop betweenMONOPTEROS(ARF5)-dependent auxin signalling and auxin transport. ThisMONOPTEROSdependent transcriptional regulation of auxin influx (AUX1, LAX1 and LAX2) and auxin efflux (PIN1 and PIN4) carriers by MONOPTEROS helps to maintain proper auxin transport to the root tip. These results indicate that auxin-dependent cell specification during embryo development requires balanced auxin transport involving both influx and efflux mechanisms, and that this transport is maintained by a positive transcriptional feedback on auxin signalling. AU - Robert, Hélène AU - Grunewald, Wim AU - Sauer, Michael AU - Cannoot, Bernard AU - Soriano, Mercedes AU - Swarup, Ranjan AU - Weijers, Dolf AU - Bennett, Malcolm AU - Boutilier, Kim AU - Friml, Jirí ID - 1865 IS - 4 JF - Development TI - Plant embryogenesis requires AUX/LAX-mediated auxin influx VL - 142 ER - TY - JOUR AB - The plant hormone auxin is a key regulator of plant growth and development. Differences in auxin distribution within tissues are mediated by the polar auxin transport machinery, and cellular auxin responses occur depending on changes in cellular auxin levels. Multiple receptor systems at the cell surface and in the interior operate to sense and interpret fluctuations in auxin distribution that occur during plant development. Until now, three proteins or protein complexes that can bind auxin have been identified. SCFTIR1 [a SKP1-cullin-1-F-box complex that contains transport inhibitor response 1 (TIR1) as the F-box protein] and S-phase-kinaseassociated protein 2 (SKP2) localize to the nucleus, whereas auxinbinding protein 1 (ABP1), predominantly associates with the endoplasmic reticulum and cell surface. In this Cell Science at a Glance article, we summarize recent discoveries in the field of auxin transport and signaling that have led to the identification of new components of these pathways, as well as their mutual interaction. AU - Grones, Peter AU - Friml, Jirí ID - 1871 IS - 1 JF - Journal of Cell Science TI - Auxin transporters and binding proteins at a glance VL - 128 ER - TY - JOUR AB - When electron microscopy (EM) was introduced in the 1930s it gave scientists their first look into the nanoworld of cells. Over the last 80 years EM has vastly increased our understanding of the complex cellular structures that underlie the diverse functions that cells need to maintain life. One drawback that has been difficult to overcome was the inherent lack of volume information, mainly due to the limit on the thickness of sections that could be viewed in a transmission electron microscope (TEM). For many years scientists struggled to achieve three-dimensional (3D) EM using serial section reconstructions, TEM tomography, and scanning EM (SEM) techniques such as freeze-fracture. Although each technique yielded some special information, they required a significant amount of time and specialist expertise to obtain even a very small 3D EM dataset. Almost 20 years ago scientists began to exploit SEMs to image blocks of embedded tissues and perform serial sectioning of these tissues inside the SEM chamber. Using first focused ion beams (FIB) and subsequently robotic ultramicrotomes (serial block-face, SBF-SEM) microscopists were able to collect large volumes of 3D EM information at resolutions that could address many important biological questions, and do so in an efficient manner. We present here some examples of 3D EM taken from the many diverse specimens that have been imaged in our core facility. We propose that the next major step forward will be to efficiently correlate functional information obtained using light microscopy (LM) with 3D EM datasets to more completely investigate the important links between cell structures and their functions. AU - Kremer, A AU - Lippens, Stefaan AU - Bartunkova, Sonia AU - Asselbergh, Bob AU - Blanpain, Cendric AU - Fendrych, Matyas AU - Goossens, A AU - Holt, Matthew AU - Janssens, Sophie AU - Krols, Michiel AU - Larsimont, Jean AU - Mc Guire, Conor AU - Nowack, Moritz AU - Saelens, Xavier AU - Schertel, Andreas AU - Schepens, B AU - Slezak, M AU - Timmerman, Vincent AU - Theunis, Clara AU - Van Brempt, Ronald AU - Visser, Y AU - Guérin, Christophe ID - 1879 IS - 2 JF - Journal of Microscopy TI - Developing 3D SEM in a broad biological context VL - 259 ER - TY - JOUR AB - Petrocoptis is a small genus of chasmophytic plants endemic to the Iberian Peninsula, with some localized populations in the French Pyrenees. Within the genus, a dozen species have been recognized based on morphological diversity, most of them with limited distribution area, in small populations and frequently with potential threats to their survival. To date, however, a molecular evaluation of the current systematic treatments has not been carried out. The aim of the present study is to infer phylogenetic relationships among its subordinate taxa by using plastidial rps16 intron and nuclear internal transcribed spacer (ITS) DNA sequences; and evaluate the phylogenetic placement of the genus Petrocoptis within the family Caryophyllaceae. The monophyly of Petrocoptis is supported by both ITS and rps16 intron sequence analyses. Furthermore, time estimates using BEAST analyses indicate a Middle to Late Miocene diversification (10.59 Myr, 6.44–15.26 Myr highest posterior densities [HPD], for ITS; 14.30 Myr, 8.61–21.00 Myr HPD, for rps16 intron). AU - Cires Rodriguez, Eduardo AU - Prieto, José ID - 1878 IS - 2 JF - Journal of Plant Research TI - Phylogenetic relationships of Petrocoptis A. Braun ex Endl. (Caryophyllaceae), a discussed genus from the Iberian Peninsula VL - 128 ER - TY - JOUR AU - Rakusová, Hana AU - Fendrych, Matyas AU - Friml, Jirí ID - 1944 IS - 2 JF - Current Opinion in Plant Biology TI - Intracellular trafficking and PIN-mediated cell polarity during tropic responses in plants VL - 23 ER - TY - JOUR AB - Ethylene is a gaseous phytohormone that plays vital roles in plant growth and development. Previous studies uncovered EIN2 as an essential signal transducer linking ethylene perception on ER to transcriptional regulation in the nucleus through a “cleave and shuttle” model. In this study, we report another mechanism of EIN2-mediated ethylene signaling, whereby EIN2 imposes the translational repression of EBF1 and EBF2 mRNA. We find that the EBF1/2 3′ UTRs mediate EIN2-directed translational repression and identify multiple poly-uridylates (PolyU) motifs as functional cis elements of 3′ UTRs. Furthermore, we demonstrate that ethylene induces EIN2 to associate with 3′ UTRs and target EBF1/2 mRNA to cytoplasmic processing-body (P-body) through interacting with multiple P-body factors, including EIN5 and PABs. Our study illustrates translational regulation as a key step in ethylene signaling and presents mRNA 3′ UTR functioning as a “signal transducer” to sense and relay cellular signaling in plants. AU - Li, Wenyang AU - Ma, Mengdi AU - Feng, Ying AU - Li, Hongjiang AU - Wang, Yichuan AU - Ma, Yutong AU - Li, Mingzhe AU - An, Fengying AU - Guo, Hongwei ID - 532 IS - 3 JF - Cell TI - EIN2-directed translational regulation of ethylene signaling in arabidopsis VL - 163 ER - TY - JOUR AB - Auxin participates in a multitude of developmental processes, as well as responses to environmental cues. Compared with other plant hormones, auxin exhibits a unique property, as it undergoes directional, cell-to-cell transport facilitated by plasma membrane-localized transport proteins. Among them, a prominent role has been ascribed to the PIN family of auxin efflux facilitators. PIN proteins direct polar auxin transport on account of their asymmetric subcellular localizations. In this review, we provide an overview of the multiple developmental roles of PIN proteins, including the atypical endoplasmic reticulum-localized members of the family, and look at the family from an evolutionary perspective. Next, we cover the cell biological and molecular aspects of PIN function, in particular the establishment of their polar subcellular localization. Hormonal and environmental inputs into the regulation of PIN action are summarized as well. AU - Adamowski, Maciek AU - Friml, Jirí ID - 1591 IS - 1 JF - Plant Cell TI - PIN-dependent auxin transport: Action, regulation, and evolution VL - 27 ER - TY - JOUR AB - The Auxin Binding Protein1 (ABP1) has been identified based on its ability to bind auxin with high affinity and studied for a long time as a prime candidate for the extracellular auxin receptor responsible for mediating in particular the fast non-transcriptional auxin responses. However, the contradiction between the embryo-lethal phenotypes of the originally described Arabidopsis T-DNA insertional knock-out alleles (abp1-1 and abp1-1s) and the wild type-like phenotypes of other recently described loss-of-function alleles (abp1-c1 and abp1-TD1) questions the biological importance of ABP1 and relevance of the previous genetic studies. Here we show that there is no hidden copy of the ABP1 gene in the Arabidopsis genome but the embryo-lethal phenotypes of abp1-1 and abp1-1s alleles are very similar to the knock-out phenotypes of the neighboring gene, BELAYA SMERT (BSM). Furthermore, the allelic complementation test between bsm and abp1 alleles shows that the embryo-lethality in the abp1-1 and abp1-1s alleles is caused by the off-target disruption of the BSM locus by the T-DNA insertions. This clarifies the controversy of different phenotypes among published abp1 knock-out alleles and asks for reflections on the developmental role of ABP1. AU - Michalko, Jaroslav AU - Dravecka, Marta AU - Bollenbach, Tobias AU - Friml, Jirí ID - 1509 JF - F1000 Research TI - Embryo-lethal phenotypes in early abp1 mutants are due to disruption of the neighboring BSM gene VL - 4 ER - TY - CHAP AB - The generation of asymmetry, at both cellular and tissue level, is one of the most essential capabilities of all eukaryotic organisms. It mediates basically all multicellular development ranging from embryogenesis and de novo organ formation till responses to various environmental stimuli. In plants, the awe-inspiring number of such processes is regulated by phytohormone auxin and its directional, cell-to-cell transport. The mediators of this transport, PIN auxin transporters, are asymmetrically localized at the plasma membrane, and this polar localization determines the directionality of intercellular auxin flow. Thus, auxin transport contributes crucially to the generation of local auxin gradients or maxima, which instruct given cell to change its developmental program. Here, we introduce and discuss the molecular components and cellular mechanisms regulating the generation and maintenance of cellular PIN polarity, as the general hallmarks of cell polarity in plants. AU - Baster, Pawel AU - Friml, Jiří ED - Zažímalová, Eva ED - Petrášek, Jan ED - Benková, Eva ID - 1806 T2 - Auxin and Its Role in Plant Development TI - Auxin on the road navigated by cellular PIN polarity ER - TY - JOUR AB - To control morphogenesis, molecular regulatory networks have to interfere with the mechanical properties of the individual cells of developing organs and tissues, but how this is achieved is not well known. We study this issue here in the shoot meristem of higher plants, a group of undifferentiated cells where complex changes in growth rates and directions lead to the continuous formation of new organs [1, 2]. Here, we show that the plant hormone auxin plays an important role in this process via a dual, local effect on the extracellular matrix, the cell wall, which determines cell shape. Our study reveals that auxin not only causes a limited reduction in wall stiffness but also directly interferes with wall anisotropy via the regulation of cortical microtubule dynamics. We further show that to induce growth isotropy and organ outgrowth, auxin somehow interferes with the cortical microtubule-ordering activity of a network of proteins, including AUXIN BINDING PROTEIN 1 and KATANIN 1. Numerical simulations further indicate that the induced isotropy is sufficient to amplify the effects of the relatively minor changes in wall stiffness to promote organogenesis and the establishment of new growth axes in a robust manner. AU - Sassi, Massimiliano AU - Ali, Olivier AU - Boudon, Frédéric AU - Cloarec, Gladys AU - Abad, Ursula AU - Cellier, Coralie AU - Chen, Xu AU - Gilles, Benjamin AU - Milani, Pascale AU - Friml, Jirí AU - Vernoux, Teva AU - Godin, Christophe AU - Hamant, Olivier AU - Traas, Jan ID - 1852 IS - 19 JF - Current Biology TI - An auxin-mediated shift toward growth isotropy promotes organ formation at the shoot meristem in Arabidopsis VL - 24 ER - TY - JOUR AB - The prominent and evolutionarily ancient role of the plant hormone auxin is the regulation of cell expansion. Cell expansion requires ordered arrangement of the cytoskeleton but molecular mechanisms underlying its regulation by signalling molecules including auxin are unknown. Here we show in the model plant Arabidopsis thaliana that in elongating cells exogenous application of auxin or redistribution of endogenous auxin induces very rapid microtubule re-orientation from transverse to longitudinal, coherent with the inhibition of cell expansion. This fast auxin effect requires auxin binding protein 1 (ABP1) and involves a contribution of downstream signalling components such as ROP6 GTPase, ROP-interactive protein RIC1 and the microtubule-severing protein katanin. These components are required for rapid auxin-and ABP1-mediated re-orientation of microtubules to regulate cell elongation in roots and dark-grown hypocotyls as well as asymmetric growth during gravitropic responses. AU - Chen, Xu AU - Grandont, Laurie AU - Li, Hongjiang AU - Hauschild, Robert AU - Paque, Sébastien AU - Abuzeineh, Anas AU - Rakusova, Hana AU - Benková, Eva AU - Perrot Rechenmann, Catherine AU - Friml, Jirí ID - 1862 IS - 729 JF - Nature SN - 0028-0836 TI - Inhibition of cell expansion by rapid ABP1-mediated auxin effect on microtubules VL - 516 ER - TY - JOUR AB - Phosphatidylinositol (PtdIns) is a structural phospholipid that can be phosphorylated into various lipid signaling molecules, designated polyphosphoinositides (PPIs). The reversible phosphorylation of PPIs on the 3, 4, or 5 position of inositol is performed by a set of organelle-specific kinases and phosphatases, and the characteristic head groups make these molecules ideal for regulating biological processes in time and space. In yeast and mammals, PtdIns3P and PtdIns(3,5)P2 play crucial roles in trafficking toward the lytic compartments, whereas the role in plants is not yet fully understood. Here we identified the role of a land plant-specific subgroup of PPI phosphatases, the suppressor of actin 2 (SAC2) to SAC5, during vacuolar trafficking and morphogenesis in Arabidopsis thaliana. SAC2-SAC5 localize to the tonoplast along with PtdIns3P, the presumable product of their activity. In SAC gain- and loss-of-function mutants, the levels of PtdIns monophosphates and bisphosphates were changed, with opposite effects on the morphology of storage and lytic vacuoles, and the trafficking toward the vacuoles was defective. Moreover, multiple sac knockout mutants had an increased number of smaller storage and lytic vacuoles, whereas extralarge vacuoles were observed in the overexpression lines, correlating with various growth and developmental defects. The fragmented vacuolar phenotype of sac mutants could be mimicked by treating wild-type seedlings with PtdIns(3,5)P2, corroborating that this PPI is important for vacuole morphology. Taken together, these results provide evidence that PPIs, together with their metabolic enzymes SAC2-SAC5, are crucial for vacuolar trafficking and for vacuolar morphology and function in plants. AU - Nováková, Petra AU - Hirsch, Sibylle AU - Feraru, Elena AU - Tejos, Ricardo AU - Van Wijk, Ringo AU - Viaene, Tom AU - Heilmann, Mareike AU - Lerche, Jennifer AU - De Rycke, Riet AU - Feraru, Mugurel AU - Grones, Peter AU - Van Montagu, Marc AU - Heilmann, Ingo AU - Munnik, Teun AU - Friml, Jirí ID - 1893 IS - 7 JF - PNAS TI - SAC phosphoinositide phosphatases at the tonoplast mediate vacuolar function in Arabidopsis VL - 111 ER - TY - JOUR AB - GNOM is one of the most characterized membrane trafficking regulators in plants, with crucial roles in development. GNOM encodes an ARF-guanine nucleotide exchange factor (ARF-GEF) that activates small GTPases of the ARF (ADP ribosylation factor) class to mediate vesicle budding at endomembranes. The crucial role of GNOM in recycling of PIN auxin transporters and other proteins to the plasma membrane was identified in studies using the ARF-GEF inhibitor brefeldin A (BFA). GNOM, the most prominent regulator of recycling in plants, has been proposed to act and localize at so far elusive recycling endosomes. Here, we report the GNOM localization in context of its cellular function in Arabidopsis thaliana. State-of-the-art imaging, pharmacological interference, and ultrastructure analysis show that GNOM predominantly localizes to Golgi apparatus. Super-resolution confocal live imaging microscopy identified GNOM and its closest homolog GNOM-like 1 at distinct subdomains on Golgi cisternae. Short-term BFA treatment stabilizes GNOM at the Golgi apparatus, whereas prolonged exposures results in GNOM translocation to trans-Golgi network (TGN)/early endosomes (EEs). Malformed TGN/EE in gnom mutants suggests a role for GNOM in maintaining TGN/EE function. Our results redefine the subcellular action of GNOM and reevaluate the identity and function of recycling endosomes in plants. AU - Naramoto, Satoshi AU - Otegui, Marisa AU - Kutsuna, Natsumaro AU - De Rycke, Riet AU - Dainobu, Tomoko AU - Karampelias, Michael AU - Fujimoto, Masaru AU - Feraru, Elena AU - Miki, Daisuke AU - Fukuda, Hiroo AU - Nakano, Akihiko AU - Friml, Jirí ID - 1897 IS - 7 JF - Plant Cell TI - Insights into the localization and function of the membrane trafficking regulator GNOM ARF-GEF at the Golgi apparatus in Arabidopsis VL - 26 ER - TY - JOUR AB - In plants, the patterning of stem cell-enriched meristems requires a graded auxin response maximum that emerges from the concerted action of polar auxin transport, auxin biosynthesis, auxin metabolism, and cellular auxin response machinery. However, mechanisms underlying this auxin response maximum-mediated root stem cell maintenance are not fully understood. Here, we present unexpected evidence that WUSCHEL-RELATED HOMEOBOX 5 (WOX5) transcription factor modulates expression of auxin biosynthetic genes in the quiescent center (QC) of the root and thus provides a robust mechanism for the maintenance of auxin response maximum in the root tip. This WOX5 action is balanced through the activity of indole-3-acetic acid 17 (IAA17) auxin response repressor. Our combined genetic, cell biology, and computational modeling studies revealed a previously uncharacterized feedback loop linking WOX5-mediated auxin production to IAA17-dependent repression of auxin responses. This WOX5-IAA17 feedback circuit further assures the maintenance of auxin response maximum in the root tip and thereby contributes to the maintenance of distal stem cell (DSC) populations. Our experimental studies and in silico computer simulations both demonstrate that the WOX5-IAA17 feedback circuit is essential for the maintenance of auxin gradient in the root tip and the auxin-mediated root DSC differentiation. AU - Tian, Huiyu AU - Wabnik, Krzysztof T AU - Niu, Tiantian AU - Li, Hongjiang AU - Yu, Qianqian AU - Pollmann, Stephan AU - Vanneste, Steffen AU - Govaerts, Willy AU - Rolčík, Jakub AU - Geisler, Markus AU - Friml, Jirí AU - Ding, Zhaojun ID - 1901 IS - 2 JF - Molecular Plant TI - WOX5-IAA17 feedback circuit-mediated cellular auxin response is crucial for the patterning of root stem cell niches in arabidopsis VL - 7 ER - TY - JOUR AB - Auxin-binding protein 1 (ABP1) was discovered nearly 40 years ago and was shown to be essential for plant development and morphogenesis, but its mode of action remains unclear. Here, we report that the plasma membrane-localized transmembrane kinase (TMK) receptor-like kinases interact with ABP1 and transduce auxin signal to activate plasma membrane-associated ROPs [Rho-like guanosine triphosphatases (GTPase) from plants], leading to changes in the cytoskeleton and the shape of leaf pavement cells in Arabidopsis. The interaction between ABP1 and TMK at the cell surface is induced by auxin and requires ABP1 sensing of auxin. These findings show that TMK proteins and ABP1 form a cell surface auxin perception complex that activates ROP signaling pathways, regulating nontranscriptional cytoplasmic responses and associated fundamental processes. AU - Xu, Tongda AU - Dai, Ning AU - Chen, Jisheng AU - Nagawa, Shingo AU - Cao, Min AU - Li, Hongjiang AU - Zhou, Zimin AU - Chen, Xu AU - De Rycke, Riet AU - Rakusová, Hana AU - Wang, Wen AU - Jones, Alan AU - Friml, Jirí AU - Patterson, Sara AU - Bleecker, Anthony AU - Yang, Zhenbiao ID - 1917 IS - 6174 JF - Science TI - Cell surface ABP1-TMK auxin sensing complex activates ROP GTPase signaling VL - 343 ER - TY - JOUR AB - ROPs (Rho of plants) belong to a large family of plant-specific Rho-like small GTPases that function as essential molecular switches to control diverse cellular processes including cytoskeleton organization, cell polarization, cytokinesis, cell differentiation and vesicle trafficking. Although the machineries of vesicle trafficking and cell polarity in plants have been individually well addressed, how ROPs co-ordinate those processes is still largely unclear. Recent progress has been made towards an understanding of the coordination of ROP signalling and trafficking of PIN (PINFORMED) transporters for the plant hormone auxin in both root and leaf pavement cells. PIN transporters constantly shuttle between the endosomal compartments and the polar plasma membrane domains, therefore the modulation of PIN-dependent auxin transport between cells is a main developmental output of ROP-regulated vesicle trafficking. The present review focuses on these cellular mechanisms, especially the integration of ROP-based vesicle trafficking and plant cell polarity. AU - Chen, Xu AU - Friml, Jirí ID - 1915 IS - 1 JF - Biochemical Society Transactions SN - 0300-5127 TI - Rho-GTPase-regulated vesicle trafficking in plant cell polarity VL - 42 ER - TY - JOUR AB - Targeting membrane proteins for degradation requires the sequential action of ESCRT sub-complexes ESCRT-0 to ESCRT-III. Although this machinery is generally conserved among kingdoms, plants lack the essential ESCRT-0 components. A new report closes this gap by identifying a novel protein family that substitutes for ESCRT-0 function in plants. AU - Sauer, Michael AU - Friml, Jirí ID - 1914 IS - 1 JF - Current Biology TI - Plant biology: Gatekeepers of the road to protein perdition VL - 24 ER - TY - JOUR AB - Cell polarity manifested by asymmetric distribution of cargoes, such as receptors and transporters, within the plasma membrane (PM) is crucial for essential functions in multicellular organisms. In plants, cell polarity (re)establishment is intimately linked to patterning processes. Despite the importance of cell polarity, its underlying mechanisms are still largely unknown, including the definition and distinctiveness of the polar domains within the PM. Here, we show in Arabidopsis thaliana that the signaling membrane components, the phosphoinositides phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4, 5-bisphosphate [PtdIns(4, 5)P2] as well as PtdIns4P 5-kinases mediating their interconversion, are specifically enriched at apical and basal polar plasma membrane domains. The PtdIns4P 5-kinases PIP5K1 and PIP5K2 are redundantly required for polar localization of specifically apical and basal cargoes, such as PIN-FORMED transporters for the plant hormone auxin. As a consequence of the polarity defects, instructive auxin gradients as well as embryonic and postembryonic patterning are severely compromised. Furthermore, auxin itself regulates PIP5K transcription and PtdIns4P and PtdIns(4, 5)P2 levels, in particular their association with polar PM domains. Our results provide insight into the polar domain-delineating mechanisms in plant cells that depend on apical and basal distribution of membrane lipids and are essential for embryonic and postembryonic patterning. AU - Tejos, Ricardo AU - Sauer, Michael AU - Vanneste, Steffen AU - Palacios-Gomez, MiriamPalacios AU - Li, Hongjiang AU - Heilmann, Mareike AU - Van Wijk, Ringo AU - Vermeer, Joop AU - Heilmann, Ingo AU - Munnik, Teun AU - Friml, Jirí ID - 1921 IS - 5 JF - Plant Cell TI - Bipolar plasma membrane distribution of phosphoinositides and their requirement for auxin-mediated cell polarity and patterning in Arabidopsis VL - 26 ER - TY - JOUR AB - Stomata are two-celled valves that control epidermal pores whose spacing optimizes shoot-atmosphere gas exchange. They develop from protodermal cells after unequal divisions followed by an equal division and differentiation. The concentration of the hormone auxin, a master plant developmental regulator, is tightly controlled in time and space, but its role, if any, in stomatal formation is obscure. Here dynamic changes of auxin activity during stomatal development are monitored using auxin input (DII-VENUS) and output (DR5:VENUS) markers by time-lapse imaging. A decrease in auxin levels in the smaller daughter cell after unequal division presages the acquisition of a guard mother cell fate whose equal division produces the two guard cells. Thus, stomatal patterning requires auxin pathway control of stem cell compartment size, as well as auxin depletion that triggers a developmental switch from unequal to equal division. AU - Le, Jie AU - Liu, Xuguang AU - Yang, Kezhen AU - Chen, Xiaolan AU - Zhu, Lingling AU - Wang, Hongzhe AU - Wang, Ming AU - Vanneste, Steffen AU - Morita, Miyo AU - Tasaka, Masao AU - Ding, Zhaojun AU - Friml, Jirí AU - Beeckman, Tom AU - Sack, Fred ID - 1924 JF - Nature Communications TI - Auxin transport and activity regulate stomatal patterning and development VL - 5 ER - TY - JOUR AB - The plant hormones auxin and cytokinin mutually coordinate their activities to control various aspects of development [1-9], and their crosstalk occurs at multiple levels [10, 11]. Cytokinin-mediated modulation of auxin transport provides an efficient means to regulate auxin distribution in plant organs. Here, we demonstrate that cytokinin does not merely control the overall auxin flow capacity, but might also act as a polarizing cue and control the auxin stream directionality during plant organogenesis. Cytokinin enhances the PIN-FORMED1 (PIN1) auxin transporter depletion at specific polar domains, thus rearranging the cellular PIN polarities and directly regulating the auxin flow direction. This selective cytokinin sensitivity correlates with the PIN protein phosphorylation degree. PIN1 phosphomimicking mutations, as well as enhanced phosphorylation in plants with modulated activities of PIN-specific kinases and phosphatases, desensitize PIN1 to cytokinin. Our results reveal conceptually novel, cytokinin-driven polarization mechanism that operates in developmental processes involving rapid auxin stream redirection, such as lateral root organogenesis, in which a gradual PIN polarity switch defines the growth axis of the newly formed organ. AU - Marhavy, Peter AU - Duclercq, Jérôme AU - Weller, Benjamin AU - Feraru, Elena AU - Bielach, Agnieszka AU - Offringa, Remko AU - Friml, Jirí AU - Schwechheimer, Claus AU - Murphy, Angus AU - Benková, Eva ID - 1934 IS - 9 JF - Current Biology TI - Cytokinin controls polarity of PIN1-dependent Auxin transport during lateral root organogenesis VL - 24 ER - TY - JOUR AB - Auxin polar transport, local maxima, and gradients have become an importantmodel system for studying self-organization. Auxin distribution is regulated by auxin-dependent positive feedback loops that are not well-understood at the molecular level. Previously, we showed the involvement of the RHO of Plants (ROP) effector INTERACTOR of CONSTITUTIVELY active ROP 1 (ICR1) in regulation of auxin transport and that ICR1 levels are posttranscriptionally repressed at the site of maximum auxin accumulation at the root tip. Here, we show that bimodal regulation of ICR1 levels by auxin is essential for regulating formation of auxin local maxima and gradients. ICR1 levels increase concomitant with increase in auxin response in lateral root primordia, cotyledon tips, and provascular tissues. However, in the embryo hypophysis and root meristem, when auxin exceeds critical levels, ICR1 is rapidly destabilized by an SCF(TIR1/AFB) [SKP, Cullin, F-box (transport inhibitor response 1/auxin signaling F-box protein)]-dependent auxin signaling mechanism. Furthermore, ectopic expression of ICR1 in the embryo hypophysis resulted in reduction of auxin accumulation and concomitant root growth arrest. ICR1 disappeared during root regeneration and lateral root initiation concomitantly with the formation of a local auxin maximum in response to external auxin treatments and transiently after gravitropic stimulation. Destabilization of ICR1 was impaired after inhibition of auxin transport and signaling, proteasome function, and protein synthesis. A mathematical model based on these findings shows that an in vivo-like auxin distribution, rootward auxin flux, and shootward reflux can be simulated without assuming preexisting tissue polarity. Our experimental results and mathematical modeling indicate that regulation of auxin distribution is tightly associated with auxin-dependent ICR1 levels. AU - Hazak, Ora AU - Obolski, Uri AU - Prat, Tomas AU - Friml, Jiří AU - Hadany, Lilach AU - Yalovsky, Shaul ID - 1996 IS - 50 JF - PNAS TI - Bimodal regulation of ICR1 levels generates self-organizing auxin distribution VL - 111 ER - TY - JOUR AB - The emergence and radiation of multicellular land plants was driven by crucial innovations to their body plans [1]. The directional transport of the phytohormone auxin represents a key, plant-specific mechanism for polarization and patterning in complex seed plants [2-5]. Here, we show that already in the early diverging land plant lineage, as exemplified by the moss Physcomitrella patens, auxin transport by PIN transporters is operational and diversified into ER-localized and plasma membrane-localized PIN proteins. Gain-of-function and loss-of-function analyses revealed that PIN-dependent intercellular auxin transport in Physcomitrella mediates crucial developmental transitions in tip-growing filaments and waves of polarization and differentiation in leaf-like structures. Plasma membrane PIN proteins localize in a polar manner to the tips of moss filaments, revealing an unexpected relation between polarization mechanisms in moss tip-growing cells and multicellular tissues of seed plants. Our results trace the origins of polarization and auxin-mediated patterning mechanisms and highlight the crucial role of polarized auxin transport during the evolution of multicellular land plants. AU - Viaene, Tom AU - Landberg, Katarina AU - Thelander, Mattias AU - Medvecka, Eva AU - Pederson, Eric AU - Feraru, Elena AU - Cooper, Endymion AU - Karimi, Mansour AU - Delwiche, Charles AU - Ljung, Karin AU - Geisler, Markus AU - Sundberg, Eva AU - Friml, Jirí ID - 1994 IS - 23 JF - Current Biology TI - Directional auxin transport mechanisms in early diverging land plants VL - 24 ER - TY - JOUR AB - Development of cambium and its activity is important for our knowledge of the mechanism of secondary growth. Arabidopsis thaliana emerges as a good model plant for such a kind of study. Thus, this paper reports on cellular events taking place in the interfascicular regions of inflorescence stems of A. thaliana, leading to the development of interfascicular cambium from differentiated interfascicular parenchyma cells (IPC). These events are as follows: appearance of auxin accumulation, PIN1 gene expression, polar PIN1 protein localization in the basal plasma membrane and periclinal divisions. Distribution of auxin was observed to be higher in differentiating into cambium parenchyma cells compared to cells within the pith and cortex. Expression of PIN1 in IPC was always preceded by auxin accumulation. Basal localization of PIN1 was already established in the cells prior to their periclinal division. These cellular events initiated within parenchyma cells adjacent to the vascular bundles and successively extended from that point towards the middle region of the interfascicular area, located between neighboring vascular bundles. The final consequence of which was the closure of the cambial ring within the stem. Changes in the chemical composition of IPC walls were also detected and included changes of pectic epitopes, xyloglucans (XG) and extensins rich in hydroxyproline (HRGPs). In summary, results presented in this paper describe interfascicular cambium ontogenesis in terms of successive cellular events in the interfascicular regions of inflorescence stems of Arabidopsis. AU - Mazur, Ewa AU - Kurczyñska, Ewa AU - Friml, Jiří ID - 2061 IS - 5 JF - Protoplasma TI - Cellular events during interfascicular cambium ontogenesis in inflorescence stems of Arabidopsis VL - 251 ER - TY - JOUR AB - Although plant and animal cells use a similar core mechanism to deliver proteins to the plasma membrane, their different lifestyle, body organization and specific cell structures resulted in the acquisition of regulatory mechanisms that vary in the two kingdoms. In particular, cell polarity regulators do not seem to be conserved, because genes encoding key components are absent in plant genomes. In plants, the broad knowledge on polarity derives from the study of auxin transporters, the PIN-FORMED proteins, in the model plant Arabidopsis thaliana. In animals, much information is provided from the study of polarity in epithelial cells that exhibit basolateral and luminal apical polarities, separated by tight junctions. In this review, we summarize the similarities and differences of the polarization mechanisms between plants and animals and survey the main genetic approaches that have been used to characterize new genes involved in polarity establishment in plants, including the frequently used forward and reverse genetics screens as well as a novel chemical genetics approach that is expected to overcome the limitation of classical genetics methods. AU - Kania, Urszula AU - Fendrych, Matyas AU - Friml, Jiřĺ ID - 2188 IS - APRIL JF - Open Biology TI - Polar delivery in plants; commonalities and differences to animal epithelial cells VL - 4 ER - TY - JOUR AB - Correct positioning of membrane proteins is an essential process in eukaryotic organisms. The plant hormone auxin is distributed through intercellular transport and triggers various cellular responses. Auxin transporters of the PIN-FORMED (PIN) family localize asymmetrically at the plasma membrane (PM) and mediate the directional transport of auxin between cells. A fungal toxin, brefeldin A (BFA), inhibits a subset of guanine nucleotide exchange factors for ADP-ribosylation factor small GTPases (ARF GEFs) including GNOM, which plays a major role in localization of PIN1 predominantly to the basal side of the PM. The Arabidopsis genome encodes 19 ARF-related putative GTPases. However, ARF components involved in PIN1 localization have been genetically poorly defined. Using a fluorescence imaging-based forward genetic approach, we identified an Arabidopsis mutant, bfa-visualized exocytic trafficking defective1 (bex1), in which PM localization of PIN1-green fluorescent protein (GFP) as well as development is hypersensitive to BFA. We found that in bex1 a member of the ARF1 gene family, ARF1A1C, was mutated. ARF1A1C localizes to the trans-Golgi network/early endosome and Golgi apparatus, acts synergistically to BEN1/MIN7 ARF GEF and is important for PIN recycling to the PM. Consistent with the developmental importance of PIN proteins, functional interference with ARF1 resulted in an impaired auxin response gradient and various developmental defects including embryonic patterning defects and growth arrest. Our results show that ARF1A1C is essential for recycling of PIN auxin transporters and for various auxin-dependent developmental processes. AU - Tanaka, Hirokazu AU - Nodzyński, Tomasz AU - Kitakura, Saeko AU - Feraru, Mugurel AU - Sasabe, Michiko AU - Ishikawa, Tomomi AU - Kleine Vehn, Jürgen AU - Kakimoto, Tatsuo AU - Friml, Jirí ID - 2223 IS - 4 JF - Plant and Cell Physiology SN - 00320781 TI - BEX1/ARF1A1C is required for BFA-sensitive recycling of PIN auxin transporters and auxin-mediated development in arabidopsis VL - 55 ER - TY - JOUR AB - Leaf venation develops complex patterns in angiosperms, but the mechanism underlying this process is largely unknown. To elucidate the molecular mechanisms governing vein pattern formation, we previously isolated vascular network defective (van) mutants that displayed venation discontinuities. Here, we report the phenotypic analysis of van4 mutants, and we identify and characterize the VAN4 gene. Detailed phenotypic analysis shows that van4 mutants are defective in procambium cell differentiation and subsequent vascular cell differentiation. Reduced shoot and root cell growth is observed in van4 mutants, suggesting that VAN4 function is important for cell growth and the establishment of venation continuity. Consistent with these phenotypes, the VAN4 gene is strongly expressed in vascular and meristematic cells. VAN4 encodes a putative TRS120, which is a known guanine nucleotide exchange factor (GEF) for Rab GTPase involved in regulating vesicle transport, and a known tethering factor that determines the specificity of membrane fusion. VAN4 protein localizes at the trans-Golgi network/early endosome (TGN/EE). Aberrant recycling of the auxin efflux carrier PIN proteins is observed in van4 mutants. These results suggest that VAN4-mediated exocytosis at the TGN plays important roles in plant vascular development and cell growth in shoot and root. Our identification of VAN4 as a putative TRS120 shows that Rab GTPases are crucial (in addition to ARF GTPases) for continuous vascular development, and provides further evidence for the importance of vesicle transport in leaf vascular formation. AU - Naramoto, Satoshi AU - Nodzyński, Tomasz AU - Dainobu, Tomoko AU - Takatsuka, Hirotomo AU - Okada, Teruyo AU - Friml, Jirí AU - Fukuda, Hiroo ID - 2222 IS - 4 JF - Plant and Cell Physiology SN - 00320781 TI - VAN4 encodes a putative TRS120 that is required for normal cell growth and vein development in arabidopsis VL - 55 ER - TY - JOUR AB - The Balkan Peninsula, characterized by high rates of endemism, is recognised as one of the most diverse and species-rich areas of Europe. However, little is known about the origin of Balkan endemics. The present study addresses the phylogenetic position of the Balkan endemic Ranunculus wettsteinii, as well as its taxonomic status and relationship with the widespread R. parnassiifolius, based on nuclear DNA (internal transcribed spacer, ITS) and plastid regions (rpl32-trnL, rps16-trnQ, trnK-matK and ycf6-psbM). Maximum parsimony and Bayesian inference analyses revealed a well-supported clade formed by accessions of R. wettsteinii. Furthermore, our phylogenetic and network analyses supported previous hypotheses of a likely allopolyploid origin for R. wettsteinii between R. montenegrinus and R. parnassiifolius, with the latter as the maternal parent. AU - Cires Rodriguez, Eduardo AU - Baltisberger, Matthias AU - Cuesta, Candela AU - Vargas, Pablo AU - Prieto, José ID - 2227 IS - 1 JF - Organisms Diversity and Evolution SN - 14396092 TI - Allopolyploid origin of the Balkan endemic Ranunculus wettsteinii (Ranunculaceae) inferred from nuclear and plastid DNA sequences VL - 14 ER - TY - JOUR AB - Clathrin-mediated endocytosis is the major mechanism for eukaryotic plasma membrane-based proteome turn-over. In plants, clathrin-mediated endocytosis is essential for physiology and development, but the identification and organization of the machinery operating this process remains largely obscure. Here, we identified an eight-core-component protein complex, the TPLATE complex, essential for plant growth via its role as major adaptor module for clathrin-mediated endocytosis. This complex consists of evolutionarily unique proteins that associate closely with core endocytic elements. The TPLATE complex is recruited as dynamic foci at the plasma membrane preceding recruitment of adaptor protein complex 2, clathrin, and dynamin-related proteins. Reduced function of different complex components severely impaired internalization of assorted endocytic cargoes, demonstrating its pivotal role in clathrin-mediated endocytosis. Taken together, the TPLATE complex is an early endocytic module representing a unique evolutionary plant adaptation of the canonical eukaryotic pathway for clathrin-mediated endocytosis. AU - Gadeyne, Astrid AU - Sánchez Rodríguez, Clara AU - Vanneste, Steffen AU - Di Rubbo, Simone AU - Zauber, Henrik AU - Vanneste, Kevin AU - Van Leene, Jelle AU - De Winne, Nancy AU - Eeckhout, Dominique AU - Persiau, Geert AU - Van De Slijke, Eveline AU - Cannoot, Bernard AU - Vercruysse, Leen AU - Mayers, Jonathan AU - Adamowski, Maciek AU - Kania, Urszula AU - Ehrlich, Matthias AU - Schweighofer, Alois AU - Ketelaar, Tijs AU - Maere, Steven AU - Bednarek, Sebastian AU - Friml, Jirí AU - Gevaert, Kris AU - Witters, Erwin AU - Russinova, Eugenia AU - Persson, Staffan AU - De Jaeger, Geert AU - Van Damme, Daniël ID - 2240 IS - 4 JF - Cell SN - 00928674 TI - The TPLATE adaptor complex drives clathrin-mediated endocytosis in plants VL - 156 ER - TY - CHAP AB - Exogenous application of biologically important molecules for plant growth promotion and/or regulation is very common both in plant research and horticulture. Plant hormones such as auxins and cytokinins are classes of compounds which are often applied exogenously. Nevertheless, plants possess a well-established machinery to regulate the active pool of exogenously applied compounds by converting them to metabolites and conjugates. Consequently, it is often very useful to know the in vivo status of applied compounds to connect them with some of the regulatory events in plant developmental processes. The in vivo status of applied compounds can be measured by incubating plants with radiolabeled compounds, followed by extraction, purification, and HPLC metabolic profiling of plant extracts. Recently we have used this method to characterize the intracellularly localized PIN protein, PIN5. Here we explain the method in detail, with a focus on general application. AU - Simon, Sibu AU - Skůpa, Petr AU - Dobrev, Petre AU - Petrášek, Jan AU - Zažímalová, Eva AU - Friml, Jirí ED - Hicks, Glenn ED - Robert, Stéphanie ID - 2245 SN - 10643745 T2 - Plant Chemical Genomics TI - Analyzing the in vivo status of exogenously applied auxins: A HPLC-based method to characterize the intracellularly localized auxin transporters VL - 1056 ER - TY - JOUR AB - Plant growth is achieved predominantly by cellular elongation, which is thought to be controlled on several levels by apoplastic auxin. Auxin export into the apoplast is achieved by plasma membrane efflux catalysts of the PIN-FORMED (PIN) and ATP-binding cassette protein subfamily B/phosphor- glycoprotein (ABCB/PGP) classes; the latter were shown to depend on interaction with the FKBP42, TWISTED DWARF1 (TWD1). Here by using a transgenic approach in combination with phenotypical, biochemical and cell biological analyses we demonstrate the importance of a putative C-terminal in-plane membrane anchor of TWD1 in the regulation of ABCB-mediated auxin transport. In contrast with dwarfed twd1 loss-of-function alleles, TWD1 gain-of-function lines that lack a putative in-plane membrane anchor (HA-TWD1-Ct) show hypermorphic plant architecture, characterized by enhanced stem length and leaf surface but reduced shoot branching. Greater hypocotyl length is the result of enhanced cell elongation that correlates with reduced polar auxin transport capacity for HA-TWD1-Ct. As a consequence, HA-TWD1-Ct displays higher hypocotyl auxin accumulation, which is shown to result in elevated auxin-induced cell elongation rates. Our data highlight the importance of C-terminal membrane anchoring for TWD1 action, which is required for specific regulation of ABCB-mediated auxin transport. These data support a model in which TWD1 controls lateral ABCB1-mediated export into the apoplast, which is required for auxin-mediated cell elongation. AU - Bailly, Aurélien AU - Wang, Bangjun AU - Zwiewka, Marta AU - Pollmann, Stephan AU - Schenck, Daniel AU - Lüthen, Hartwig AU - Schulz, Alexander AU - Friml, Jirí AU - Geisler, Markus ID - 2253 IS - 1 JF - Plant Journal SN - 09607412 TI - Expression of TWISTED DWARF1 lacking its in-plane membrane anchor leads to increased cell elongation and hypermorphic growth VL - 77 ER - TY - JOUR AB - The unfolded protein response (UPR) is a signaling network triggered by overload of protein-folding demand in the endoplasmic reticulum (ER), a condition termed ER stress. The UPR is critical for growth and development; nonetheless, connections between the UPR and other cellular regulatory processes remain largely unknown. Here, we identify a link between the UPR and the phytohormone auxin, a master regulator of plant physiology. We show that ER stress triggers down-regulation of auxin receptors and transporters in Arabidopsis thaliana. We also demonstrate that an Arabidopsis mutant of a conserved ER stress sensor IRE1 exhibits defects in the auxin response and levels. These data not only support that the plant IRE1 is required for auxin homeostasis, they also reveal a species-specific feature of IRE1 in multicellular eukaryotes. Furthermore, by establishing that UPR activation is reduced in mutants of ER-localized auxin transporters, including PIN5, we define a long-neglected biological significance of ER-based auxin regulation. We further examine the functional relationship of IRE1 and PIN5 by showing that an ire1 pin5 triple mutant enhances defects of UPR activation and auxin homeostasis in ire1 or pin5. Our results imply that the plant UPR has evolved a hormone-dependent strategy for coordinating ER function with physiological processes. AU - Chen, Yani AU - Aung, Kyaw AU - Rolčík, Jakub AU - Walicki, Kathryn AU - Friml, Jirí AU - Brandizzí, Federica ID - 2249 IS - 1 JF - Plant Journal SN - 09607412 TI - Inter-regulation of the unfolded protein response and auxin signaling VL - 77 ER - TY - THES AB - Phosphatidylinositol (Ptdlns) is a structural phospholipid that can be phosphorylated into various lipid signaling molecules, designated polyphosphoinositides (PPIs). The reversible phosphorylation of PPIs on the 3, 4, or 5 position of inositol is performed by a set of organelle-specific kinases and phosphatases, and the characteristic head groups make these molecules ideal for regulating biological processes in time and space. In yeast and mammals, Ptdlns3P and Ptdlns(3,5)P2 play crucial roles in trafficking toward the lytic compartments, whereas the role in plants is not yet fully understood. Here we identified the role of a land plant-specific subgroup of PPI phosphatases, the suppressor of actin 2 (SAC2) to SAC5, during vauolar trafficking and morphogenesis in Arabidopsis thaliana. SAC2-SAC5 localize to the tonoplast along with Ptdlns3P, the presumable product of their activity. in SAC gain- and loss-of-function mutants, the levels of Ptdlns monophosphates and bisphosphates were changed, with opposite effects on the morphology of storage and lytic vacuoles, and the trafficking toward the vacuoles was defective. Moreover, multiple sac knockout mutants had an increased number of smaller storage and lytic vacuoles, whereas extralarge vacuoles were observed in the overexpression lines, correlating with various growth and developmental defects. The fragmented vacuolar phenotype of sac mutants could be mimicked by treating wild-type seedlings with Ptdlns(3,5)P2, corroborating that this PPI is important for vacuole morphology. Taken together, these results provide evidence that PPIs, together with their metabolic enzymes SAC2-SAC5, are crucial for vacuolar trafficking and for vacuolar morphology and function in plants. AU - Marhavá, Petra ID - 1402 SN - 2663-337X TI - Molecular mechanisms of patterning and subcellular trafficking in Arabidopsis thaliana ER - TY - JOUR AB - Due to their sessile lifestyles, plants need to deal with the limitations and stresses imposed by the changing environment. Plants cope with these by a remarkable developmental flexibility, which is embedded in their strategy to survive. Plants can adjust their size, shape and number of organs, bend according to gravity and light, and regenerate tissues that were damaged, utilizing a coordinating, intercellular signal, the plant hormone, auxin. Another versatile signal is the cation, Ca2+, which is a crucial second messenger for many rapid cellular processes during responses to a wide range of endogenous and environmental signals, such as hormones, light, drought stress and others. Auxin is a good candidate for one of these Ca2+-activating signals. However, the role of auxin-induced Ca2+ signaling is poorly understood. Here, we will provide an overview of possible developmental and physiological roles, as well as mechanisms underlying the interconnection of Ca2+ and auxin signaling. AU - Vanneste, Steffen AU - Friml, Jiří ID - 10895 IS - 4 JF - Plants KW - Plant Science KW - Ecology KW - Ecology KW - Evolution KW - Behavior and Systematics SN - 2223-7747 TI - Calcium: The missing link in auxin action VL - 2 ER - TY - JOUR AB - The plant hormone indole-acetic acid (auxin) is essential for many aspects of plant development. Auxin-mediated growth regulation typically involves the establishment of an auxin concentration gradient mediated by polarly localized auxin transporters. The localization of auxin carriers and their amount at the plasma membrane are controlled by membrane trafficking processes such as secretion, endocytosis, and recycling. In contrast to endocytosis or recycling, how the secretory pathway mediates the localization of auxin carriers is not well understood. In this study we have used the differential cell elongation process during apical hook development to elucidate the mechanisms underlying the post-Golgi trafficking of auxin carriers in Arabidopsis. We show that differential cell elongation during apical hook development is defective in Arabidopsis mutant echidna (ech). ECH protein is required for the trans-Golgi network (TGN)-mediated trafficking of the auxin influx carrier AUX1 to the plasma membrane. In contrast, ech mutation only marginally perturbs the trafficking of the highly related auxin influx carrier LIKE-AUX1-3 or the auxin efflux carrier PIN-FORMED-3, both also involved in hook development. Electron tomography reveals that the trafficking defects in ech mutant are associated with the perturbation of secretory vesicle genesis from the TGN. Our results identify differential mechanisms for the post-Golgi trafficking of de novo-synthesized auxin carriers to plasma membrane from the TGN and reveal how trafficking of auxin influx carriers mediates the control of differential cell elongation in apical hook development. AU - Boutté, Yohann AU - Jonsson, Kristoffer AU - Mcfarlane, Heather AU - Johnson, Errin AU - Gendre, Delphine AU - Swarup, Ranjan AU - Friml, Jirí AU - Samuels, Lacey AU - Robert, Stéphanie AU - Bhalerao, Rishikesh ID - 2290 IS - 40 JF - PNAS TI - ECHIDNA mediated post Golgi trafficking of auxin carriers for differential cell elongation VL - 110 ER - TY - JOUR AB - The mode of action of auxin is based on its non-uniform distribution within tissues and organs. Despite the wide use of several auxin analogues in research and agriculture, little is known about the specificity of different auxin-related transport and signalling processes towards these compounds. Using seedlings of Arabidopsis thaliana and suspension-cultured cells of Nicotiana tabacum (BY-2), the physiological activity of several auxin analogues was investigated, together with their capacity to induce auxin-dependent gene expression, to inhibit endocytosis and to be transported across the plasma membrane. This study shows that the specificity criteria for different auxin-related processes vary widely. Notably, the special behaviour of some synthetic auxin analogues suggests that they might be useful tools in investigations of the molecular mechanism of auxin action. Thus, due to their differential stimulatory effects on DR5 expression, indole-3-propionic (IPA) and 2,4,5-trichlorophenoxy acetic (2,4,5-T) acids can serve in studies of TRANSPORT INHIBITOR RESPONSE 1/AUXIN SIGNALLING F-BOX (TIR1/AFB)-mediated auxin signalling, and 5-fluoroindole-3-acetic acid (5-F-IAA) can help to discriminate between transcriptional and non-transcriptional pathways of auxin signalling. The results demonstrate that the major determinants for the auxin-like physiological potential of a particular compound are very complex and involve its chemical and metabolic stability, its ability to distribute in tissues in a polar manner and its activity towards auxin signalling machinery. AU - Simon, Sibu AU - Kubeš, Martin AU - Baster, Pawel AU - Robert, Stéphanie AU - Dobrev, Petre AU - Friml, Jirí AU - Petrášek, Jan AU - Zažímalová, Eva ID - 2443 IS - 4 JF - New Phytologist TI - Defining the selectivity of processes along the auxin response chain: A study using auxin analogues VL - 200 ER - TY - JOUR AB - Intracellular protein routing is mediated by vesicular transport which is tightly regulated in eukaryotes. The protein and lipid homeostasis depends on coordinated delivery of de novo synthesized or recycled cargoes to the plasma membrane by exocytosis and their subsequent removal by rerouting them for recycling or degradation. Here, we report the characterization of protein affected trafficking 3 (pat3) mutant that we identified by an epifluorescence-based forward genetic screen for mutants defective in subcellular distribution of Arabidopsis auxin transporter PIN1–GFP. While pat3 displays largely normal plant morphology and development in nutrient-rich conditions, it shows strong ectopic intracellular accumulations of different plasma membrane cargoes in structures that resemble prevacuolar compartments (PVC) with an aberrant morphology. Genetic mapping revealed that pat3 is defective in vacuolar protein sorting 35A (VPS35A), a putative subunit of the retromer complex that mediates retrograde trafficking between the PVC and trans-Golgi network. Similarly, a mutant defective in another retromer subunit, vps29, shows comparable subcellular defects in PVC morphology and protein accumulation. Thus, our data provide evidence that the retromer components VPS35A and VPS29 are essential for normal PVC morphology and normal trafficking of plasma membrane proteins in plants. In addition, we show that, out of the three VPS35 retromer subunits present in Arabidopsis thaliana genome, the VPS35 homolog A plays a prevailing role in trafficking to the lytic vacuole, presenting another level of complexity in the retromer-dependent vacuolar sorting. AU - Nodzyński, Tomasz AU - Feraru, Murguel AU - Hirsch, Sibylle AU - De Rycke, Riet AU - Nicuales, Claudiu AU - Van Leene, Jelle AU - De Jaeger, Geert AU - Vanneste, Steffen AU - Friml, Jirí ID - 2449 IS - 6 JF - Molecular Plant TI - Retromer subunits VPS35A and VPS29 mediate prevacuolar compartment (PVC) function in Arabidopsis VL - 6 ER - TY - JOUR AB - Plant-specific PIN-formed (PIN) efflux transporters for the plant hormone auxin are required for tissue-specific directional auxin transport and cellular auxin homeostasis. The Arabidopsis PIN protein family has been shown to play important roles in developmental processes such as embryogenesis, organogenesis, vascular tissue differentiation, root meristem patterning and tropic growth. Here we analyzed roles of the less characterised Arabidopsis PIN6 auxin transporter. PIN6 is auxin-inducible and is expressed during multiple auxin-regulated developmental processes. Loss of pin6 function interfered with primary root growth and lateral root development. Misexpression of PIN6 affected auxin transport and interfered with auxin homeostasis in other growth processes such as shoot apical dominance, lateral root primordia development, adventitious root formation, root hair outgrowth and root waving. These changes in auxin-regulated growth correlated with a reduction in total auxin transport as well as with an altered activity of DR5-GUS auxin response reporter. Overall, the data indicate that PIN6 regulates auxin homeostasis during plant development. AU - Cazzonelli, Christopher AU - Vanstraelen, Marleen AU - Simon, Sibu AU - Yin, Kuide AU - Carron Arthur, Ashley AU - Nisar, Nazia AU - Tarle, Gauri AU - Cuttriss, Abby AU - Searle, Iain AU - Benková, Eva AU - Mathesius, Ulrike AU - Masle, Josette AU - Friml, Jirí AU - Pogson, Barry ID - 2472 IS - 7 JF - PLoS One TI - Role of the Arabidopsis PIN6 auxin transporter in auxin homeostasis and auxin-mediated development VL - 8 ER - TY - JOUR AB - Background:Auxin binding protein 1 (ABP1) is a putative auxin receptor and its function is indispensable for plant growth and development. ABP1 has been shown to be involved in auxin-dependent regulation of cell division and expansion, in plasma-membrane-related processes such as changes in transmembrane potential, and in the regulation of clathrin-dependent endocytosis. However, the ABP1-regulated downstream pathway remains elusive.Methodology/Principal Findings:Using auxin transport assays and quantitative analysis of cellular morphology we show that ABP1 regulates auxin efflux from tobacco BY-2 cells. The overexpression of ABP1can counterbalance increased auxin efflux and auxin starvation phenotypes caused by the overexpression of PIN auxin efflux carrier. Relevant mechanism involves the ABP1-controlled vesicle trafficking processes, including positive regulation of endocytosis of PIN auxin efflux carriers, as indicated by fluorescence recovery after photobleaching (FRAP) and pharmacological manipulations.Conclusions/Significance:The findings indicate the involvement of ABP1 in control of rate of auxin transport across plasma membrane emphasizing the role of ABP1 in regulation of PIN activity at the plasma membrane, and highlighting the relevance of ABP1 for the formation of developmentally important, PIN-dependent auxin gradients. AU - Čovanová, Milada AU - Sauer, Michael AU - Rychtář, Jan AU - Friml, Jirí AU - Petrášek, Jan AU - Zažímalová, Eva ID - 2470 IS - 7 JF - PLoS One TI - Overexpression of the auxin binding PROTEIN1 modulates PIN-dependent auxin transport in tobacco cells VL - 8 ER - TY - JOUR AB - In order to establish a reference for analysis of the function of auxin and the auxin biosynthesis regulators SHORT INTERNODE/ STYLISH (SHI/STY) during Physcomitrella patens reproductive development, we have described male (antheridial) and female (archegonial) development in detail, including temporal and positional information of organ initiation. This has allowed us to define discrete stages of organ morphogenesis and to show that reproductive organ development in P. patens is highly organized and that organ phyllotaxis differs between vegetative and reproductive development. Using the PpSHI1 and PpSHI2 reporter and knockout lines, the auxin reporters GmGH3pro:GUS and PpPINApro:GFP-GUS, and the auxin-conjugating transgene PpSHI2pro:IAAL, we could show that the PpSHI genes, and by inference also auxin, play important roles for reproductive organ development in moss. The PpSHI genes are required for the apical opening of the reproductive organs, the final differentiation of the egg cell, and the progression of canal cells into a cell death program. The apical cells of the archegonium, the canal cells, and the egg cell are also sites of auxin responsiveness and are affected by reduced levels of active auxin, suggesting that auxin mediates PpSHI function in the reproductive organs. AU - Landberg, Katarina AU - Pederson, Eric AU - Viaene, Tom AU - Bozorg, Behruz AU - Friml, Jirí AU - Jönsson, Henrik AU - Thelander, Mattias AU - Sundberg, Eva ID - 2808 IS - 3 JF - Plant Physiology TI - The moss physcomitrella patens reproductive organ development is highly organized, affected by the two SHI/STY genes and by the level of active auxin in the SHI/STY expression domain VL - 162 ER - TY - JOUR AB - Many key aspects of plant development are regulated by the polarized transport of the phytohormone auxin. Cellular auxin efflux, the rate-limiting step in this process, has been shown to rely on the coordinated action of PIN-formed (PIN) and B-type ATP binding cassette (ABCB) carriers. Here, we report that polar auxin transport in the Arabidopsis thaliana root also requires the action of a Major Facilitator Superfamily (MFS) transporter, Zinc-Induced Facilitator-Like 1 (ZIFL1). Sequencing, promoter-reporter, and fluorescent protein fusion experiments indicate that the full-length ZIFL1.1 protein and a truncated splice isoform, ZIFL1.3, localize to the tonoplast of root cells and the plasma membrane of leaf stomatal guard cells, respectively. Using reverse genetics, we show that the ZIFL1.1 transporter regulates various root auxin-related processes, while the ZIFL1.3 isoform mediates drought tolerance by regulating stomatal closure. Auxin transport and immunolocalization assays demonstrate that ZIFL1.1 indirectly modulates cellular auxin efflux during shootward auxin transport at the root tip, likely by regulating plasma membrane PIN2 abundance. Finally, heterologous expression in yeast revealed that ZIFL1.1 and ZIFL1.3 share H+-coupled K+ transport activity. Thus, by determining the subcellular and tissue distribution of two isoforms, alternative splicing dictates a dual function for the ZIFL1 transporter. We propose that this MFS carrier regulates stomatal movements and polar auxin transport by modulating potassium and proton fluxes in Arabidopsis cells. AU - Remy, Estelle AU - Cabrito, Tânia AU - Baster, Pawel AU - Batista, Rita AU - Teixeira, Miguel AU - Friml, Jirí AU - Sá Correia, Isabel AU - Duque, Paula ID - 2821 IS - 3 JF - Plant Cell TI - A major facilitator superfamily transporter plays a dual role in polar auxin transport and drought stress tolerance in Arabidopsis VL - 25 ER - TY - JOUR AB - Removal of cargos from the cell surface via endocytosis is an efficient mechanism to regulate activities of plasma membrane (PM)-resident proteins, such as receptors or transporters. Salicylic acid (SA) is an important plant hormone that is traditionally associated with pathogen defense. Here, we describe an unanticipated effect of SA on subcellular endocytic cycling of proteins. Both exogenous treatments and endogenously enhanced SA levels repressed endocytosis of different PM proteins. The SA effect on endocytosis did not involve transcription or known components of the SA signaling pathway for transcriptional regulation. SA likely targets an endocytic mechanism that involves the coat protein clathrin, because SA interfered with the clathrin incidence at the PM and clathrin-deficient mutants were less sensitive to the impact of SA on the auxin distribution and root bending during the gravitropic response. By contrast, SA did not affect the ligand-induced endocytosis of the FLAGELLIN SENSING2 (FLS2) receptor during pathogen responses. Our data suggest that the established SA impact on transcription in plant immunity and the nontranscriptional effect of SA on clathrin-mediated endocytosis are independent mechanisms by which SA regulates distinct aspects of plant physiology. AU - Du, Yunlong AU - Tejos, Ricardo AU - Beck, Martina AU - Himschoot, Ellie AU - Li, Hongjiang AU - Robatzek, Silke AU - Vanneste, Steffen AU - Friml, Jirí ID - 2827 IS - 19 JF - PNAS TI - Salicylic acid interferes with clathrin-mediated endocytic protein trafficking VL - 110 ER - TY - JOUR AB - PIN-FORMED (PIN) proteins localize asymmetrically at the plasma membrane and mediate intercellular polar transport of the plant hormone auxin that is crucial for a multitude of developmental processes in plants. PIN localization is under extensive control by environmental or developmental cues, but mechanisms regulating PIN localization are not fully understood. Here we show that early endosomal components ARF GEF BEN1 and newly identified Sec1/Munc18 family protein BEN2 are involved in distinct steps of early endosomal trafficking. BEN1 and BEN2 are collectively required for polar PIN localization, for their dynamic repolarization, and consequently for auxin activity gradient formation and auxin-related developmental processes including embryonic patterning, organogenesis, and vasculature venation patterning. These results show that early endosomal trafficking is crucial for cell polarity and auxin-dependent regulation of plant architecture. AU - Tanaka, Hirokazu AU - Kitakura, Saeko AU - Rakusová, Hana AU - Uemura, Tomohiro AU - Feraru, Mugurel AU - De Rycke, Riet AU - Robert, Stéphanie AU - Kakimoto, Tatsuo AU - Friml, Jirí ID - 2832 IS - 5 JF - PLoS Genetics TI - Cell polarity and patterning by PIN trafficking through early endosomal compartments in arabidopsis thaliana VL - 9 ER - TY - JOUR AB - The phytohormone auxin regulates virtually every aspect of plant development. To identify new genes involved in auxin activity, a genetic screen was performed for Arabidopsis (Arabidopsis thaliana) mutants with altered expression of the auxin-responsive reporter DR5rev:GFP. One of the mutants recovered in the screen, designated as weak auxin response3 (wxr3), exhibits much lower DR5rev:GFP expression when treated with the synthetic auxin 2,4-dichlorophenoxyacetic acid and displays severe defects in root development. The wxr3 mutant decreases polar auxin transport and results in a disruption of the asymmetric auxin distribution. The levels of the auxin transporters AUXIN1 and PIN-FORMED are dramatically reduced in the wxr3 root tip. Molecular analyses demonstrate that WXR3 is ROOT ULTRAVIOLET B-SENSITIVE1 (RUS1), a member of the conserved Domain of Unknown Function647 protein family found in diverse eukaryotic organisms. Our data suggest that RUS1/WXR3 plays an essential role in the regulation of polar auxin transport by maintaining the proper level of auxin transporters on the plasma membrane. AU - Yu, Hong AU - Karampelias, Michael AU - Robert, Stéphanie AU - Peer, Wendy AU - Swarup, Ranjan AU - Ye, Songqing AU - Ge, Lei AU - Cohen, Jerry AU - Murphy, Angus AU - Friml, Jirí AU - Estelle, Mark ID - 2835 IS - 2 JF - Plant Physiology TI - Root ultraviolet b-sensitive1/weak auxin response3 is essential for polar auxin transport in arabidopsis VL - 162 ER - TY - JOUR AB - As soon as a seed germinates, plant growth relates to gravity to ensure that the root penetrates the soil and the shoot expands aerially. Whereas mechanisms of positive and negative orthogravitropism of primary roots and shoots are relatively well understood [1-3], lateral organs often show more complex growth behavior [4]. Lateral roots (LRs) seemingly suppress positive gravitropic growth and show a defined gravitropic set-point angle (GSA) that allows radial expansion of the root system (plagiotropism) [3, 4]. Despite its eminent importance for root architecture, it so far remains completely unknown how lateral organs partially suppress positive orthogravitropism. Here we show that the phytohormone auxin steers GSA formation and limits positive orthogravitropism in LR. Low and high auxin levels/signaling lead to radial or axial root systems, respectively. At a cellular level, it is the auxin transport-dependent regulation of asymmetric growth in the elongation zone that determines GSA. Our data suggest that strong repression of PIN4/PIN7 and transient PIN3 expression limit auxin redistribution in young LR columella cells. We conclude that PIN activity, by temporally limiting the asymmetric auxin fluxes in the tip of LRs, induces transient, differential growth responses in the elongation zone and, consequently, controls root architecture. AU - Rosquete, Michel AU - Von Wangenheim, Daniel AU - Marhavy, Peter AU - Barbez, Elke AU - Stelzer, Ernst AU - Benková, Eva AU - Maizel, Alexis AU - Kleine Vehn, Jürgen ID - 2844 IS - 9 JF - Current Biology TI - An auxin transport mechanism restricts positive orthogravitropism in lateral roots VL - 23 ER - TY - JOUR AB - Plant architecture is influenced by the polar, cell-to-cell transport of auxin that is primarily provided and regulated by plasma membrane efflux catalysts of the PIN-FORMED and B family of ABC transporter (ABCB) classes. The latter were shown to require the functionality of the FK506 binding protein42 TWISTED DWARF1 (TWD1), although underlying mechanisms are unclear. By genetic manipulation of TWD1 expression, we show here that TWD1 affects shootward root auxin reflux and, thus, downstream developmental traits, such as epidermal twisting and gravitropism of the root. Using immunological assays, we demonstrate a predominant lateral, mainly outward-facing, plasma membrane location for TWD1 in the root epidermis characterized by the lateral marker ABC transporter G36/PLEIOTROPIC DRUG-RESISTANCE8/PENETRATION3. At these epidermal plasma membrane domains, TWD1 colocalizes with nonpolar ABCB1. In planta bioluminescence resonance energy transfer analysis was used to verify specific ABC transporter B1 (ABCB1)-TWD1 interaction. Our data support a model in which TWD1 promotes lateral ABCB-mediated auxin efflux via protein-protein interaction at the plasma membrane, minimizing reflux from the root apoplast into the cytoplasm. AU - Wang, Bangjun AU - Bailly, Aurélien AU - Zwiewk, Marta AU - Henrichs, Sina AU - Azzarello, Elisa AU - Mancuso, Stefano AU - Maeshima, Masayoshi AU - Friml, Jirí AU - Schulz, Alexander AU - Geisler, Markus ID - 2883 IS - 1 JF - Plant Cell TI - Arabidopsis TWISTED DWARF1 functionally interacts with auxin exporter ABCB1 on the root plasma membrane VL - 25 ER - TY - JOUR AB - Gravitropic bending of plant organs is mediated by an asymmetric signaling of the plant hormone auxin between the upper and lower side of the respective organ. Here, we show that also another plant hormone, gibberellic acid (GA), shows asymmetric action during gravitropic responses. Immunodetection using an antibody against GA and monitoring GA signaling output by downstream degradation of DELLA proteins revealed an asymmetric GA distribution and response with the maximum at the lower side of gravistimulated roots. Genetic or pharmacological manipulation of GA levels or response affects gravity-mediated auxin redistribution and root bending response. The higher GA levels at the lower side of the root correlate with increased amounts of PIN-FORMED2 (PIN2) auxin transporter at the plasma membrane. The observed increase in PIN2 stability is caused by a specific GA effect on trafficking of PIN proteins to lytic vacuoles that presumably occurs downstream of brefeldin A-sensitive endosomes. Our results suggest that asymmetric auxin distribution instructive for gravity-induced differential growth is consolidated by the asymmetric action of GA that stabilizes the PIN-dependent auxin stream along the lower side of gravistimulated roots. AU - Löfke, Christian AU - Zwiewka, Marta AU - Heilmann, Ingo AU - Van Montagu, Marc AU - Teichmann, Thomas AU - Friml, Jirí ID - 2882 IS - 9 JF - PNAS TI - Asymmetric gibberellin signaling regulates vacuolar trafficking of PIN auxin transporters during root gravitropism VL - 110 ER - TY - JOUR AB - The distribution of the phytohormone auxin regulates many aspects of plant development including growth response to gravity. Gravitropic root curvature involves coordinated and asymmetric cell elongation between the lower and upper side of the root, mediated by differential cellular auxin levels. The asymmetry in the auxin distribution is established and maintained by a spatio-temporal regulation of the PIN-FORMED (PIN) auxin transporter activity. We provide novel insights into the complex regulation of PIN abundance and activity during root gravitropism. We show that PIN2 turnover is differentially regulated on the upper and lower side of gravistimulated roots by distinct but partially overlapping auxin feedback mechanisms. In addition to regulating transcription and clathrin-mediated internalization, auxin also controls PIN abundance at the plasma membrane by promoting their vacuolar targeting and degradation. This effect of elevated auxin levels requires the activity of SKP-Cullin-F-box TIR1/AFB (SCF TIR1/AFB)-dependent pathway. Importantly, also suboptimal auxin levels mediate PIN degradation utilizing the same signalling pathway. These feedback mechanisms are functionally important during gravitropic response and ensure fine-tuning of auxin fluxes for maintaining as well as terminating asymmetric growth. AU - Baster, Pawel AU - Robert, Stéphanie AU - Kleine Vehn, Jürgen AU - Vanneste, Steffen AU - Kania, Urszula AU - Grunewald, Wim AU - De Rybel, Bert AU - Beeckman, Tom AU - Friml, Jirí ID - 2919 IS - 2 JF - EMBO Journal TI - SCF^TIR1 AFB-auxin signalling regulates PIN vacuolar trafficking and auxin fluxes during root gravitropism VL - 32 ER - TY - JOUR AB - Clathrin-mediated endocytosis (CME) regulates many aspects of plant development, including hormone signaling and responses to environmental stresses. Despite the importance of this process, the machinery that regulates CME in plants is largely unknown. In mammals, the heterotetrameric ADAPTOR PROTEIN COMPLEX-2 (AP-2) is required for the formation of clathrin-coated vesicles at the plasma membrane (PM). Although the existence of AP-2 has been predicted in Arabidopsis thaliana, the biochemistry and functionality of the complex is still uncharacterized. Here, we identified all the subunits of the Arabidopsis AP-2 by tandem affinity purification and found that one of the large AP-2 subunits, AP2A1, localized at the PM and interacted with clathrin. Furthermore, endocytosis of the leucine-rich repeat receptor kinase, BRASSINOSTEROID INSENSITIVE1 (BRI1), was shown to depend on AP-2. Knockdown of the two Arabidopsis AP2A genes or overexpression of a dominant-negative version of the medium AP-2 subunit, AP2M, impaired BRI1 endocytosis and enhanced the brassinosteroid signaling. Our data reveal that the CME machinery in Arabidopsis is evolutionarily conserved and that AP-2 functions in receptormediated endocytosis. AU - Di Rubbo, Simone AU - Irani, Niloufer AU - Kim, Soo AU - Xu, Zheng AU - Gadeyne, Astrid AU - Dejonghe, Wim AU - Vanhoutte, Isabelle AU - Persiau, Geert AU - Eeckhout, Dominique AU - Simon, Sibu AU - Song, Kyungyoung AU - Kleine Vehn, Jürgen AU - Friml, Jirí AU - De Jaeger, Geert AU - Van Damme, Daniël AU - Hwang, Inhwan AU - Russinova, Eugenia ID - 509 IS - 8 JF - Plant Cell TI - The clathrin adaptor complex AP-2 mediates endocytosis of brassinosteroid INSENSITIVE1 in arabidopsis VL - 25 ER - TY - JOUR AB - Fertilization in flowering plants requires the temporal and spatial coordination of many developmental processes, including pollen production, anther dehiscence, ovule production, and pollen tube elongation. However, it remains elusive as to how this coordination occurs during reproduction. Here, we present evidence that endocytosis, involving heterotetrameric adaptor protein complex 2 (AP-2), plays a crucial role in fertilization. An Arabidopsis thaliana mutant ap2m displays multiple defects in pollen production and viability, as well as elongation of staminal filaments and pollen tubes, all of which are pivotal processes needed for fertilization. Of these abnormalities, the defects in elongation of staminal filaments and pollen tubes were partially rescued by exogenous auxin. Moreover, DR5rev:GFP (for green fluorescent protein) expression was greatly reduced in filaments and anthers in ap2m mutant plants. At the cellular level, ap2m mutants displayed defects in both endocytosis of N-(3-triethylammonium-propyl)-4- (4-diethylaminophenylhexatrienyl) pyridinium dibromide, a lypophilic dye used as an endocytosis marker, and polar localization of auxin-efflux carrier PIN FORMED2 (PIN2) in the stamen filaments. Moreover, these defects were phenocopied by treatment with Tyrphostin A23, an inhibitor of endocytosis. Based on these results, we propose that AP-2-dependent endocytosis plays a crucial role in coordinating the multiple developmental aspects of male reproductive organs by modulating cellular auxin level through the regulation of the amount and polarity of PINs. AU - Kim, Soo AU - Xu, Zheng AU - Song, Kyungyoung AU - Kim, Dae AU - Kang, Hyangju AU - Reichardt, Ilka AU - Sohn, Eun AU - Friml, Jirí AU - Juergens, Gerd AU - Hwang, Inhwan ID - 507 IS - 8 JF - Plant Cell TI - Adaptor protein complex 2-mediated endocytosis is crucial for male reproductive organ development in arabidopsis VL - 25 ER - TY - JOUR AB - The native auxin, indole-3-acetic acid (IAA), is a major regulator of plant growth and development. Its nonuniform distribution between cells and tissues underlies the spatiotemporal coordination of many developmental events and responses to environmental stimuli. The regulation of auxin gradients and the formation of auxin maxima/minima most likely involve the regulation of both metabolic and transport processes. In this article, we have demonstrated that 2-oxindole-3-acetic acid (oxIAA) is a major primary IAA catabolite formed in Arabidopsis thaliana root tissues. OxIAA had little biological activity and was formed rapidly and irreversibly in response to increases in auxin levels. We further showed that there is cell type-specific regulation of oxIAA levels in the Arabidopsis root apex. We propose that oxIAA is an important element in the regulation of output from auxin gradients and, therefore, in the regulation of auxin homeostasis and response mechanisms. AU - Pěnčík, Aleš AU - Simonovik, Biljana AU - Petersson, Sara AU - Henyková, Eva AU - Simon, Sibu AU - Greenham, Kathleen AU - Zhang, Yi AU - Kowalczyk, Mariusz AU - Estelle, Mark AU - Zažímalová, Eva AU - Novák, Ondřej AU - Sandberg, Göran AU - Ljung, Karin ID - 511 IS - 10 JF - Plant Cell TI - Regulation of auxin homeostasis and gradients in Arabidopsis roots through the formation of the indole-3-acetic acid catabolite 2-oxindole-3-acetic acid VL - 25 ER - TY - JOUR AB - In plants, changes in local auxin concentrations can trigger a range of developmental processes as distinct tissues respond differently to the same auxin stimulus. However, little is known about how auxin is interpreted by individual cell types. We performed a transcriptomic analysis of responses to auxin within four distinct tissues of the Arabidopsis thaliana root and demonstrate that different cell types show competence for discrete responses. The majority of auxin‐responsive genes displayed a spatial bias in their induction or repression. The novel data set was used to examine how auxin influences tissue‐specific transcriptional regulation of cell‐identity markers. Additionally, the data were used in combination with spatial expression maps of the root to plot a transcriptomic auxin‐response gradient across the apical and basal meristem. The readout revealed a strong correlation for thousands of genes between the relative response to auxin and expression along the longitudinal axis of the root. This data set and comparative analysis provide a transcriptome‐level spatial breakdown of the response to auxin within an organ where this hormone mediates many aspects of development. AU - Bargmann, Bastiaan AU - Vanneste, Steffen AU - Krouk, Gabriel AU - Nawy, Tal AU - Efroni, Idan AU - Shani, Eilon AU - Choe, Goh AU - Friml, Jirí AU - Bergmann, Dominique AU - Estelle, Mark AU - Birnbaum, Kenneth ID - 516 IS - 1 JF - Molecular Systems Biology TI - A map of cell type‐specific auxin responses VL - 9 ER - TY - JOUR AB - Establishment of the embryonic axis foreshadows the main body axis of adults both in plants and in animals, but underlying mechanisms are considered distinct. Plants utilize directional, cell-to-cell transport of the growth hormone auxin [1, 2] to generate an asymmetric auxin response that specifies the embryonic apical-basal axis [3-6]. The auxin flow directionality depends on the polarized subcellular localization of PIN-FORMED (PIN) auxin transporters [7, 8]. It remains unknown which mechanisms and spatial cues guide cell polarization and axis orientation in early embryos. Herein, we provide conceptually novel insights into the formation of embryonic axis in Arabidopsis by identifying a crucial role of localized tryptophan-dependent auxin biosynthesis [9-12]. Local auxin production at the base of young embryos and the accompanying PIN7-mediated auxin flow toward the proembryo are required for the apical auxin response maximum and the specification of apical embryonic structures. Later in embryogenesis, the precisely timed onset of localized apical auxin biosynthesis mediates PIN1 polarization, basal auxin response maximum, and specification of the root pole. Thus, the tight spatiotemporal control of distinct local auxin sources provides a necessary, non-cell-autonomous trigger for the coordinated cell polarization and subsequent apical-basal axis orientation during embryogenesis and, presumably, also for other polarization events during postembryonic plant life [13, 14]. AU - Robert, Hélène AU - Grones, Peter AU - Stepanova, Anna AU - Robles, Linda AU - Lokerse, Annemarie AU - Alonso, Jose AU - Weijers, Dolf AU - Friml, Jirí ID - 528 IS - 24 JF - Current Biology TI - Local auxin sources orient the apical basal axis in arabidopsis embryos VL - 23 ER - TY - JOUR AB - The apical-basal axis of the early plant embryo determines the body plan of the adult organism. To establish a polarized embryonic axis, plants evolved a unique mechanism that involves directional, cell-to-cell transport of the growth regulator auxin. Auxin transport relies on PIN auxin transporters [1], whose polar subcellular localization determines the flow directionality. PIN-mediated auxin transport mediates the spatial and temporal activity of the auxin response machinery [2-7] that contributes to embryo patterning processes, including establishment of the apical (shoot) and basal (root) embryo poles [8]. However, little is known of upstream mechanisms guiding the (re)polarization of auxin fluxes during embryogenesis [9]. Here, we developed a model of plant embryogenesis that correctly generates emergent cell polarities and auxin-mediated sequential initiation of apical-basal axis of plant embryo. The model relies on two precisely localized auxin sources and a feedback between auxin and the polar, subcellular PIN transporter localization. Simulations reproduced PIN polarity and auxin distribution, as well as previously unknown polarization events during early embryogenesis. The spectrum of validated model predictions suggests that our model corresponds to a minimal mechanistic framework for initiation and orientation of the apical-basal axis to guide both embryonic and postembryonic plant development. AU - Wabnik, Krzysztof T AU - Robert, Hélène AU - Smith, Richard AU - Friml, Jirí ID - 527 IS - 24 JF - Current Biology TI - Modeling framework for the establishment of the apical-basal embryonic axis in plants VL - 23 ER - TY - JOUR AB - Cell-to-cell directional flow of the phytohormone auxin is primarily established by polar localization of the PIN auxin transporters, a process tightly regulated at multiple levels by auxin itself. We recently reported that, in the context of strong auxin flows, activity of the vacuolar ZIFL1.1 transporter is required for fine-tuning of polar auxin transport rates in the Arabidopsis root. In particular, ZIFL1.1 function protects plasma-membrane stability of the PIN2 carrier in epidermal root tip cells under conditions normally triggering PIN2 degradation. Here, we show that ZIFL1.1 activity at the root tip also promotes PIN1 plasma-membrane abundance in central cylinder cells, thus supporting the notion that ZIFL1.1 acts as a general positive modulator of polar auxin transport in roots. AU - Remy, Estelle AU - Baster, Pawel AU - Friml, Jirí AU - Duque, Paula ID - 2448 IS - 10 JF - Plant Signaling & Behavior TI - ZIFL1.1 transporter modulates polar auxin transport by stabilizing membrane abundance of multiple PINs in Arabidopsis root tip VL - 8 ER -