TY - JOUR AB - Amid the delays due to the global pandemic, in early October 2022, the auxin community gathered in the idyllic peninsula of Cavtat, Croatia. More than 170 scientists from across the world converged to discuss the latest advancements in fundamental and applied research in the field. The topics, from signalling and transport to plant architecture and response to the environment, show how auxin research must bridge from the molecular realm to macroscopic developmental responses. This is mirrored in this collection of reviews, contributed by participants of the Auxin 2022 meeting. AU - Del Bianco, Marta AU - Friml, Jiří AU - Strader, Lucia AU - Kepinski, Stefan ID - 14709 IS - 22 JF - Journal of Experimental Botany SN - 0022-0957 TI - Auxin research: Creating tools for a greener future VL - 74 ER - TY - JOUR AB - Soluble chaperones residing in the endoplasmic reticulum (ER) play vitally important roles in folding and quality control of newly synthesized proteins that transiently pass through the ER en route to their final destinations. These soluble residents of the ER are themselves endowed with an ER retrieval signal that enables the cell to bring the escaped residents back from the Golgi. Here, by using purified proteins, we showed that Nicotiana tabacum phytaspase, a plant aspartate-specific protease, introduces two breaks at the C-terminus of the N. tabacum ER resident calreticulin-3. These cleavages resulted in removal of either a dipeptide or a hexapeptide from the C-terminus of calreticulin-3 encompassing part or all of the ER retrieval signal. Consistently, expression of the calreticulin-3 derivative mimicking the phytaspase cleavage product in Nicotiana benthamiana cells demonstrated loss of the ER accumulation of the protein. Notably, upon its escape from the ER, calreticulin-3 was further processed by an unknown protease(s) to generate the free N-terminal (N) domain of calreticulin-3, which was ultimately secreted into the apoplast. Our study thus identified a specific proteolytic enzyme capable of precise detachment of the ER retrieval signal from a plant ER resident protein, with implications for the further fate of the escaped resident. AU - Teplova, Anastasiia AU - Pigidanov, Artemii A. AU - Serebryakova, Marina V. AU - Golyshev, Sergei A. AU - Galiullina, Raisa A. AU - Chichkova, Nina V. AU - Vartapetian, Andrey B. ID - 14776 IS - 22 JF - International Journal of Molecular Sciences KW - Inorganic Chemistry KW - Organic Chemistry KW - Physical and Theoretical Chemistry KW - Computer Science Applications KW - Spectroscopy KW - Molecular Biology KW - General Medicine KW - Catalysis SN - 1422-0067 TI - Phytaspase Is capable of detaching the endoplasmic reticulum retrieval signal from tobacco calreticulin-3 VL - 24 ER - TY - JOUR AB - Auxin is the major plant hormone regulating growth and development (Friml, 2022). Forward genetic approaches in the model plant Arabidopsis thaliana have identified major components of auxin signalling and established the canonical mechanism mediating transcriptional and thus developmental reprogramming. In this textbook view, TRANSPORT INHIBITOR RESPONSE 1 (TIR1)/AUXIN-SIGNALING F-BOX (AFBs) are auxin receptors, which act as F-box subunits determining the substrate specificity of the Skp1-Cullin1-F box protein (SCF) type E3 ubiquitin ligase complex. Auxin acts as a “molecular glue” increasing the affinity between TIR1/AFBs and the Aux/IAA repressors. Subsequently, Aux/IAAs are ubiquitinated and degraded, thus releasing auxin transcription factors from their repression making them free to mediate transcription of auxin response genes (Yu et al., 2022). Nonetheless, accumulating evidence suggests existence of rapid, non-transcriptional responses downstream of TIR1/AFBs such as auxin-induced cytosolic calcium (Ca2+) transients, plasma membrane depolarization and apoplast alkalinisation, all converging on the process of root growth inhibition and root gravitropism (Li et al., 2022). Particularly, these rapid responses are mostly contributed by predominantly cytosolic AFB1, while the long-term growth responses are mediated by mainly nuclear TIR1 and AFB2-AFB5 (Li et al., 2021; Prigge et al., 2020; Serre et al., 2021). How AFB1 conducts auxin-triggered rapid responses and how it is different from TIR1 and AFB2-AFB5 remains elusive. Here, we compare the roles of TIR1 and AFB1 in transcriptional and rapid responses by modulating their subcellular localization in Arabidopsis and by testing their ability to mediate transcriptional responses when part of the minimal auxin circuit reconstituted in yeast. AU - Chen, Huihuang AU - Li, Lanxin AU - Zou, Minxia AU - Qi, Linlin AU - Friml, Jiří ID - 13212 IS - 7 JF - Molecular Plant SN - 1752-9867 TI - Distinct functions of TIR1 and AFB1 receptors in auxin signalling. VL - 16 ER - TY - JOUR AB - The 3′,5′-cyclic adenosine monophosphate (cAMP) is a versatile second messenger in many mammalian signaling pathways. However, its role in plants remains not well-recognized. Recent discovery of adenylate cyclase (AC) activity for transport inhibitor response 1/auxin-signaling F-box proteins (TIR1/AFB) auxin receptors and the demonstration of its importance for canonical auxin signaling put plant cAMP research back into spotlight. This insight briefly summarizes the well-established cAMP signaling pathways in mammalian cells and describes the turbulent and controversial history of plant cAMP research highlighting the major progress and the unresolved points. We also briefly review the current paradigm of auxin signaling to provide a background for the discussion on the AC activity of TIR1/AFB auxin receptors and its potential role in transcriptional auxin signaling as well as impact of these discoveries on plant cAMP research in general. AU - Qi, Linlin AU - Friml, Jiří ID - 13266 IS - 2 JF - New Phytologist SN - 0028-646X TI - Tale of cAMP as a second messenger in auxin signaling and beyond VL - 240 ER - TY - JOUR AB - The phytohormone auxin plays central roles in many growth and developmental processes in plants. Development of chemical tools targeting the auxin pathway is useful for both plant biology and agriculture. Here we reveal that naproxen, a synthetic compound with anti-inflammatory activity in humans, acts as an auxin transport inhibitor targeting PIN-FORMED (PIN) transporters in plants. Physiological experiments indicate that exogenous naproxen treatment affects pleiotropic auxin-regulated developmental processes. Additional cellular and biochemical evidence indicates that naproxen suppresses auxin transport, specifically PIN-mediated auxin efflux. Moreover, biochemical and structural analyses confirm that naproxen binds directly to PIN1 protein via the same binding cavity as the indole-3-acetic acid substrate. Thus, by combining cellular, biochemical, and structural approaches, this study clearly establishes that naproxen is a PIN inhibitor and elucidates the underlying mechanisms. Further use of this compound may advance our understanding of the molecular mechanisms of PIN-mediated auxin transport and expand our toolkit in auxin biology and agriculture. AU - Xia, Jing AU - Kong, Mengjuan AU - Yang, Zhisen AU - Sun, Lianghanxiao AU - Peng, Yakun AU - Mao, Yanbo AU - Wei, Hong AU - Ying, Wei AU - Gao, Yongxiao AU - Friml, Jiří AU - Weng, Jianping AU - Liu, Xin AU - Sun, Linfeng AU - Tan, Shutang ID - 13209 IS - 6 JF - Plant Communications TI - Chemical inhibition of Arabidopsis PIN-FORMED auxin transporters by the anti-inflammatory drug naproxen VL - 4 ER - TY - JOUR AB - As a crucial nitrogen source, nitrate (NO3−) is a key nutrient for plants. Accordingly, root systems adapt to maximize NO3− availability, a developmental regulation also involving the phytohormone auxin. Nonetheless, the molecular mechanisms underlying this regulation remain poorly understood. Here, we identify low-nitrate-resistant mutant (lonr) in Arabidopsis (Arabidopsis thaliana), whose root growth fails to adapt to low-NO3− conditions. lonr2 is defective in the high-affinity NO3− transporter NRT2.1. lonr2 (nrt2.1) mutants exhibit defects in polar auxin transport, and their low-NO3−-induced root phenotype depends on the PIN7 auxin exporter activity. NRT2.1 directly associates with PIN7 and antagonizes PIN7-mediated auxin efflux depending on NO3− levels. These results reveal a mechanism by which NRT2.1 in response to NO3− limitation directly regulates auxin transport activity and, thus, root growth. This adaptive mechanism contributes to the root developmental plasticity to help plants cope with changes in NO3− availability. AU - Wang, Yalu AU - Yuan, Zhi AU - Wang, Jinyi AU - Xiao, Huixin AU - Wan, Lu AU - Li, Lanxin AU - Guo, Yan AU - Gong, Zhizhong AU - Friml, Jiří AU - Zhang, Jing ID - 13201 IS - 25 JF - Proceedings of the National Academy of Sciences of the United States of America SN - 0027-8424 TI - The nitrate transporter NRT2.1 directly antagonizes PIN7-mediated auxin transport for root growth adaptation VL - 120 ER - TY - THES AU - Gnyliukh, Nataliia ID - 14510 KW - Clathrin-Mediated Endocytosis KW - vesicle scission KW - Dynamin-Related Protein 2 KW - SH3P2 KW - TPLATE complex KW - Total internal reflection fluorescence microscopy KW - Arabidopsis thaliana SN - 2663-337X TI - Mechanism of clathrin-coated vesicle formation during endocytosis in plants ER - TY - JOUR AB - Auxin has always been at the forefront of research in plant physiology and development. Since the earliest contemplations by Julius von Sachs and Charles Darwin, more than a century-long struggle has been waged to understand its function. This largely reflects the failures, successes, and inevitable progress in the entire field of plant signaling and development. Here I present 14 stations on our long and sometimes mystical journey to understand auxin. These highlights were selected to give a flavor of the field and to show the scope and limits of our current knowledge. A special focus is put on features that make auxin unique among phytohormones, such as its dynamic, directional transport network, which integrates external and internal signals, including self-organizing feedback. Accented are persistent mysteries and controversies. The unexpected discoveries related to rapid auxin responses and growth regulation recently disturbed our contentment regarding understanding of the auxin signaling mechanism. These new revelations, along with advances in technology, usher us into a new, exciting era in auxin research. AU - Friml, Jiří ID - 10016 IS - 5 JF - Cold Spring Harbor Perspectives in Biology SN - 1943-0264 TI - Fourteen stations of auxin VL - 14 ER - TY - JOUR AB - The synthetic strigolactone (SL) analog, rac-GR24, has been instrumental in studying the role of SLs as well as karrikins because it activates the receptors DWARF14 (D14) and KARRIKIN INSENSITIVE 2 (KAI2) of their signaling pathways, respectively. Treatment with rac-GR24 modifies the root architecture at different levels, such as decreasing the lateral root density (LRD), while promoting root hair elongation or flavonol accumulation. Previously, we have shown that the flavonol biosynthesis is transcriptionally activated in the root by rac-GR24 treatment, but, thus far, the molecular players involved in that response have remained unknown. To get an in-depth insight into the changes that occur after the compound is perceived by the roots, we compared the root transcriptomes of the wild type and the more axillary growth2 (max2) mutant, affected in both SL and karrikin signaling pathways, with and without rac-GR24 treatment. Quantitative reverse transcription (qRT)-PCR, reporter line analysis and mutant phenotyping indicated that the flavonol response and the root hair elongation are controlled by the ELONGATED HYPOCOTYL 5 (HY5) and MYB12 transcription factors, but HY5, in contrast to MYB12, affects the LRD as well. Furthermore, we identified the transcription factors TARGET OF MONOPTEROS 5 (TMO5) and TMO5 LIKE1 as negative and the Mediator complex as positive regulators of the rac-GR24 effect on LRD. Altogether, hereby, we get closer toward understanding the molecular mechanisms that underlay the rac-GR24 responses in the root. AU - Struk, Sylwia AU - Braem, Lukas AU - Matthys, Cedrick AU - Walton, Alan AU - Vangheluwe, Nick AU - Van Praet, Stan AU - Jiang, Lingxiang AU - Baster, Pawel AU - De Cuyper, Carolien AU - Boyer, Francois-Didier AU - Stes, Elisabeth AU - Beeckman, Tom AU - Friml, Jiří AU - Gevaert, Kris AU - Goormachtig, Sofie ID - 10583 IS - 1 JF - Plant & Cell Physiology KW - flavonols KW - MAX2 KW - rac-Gr24 KW - RNA-seq KW - root development KW - transcriptional regulation SN - 0032-0781 TI - Transcriptional analysis in the Arabidopsis roots reveals new regulators that link rac-GR24 treatment with changes in flavonol accumulation, root hair elongation and lateral root density VL - 63 ER - TY - JOUR AB - Much of what we know about the role of auxin in plant development derives from exogenous manipulations of auxin distribution and signaling, using inhibitors, auxins and auxin analogs. In this context, synthetic auxin analogs, such as 1-Naphtalene Acetic Acid (1-NAA), are often favored over the endogenous auxin indole-3-acetic acid (IAA), in part due to their higher stability. While such auxin analogs have proven to be instrumental to reveal the various faces of auxin, they display in some cases distinct bioactivities compared to IAA. Here, we focused on the effect of auxin analogs on the accumulation of PIN proteins in Brefeldin A-sensitive endosomal aggregations (BFA bodies), and the correlation with the ability to elicit Ca 2+ responses. For a set of commonly used auxin analogs, we evaluated if auxin-analog induced Ca 2+ signaling inhibits PIN accumulation. Not all auxin analogs elicited a Ca 2+ response, and their differential ability to elicit Ca 2+ responses correlated partially with their ability to inhibit BFA-body formation. However, in tir1/afb and cngc14, 1-NAA-induced Ca 2+ signaling was strongly impaired, yet 1-NAA still could inhibit PIN accumulation in BFA bodies. This demonstrates that TIR1/AFB-CNGC14-dependent Ca 2+ signaling does not inhibit BFA body formation in Arabidopsis roots. AU - Wang, R AU - Himschoot, E AU - Grenzi, M AU - Chen, J AU - Safi, A AU - Krebs, M AU - Schumacher, K AU - Nowack, MK AU - Moeder, W AU - Yoshioka, K AU - Van Damme, D AU - De Smet, I AU - Geelen, D AU - Beeckman, T AU - Friml, Jiří AU - Costa, A AU - Vanneste, S ID - 10717 IS - 8 JF - Journal of Experimental Botany SN - 0022-0957 TI - Auxin analog-induced Ca2+ signaling is independent of inhibition of endosomal aggregation in Arabidopsis roots VL - 73 ER - TY - JOUR AB - Auxin, one of the first identified and most widely studied phytohormones, has been and will remain a hot topic in plant biology. After more than a century of passionate exploration, the mysteries of its synthesis, transport, signaling, and metabolism have largely been unlocked. Due to the rapid development of new technologies, new methods, and new genetic materials, the study of auxin has entered the fast lane over the past 30 years. Here, we highlight advances in understanding auxin signaling, including auxin perception, rapid auxin responses, TRANSPORT INHIBITOR RESPONSE 1 and AUXIN SIGNALING F-boxes (TIR1/AFBs)-mediated transcriptional and non-transcriptional branches, and the epigenetic regulation of auxin signaling. We also focus on feedback inhibition mechanisms that prevent the over-amplification of auxin signals. In addition, we cover the TRANSMEMBRANE KINASEs (TMKs)-mediated non-canonical signaling, which converges with TIR1/AFBs-mediated transcriptional regulation to coordinate plant growth and development. The identification of additional auxin signaling components and their regulation will continue to open new avenues of research in this field, leading to an increasingly deeper, more comprehensive understanding of how auxin signals are interpreted at the cellular level to regulate plant growth and development. AU - Yu, Z AU - Zhang, F AU - Friml, Jiří AU - Ding, Z ID - 10719 IS - 2 JF - Journal of Integrative Plant Biology SN - 1672-9072 TI - Auxin signaling: Research advances over the past 30 years VL - 64 ER - TY - JOUR AB - Among the most fascinated properties of the plant hormone auxin is its ability to promote formation of its own directional transport routes. These gradually narrowing auxin channels form from the auxin source toward the sink and involve coordinated, collective polarization of individual cells. Once established, the channels provide positional information, along which new vascular strands form, for example, during organogenesis, regeneration, or leave venation. The main prerequisite of this still mysterious auxin canalization mechanism is a feedback between auxin signaling and its directional transport. This is manifested by auxin-induced re-arrangements of polar, subcellular localization of PIN-FORMED (PIN) auxin exporters. Immanent open questions relate to how position of auxin source and sink as well as tissue context are sensed and translated into tissue polarization and how cells communicate to polarize coordinately. Recently, identification of the first molecular players opens new avenues into molecular studies of this intriguing example of self-organizing plant development. AU - Hajny, Jakub AU - Tan, Shutang AU - Friml, Jiří ID - 10768 IS - 2 JF - Current Opinion in Plant Biology SN - 1369-5266 TI - Auxin canalization: From speculative models toward molecular players VL - 65 ER - TY - JOUR AB - In eukaryotes, clathrin-coated vesicles (CCVs) facilitate the internalization of material from the cell surface as well as the movement of cargo in post-Golgi trafficking pathways. This diversity of functions is partially provided by multiple monomeric and multimeric clathrin adaptor complexes that provide compartment and cargo selectivity. The adaptor-protein assembly polypeptide-1 (AP-1) complex operates as part of the secretory pathway at the trans-Golgi network (TGN), while the AP-2 complex and the TPLATE complex jointly operate at the plasma membrane to execute clathrin-mediated endocytosis. Key to our further understanding of clathrin-mediated trafficking in plants will be the comprehensive identification and characterization of the network of evolutionarily conserved and plant-specific core and accessory machinery involved in the formation and targeting of CCVs. To facilitate these studies, we have analyzed the proteome of enriched TGN/early endosome-derived and endocytic CCVs isolated from dividing and expanding suspension-cultured Arabidopsis (Arabidopsis thaliana) cells. Tandem mass spectrometry analysis results were validated by differential chemical labeling experiments to identify proteins co-enriching with CCVs. Proteins enriched in CCVs included previously characterized CCV components and cargos such as the vacuolar sorting receptors in addition to conserved and plant-specific components whose function in clathrin-mediated trafficking has not been previously defined. Notably, in addition to AP-1 and AP-2, all subunits of the AP-4 complex, but not AP-3 or AP-5, were found to be in high abundance in the CCV proteome. The association of AP-4 with suspension-cultured Arabidopsis CCVs is further supported via additional biochemical data. AU - Dahhan, DA AU - Reynolds, GD AU - Cárdenas, JJ AU - Eeckhout, D AU - Johnson, Alexander J AU - Yperman, K AU - Kaufmann, Walter AU - Vang, N AU - Yan, X AU - Hwang, I AU - Heese, A AU - De Jaeger, G AU - Friml, Jiří AU - Van Damme, D AU - Pan, J AU - Bednarek, SY ID - 10841 IS - 6 JF - Plant Cell SN - 1040-4651 TI - Proteomic characterization of isolated Arabidopsis clathrin-coated vesicles reveals evolutionarily conserved and plant-specific components VL - 34 ER - TY - JOUR AB - Despite the growing interest in using chemical genetics in plant research, small molecule target identification remains a major challenge. The cellular thermal shift assay coupled with high-resolution mass spectrometry (CETSA MS) that monitors changes in the thermal stability of proteins caused by their interactions with small molecules, other proteins, or posttranslational modifications, allows the discovery of drug targets or the study of protein–metabolite and protein–protein interactions mainly in mammalian cells. To showcase the applicability of this method in plants, we applied CETSA MS to intact Arabidopsis thaliana cells and identified the thermal proteome of the plant-specific glycogen synthase kinase 3 (GSK3) inhibitor, bikinin. A comparison between the thermal and the phosphoproteomes of bikinin revealed the auxin efflux carrier PIN-FORMED1 (PIN1) as a substrate of the Arabidopsis GSK3s that negatively regulate the brassinosteroid signaling. We established that PIN1 phosphorylation by the GSK3s is essential for maintaining its intracellular polarity that is required for auxin-mediated regulation of vascular patterning in the leaf, thus revealing cross-talk between brassinosteroid and auxin signaling. AU - Lu, Qing AU - Zhang, Yonghong AU - Hellner, Joakim AU - Giannini, Caterina AU - Xu, Xiangyu AU - Pauwels, Jarne AU - Ma, Qian AU - Dejonghe, Wim AU - Han, Huibin AU - Van De Cotte, Brigitte AU - Impens, Francis AU - Gevaert, Kris AU - De Smet, Ive AU - Friml, Jiří AU - Molina, Daniel Martinez AU - Russinova, Eugenia ID - 10888 IS - 11 JF - Proceedings of the National Academy of Sciences of the United States of America TI - Proteome-wide cellular thermal shift assay reveals unexpected cross-talk between brassinosteroid and auxin signaling VL - 119 ER - TY - JOUR AB - Calcium-dependent protein kinases (CPK) are key components of a wide array of signaling pathways, translating stress and nutrient signaling into the modulation of cellular processes such as ion transport and transcription. However, not much is known about CPKs in endomembrane trafficking. Here, we screened for CPKs that impact on root growth and gravitropism, by overexpressing constitutively active forms of CPKs under the control of an inducible promoter in Arabidopsis thaliana. We found that inducible overexpression of an constitutive active CPK30 (CA-CPK30) resulted in a loss of root gravitropism and ectopic auxin accumulation in the root tip. Immunolocalization revealed that CA-CPK30 roots have reduced PIN protein levels, PIN1 polarity defects and impaired Brefeldin A (BFA)-sensitive trafficking. Moreover, FM4-64 uptake was reduced, indicative of a defect in endocytosis. The effects on BFA-sensitive trafficking were not specific to PINs, as BFA could not induce aggregation of ARF1- and CHC-labeled endosomes in CA-CPK30. Interestingly, the interference with BFA-body formation, could be reverted by increasing the extracellular pH, indicating a pH-dependence of this CA-CPK30 effect. Altogether, our data reveal an important role for CPK30 in root growth regulation and endomembrane trafficking in Arabidopsis thaliana. AU - Wang, Ren AU - Himschoot, Ellie AU - Chen, Jian AU - Boudsocq, Marie AU - Geelen, Danny AU - Friml, Jiří AU - Beeckman, Tom AU - Vanneste, Steffen ID - 11589 JF - Frontiers in Plant Science TI - Constitutive active CPK30 interferes with root growth and endomembrane trafficking in Arabidopsis thaliana VL - 13 ER - TY - JOUR AB - Plant cell growth responds rapidly to various stimuli, adapting architecture to environmental changes. Two major endogenous signals regulating growth are the phytohormone auxin and the secreted peptides rapid alkalinization factors (RALFs). Both trigger very rapid cellular responses and also exert long-term effects [Du et al., Annu. Rev. Plant Biol. 71, 379–402 (2020); Blackburn et al., Plant Physiol. 182, 1657–1666 (2020)]. However, the way, in which these distinct signaling pathways converge to regulate growth, remains unknown. Here, using vertical confocal microscopy combined with a microfluidic chip, we addressed the mechanism of RALF action on growth. We observed correlation between RALF1-induced rapid Arabidopsis thaliana root growth inhibition and apoplast alkalinization during the initial phase of the response, and revealed that RALF1 reversibly inhibits primary root growth through apoplast alkalinization faster than within 1 min. This rapid apoplast alkalinization was the result of RALF1-induced net H+ influx and was mediated by the receptor FERONIA (FER). Furthermore, we investigated the cross-talk between RALF1 and the auxin signaling pathways during root growth regulation. The results showed that RALF-FER signaling triggered auxin signaling with a delay of approximately 1 h by up-regulating auxin biosynthesis, thus contributing to sustained RALF1-induced growth inhibition. This biphasic RALF1 action on growth allows plants to respond rapidly to environmental stimuli and also reprogram growth and development in the long term. AU - Li, Lanxin AU - Chen, Huihuang AU - Alotaibi, Saqer S. AU - Pěnčík, Aleš AU - Adamowski, Maciek AU - Novák, Ondřej AU - Friml, Jiří ID - 11723 IS - 31 JF - Proceedings of the National Academy of Sciences KW - Multidisciplinary SN - 0027-8424 TI - RALF1 peptide triggers biphasic root growth inhibition upstream of auxin biosynthesis VL - 119 ER - TY - JOUR AB - Strigolactones (SLs) are a class of phytohormones that regulate plant shoot branching and adventitious root development. However, little is known regarding the role of SLs in controlling the behavior of the smallest unit of the organism, the single cell. Here, taking advantage of a classic single-cell model offered by the cotton (Gossypium hirsutum) fiber cell, we show that SLs, whose biosynthesis is fine-tuned by gibberellins (GAs), positively regulate cell elongation and cell wall thickness by promoting the biosynthesis of very-long-chain fatty acids (VLCFAs) and cellulose, respectively. Furthermore, we identified two layers of transcription factors (TFs) involved in the hierarchical regulation of this GA-SL crosstalk. The top-layer TF GROWTH-REGULATING FACTOR 4 (GhGRF4) directly activates expression of the SL biosynthetic gene DWARF27 (D27) to increase SL accumulation in fiber cells and GAs induce GhGRF4 expression. SLs induce the expression of four second-layer TF genes (GhNAC100-2, GhBLH51, GhGT2, and GhB9SHZ1), which transmit SL signals downstream to two ketoacyl-CoA synthase genes (KCS) and three cellulose synthase (CesA) genes by directly activating their transcription. Finally, the KCS and CesA enzymes catalyze the biosynthesis of very long chain fatty acids and cellulose, respectively, to regulate development of high-grade cotton fibers. In addition to providing a theoretical basis for cotton fiber improvement, our results shed light on SL signaling in plant development at the single-cell level. AU - Tian, Z AU - Zhang, Yuzhou AU - Zhu, L AU - Jiang, B AU - Wang, H AU - Gao, R AU - Friml, Jiří AU - Xiao, G ID - 12053 IS - 12 JF - The Plant Cell SN - 1040-4651 TI - Strigolactones act downstream of gibberellins to regulate fiber cell elongation and cell wall thickness in cotton (Gossypium hirsutum) VL - 34 ER - TY - JOUR AB - Directionality in the intercellular transport of the plant hormone auxin is determined by polar plasma membrane localization of PIN-FORMED (PIN) auxin transport proteins. However, apart from PIN phosphorylation at conserved motifs, no further determinants explicitly controlling polar PIN sorting decisions have been identified. Here we present Arabidopsis WAVY GROWTH 3 (WAV3) and closely related RING-finger E3 ubiquitin ligases, whose loss-of-function mutants show a striking apical-to-basal polarity switch in PIN2 localization in root meristem cells. WAV3 E3 ligases function as essential determinants for PIN polarity, acting independently from PINOID/WAG-dependent PIN phosphorylation. They antagonize ectopic deposition of de novo synthesized PIN proteins already immediately following completion of cell division, presumably via preventing PIN sorting into basal, ARF GEF-mediated trafficking. Our findings reveal an involvement of E3 ligases in the selective targeting of apically localized PINs in higher plants. AU - Konstantinova, N AU - Hörmayer, Lukas AU - Glanc, Matous AU - Keshkeih, R AU - Tan, Shutang AU - Di Donato, M AU - Retzer, K AU - Moulinier-Anzola, J AU - Schwihla, M AU - Korbei, B AU - Geisler, M AU - Friml, Jiří AU - Luschnig, C ID - 12052 JF - Nature Communications SN - 2041-1723 TI - WAVY GROWTH Arabidopsis E3 ubiquitin ligases affect apical PIN sorting decisions VL - 13 ER - TY - JOUR AB - Polar auxin transport is unique to plants and coordinates their growth and development1,2. The PIN-FORMED (PIN) auxin transporters exhibit highly asymmetrical localizations at the plasma membrane and drive polar auxin transport3,4; however, their structures and transport mechanisms remain largely unknown. Here, we report three inward-facing conformation structures of Arabidopsis thaliana PIN1: the apo state, bound to the natural auxin indole-3-acetic acid (IAA), and in complex with the polar auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). The transmembrane domain of PIN1 shares a conserved NhaA fold5. In the substrate-bound structure, IAA is coordinated by both hydrophobic stacking and hydrogen bonding. NPA competes with IAA for the same site at the intracellular pocket, but with a much higher affinity. These findings inform our understanding of the substrate recognition and transport mechanisms of PINs and set up a framework for future research on directional auxin transport, one of the most crucial processes underlying plant development. AU - Yang, Z AU - Xia, J AU - Hong, J AU - Zhang, C AU - Wei, H AU - Ying, W AU - Sun, C AU - Sun, L AU - Mao, Y AU - Gao, Y AU - Tan, S AU - Friml, Jiří AU - Li, D AU - Liu, X AU - Sun, L ID - 12054 IS - 7927 JF - Nature SN - 0028-0836 TI - Structural insights into auxin recognition and efflux by Arabidopsis PIN1 VL - 609 ER - TY - JOUR AB - Autophagosomes are double-membraned vesicles that traffic harmful or unwanted cellular macromolecules to the vacuole for recycling. Although autophagosome biogenesis has been extensively studied, autophagosome maturation, i.e., delivery and fusion with the vacuole, remains largely unknown in plants. Here, we have identified an autophagy adaptor, CFS1, that directly interacts with the autophagosome marker ATG8 and localizes on both membranes of the autophagosome. Autophagosomes form normally in Arabidopsis thaliana cfs1 mutants, but their delivery to the vacuole is disrupted. CFS1’s function is evolutionarily conserved in plants, as it also localizes to the autophagosomes and plays a role in autophagic flux in the liverwort Marchantia polymorpha. CFS1 regulates autophagic flux by bridging autophagosomes with the multivesicular body-localized ESCRT-I component VPS23A, leading to the formation of amphisomes. Similar to CFS1-ATG8 interaction, disrupting the CFS1-VPS23A interaction blocks autophagic flux and renders plants sensitive to nitrogen starvation. Altogether, our results reveal a conserved vacuolar sorting hub that regulates autophagic flux in plants. AU - Zhao, Jierui AU - Bui, Mai Thu AU - Ma, Juncai AU - Künzl, Fabian AU - Picchianti, Lorenzo AU - De La Concepcion, Juan Carlos AU - Chen, Yixuan AU - Petsangouraki, Sofia AU - Mohseni, Azadeh AU - García-Leon, Marta AU - Gomez, Marta Salas AU - Giannini, Caterina AU - Gwennogan, Dubois AU - Kobylinska, Roksolana AU - Clavel, Marion AU - Schellmann, Swen AU - Jaillais, Yvon AU - Friml, Jiří AU - Kang, Byung-Ho AU - Dagdas, Yasin ID - 12121 IS - 12 JF - Journal of Cell Biology KW - Cell Biology SN - 0021-9525 TI - Plant autophagosomes mature into amphisomes prior to their delivery to the central vacuole VL - 221 ER -