TY - JOUR AB - The primary cell wall is a fundamental plant constituent that is flexible but sufficiently rigid to support the plant cell shape. Although many studies have demonstrated that reactive oxygen species (ROS) serve as important signaling messengers to modify the cell wall structure and affect cellular growth, the regulatory mechanism underlying the spatial-temporal regulation of ROS activity for cell wall maintenance remains largely unclear. Here, we demonstrate the role of the Arabidopsis (Arabidopsis thaliana) multicopper oxidase-like protein skewed 5 (SKU5) and its homolog SKU5-similar 1 (SKS1) in root cell wall formation through modulating ROS homeostasis. Loss of SKU5 and SKS1 function resulted in aberrant division planes, protruding cell walls, ectopic deposition of iron, and reduced nicotinamide adeninedinucleotide phosphate (NADPH) oxidase-dependent ROS overproduction in the root epidermis–cortex and cortex–endodermis junctions. A decrease in ROS level or inhibition of NADPH oxidase activity rescued the cell wall defects of sku5 sks1 double mutants. SKU5 and SKS1 proteins were activated by iron treatment, and iron over-accumulated in the walls between the root epidermis and cortex cell layers of sku5 sks1. The glycosylphosphatidylinositol-anchored motif was crucial for membrane association and functionality of SKU5 and SKS1. Overall, our results identified SKU5 and SKS1 as regulators of ROS at the cell surface for regulation of cell wall structure and root cell growth. AU - Chen, C AU - Zhang, Y AU - Cai, J AU - Qiu, Y AU - Li, L AU - Gao, C AU - Gao, Y AU - Ke, M AU - Wu, S AU - Wei, C AU - Chen, J AU - Xu, T AU - Friml, Jiří AU - Wang, J AU - Li, R AU - Chao, D AU - Zhang, B AU - Chen, X AU - Gao, Z ID - 13213 IS - 3 JF - Plant Physiology SN - 0032-0889 TI - Multi-copper oxidases SKU5 and SKS1 coordinate cell wall formation using apoplastic redox-based reactions in roots VL - 192 ER - TY - JOUR AB - The quality control system for messenger RNA (mRNA) is fundamental for cellular activities in eukaryotes. To elucidate the molecular mechanism of 3'-Phosphoinositide-Dependent Protein Kinase1 (PDK1), a master regulator that is essential throughout eukaryotic growth and development, we employed a forward genetic approach to screen for suppressors of the loss-of-function T-DNA insertion double mutant pdk1.1 pdk1.2 in Arabidopsis thaliana. Notably, the severe growth attenuation of pdk1.1 pdk1.2 was rescued by sop21 (suppressor of pdk1.1 pdk1.2), which harbours a loss-of-function mutation in PELOTA1 (PEL1). PEL1 is a homologue of mammalian PELOTA and yeast (Saccharomyces cerevisiae) DOM34p, which each form a heterodimeric complex with the GTPase HBS1 (HSP70 SUBFAMILY B SUPPRESSOR1, also called SUPERKILLER PROTEIN7, SKI7), a protein that is responsible for ribosomal rescue and thereby assures the quality and fidelity of mRNA molecules during translation. Genetic analysis further revealed that a dysfunctional PEL1-HBS1 complex failed to degrade the T-DNA-disrupted PDK1 transcripts, which were truncated but functional, and thus rescued the growth and developmental defects of pdk1.1 pdk1.2. Our studies demonstrated the functionality of a homologous PELOTA-HBS1 complex and identified its essential regulatory role in plants, providing insights into the mechanism of mRNA quality control. AU - Kong, W AU - Tan, Shutang AU - Zhao, Q AU - Lin, DL AU - Xu, ZH AU - Friml, Jiří AU - Xue, HW ID - 9368 IS - 4 JF - Plant Physiology SN - 0032-0889 TI - mRNA surveillance complex PELOTA-HBS1 eegulates phosphoinositide-sependent protein kinase1 and plant growth VL - 186 ER - TY - JOUR AB - The phytohormone auxin and its directional transport through tissues are intensively studied. However, a mechanistic understanding of auxin-mediated feedback on endocytosis and polar distribution of PIN auxin transporters remains limited due to contradictory observations and interpretations. Here, we used state-of-the-art methods to reexamine the auxin effects on PIN endocytic trafficking. We used high auxin concentrations or longer treatments versus lower concentrations and shorter treatments of natural (IAA) and synthetic (NAA) auxins to distinguish between specific and nonspecific effects. Longer treatments of both auxins interfere with Brefeldin A-mediated intracellular PIN2 accumulation and also with general aggregation of endomembrane compartments. NAA treatment decreased the internalization of the endocytic tracer dye, FM4-64; however, NAA treatment also affected the number, distribution, and compartment identity of the early endosome/trans-Golgi network (EE/TGN), rendering the FM4-64 endocytic assays at high NAA concentrations unreliable. To circumvent these nonspecific effects of NAA and IAA affecting the endomembrane system, we opted for alternative approaches visualizing the endocytic events directly at the plasma membrane (PM). Using Total Internal Reflection Fluorescence (TIRF) microscopy, we saw no significant effects of IAA or NAA treatments on the incidence and dynamics of clathrin foci, implying that these treatments do not affect the overall endocytosis rate. However, both NAA and IAA at low concentrations rapidly and specifically promoted endocytosis of photo-converted PIN2 from the PM. These analyses identify a specific effect of NAA and IAA on PIN2 endocytosis, thus contributing to its polarity maintenance and furthermore illustrate that high auxin levels have nonspecific effects on trafficking and endomembrane compartments. AU - Narasimhan, Madhumitha AU - Gallei, Michelle C AU - Tan, Shutang AU - Johnson, Alexander J AU - Verstraeten, Inge AU - Li, Lanxin AU - Rodriguez Solovey, Lesia AU - Han, Huibin AU - Himschoot, E AU - Wang, R AU - Vanneste, S AU - Sánchez-Simarro, J AU - Aniento, F AU - Adamowski, Maciek AU - Friml, Jiří ID - 9287 IS - 2 JF - Plant Physiology SN - 0032-0889 TI - Systematic analysis of specific and nonspecific auxin effects on endocytosis and trafficking VL - 186 ER - TY - JOUR AB - The TPLATE complex (TPC) is a key endocytic adaptor protein complex in plants. TPC in Arabidopsis (Arabidopsis thaliana) contains six evolutionarily conserved subunits and two plant-specific subunits, AtEH1/Pan1 and AtEH2/Pan1, although cytoplasmic proteins are not associated with the hexameric subcomplex in the cytoplasm. To investigate the dynamic assembly of the octameric TPC at the plasma membrane (PM), we performed state-of-the-art dual-color live cell imaging at physiological and lowered temperatures. Lowering the temperature slowed down endocytosis, thereby enhancing the temporal resolution of the differential recruitment of endocytic components. Under both normal and lowered temperature conditions, the core TPC subunit TPLATE and the AtEH/Pan1 proteins exhibited simultaneous recruitment at the PM. These results, together with co-localization analysis of different TPC subunits, allow us to conclude that TPC in plant cells is not recruited to the PM sequentially but as an octameric complex. AU - Wang, J AU - Mylle, E AU - Johnson, Alexander J AU - Besbrugge, N AU - De Jaeger, G AU - Friml, Jiří AU - Pleskot, R AU - van Damme, D ID - 7695 IS - 3 JF - Plant Physiology SN - 0032-0889 TI - High temporal resolution reveals simultaneous plasma membrane recruitment of TPLATE complex subunits VL - 183 ER - TY - JOUR AU - Han, Huibin AU - Rakusova, Hana AU - Verstraeten, Inge AU - Zhang, Yuzhou AU - Friml, Jiří ID - 7643 IS - 5 JF - Plant Physiology SN - 0032-0889 TI - SCF TIR1/AFB auxin signaling for bending termination during shoot gravitropism VL - 183 ER - TY - JOUR AB - Nitrate regulation of root stem cell activity is auxin-dependent. AU - Wang, Y AU - Gong, Z AU - Friml, Jiří AU - Zhang, J ID - 6261 IS - 1 JF - Plant Physiology SN - 0032-0889 TI - Nitrate modulates the differentiation of root distal stem cells VL - 180 ER - TY - JOUR AB - Plants have a remarkable capacity to adjust their growth and development to elevated ambient temperatures. Increased elongation growth of roots, hypocotyls and petioles in warm temperatures are hallmarks of seedling thermomorphogenesis. In the last decade, significant progress has been made to identify the molecular signaling components regulating these growth responses. Increased ambient temperature utilizes diverse components of the light sensing and signal transduction network to trigger growth adjustments. However, it remains unknown whether temperature sensing and responses are universal processes that occur uniformly in all plant organs. Alternatively, temperature sensing may be confined to specific tissues or organs, which would require a systemic signal that mediates responses in distal parts of the plant. Here we show that Arabidopsis (Arabidopsis thaliana) seedlings show organ-specific transcriptome responses to elevated temperatures, and that thermomorphogenesis involves both autonomous and organ-interdependent temperature sensing and signaling. Seedling roots can sense and respond to temperature in a shoot-independent manner, whereas shoot temperature responses require both local and systemic processes. The induction of cell elongation in hypocotyls requires temperature sensing in cotyledons, followed by generation of a mobile auxin signal. Subsequently, auxin travels to the hypocotyl where it triggers local brassinosteroid-induced cell elongation in seedling stems, which depends upon a distinct, permissive temperature sensor in the hypocotyl. AU - Bellstaedt, Julia AU - Trenner, Jana AU - Lippmann, Rebecca AU - Poeschl, Yvonne AU - Zhang, Xixi AU - Friml, Jiří AU - Quint, Marcel AU - Delker, Carolin ID - 6366 IS - 2 JF - Plant Physiology SN - 0032-0889 TI - A mobile auxin signal connects temperature sensing in cotyledons with growth responses in hypocotyls VL - 180 ER - TY - JOUR AB - Polar auxin transport plays a pivotal role in plant growth and development. PIN auxin efflux carriers regulate directional auxin movement by establishing local auxin maxima, minima, and gradients that drive multiple developmental processes and responses to environmental signals. Auxin has been proposed to modulate its own transport by regulating subcellular PIN trafficking via processes such as clathrin-mediated PIN endocytosis and constitutive recycling. Here, we further investigated the mechanisms by which auxin affects PIN trafficking by screening auxin analogs and identified pinstatic acid (PISA) as a positive modulator of polar auxin transport in Arabidopsis thaliana. PISA had an auxin-like effect on hypocotyl elongation and adventitious root formation via positive regulation of auxin transport. PISA did not activate SCFTIR1/AFB signaling and yet induced PIN accumulation at the cell surface by inhibiting PIN internalization from the plasma membrane. This work demonstrates PISA to be a promising chemical tool to dissect the regulatory mechanisms behind subcellular PIN trafficking and auxin transport. AU - Oochi, A AU - Hajny, Jakub AU - Fukui, K AU - Nakao, Y AU - Gallei, Michelle C AU - Quareshy, M AU - Takahashi, K AU - Kinoshita, T AU - Harborough, SR AU - Kepinski, S AU - Kasahara, H AU - Napier, RM AU - Friml, Jiří AU - Hayashi, KI ID - 6260 IS - 2 JF - Plant Physiology SN - 0032-0889 TI - Pinstatic acid promotes auxin transport by inhibiting PIN internalization VL - 180 ER - TY - JOUR AB - Auxin steers numerous physiological processes in plants, making the tight control of its endogenous levels and spatiotemporal distribution a necessity. This regulation is achieved by different mechanisms, including auxin biosynthesis, metabolic conversions, degradation, and transport. Here, we introduce cis-cinnamic acid (c-CA) as a novel and unique addition to a small group of endogenous molecules affecting in planta auxin concentrations. c-CA is the photo-isomerization product of the phenylpropanoid pathway intermediate trans-CA (t-CA). When grown on c-CA-containing medium, an evolutionary diverse set of plant species were shown to exhibit phenotypes characteristic for high auxin levels, including inhibition of primary root growth, induction of root hairs, and promotion of adventitious and lateral rooting. By molecular docking and receptor binding assays, we showed that c-CA itself is neither an auxin nor an anti-auxin, and auxin profiling data revealed that c-CA does not significantly interfere with auxin biosynthesis. Single cell-based auxin accumulation assays showed that c-CA, and not t-CA, is a potent inhibitor of auxin efflux. Auxin signaling reporters detected changes in spatiotemporal distribution of the auxin response along the root of c-CA-treated plants, and long-distance auxin transport assays showed no inhibition of rootward auxin transport. Overall, these results suggest that the phenotypes of c-CA-treated plants are the consequence of a local change in auxin accumulation, induced by the inhibition of auxin efflux. This work reveals a novel mechanism how plants may regulate auxin levels and adds a novel, naturally occurring molecule to the chemical toolbox for the studies of auxin homeostasis. AU - Steenackers, Ward AU - Klíma, Petr AU - Quareshy, Mussa AU - Cesarino, Igor AU - Kumpf, Robert AU - Corneillie, Sander AU - Araújo, Pedro AU - Viaene, Tom AU - Goeminne, Geert AU - Nowack, Moritz AU - Ljung, Karin AU - Friml, Jirí AU - Blakeslee, Joshua AU - Novák, Ondřej AU - Zažímalová, Eva AU - Napier, Richard AU - Boerjan, Wout AU - Vanholme, Bartel ID - 1159 IS - 1 JF - Plant Physiology SN - 0032-0889 TI - Cis-cinnamic acid is a novel natural auxin efflux inhibitor that promotes lateral root formation VL - 173 ER - TY - JOUR AB - Cytokinin is a phytohormone that is well known for its roles in numerous plant growth and developmental processes, yet it has also been linked to abiotic stress response in a less defined manner. Arabidopsis (Arabidopsis thaliana) Cytokinin Response Factor 6 (CRF6) is a cytokinin-responsive AP2/ERF-family transcription factor that, through the cytokinin signaling pathway, plays a key role in the inhibition of dark-induced senescence. CRF6 expression is also induced by oxidative stress, and here we show a novel function for CRF6 in relation to oxidative stress and identify downstream transcriptional targets of CRF6 that are repressed in response to oxidative stress. Analysis of transcriptomic changes in wild-type and crf6 mutant plants treated with H2O2 identified CRF6-dependent differentially expressed transcripts, many of which were repressed rather than induced. Moreover, many repressed genes also show decreased expression in 35S:CRF6 overexpressing plants. Together, these findings suggest that CRF6 functions largely as a transcriptional repressor. Interestingly, among the H2O2 repressed CRF6-dependent transcripts was a set of five genes associated with cytokinin processes: (signaling) ARR6, ARR9, ARR11, (biosynthesis) LOG7, and (transport) ABCG14. We have examined mutants of these cytokinin-associated target genes to reveal novel connections to oxidative stress. Further examination of CRF6-DNA interactions indicated that CRF6 may regulate its targets both directly and indirectly. Together, this shows that CRF6 functions during oxidative stress as a negative regulator to control this cytokinin-associated module of CRF6- dependent genes and establishes a novel connection between cytokinin and oxidative stress response. AU - Zwack, Paul AU - De Clercq, Inge AU - Howton, Timothy AU - Hallmark, H Tucker AU - Hurny, Andrej AU - Keshishian, Erika AU - Parish, Alyssa AU - Benková, Eva AU - Mukhtar, M Shahid AU - Van Breusegem, Frank AU - Rashotte, Aaron ID - 1331 IS - 2 JF - Plant Physiology SN - 0032-0889 TI - Cytokinin response factor 6 represses cytokinin-associated genes during oxidative stress VL - 172 ER - TY - JOUR AB - Although cytokinins (CKs) affect a number of processes connected with chloroplasts, it has never been rigorously proven that chloroplasts contain CKs. We isolated intact chloroplasts from tobacco (Nicotiana tabacum L. cv SR1) and wheat (Triticum aestivum L. cv Ritmo) leaves and determined their CKs by liquid chromatography/tandem mass spectroscopy. Chloroplasts from both species contained a whole spectrum of CKs, including free bases (zeatin and isopentenyladenine), ribosides (zeatin riboside, and isopentenyladenosine), ribotides (isopentenyladenosine-5′-monophosphate, zeatin riboside-5′-monophosphate, and dihydrozeatin riboside-5′-monophosphate), and N-glucosides (zeatin-N 9-glucoside, dihydrozeatin-N 9-glucoside, zeatin-N 7-glucoside, and isopentenyladenine-N-glucosides). In chloroplasts there was a moderately higher relative amount of bases, ribosides, and ribotides than in leaves, and a significantly increased level ofN 9-glucosides of zeatin and dihydrozeatin. Tobacco and wheat chloroplasts were prepared from leaves at the end of either a dark or light period. After a dark period, chloroplasts accumulated more CKs than after a light period. The differences were moderate for free bases and ribosides, but highly significant for glucosides. Tobacco chloroplasts from dark-treated leaves contained zeatin riboside-O-glucoside and dihydrozeatin riboside-O-glucoside, as well as a relatively high CK oxidase activity. These data show that chloroplasts contain a whole spectrum of CKs and the enzymatic activity necessary for their metabolism. AU - Benková, Eva AU - Witters, Erwin AU - Van Dongen, Walter AU - Kolář, Jan AU - Motyka, Václav AU - Brzobohatý, Břetislav AU - Van Onckelen, Henri AU - Macháčková, Ivana ID - 2865 IS - 1 JF - Plant Physiology SN - 0032-0889 TI - Cytokinins in tobacco and wheat chloroplasts. Occurrence and changes due to light/dark treatment VL - 121 ER -