@article{1562, abstract = {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.}, author = {Grones, Peter and Chen, Xu and Simon, Sibu and Kaufmann, Walter and De Rycke, Riet and Nodzyński, Tomasz and Zažímalová, Eva and Friml, Jirí}, journal = {Journal of Experimental Botany}, number = {16}, pages = {5055 -- 5065}, publisher = {Oxford University Press}, title = {{Auxin-binding pocket of ABP1 is crucial for its gain-of-function cellular and developmental roles}}, doi = {10.1093/jxb/erv177}, volume = {66}, year = {2015}, } @article{1569, abstract = {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.}, author = {Doyle, Siamsa and Haegera, Ash and Vain, Thomas and Rigala, Adeline and Viotti, Corrado and Łangowskaa, Małgorzata and Maa, Qian and Friml, Jirí and Raikhel, Natasha and Hickse, Glenn and Robert, Stéphanie}, journal = {PNAS}, number = {7}, pages = {E806 -- E815}, publisher = {National Academy of Sciences}, title = {{An early secretory pathway mediated by gnom-like 1 and gnom is essential for basal polarity establishment in Arabidopsis thaliana}}, doi = {10.1073/pnas.1424856112}, volume = {112}, year = {2015}, } @article{1574, abstract = {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.}, author = {Chen, Qian and Liu, Yang and Maere, Steven and Lee, Eunkyoung and Van Isterdael, Gert and Xie, Zidian and Xuan, Wei and Lucas, Jessica and Vassileva, Valya and Kitakura, Saeko and Marhavy, Peter and Wabnik, Krzysztof T and Geldner, Niko and Benková, Eva and Le, Jie and Fukaki, Hidehiro and Grotewold, Erich and Li, Chuanyou and Friml, Jirí and Sack, Fred and Beeckman, Tom and Vanneste, Steffen}, journal = {Nature Communications}, publisher = {Nature Publishing Group}, title = {{A coherent transcriptional feed-forward motif model for mediating auxin-sensitive PIN3 expression during lateral root development}}, doi = {10.1038/ncomms9821}, volume = {6}, year = {2015}, } @article{1591, abstract = {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.}, author = {Adamowski, Maciek and Friml, Jirí}, journal = {Plant Cell}, number = {1}, pages = {20 -- 32}, publisher = {American Society of Plant Biologists}, title = {{PIN-dependent auxin transport: Action, regulation, and evolution}}, doi = {10.1105/tpc.114.134874}, volume = {27}, year = {2015}, } @article{1383, abstract = {In plants, vacuolar H+-ATPase (V-ATPase) activity acidifies both the trans-Golgi network/early endosome (TGN/EE) and the vacuole. This dual V-ATPase function has impeded our understanding of how the pH homeostasis within the plant TGN/EE controls exo- and endocytosis. Here, we show that the weak V-ATPase mutant deetiolated3 (det3) displayed a pH increase in the TGN/EE, but not in the vacuole, strongly impairing secretion and recycling of the brassinosteroid receptor and the cellulose synthase complexes to the plasma membrane, in contrast to mutants lacking tonoplast-localized V-ATPase activity only. The brassinosteroid insensitivity and the cellulose deficiency defects in det3 were tightly correlated with reduced Golgi and TGN/EE motility. Thus, our results provide strong evidence that acidification of the TGN/EE, but not of the vacuole, is indispensable for functional secretion and recycling in plants.}, author = {Yu, Luo and Scholl, Stefan and Doering, Anett and Yi, Zhang and Irani, Niloufer and Di Rubbo, Simone and Neumetzler, Lutz and Krishnamoorthy, Praveen and Van Houtte, Isabelle and Mylle, Evelien and Bischoff, Volker and Vernhettes, Samantha and Winne, Johan and Friml, Jirí and Stierhof, York and Schumacher, Karin and Persson, Staffan and Russinova, Eugenia}, journal = {Nature Plants}, number = {7}, publisher = {Nature Publishing Group}, title = {{V-ATPase activity in the TGN/EE is required for exocytosis and recycling in Arabidopsis}}, doi = {10.1038/nplants.2015.94}, volume = {1}, year = {2015}, } @inbook{1806, abstract = {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.}, author = {Baster, Pawel and Friml, Jiří}, booktitle = {Auxin and Its Role in Plant Development}, editor = {Zažímalová, Eva and Petrášek, Jan and Benková, Eva}, pages = {143 -- 170}, publisher = {Springer}, title = {{Auxin on the road navigated by cellular PIN polarity}}, doi = {10.1007/978-3-7091-1526-8_8}, year = {2014}, } @article{1852, abstract = {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.}, author = {Sassi, Massimiliano and Ali, Olivier and Boudon, Frédéric and Cloarec, Gladys and Abad, Ursula and Cellier, Coralie and Chen, Xu and Gilles, Benjamin and Milani, Pascale and Friml, Jirí and Vernoux, Teva and Godin, Christophe and Hamant, Olivier and Traas, Jan}, journal = {Current Biology}, number = {19}, pages = {2335 -- 2342}, publisher = {Cell Press}, title = {{An auxin-mediated shift toward growth isotropy promotes organ formation at the shoot meristem in Arabidopsis}}, doi = {10.1016/j.cub.2014.08.036}, volume = {24}, year = {2014}, } @article{1862, abstract = {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.}, author = {Chen, Xu and Grandont, Laurie and Li, Hongjiang and Hauschild, Robert and Paque, Sébastien and Abuzeineh, Anas and Rakusova, Hana and Benková, Eva and Perrot Rechenmann, Catherine and Friml, Jirí}, issn = {1476-4687}, journal = {Nature}, number = {729}, pages = {90 -- 93}, publisher = {Nature Publishing Group}, title = {{Inhibition of cell expansion by rapid ABP1-mediated auxin effect on microtubules}}, doi = {10.1038/nature13889}, volume = {516}, year = {2014}, } @article{1893, abstract = {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.}, author = {Nováková, Petra and Hirsch, Sibylle and Feraru, Elena and Tejos, Ricardo and Van Wijk, Ringo and Viaene, Tom and Heilmann, Mareike and Lerche, Jennifer and De Rycke, Riet and Feraru, Mugurel and Grones, Peter and Van Montagu, Marc and Heilmann, Ingo and Munnik, Teun and Friml, Jirí}, journal = {PNAS}, number = {7}, pages = {2818 -- 2823}, publisher = {National Academy of Sciences}, title = {{SAC phosphoinositide phosphatases at the tonoplast mediate vacuolar function in Arabidopsis}}, doi = {10.1073/pnas.1324264111}, volume = {111}, year = {2014}, } @article{1897, abstract = {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.}, author = {Naramoto, Satoshi and Otegui, Marisa and Kutsuna, Natsumaro and De Rycke, Riet and Dainobu, Tomoko and Karampelias, Michael and Fujimoto, Masaru and Feraru, Elena and Miki, Daisuke and Fukuda, Hiroo and Nakano, Akihiko and Friml, Jirí}, journal = {Plant Cell}, number = {7}, pages = {3062 -- 3076}, publisher = {American Society of Plant Biologists}, title = {{Insights into the localization and function of the membrane trafficking regulator GNOM ARF-GEF at the Golgi apparatus in Arabidopsis}}, doi = {10.1105/tpc.114.125880}, volume = {26}, year = {2014}, } @article{1901, abstract = {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.}, author = {Tian, Huiyu and Wabnik, Krzysztof T and Niu, Tiantian and Li, Hongjiang and Yu, Qianqian and Pollmann, Stephan and Vanneste, Steffen and Govaerts, Willy and Rolčík, Jakub and Geisler, Markus and Friml, Jirí and Ding, Zhaojun}, journal = {Molecular Plant}, number = {2}, pages = {277 -- 289}, publisher = {Oxford University Press}, title = {{WOX5-IAA17 feedback circuit-mediated cellular auxin response is crucial for the patterning of root stem cell niches in arabidopsis}}, doi = {10.1093/mp/sst118}, volume = {7}, year = {2014}, } @article{1914, abstract = {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.}, author = {Sauer, Michael and Friml, Jirí}, journal = {Current Biology}, number = {1}, pages = {R27 -- R29}, publisher = {Cell Press}, title = {{Plant biology: Gatekeepers of the road to protein perdition}}, doi = {10.1016/j.cub.2013.11.019}, volume = {24}, year = {2014}, } @article{1915, abstract = {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.}, author = {Chen, Xu and Friml, Jirí}, issn = {1470-8752}, journal = {Biochemical Society Transactions}, number = {1}, pages = {212 -- 218}, publisher = {Portland Press}, title = {{Rho-GTPase-regulated vesicle trafficking in plant cell polarity}}, doi = {10.1042/BST20130269}, volume = {42}, year = {2014}, } @article{1917, abstract = {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.}, author = {Xu, Tongda and Dai, Ning and Chen, Jisheng and Nagawa, Shingo and Cao, Min and Li, Hongjiang and Zhou, Zimin and Chen, Xu and De Rycke, Riet and Rakusová, Hana and Wang, Wen and Jones, Alan and Friml, Jirí and Patterson, Sara and Bleecker, Anthony and Yang, Zhenbiao}, journal = {Science}, number = {6174}, pages = {1025 -- 1028}, publisher = {American Association for the Advancement of Science}, title = {{Cell surface ABP1-TMK auxin sensing complex activates ROP GTPase signaling}}, doi = {10.1126/science.1245125}, volume = {343}, year = {2014}, } @article{1921, abstract = {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.}, author = {Tejos, Ricardo and Sauer, Michael and Vanneste, Steffen and Palacios-Gomez, MiriamPalacios and Li, Hongjiang and Heilmann, Mareike and Van Wijk, Ringo and Vermeer, Joop and Heilmann, Ingo and Munnik, Teun and Friml, Jirí}, journal = {Plant Cell}, number = {5}, pages = {2114 -- 2128}, publisher = {American Society of Plant Biologists}, title = {{Bipolar plasma membrane distribution of phosphoinositides and their requirement for auxin-mediated cell polarity and patterning in Arabidopsis}}, doi = {10.1105/tpc.114.126185}, volume = {26}, year = {2014}, } @article{1924, abstract = {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.}, author = {Le, Jie and Liu, Xuguang and Yang, Kezhen and Chen, Xiaolan and Zhu, Lingling and Wang, Hongzhe and Wang, Ming and Vanneste, Steffen and Morita, Miyo and Tasaka, Masao and Ding, Zhaojun and Friml, Jirí and Beeckman, Tom and Sack, Fred}, journal = {Nature Communications}, publisher = {Nature Publishing Group}, title = {{Auxin transport and activity regulate stomatal patterning and development}}, doi = {10.1038/ncomms4090}, volume = {5}, year = {2014}, } @article{1934, abstract = {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.}, author = {Marhavy, Peter and Duclercq, Jérôme and Weller, Benjamin and Feraru, Elena and Bielach, Agnieszka and Offringa, Remko and Friml, Jirí and Schwechheimer, Claus and Murphy, Angus and Benková, Eva}, journal = {Current Biology}, number = {9}, pages = {1031 -- 1037}, publisher = {Cell Press}, title = {{Cytokinin controls polarity of PIN1-dependent Auxin transport during lateral root organogenesis}}, doi = {10.1016/j.cub.2014.04.002}, volume = {24}, year = {2014}, } @article{1994, abstract = {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.}, author = {Viaene, Tom and Landberg, Katarina and Thelander, Mattias and Medvecka, Eva and Pederson, Eric and Feraru, Elena and Cooper, Endymion and Karimi, Mansour and Delwiche, Charles and Ljung, Karin and Geisler, Markus and Sundberg, Eva and Friml, Jirí}, journal = {Current Biology}, number = {23}, pages = {2786 -- 2791}, publisher = {Cell Press}, title = {{Directional auxin transport mechanisms in early diverging land plants}}, doi = {10.1016/j.cub.2014.09.056}, volume = {24}, year = {2014}, } @article{1996, abstract = {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.}, author = {Hazak, Ora and Obolski, Uri and Prat, Tomas and Friml, Jiří and Hadany, Lilach and Yalovsky, Shaul}, journal = {PNAS}, number = {50}, pages = {E5471 -- E5479}, publisher = {National Academy of Sciences}, title = {{Bimodal regulation of ICR1 levels generates self-organizing auxin distribution}}, doi = {10.1073/pnas.1413918111}, volume = {111}, year = {2014}, } @article{2061, abstract = {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.}, author = {Mazur, Ewa and Kurczyñska, Ewa and Friml, Jiří}, journal = {Protoplasma}, number = {5}, pages = {1125 -- 1139}, publisher = {Springer}, title = {{Cellular events during interfascicular cambium ontogenesis in inflorescence stems of Arabidopsis}}, doi = {10.1007/s00709-014-0620-5}, volume = {251}, year = {2014}, }