TY - JOUR AB - Plant development mediated by the phytohormone auxin depends on tightly controlled cellular auxin levels at its target tissue that are largely established by intercellular and intracellular auxin transport mediated by PIN auxin transporters. Among the eight members of the Arabidopsis PIN family, PIN6 is the least characterized candidate. In this study we generated functional, fluorescent protein-tagged PIN6 proteins and performed comprehensive analysis of their subcellular localization and also performed a detailed functional characterization of PIN6 and its developmental roles. The localization study of PIN6 revealed a dual localization at the plasma membrane (PM) and endoplasmic reticulum (ER). Transport and metabolic profiling assays in cultured cells and Arabidopsis strongly suggest that PIN6 mediates both auxin transport across the PM and intracellular auxin homeostasis, including the regulation of free auxin and auxin conjugates levels. As evidenced by the loss- and gain-of-function analysis, the complex function of PIN6 in auxin transport and homeostasis is required for auxin distribution during lateral and adventitious root organogenesis and for progression of these developmental processes. These results illustrate a unique position of PIN6 within the family of PIN auxin transporters and further add complexity to the developmentally crucial process of auxin transport. AU - Simon, Sibu AU - Skůpa, Petr AU - Viaene, Tom AU - Zwiewka, Marta AU - Tejos, Ricardo AU - Klíma, Petr AU - Čarná, Mária AU - Rolčík, Jakub AU - De Rycke, Riet AU - Moreno, Ignacio AU - Dobrev, Petre AU - Orellana, Ariel AU - Zažímalová, Eva AU - Friml, Jirí ID - 1417 IS - 1 JF - New Phytologist TI - PIN6 auxin transporter at endoplasmic reticulum and plasma membrane mediates auxin homeostasis and organogenesis in Arabidopsis VL - 211 ER - TY - JOUR AB - Plants have the ability to continously generate new organs by maintaining populations of stem cells throught their lives. The shoot apical meristem (SAM) provides a stable environment for the maintenance of stem cells. All cells inside the SAM divide, yet boundaries and patterns are maintained. Experimental evidence indicates that patterning is independent of cell lineage, thus a dynamic self-regulatory mechanism is required. A pivotal role in the organization of the SAM is played by the WUSCHEL gene (WUS). An important question in this regard is that how WUS expression is positioned in the SAM via a cell-lineage independent signaling mechanism. In this study we demonstrate via mathematical modeling that a combination of an inhibitor of the Cytokinin (CK) receptor, Arabidopsis histidine kinase 4 (AHK4) and two morphogens originating from the top cell layer, can plausibly account for the cell lineage-independent centering of WUS expression within SAM. Furthermore, our laser ablation and microsurgical experiments support the hypothesis that patterning in SAM occurs at the level of CK reception and signaling. The model suggests that the interplay between CK signaling, WUS/CLV feedback loop and boundary signals can account for positioning of the WUS expression, and provides directions for further experimental investigation. AU - Adibi, Milad AU - Yoshida, Saiko AU - Weijers, Dolf AU - Fleck, Christian ID - 1482 IS - 2 JF - PLoS One TI - Centering the organizing center in the Arabidopsis thaliana shoot apical meristem by a combination of cytokinin signaling and self-organization VL - 11 ER - TY - JOUR AU - Chen, Xu AU - Wu, Shuang AU - Liu, Zengyu AU - Friml, Jiřĺ ID - 1484 IS - 6 JF - Trends in Cell Biology TI - Environmental and endogenous control of cortical microtubule orientation VL - 26 ER - TY - JOUR AB - The plant hormone auxin (indole-3-acetic acid) is a major regulator of plant growth and development including embryo and root patterning, lateral organ formation and growth responses to environmental stimuli. Auxin is directionally transported from cell to cell by the action of specific auxin influx [AUXIN-RESISTANT1 (AUX1)] and efflux [PIN-FORMED (PIN)] transport regulators, whose polar, subcellular localizations are aligned with the direction of the auxin flow. Auxin itself regulates its own transport by modulation of the expression and subcellular localization of the auxin transporters. Increased auxin levels promote the transcription of PIN2 and AUX1 genes as well as stabilize PIN proteins at the plasma membrane, whereas prolonged auxin exposure increases the turnover of PIN proteins and their degradation in the vacuole. In this study, we applied a forward genetic approach, to identify molecular components playing a role in the auxin-mediated degradation. We generated EMS-mutagenized Arabidopsis PIN2::PIN2:GFP, AUX1::AUX1:YFP eir1aux1 populations and designed a screen for mutants with persistently strong fluorescent signals of the tagged PIN2 and AUX1 after prolonged treatment with the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D). This approach yielded novel auxin degradation mutants defective in trafficking and degradation of PIN2 and AUX1 proteins and established a role for auxin-mediated degradation in plant development. AU - Zemová, Radka AU - Zwiewka, Marta AU - Bielach, Agnieszka AU - Robert, Hélène AU - Friml, Jirí ID - 1641 IS - 2 JF - Journal of Plant Growth Regulation TI - A forward genetic screen for new regulators of auxin mediated degradation of auxin transport proteins in Arabidopsis thaliana VL - 35 ER - TY - JOUR AB - ATP production requires the establishment of an electrochemical proton gradient across the inner mitochondrial membrane. Mitochondrial uncouplers dissipate this proton gradient and disrupt numerous cellular processes, including vesicular trafficking, mainly through energy depletion. Here we show that Endosidin9 (ES9), a novel mitochondrial uncoupler, is a potent inhibitor of clathrin-mediated endocytosis (CME) in different systems and that ES9 induces inhibition of CME not because of its effect on cellular ATP, but rather due to its protonophore activity that leads to cytoplasm acidification. We show that the known tyrosine kinase inhibitor tyrphostinA23, which is routinely used to block CME, displays similar properties, thus questioning its use as a specific inhibitor of cargo recognition by the AP-2 adaptor complex via tyrosine motif-based endocytosis signals. Furthermore, we show that cytoplasm acidification dramatically affects the dynamics and recruitment of clathrin and associated adaptors, and leads to reduction of phosphatidylinositol 4,5-biphosphate from the plasma membrane. AU - Dejonghe, Wim AU - Kuenen, Sabine AU - Mylle, Evelien AU - Vasileva, Mina K AU - Keech, Olivier AU - Viotti, Corrado AU - Swerts, Jef AU - Fendrych, Matyas AU - Ortiz Morea, Fausto AU - Mishev, Kiril AU - Delang, Simon AU - Scholl, Stefan AU - Zarza, Xavier AU - Heilmann, Mareike AU - Kourelis, Jiorgos AU - Kasprowicz, Jaroslaw AU - Nguyen, Le AU - Drozdzecki, Andrzej AU - Van Houtte, Isabelle AU - Szatmári, Anna AU - Majda, Mateusz AU - Baisa, Gary AU - Bednarek, Sebastian AU - Robert, Stéphanie AU - Audenaert, Dominique AU - Testerink, Christa AU - Munnik, Teun AU - Van Damme, Daniël AU - Heilmann, Ingo AU - Schumacher, Karin AU - Winne, Johan AU - Friml, Jirí AU - Verstreken, Patrik AU - Russinova, Eugenia ID - 1346 JF - Nature Communications TI - Mitochondrial uncouplers inhibit clathrin-mediated endocytosis largely through cytoplasmic acidification VL - 7 ER - TY - JOUR AB - The CLE (CLAVATA3/Embryo Surrounding Region-related) peptides are small secreted signaling peptides that are primarily involved in the regulation of stem cell homeostasis in different plant meristems. Particularly, the characterization of the CLE41-PXY/TDR signaling pathway has greatly advanced our understanding on the potential roles of CLE peptides in vascular development and wood formation. Nevertheless, our knowledge on this gene family in a tree species is limited. In a recent study, we reported on a systematically investigation of the CLE gene family in Populus trichocarpa . The potential roles of PtCLE genes were studied by comparative analysis and transcriptional pro fi ling. Among fi fty PtCLE members, many PtCLE proteins share identical CLE motifs or contain the same CLE motif as that of AtCLEs, while PtCLE genes exhibited either comparable or distinct expression patterns comparing to their Arabidopsis counterparts. These fi ndings indicate the existence of both functional conservation and functional divergence between PtCLEs and their AtCLE orthologues. Our results provide valuable resources for future functional investigations of these critical signaling molecules in woody plants. AU - Liu, Zhijun AU - Yang, Nan AU - Lv, Yanting AU - Pan, Lixia AU - Lv, Shuo AU - Han, Huibin AU - Wang, Guodong ID - 510 IS - 6 JF - Plant Signaling & Behavior TI - The CLE gene family in Populus trichocarpa VL - 11 ER - TY - JOUR AB - Synchronized tissue polarization during regeneration or de novo vascular tissue formation is a plant-specific example of intercellular communication and coordinated development. According to the canalization hypothesis, the plant hormone auxin serves as polarizing signal that mediates directional channel formation underlying the spatio-temporal vasculature patterning. A necessary part of canalization is a positive feedback between auxin signaling and polarity of the intercellular auxin flow. The cellular and molecular mechanisms of this process are still poorly understood, not the least, because of a lack of a suitable model system. We show that the main genetic model plant, Arabidopsis (Arabidopsis thaliana) can be used to study the canalization during vascular cambium regeneration and new vasculature formation. We monitored localized auxin responses, directional auxin-transport channels formation, and establishment of new vascular cambium polarity during regenerative processes after stem wounding. The increased auxin response above and around the wound preceded the formation of PIN1 auxin transporter-marked channels from the primarily homogenous tissue and the transient, gradual changes in PIN1 localization preceded the polarity of newly formed vascular tissue. Thus, Arabidopsis is a useful model for studies of coordinated tissue polarization and vasculature formation after wounding allowing for genetic and mechanistic dissection of the canalization hypothesis. AU - Mazur, Ewa AU - Benková, Eva AU - Friml, Jirí ID - 1274 JF - Scientific Reports TI - Vascular cambium regeneration and vessel formation in wounded inflorescence stems of Arabidopsis VL - 6 ER - TY - JOUR AB - 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. AU - Yu, Luo AU - Scholl, Stefan AU - Doering, Anett AU - Yi, Zhang AU - Irani, Niloufer AU - Di Rubbo, Simone AU - Neumetzler, Lutz AU - Krishnamoorthy, Praveen AU - Van Houtte, Isabelle AU - Mylle, Evelien AU - Bischoff, Volker AU - Vernhettes, Samantha AU - Winne, Johan AU - Friml, Jirí AU - Stierhof, York AU - Schumacher, Karin AU - Persson, Staffan AU - Russinova, Eugenia ID - 1383 IS - 7 JF - Nature Plants TI - V-ATPase activity in the TGN/EE is required for exocytosis and recycling in Arabidopsis VL - 1 ER - TY - JOUR AB - Ammonium is the major nitrogen source in some plant ecosystems but is toxic at high concentrations, especially when available as the exclusive nitrogen source. Ammonium stress rapidly leads to various metabolic and hormonal imbalances that ultimately inhibit root and shoot growth in many plant species, including Arabidopsis thaliana (L.) Heynh. To identify molecular and genetic factors involved in seedling survival with prolonged exclusive NH4+ nutrition, a transcriptomic analysis with microarrays was used. Substantial transcriptional differences were most pronounced in (NH4)2SO4-grown seedlings, compared with plants grown on KNO3 or NH4NO3. Consistent with previous physiological analyses, major differences in the expression modules of photosynthesis-related genes, an altered mitochondrial metabolism, differential expression of the primary NH4+ assimilation, alteration of transporter gene expression and crucial changes in cell wall biosynthesis were found. A major difference in plant hormone responses, particularly of auxin but not cytokinin, was striking. The activity of the DR5::GUS reporter revealed a dramatically decreased auxin response in (NH4)2SO4-grown primary roots. The impaired root growth on (NH4)2SO4 was partially rescued by exogenous auxin or in specific mutants in the auxin pathway. The data suggest that NH4+-induced nutritional and metabolic imbalances can be partially overcome by elevated auxin levels. AU - Yang, Huaiyu AU - Von Der Fecht Bartenbach, Jenny AU - Friml, Jirí AU - Lohmann, Jan AU - Neuhäuser, Benjamin AU - Ludewig, Uwe ID - 1532 IS - 3 JF - Functional Plant Biology SN - 1445-4408 TI - Auxin-modulated root growth inhibition in Arabidopsis thaliana seedlings with ammonium as the sole nitrogen source VL - 42 ER - TY - JOUR AB - PIN proteins are auxin export carriers that direct intercellular auxin flow and in turn regulate many aspects of plant growth and development including responses to environmental changes. The Arabidopsis R2R3-MYB transcription factor FOUR LIPS (FLP) and its paralogue MYB88 regulate terminal divisions during stomatal development, as well as female reproductive development and stress responses. Here we show that FLP and MYB88 act redundantly but differentially in regulating the transcription of PIN3 and PIN7 in gravity-sensing cells of primary and lateral roots. On the one hand, FLP is involved in responses to gravity stimulation in primary roots, whereas on the other, FLP and MYB88 function complementarily in establishing the gravitropic set-point angles of lateral roots. Our results support a model in which FLP and MYB88 expression specifically determines the temporal-spatial patterns of PIN3 and PIN7 transcription that are closely associated with their preferential functions during root responses to gravity. AU - Wang, Hongzhe AU - Yang, Kezhen AU - Zou, Junjie AU - Zhu, Lingling AU - Xie, Zidian AU - Morita, Miyoterao AU - Tasaka, Masao AU - Friml, Jirí AU - Grotewold, Erich AU - Beeckman, Tom AU - Vanneste, Steffen AU - Sack, Fred AU - Le, Jie ID - 1534 JF - Nature Communications TI - Transcriptional regulation of PIN genes by FOUR LIPS and MYB88 during Arabidopsis root gravitropism VL - 6 ER -