A receptor-like kinase mutant with absent endodermal diffusion barrier displays selective nutrient homeostasis defects

We thank the Genomic Technologies Facility (GTF) and the Central Imaging Facility (CIF) of the University of Lausanne for expert technical support. We thank Valérie Dénervaud Tendon, Guillaume Germion, Deborah Mühlemann, and Kayo Konishi for technical assistance and John Danku and Véronique Vacchina for ICP-MS analysis. This work was funded by grants from the Swiss National Science Foundation (SNSF), the European Research Council (ERC) to NG and a Human Frontiers Science Program (HFSP) grant to JT and NG. GL and CM were supported by the Agropolis foundation (Rhizopolis) and the Agence Nationale de la Recherche (HydroRoot; ANR-11-BSV6-018). MB was supported by a EMBO long-term postdoctoral fellowship, JEMV by a Marie Curie IEF fellowship and TK by the Japan Society for the Promotion of Sciences (JSPS).Peer reviewedPublisher PD

Surveillance of cell wall diffusion barrier integrity modulates water and solute transport in plants

We acknowledge support from the ERA-NET Coordinating Action in Plant Sciences program project ERACAPS13.089_RootBarriers, with support from Biotechnology and Biological Sciences Research Council (grant no. BB/N023927/1 to D.E.S.), the German Research Foundation (DFG; grant no. FR 1721/2-1 to R.B.F. and the AgreenSkills+ fellowship programme to MC-P which has received funding from the EU’s Seventh Framework Programme under grant agreement N° FP7-609398 (AgreenSkills+ contract). This work was also funded by the Ministry of Education, Youth and Sports of the Czech Republic (National Program for Sustainability I, grant no. LO1204), the Swedish Governmental Agency for Innovation Systems (Vinnova) and the Swedish Research Council (VR). We thank Kevin Mackenzie (University of Aberdeen–Microscopy Histology Facility) and Carine Alcon (BPMP-PHIV microscopy platform) for assistance using the confocal microscope and stereo microscope for observing the root samples, and the Swedish Metabolomics Centre (http://www.swedishmetabolomicscentre.se/) for access to instrumentation.Peer reviewedPublisher PD

Suberin plasticity to developmental and exogenous cues is regulated by a set of MYB transcription factors

Suberin is a hydrophobic biopolymer that can be deposited at the periphery of cells, forming protective barriers against biotic and abiotic stress. In roots, suberin forms lamellae at the periphery of endodermal cells where it plays crucial roles in the control of water and mineral transport. Suberin formation is highly regulated by developmental and environmental cues. However, the mechanisms controlling its spatiotemporal regulation are poorly understood. Here, we show that endodermal suberin is regulated independently by developmental and exogenous signals to fine tune suberin deposition in roots. We found a set of four MYB transcription factors (MYB41, MYB53, MYB92 and MYB93), that are regulated by these two signals, and are sufficient to promote endodermal suberin. Mutation of these four transcription factors simultaneously through genome editing, lead to a dramatic reduction of suberin formation in response to both developmental and environmental signals. Most suberin mutants analyzed at physiological levels are also affected in another endodermal barrier made of lignin (Casparian strips), through a compensatory mechanism. Through the functional analysis of these four MYBs we generated plants allowing unbiased investigations of endodermal suberin function without accounting for confounding effects due to Casparian strip defects, and could unravel specific roles of suberin in nutrient homeostasis

Mécanismes moléculaires du trafic intracellulaire du transporteur de fer IRT1 chez Arabidopsis thaliana

Iron is an essential element for plants but toxic when present in excess. IRT1 is the major root iron transporter responsible for iron uptake from the soil under iron limitation in Arabidopsis thaliana. IRT1 is transcriptionally regulated by iron, resulting in a high IRT1 expression in iron-starved root epidermal cells. In addition, IRT1 was suggested to be controlled at the post-translational level, with iron affecting IRT1 protein stability, in a similar fashion with the yeast ZRT1 zinc transporter. To shed light on two poorly-understood phenomena in plants, endocytosis and degradation of plasma membrane proteins, we studied the proposed post-translational regulation of IRT1 in Arabidopsis thaliana. Interestingly IRT1 protein is found in early endosomes of root hair cells. Pharmacological approaches reveal that IRT1 cycles back and forth with the plasma membrane to perform iron uptake, and is sent to the vacuole for proper turnover. We also demonstrate that iron nutrition have no effect on the levels and the subcellular localization of IRT1 protein. The internalization of IRT1 is dependent on the monoubiquitination of several cytosol-exposed lysine residues. Together, these data suggest a model where monoubiquitin-dependent endocytosis/recycling of IRT1 keeps the plasma membrane pool of IRT1 low, to better deal with metal uptake. Finally, in order to indentify genes involves in IRT1 endocytosis/recycling and turnover, we perform a yeast two-hybrid screen with IRT1 cytosolic loop. This screen allows the identification of a FYVE domain-containing protein localized in endocytic compartment which functional characterization was initiated.Le fer est un élément essentiel pour les plantes, mais toxique lorsqu'il est accumulé en excès. Chez Arabidopsis thaliana, le transporteur IRT1 joue un rôle essentiel dans l'acquisition du Fe depuis la solution du sol, en conditions limitantes en cet élément. Le gène IRT1 est régulé transcriptionnellement par le fer conduisant à une accumulation des transcrits IRT1 dans l'épiderme des racines carencées en fer. Par homologie avec les mécanismes décrits pour le transporteur de zinc ZRT1 de levure, une régulation post-traductionnelle d'IRT1, contrôlant la stabilité de celui-ci en présence de fer a été envisagée. IRT1 a donc été utilisé comme modèle pour caractériser le système endocytique des plantes. Nos travaux révèlent que la protéine IRT1 est localisée au niveau des endosomes précoces (TGN/EE) des cellules de poils racinaires. Des approches pharmacologiques ont permis de révéler un cyclage d'IRT1 entre la membrane plasmique et le TGN/EE ainsi qu'une dégradation vacuolaire. Nous avons également pu montrer que l'internalisation et la dégradation d'IRT1 ne sont pas affectées par la disponibilité en fer et sont sous le contrôle de la monoubiquitination de résidus lysines présents dans les parties cytosoliques de la protéine IRT1. Nos travaux suggèrent un modèle où l'internalisation d'IRT1 depuis la membrane plasmique, contrôlée par monoubiquitination, permet aux plantes de se prémunir contre la toxicité des métaux transportés par IRT1. Enfin, nous avons réalisé un crible double hybride en utilisant la boucle cytosolique d'IRT1 afin d'identifier des protéines contrôlant son trafic et/ou sa dégradation. Ce crible a permis notamment l'identification d'une protéine à domaine FYVE, localisée aux endosomes et dont la caractérisation fonctionnelle a été initiée

Molecular mechanisms of IRT1 trafficking in Arabidopsis thaliana

Le fer est un élément essentiel pour les plantes, mais toxique lorsqu'il est accumulé en excès. Chez Arabidopsis thaliana, le transporteur IRT1 joue un rôle essentiel dans l'acquisition du Fe depuis la solution du sol, en conditions limitantes en cet élément. Le gène IRT1 est régulé transcriptionnellement par le fer conduisant à une accumulation des transcrits IRT1 dans l'épiderme des racines carencées en fer. Par homologie avec les mécanismes décrits pour le transporteur de zinc ZRT1 de levure, une régulation post-traductionnelle d'IRT1, contrôlant la stabilité de celui-ci en présence de fer a été envisagée. IRT1 a donc été utilisé comme modèle pour caractériser le système endocytique des plantes. Nos travaux révèlent que la protéine IRT1 est localisée au niveau des endosomes précoces (TGN/EE) des cellules de poils racinaires. Des approches pharmacologiques ont permis de révéler un cyclage d'IRT1 entre la membrane plasmique et le TGN/EE ainsi qu'une dégradation vacuolaire. Nous avons également pu montrer que l'internalisation et la dégradation d'IRT1 ne sont pas affectées par la disponibilité en fer et sont sous le contrôle de la monoubiquitination de résidus lysines présents dans les parties cytosoliques de la protéine IRT1. Nos travaux suggèrent un modèle où l'internalisation d'IRT1 depuis la membrane plasmique, contrôlée par monoubiquitination, permet aux plantes de se prémunir contre la toxicité des métaux transportés par IRT1. Enfin, nous avons réalisé un crible double hybride en utilisant la boucle cytosolique d'IRT1 afin d'identifier des protéines contrôlant son trafic et/ou sa dégradation. Ce crible a permis notamment l'identification d'une protéine à domaine FYVE, localisée aux endosomes et dont la caractérisation fonctionnelle a été initiéeIron is an essential element for plants but toxic when present in excess. IRT1 is the major root iron transporter responsible for iron uptake from the soil under iron limitation in Arabidopsis thaliana. IRT1 is transcriptionally regulated by iron, resulting in a high IRT1 expression in iron-starved root epidermal cells. In addition, IRT1 was suggested to be controlled at the post-translational level, with iron affecting IRT1 protein stability, in a similar fashion with the yeast ZRT1 zinc transporter. To shed light on two poorly-understood phenomena in plants, endocytosis and degradation of plasma membrane proteins, we studied the proposed post-translational regulation of IRT1 in Arabidopsis thaliana. Interestingly IRT1 protein is found in early endosomes of root hair cells. Pharmacological approaches reveal that IRT1 cycles back and forth with the plasma membrane to perform iron uptake, and is sent to the vacuole for proper turnover. We also demonstrate that iron nutrition have no effect on the levels and the subcellular localization of IRT1 protein. The internalization of IRT1 is dependent on the monoubiquitination of several cytosol-exposed lysine residues. Together, these data suggest a model where monoubiquitin-dependent endocytosis/recycling of IRT1 keeps the plasma membrane pool of IRT1 low, to better deal with metal uptake. Finally, in order to indentify genes involves in IRT1 endocytosis/recycling and turnover, we perform a yeast two-hybrid screen with IRT1 cytosolic loop. This screen allows the identification of a FYVE domain-containing protein localized in endocytic compartment which functional characterization was initiated

Polarized transport across root epithelia

Plant roots explore the soil to acquire water and nutrients which are often available at concentrations that drastically differ from the plant's actual need for growth and development. This stark difference between availability and requirement can be dealt with owing to the root's architecture as an inverted gut. In roots, the two epithelial characteristics (selective acquisition and diffusion barrier) are split between two cell layers: the epidermis at the root periphery and the endodermis as the innermost cortical cell layer around the vasculature. Polarized transport of nutrients across the root epithelium can be achieved through different pathways: apoplastic, symplastic, or coupled transcellular. This review highlights different features of the root that allow this polarized transport. Special emphasis is placed on the coupled transcellular pathway, facilitated by polarized nutrient carriers along root cell layers but barred by suberin lamellae in endodermal cells

Nutrient carriers at the heart of plant nutrition and sensing

Plants require water and several essential nutrients for their development. The radial transport of nutrients from the soil to the root vasculature is achieved through a combination of three different pathways: apoplastic, symplastic, and transcellular. A common feature for these pathways is the requirement of carriers to transport nutrients across the plasma membrane. An efficient transport of nutrients across the root cell layers relies on a large number of carriers, each of them having their own substrate specificity, tissular and subcellular localization. Polarity is also emerging as a major feature allowing their function. Recent advances on radial transport of nutrients, especially carrier mediated nutrient transport will be discussed in this review, as well as the role of transporters as nutrient sensors