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Background In plants, the shoot apical meristem (SAM) has two main functions, involving the production of all aerial organs on the one hand and self-maintenance on the other, allowing the production of organs during the entire post-embryonic life of the plant. Transcription factors, microRNA, hormones, peptides and forces have been involved in meristem function. Whereas phosphatidylinositol phosphates (PIPs) have been involved in almost all biological functions, including stem cell maintenance and organogenesis in animals, the processes in meristem biology to which PIPs contribute still need to be delineated. Results Using biosensors for PI4P and PI(4,5)P2, the two most abundant PIPs at the plasma membrane, we reveal that meristem functions are associated with a stereotypical PIP tissue-scale pattern, with PI(4,5)P2 always displaying a more clear-cut pattern than PI4P. Using clavata3 and pin-formed1 mutants, we show that stem cell maintenance is associated with reduced levels of PIPs. In contrast, high PIP levels are signatures for organ-meristem boundaries. Interestingly, this pattern echoes that of cortical microtubules and stress anisotropy at the meristem. Using ablations and pharmacological approaches, we further show that PIP levels can be increased when the tensile stress pattern is altered. Conversely, we find that katanin mutant meristems, with increased isotropy of microtubule arrays and slower response to mechanical perturbations, exhibit reduced PIP gradients within the SAM. Comparable PIP pattern defects were observed in phospholipase A3β overexpressor lines, which largely phenocopy katanin mutants at the whole plant level. Conclusions Using phospholipid biosensors, we identified a stereotypical PIP accumulation pattern in the SAM that negatively correlates with stem cell maintenance and positively correlates with organ-boundary establishment. While other cues are very likely to contribute to the final PIP pattern, we provide evidence that the patterns of PIP, cortical microtubules and mechanical stress are positively correlated, suggesting that the PIP pattern, and its reproducibility, relies at least in part on the mechanical status of the SAM. Electronic supplementary material The online version of this article (10.1186/s12915-018-0490-y) contains supplementary material, which is available to authorized users.

Development of diverse multicellular organisms relies on coordination of single-cell polarities within the plane of the tissue layer (planar polarity). Cell polarity often involves plasma membrane heterogeneity generated by accumulation of specific lipids and proteins into membrane subdomains. Coordinated hair positioning along Arabidopsis root epidermal cells provides a planar polarity model in plants, but knowledge about the functions of proteo-lipid domains in planar polarity signalling remains limited. Here we show that Rho-of-plant (ROP) 2 and 6, phosphatidylinositol-4-phosphate 5-kinase 3 (PIP5K3), DYNAMIN-RELATED PROTEIN (DRP) 1A and DRP2B accumulate in a sterol-enriched, polar membrane domain during root hair initiation. DRP1A, DRP2B, PIP5K3 and sterols are required for planar polarity and the AGCVIII kinase D6 PROTEIN KINASE (D6PK) is a modulator of this process. D6PK undergoes phosphatidylinositol-4,5-bisphosphate- and sterol-dependent basal-to-planar polarity switching into the polar, lipid-enriched domain just before hair formation, unravelling lipid-dependent D6PK localization during late planar polarity signalling.

Group 1 isoform 3 remorin from Solanum tuberosum (StREM1.3) is a membrane protein belonging to the multigenic family of plant proteins called remorins (REMs), involved in plant immunity, symbiosis, abiotic stress resistance and hormone signalling. REMs’ most well known feature is their ability to segregate into nanodomains at the plasma membrane’s (PM) inner leaflet. For StREM1.3, this is achieved by an interaction between two lysines of the remorin C-terminal anchor (RemCA) and negatively charged phosphatidylinositol 4-phosphate (PI4P). Thus, RemCA undergoes conformational changes and partially buries itself in the PM, resulting in an intrinsic membrane anchoring. Capitalising on pre-existing structural data about this isoform, we investigate StREM1.3’s membrane-interacting properties further, using a wide array of techniques, ranging from fluorescence microscopy and solid-state nuclear magnetic resonance (ssNMR) to atomic force microscopy (AFM), cryo-electron microscopy (cryoEM) and computational modelling. We aim to discover the impact of StREM1.3’s oligomerisation and phosphorylation on its membrane interactions and biological activity, and to assess its influence on lipid dynamics as well as its lipid requirements for membrane binding and nanoclustering. Finally, based on all available structural data, we will undertake the in vitro reconstruction and characterisation of minimal nanodomains of StREM1.3., La rémorine du groupe 1 isoforme 3 de Solanum tuberosum (StREM1.3) est une protéine membranaire de la famille multigénique de protéines de plante appelée rémorines (REMs), impliquées dans l’immunité des plantes, la symbiose, la résistance aux stress abiotiques et la signalisation hormonale. La caractéristique la plus connue des REMs est leur capacité à se ségréger en nanodomaines au feuillet interne de la membrane plasmique (MP). Pour StREM1.3, ceci se fait via une interaction entre deux lysines de l’ancre C-terminale de la rémorine (RemCA) et le phosphatidylinositol 4-phosphate (PI4P) négativement chargé. Ainsi, RemCA modifie sa conformation et s’enfonce partiellement dans la MP, résultant en un accrochage membranaire intrinsèque. Capitalisant sur les données structurales déjà disponibles concernant cet isoforme, nous investiguons StREM1.3 davantage quant à ses propriétés d’interaction membranaire, en utilisant un large éventail de techniques, allant de la microscopie de fluorescence et de la RMN à l’état solide (ssNMR) à la microscopie de force atomique (AFM), la cryo-microscopie électronique (cryoEM) et la modélisation informatique. Nous souhaitons découvrir l’impact de l’oligomérisation et de la phosphorylation de StREM1.3 sur ses interactions membranaires et son activité biologique, ainsi que d’examiner son influence sur la dynamique des lipides et les lipides requis pour l’accrochage à la membrane et le regroupement en nanodomaines. Enfin, forts de toutes les données structurales disponibles, nous entreprendrons la reconstruction in vitro et la caractérisation de nanodomaines minimaux de StREM1.3.