Sepal shape variability is robust to cell size heterogeneity in Arabidopsis

Assess the impacts of uniform cell types on organ shape robustness using Arabidopsis sepal as the mode

Sepal shape variability is robust to cell size heterogeneity in Arabidopsis

International audienceHow organisms produce organs with robust shapes and sizes is still an open question. In recent years, the Arabidopsis sepal has been used as a model system to study this question because of its highly reproducible shape and size. One interesting aspect of the sepal is that its epidermis contains cells of very different sizes. Previous reports have qualitatively shown that sepals with more or less giant cells exhibit comparable final size and shape. Here, we investigate this question using quantitative approaches. We find that a mixed population of cell size modestly contribute to the normal width of the sepal but is not essential for its shape robustness. Furthermore, in a mutant with increased cell and organ growth variability, the change in final sepal shape caused by giant cells is exaggerated but the shape robustness is not affected. This formally demonstrates that sepal shape variability is robust to cell size heterogeneity

Water fluxes contribute to growth patterning in shoot meristems

Abstract In multicellular organisms, localized tissue outgrowth creates a new water sink thereby modifying hydraulic patterns at the organ level. These fluxes are often considered passive by-products of development and their patterning and potential contribution to morphogenesis remains largely unexplored. Here, we generated a complete map of cell volumetric growth and deformation across the shoot apex in Arabidopsis thaliana . Within the organ-meristem boundary, we found that a subpopulation of cells next to fast-growing cells experiences volumetric shrinkage. To understand this process, we used a vertex-based model integrating mechanics and hydraulics, informed by the measured growth rates. Organ outgrowth simulations revealed the emerging water fluxes and predicted water deficit with volume loss for a few cells at the boundary. Consistently, in planta, a water-soluble dye is preferentially allocated to fast-growing tissues and fails to enter the boundary domain. Analysis of intact meristems further validated our model by revealing cell shrinkage next to fast-growing cells in different contexts of tissue surface curvature and cell deformation. A molecular signature of water deficit at the boundary further confirmed our conclusion. Taken together, we propose a model where the differential sink strength of emerging organs prescribes the hydraulic patterns that define the boundary domain at the shoot apex

Lipid anchoring and electrostatic interactions target NOT-LIKE-DAD to pollen endo-plasma membrane

International audiencePhospholipases cleave phospholipids, major membrane constituents. They are thus essential for many developmental processes, including male gamete development. In flowering plants, mutation of phospholipase NOT-LIKE-DAD (NLD, also known as MTL or ZmPLA1) leads to peculiar defects in sexual reproduction, notably the induction of maternal haploid embryos. Contrary to previous reports, NLD does not localize to cytosol and plasma membrane of sperm cells but to the pollen endo-plasma membrane (endo-PM), a specific membrane derived from the PM of the pollen vegetative cell that encircles the two sperm cells. After pollen tube burst, NLD localizes at the apical region of the egg apparatus. Pharmacological approaches coupled with targeted mutagenesis revealed that lipid anchoring together with electrostatic interactions are involved in the attachment of NLD to this atypical endo-PM. Membrane surface-charge and lipid biosensors indicated that phosphatidylinositol-4,5-bisphosphate is enriched in the endo-PM, uncovering a unique example of how membrane electrostatic properties can define a specific polar domain (i.e., endo-PM), which is critical for plant reproduction and gamete formation

Intracellular trafficking in pollen and its importance for maize reproduction

International audienc

Water fluxes pattern growth and identity in shoot meristems

International audienceIn multicellular organisms, tissue outgrowth creates a new water sink, modifying local hydraulic patterns. Although water fluxes are often considered passive by-products of development, their contribution to morphogenesis remains largely unexplored. Here, we mapped cell volumetric growth across the shoot apex in Arabidopsis thaliana. We found that, as organs grow, a subpopulation of cells at the organ-meristem boundary shrinks. Growth simulations using a model that integrates hydraulics and mechanics revealed water fluxes and predicted a water deficit for boundary cells. In planta, a watersoluble dye preferentially allocated to fast-growing tissues and failed to enter the boundary domain. Cell shrinkage next to fast-growing domains was also robust to different growth conditions and different topographies. Finally, a molecular signature of water deficit at the boundary confirmed our conclusion. Taken together, we propose that the differential sink strength of emerging organs prescribes the hydraulic patterns that define boundary domains at the shoot apex

Xyloglucans and Microtubules Synergistically Maintain Meristem Geometry and Phyllotaxis

International audienceThe shoot apical meristem (SAM) gives rise to all aerial plant organs. Cell walls are thought to play a central role in this process, translating molecular regulation into dynamic changes in growth rate and direction, although their precise role in morphogenesis during organ formation is poorly understood. Here, we investigated the role of xyloglucans (XyGs), a major, yet functionally poorly characterized, wall component in the SAM of Arabidopsis (Arabidopsis thaliana). Using immunolabeling, biochemical analysis, genetic approaches, microindentation, laser ablation, and live imaging, we showed that XyGs are important for meristem shape and phyllotaxis. No difference in the Young's modulus (i.e. an indicator of wall stiffness) of the cell walls was observed when XyGs were perturbed. Mutations in enzymes required for XyG synthesis also affect other cell wall components such as cellulose content and pectin methylation status. Interestingly, control of cortical microtubule dynamics by the severing enzyme KATANIN became vital when XyGs were perturbed or absent. This suggests that the cytoskeleton plays an active role in compensating for altered cell wall composition