Morphogenesis is the remarkable process by which a developing organism acquires its shape. While molecular and genetic studies have been highly successful in explaining the cellular basis of development and the role of biochemical gradients in coordinating cell fate, understanding morphogenesis remains a central challenge for both biophysics and developmental biology. Indeed, shape is imposed by structural elements, so that an investigation of morphogenesis must address how these elements are controlled at the cell level, and how the mechanical properties of these elements lead to specific growth patterns. Using plants as model systems, we will tackle the following questions:i. Does the genetic identity of a cell correspond to a mechanical identity?ii. Do the mechanical properties of the different cell domains predict shape changes?iii. How does the intrinsic stochasticity of cell mechanics and cell growth lead to reproducible shapes?To do so, we will develop a unique combination of physical and biological approaches. For instance, we will measure simultaneously physical properties and growth in specific cell groups by building a novel tool coupling atomic force microscopy and upright confocal microscopy; we will integrate the data within physical growth models; and we will validate our approaches using genetic and pharmacological alterations of cell mechanics.In plants, shape is entirely determined by the extracellular matrix (cell walls) and osmotic pressure. From that perspective, plants cells involve fewer mechanical parameters than animal cells and are thus perfectly suited to study the physical basis of morphogenesis. Therefore we propose such a study within the shoot apical meristem of Arabidopsis thaliana, a small population of stem cells that orchestrates the aerial architecture of the plant.This work will unravel the physical basis of morphogenesis and shed light on how stochastic cell behaviour can lead to robust shapes.