Final Report Summary - MORPHODYNAMICS (Morphodynamics in Plants: from gene to shape) Morphodynamics was aimed at understanding how shape in plants is controlled during development, a major issue in developmental biology. Using recent technological advances, we have initiated an interdisciplinary analysis, based on the quantitative analysis of molecular and biophysical parameters of growth from the molecular to the organ level. This was performed using the developing flower in Arabidopsis, one of the best studied systems in biology and which, from the modelling point of view, has the strong advantage to grow without cell migration or rearrangements, facilitating the dialog between the observations and the predictions from the models.Because the mechanical properties of the cell wall control the local growth rates and directions, their contribution to morphogenesis are a central focus. How the molecular regulatory networks influence cell wall synthesis and structure to induce local growth rates and directions was largely unknown at present. In fact, the contribution of cell wall regulation to morphogenesis and patterning was difficult to grasp, mainly because our knowledge lacked integration at different levels of complexity. In addition to the quantitative and interdisciplinary nature of this proposal, an original aspect of our approach resided in fully addressing the multi-scale nature of a growing tissue, thus establishing a causality link between local wall properties and multi-cellular outputs.To address this issue, we have combined live imaging tools and micromechanical approaches with a novel, specially designed modelling framework. Results indicate that cell wall restructuring is under the control of transcriptional regulation as genes encoding cell wall remodelling enzymes show very specific patterns of expression. In parallel, we have shown that molecular regulatory networks directly control the anisotropic properties of the cell wall, thus directly intefering with growth directions. A computational model in the form of a virtual tissue has been developed and used to show how changes in wall elasticity act together with changes in the anisotropic properties of the wall to initiate organ outgrowth. In other words, the plant appears to combine synergistically subtle regulations in local growth rates and directions to produce new lateral organs.
