Resolving the mechanism of plant cell expansion at high spatio-temporal resolution.

Plants critically shape ecosystems and our societies by converting sunlight and CO2 into O2 and bio-mass while they grow. Understanding this growth process constitutes a major frontier in plant research. Growth is a multi-scale process. At a subcellular scale, it depends on the expansion of the cell walls, which involves changes in the chemistry and architecture of constituent polymer networks. Very little is known on the nature and the control of the cell wall changes that are critical for growth, in striking contrast to the, often detailed, knowledge of growth-regulating signaling networks. This is in part due to the lack of appropriate tools to study changes in the complex cell wall polymer assemblies that often occur at fast (~s) and small (<micrometer) scales. In this project, I propose firstly, to breach the spatial limits of the tools by using multi-target optical nanoscopy to visualize cell wall architecture and remodeling, and secondly, to overcome their temporal limits by using light-gated actuators and multiplexed intracellular biosensors to simultaneously perturb and monitor the system dynamics in vivo. In particular, I will address pectin remodeling, the role of which in plant growth was shown to be critical, but without clearly understanding the mechanism. My objectives are to (1) reveal the key changes in cell wall architecture and chemistry during growth, (2) understand the fast signaling by which cells perceive and coordinate wall remodeling, and (3) build a dynamic hybrid model to explain how plants coordinate wall expansion. This interdisciplinary project will provide new insights into the nanoscale organization of cell walls and propose a novel pectin-based mechanism for its active reorganization during growth. This will provide an essential framework, not only for understanding plant growth and morphogenesis but also for the study of life beyond the plasma membrane, for instance in relation to immunity, multicellularity, or symbiosis.