Dr Zoe NEMEC VENZA, Reproduction et Développement des Plantes, ENS Lyon France, invitée par H. Renault
Cell identity and growth in plant epidermis
For the development of multilayered organs, plants need to coordinate cell growth between layers. To do so, internal cells and cells at the organ surface need to acquire different properties by integrating positional and lineage-based information. Can mechanical cues act as positional signals to differentially regulate gene expression and cell growth? To address this question, I used Arabidopsis lateral roots, where the epidermal layer is initially covered by the root cap, but becomes exposed to the organ surface after root cap death. RabA5c is a RabGTPase needed for directional growth of root cells, and is only activated in epidermal cells following root cap death. RabA5c activation follows root cap cover, however root cap presence is not sufficient to repress RabA5c, suggesting that this effect is mediated by the mechanical action of the root cap. Our model, based on the mechanical characterization of covered and uncovered cells, predicts higher cell wall tension in the epidermis after root cap death, and we showed experimentally that increasing cell wall tension results in an increase in RabA5c levels. Overall, these data illustrate how cells at the organ surface use mechanical signals to regulate their growth by activating RabA5c, thus enabling growth directionality. This study is an example of how a gene can be activated only in a subset of epidermal cells based on their position at the organ surface.
