Plant cells at the organ surface use mechanical cues to activate a specific growth control programme

During morphogenesis of multicellular organs, cells acquire distinct identities that meet specific functional requirements. Epidermal identity is widely considered essential for plant morphogenesis due to the role of the epidermis in both restricting and promoting growth. In the root, epidermal cells are partially covered by a protective root cap, and partially positioned at the organ surface. Here, we propose that epidermal cells at the organ surface have unique requirements for growth control due to high mechanical tension, while covered epidermal cells are mechanically shielded by the root cap. We present in silico and in vivo evidence that plants use surface mechanical cues to activate a cell-type specific growth control programme involving the small GTPase RAB-A5c, allowing them to maintain directional growth at the organ surface. Positional mechanical cues may thus be used to control expression of a sub-population of epidermal genes, linking gene regulation to surface-specific functional requirements.