Passive and active regulation of cell wall mechanical properties.

Plant cells are turgid and exert pressure against a stiff extracellular matrix, the plant cell wall, which resists turgor pressure and prevents cell bursting due to osmotic pressure. During growth, the cell wall yields under turgor pressure and deforms to guide the expansion of the cytoplasm. Together, these suggest that the mechanical properties of the cell wall are tightly regulated during development and that a tight coordination between turgor pressure and cell wall plasticity is required. In this review we explore the anisotropic mechanical properties of the cell wall and the mechanisms involved in its regulation. We discuss some of the theories supporting passive regulation of the cell wall such as the multinet theory and the scaffolding theory. We then discuss the role of CrRLK1Ls such as FERONIA and mechanosensing ion channels like MSL8 in the perception of mechanical stress and the role of Ca2+ as a central second messenger of mechanical stress response. Finally, we highlight some of the transcriptional responses induced by mechanosensing via small signal peptides such as SCOOP and Pep1 and cell wall remodelling enzymes such as TCH4.