Mechanosensation Promotes Local Cell Wall Repair

Walled cells, such as those of fungi, plants and bacteria, must continuously survey the integrity of their protective cell wall (CW), as they grow, divide, or face mechanical challenges from their high internal turgor and environment. To date, however, how cells detect defects in their CW to activate local reinforcement or repair machineries remains unclear. We implemented a laser irradiation assay to locally wound the CW of model rod-shaped fission yeast cells. We found that laser irradiation causes a near instantaneous local thinning of the CW accompanied by the formation of a local bulge, a drop in turgor and growth arrest, followed by a progressive recovery of CW thickness over tens of minutes with cells eventually resuming growth. Remarkably, wounding the CW away from cell tips, caused the re-localization of canonical polarity regulators including the Rho GTPases Cdc42 and Rho1, that recruited actin assembly and vesicular trafficking of CW synthases to repair the CW. A candidate screen approach suggests that the transmembrane surface mechanosensors Wsc1 and Mlt2 detect local CW defects and promote the recruitment of the Rho GEFs Gef1 and Rgf1 that activate Cdc42 and Rho1. Therefore, these findings delineate a mechanochemical pathway, coupling surface mechanosensing to polarity regulation and CW synthesis, that defines how walled cells may detect and repair local defects in their CWs to safeguard surface integrity.