A sequential MAP kinase cascade regulates mechanical signalling

Plants respond to mechanical stimulations like wind, touching or wounding to safeguard their development and survival. Mitogen Activated Protein Kinases (MAPKs) activation by mechanostimuli was reported 26 years ago, but the upstream regulatory mechanism and function remained unknown. We report that mechanostimulation activates a MAPKKK3/4/5-MKK4/5-MPK3/6 cascade within 60 seconds, leading to induction of ~800 genes, encompassing most of the early touch response. Most genes overlap with touch-responsive genes regulated by CAMTA1/2/3, exposing an interplay between MAPKs and CAMTA transcription factors. Furthermore, loss of MKK4/5 leads to global impairment of touch-regulated protein phosphorylation, demonstrating they are crucial regulators. In contrast, phosphorylation does not clearly affect early activation of the touch-induced jasmonic acid (JA) signalling pathway, nor does loss of JA affect the overall early touch-phosphoproteome. Lastly, loss of MAPKKK3/4/5 and MKK4/5 reduces thigmomorphogenesis, underlining the importance of the identified MAPK cascade for steering plant growth during stress. In summary, we have now identified a MAPKKK3/4/5-MKK4/5-MPK3/6 cascade as a key touch- and wounding signalling pathway in plants.