RBOH1-dependent H2O2 production and subsequent activation of MPK1/2 play an important role in acclimation-induced cross-tolerance in tomato.

H2O2 and mitogen-activated protein kinase (MAPK) cascades play important functions in plant stress responses, but their roles in acclimation response remain unclear. This study examined the functions of H2O2 and MPK1/2 in acclimation-induced cross-tolerance in tomato plants. Mild cold, paraquat, and drought as acclimation stimuli enhanced tolerance to more severe subsequent chilling, photooxidative, and drought stresses. Acclimation-induced cross-tolerance was associated with increased transcript levels of RBOH1 and stress- and defence-related genes, elevated apoplastic H2O2 accumulation, increased activity of NADPH oxidase and antioxidant enzymes, reduced glutathione redox state, and activation of MPK1/2 in tomato. Virus-induced gene silencing of RBOH1, MPK1, and MPK2 or MPK1/2 all compromised acclimation-induced cross-tolerance and associated stress responses. Taken together, these results strongly suggest that acclimation-induced cross-tolerance is largely attributed to RBOH1-dependent H2O2 production at the apoplast, which may subsequently activate MPK1/2 to induce stress responses.