Ca 2+ /CaM increases the necrotrophic pathogen resistance through the inhibition of a CaM-regulated dual-specificity protein phosphatase 1 in Arabidopsis

Jasmonic acid (JA) is a phytohormone that plays a central role in plant defense against necrotrophic pathogens. JA signaling stimulates the increase of cytosolic calcium ion (Ca 2+ ) and implicates the activity of mitogen-activated protein kinases (MPKs). We previously characterized that Ca 2+ /calmodulin (CaM) activates MPKs by inhibiting a CaM-regulated dual-specificity protein phosphatase1 (DsPTP1) at the biochemical level. In this study, we reported that Ca 2+ /CaM-mediated DsPTP1 negatively regulates the resistance to necrotrophic pathogens through the inhibition of JA-responsive MPK6. To elucidate the physiological function of inhibiting DsPTP1 activity by Ca 2+ /CaM, we constructed transgenic plants overexpressing DsPTP1 wild type (DsPTP1 WT OX) and CaM deregulated mutant (DsPTP1 K166E OX). Interestingly, the MPK6 activity was significantly reduced in DsPTP1 K166E OX plants in response to JA compared to DsPTP1 WT OX plants. Moreover, transcript levels of JA-responsive gene PDF1.2 and VSP1 were also highly decreased in DsPTP1 K166E OX plants compared to DsPTP1 WT OX plants. Furthermore, DsPTP1 K166E OX plants showed more susceptibility to necrotrophic pathogens than DsPTP1 WT OX plants. Conclusively, these results suggest that Ca 2+ /CaM activates the JA-responsive MPKs by inhibiting DsPTP1 for the resistance to the necrotrophic pathogen.