Unsaturated fatty acids inhibit MP2C, a protein phosphatase 2C involved inthe wound-induced MAP kinase pathway regulation

When mechanically injured, plants develop multiple defense systems includin g the activation of specific genes. These responses are triggered by a comp lex network of signalling events that include Ca2+ fluxes, the production o f free fatty acids from membrane lipids, as well as the activation of mitog en-activated protein kinases (MAPK). In the present paper, we address the q uestion of the regulation of the MAPK pathway by wound-induced Ca2+ and fat ty acid signals. We report that MP2C, a serine/threonine protein phosphatas e 2C from alfalfa involved in MAPK pathway inactivation, is inhibited speci fically in vitro by long-carbon-chain polyunsaturated fatty acids, and alph a-linolenic acid, the primary product of the octadecanoid pathway, was foun d to be the most potent inhibitor. Ca2+ also inhibits MP2C, but only at hig h concentrations, and other divalent cations show similar inhibitory effect , making it unlikely that Ca2+ is involved in the regulation of MP2C in viv o. Overall, our data suggest that cross-talk between wound-induced MAPK and octadecanoid pathways may occur at the level of protein phosphatase 2C and linolenic acid.