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

When mechanically injured, plants develop multiple defense systems including the activation of specific genes. These responses are triggered by a complex network of signalling events that include Ca²⁺ fluxes, the production of free fatty acids from membrane lipids, as well as the activation of mitogen-activated protein kinases (MAPK). In the present paper, we address the question of the regulation of the MAPK pathway by wound-induced Ca²⁺ and fatty acid signals. We report that MP2C, a serine/threonine protein phosphatase 2C from alfalfa involved in MAPK pathway inactivation, is inhibited specifically in vitro by long-carbon-chain polyunsaturated fatty acids, and α-linolenic acid, the primary product of the octadecanoid pathway, was found to be the most potent inhibitor. Ca²⁺ also inhibits MP2C, but only at high concentrations, and other divalent cations show similar inhibitory effect, making it unlikely that Ca²⁺ is involved in the regulation of MP2C in vivo. 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.