Functional Analysis of a Novel MAP Kinase Cascade in Jasmonate Signaling in Arabidopsis

Abstract

Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules in eukaryotes. In plants, MAPK cascades are known to function in various biotic and abiotic stress signaling. Arabidopsis genome-sequencing project has revealed the existence of a large number of MAPK family genes in its genome. However, detailed functions of each MAPK cascades are still unknown. We have been focused on MKK3, one of the Arabidopsis MAPKK, and found the novel MKK3-MPK6 cascade. Analyzing the phenotype of MKK3DD plants and the regulated gene expressions of MKK3, we also demonstrated that MKK3-MPK6 cascade mediates JA signaling. Exogenous application of JA activated MPK6 and this activation was severely impaired in mkk3 mutant and JA-insensitive coi1 mutant. Plants overexpressing either MKK3 or MPK6 were insensitive, by contrast, either mkk3 or mpk6 showed the increased sensitivity to JA. These results indicated that the MKK3-MPK6 cascade plays a crucial role in JA signaling in Arabidopsis.