Abstract
Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules in eukaryotes. In Arabidopsis, it is suggested that there are 20 genes encoding possible MAPKs, and these MAPKs can be divided into at least four groups (A-D). Group D has 8 members, and forms the largest subgroup. Group D MAPKs contain TDY motifs instead of TEY motifs in their T-loop and larger C-terminal regions relative to other groups. We have been focused on MPK8, one of the group D MAPK, for further analysis. MPK8 functioned as a member of MAPK in yeast mpk1 mutant based on complementation. Yeast two-hybrid analysis revealed that MPK8 interacts with various types of calmodulin. We showed that calmodulin activates MPK8 without calcium in vitro. We also showed that MPK8 is activated by MKK3. These results suggest novel activation mechanisms of MAPK in plant. We will discuss the activation mechanism of MPK8 both calmodulin and MKK3.
