Abstract
Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules in eukaryotes. In plants, the MAPK cascade plays a crucial role in various biotic and abiotic stress responses, hormone responses, cell division, and developmental processes. In Arabidopsis genome, 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, which is generally phosphorylated by MAPKKs, instead of TEY motifs in their T-loop and larger C-terminal regions relative to other groups. We have focused our work on MPK8, one of the plant specific group D MAPK. MPK8 was shown to function as a member of MAPK in yeast mpk1 mutant based on complementation analysis. We also found that calmodulins (CaMs) interact with MPK8 by using yeast two-hybrid screening. The BiFC analysis in Arabidopsis protoplast revealed that MPK8 interacts with CaMs not only in yeast but also in plant cells. We have shown that CaM can activate MPK8. These results suggest a novel activation mechanism of MAPK by CaM. We will discuss the activation mechanism of MPK8.
