Plant mitogen-activated protein kinase phosphatase interacts with calmodulins

Abstract

Calmodulin (CaM), a ubiquitous Ca²⁺ sensor in eukaryotes, modulates a number of target proteins in a Ca²⁺-dependent manner. We cloned 13 tobacco CaM genes (NtCaM1~13), which were subdivided into 3 groups. They showed different expression profiles and affinities to target proteins. To study CaM-mediated signal transduction after wounding or pathogen infection, we screened cDNA expression library, and identified mitogen-activated protein kinase (MAPK) phosphatase (NtMKP1) as a novel CaM-binding protein. Recombinant NtMKP1, expressed in E. coli, showed higher binding affinity to NtCaM1 and 3 than 13. Deletion and site-directed mutagenesis of NtMKP1 revealed that Baa motif located near the center was essential for binding to CaMs. Moreover, wound-induced activation of WIPK and SIPK, tobacco defense-related MAPKs, was compromised by overexpression of NtMKP1, suggesting the involvement of Ca²⁺/CaM signaling in MAPK activation via MAPK phosphatase.