Auxin and heat shock activation of a novel member of the calmodulin like domain protein kinase gene family in cultured alfalfa cells

A calmodulin like domain protein kinase (CPK) homologue was identified in alfalfa and termed MsCPK3. The full-length sequence of cDNA encoded a 535 amino acid polypeptide with a molecular weight of 60.2 kDa. The deduced amino acid sequence showed all the conserved motifs that define other members of this kinase family, such as serine-threonine kinase domain, a junction region and four potential Ca2+-binding EF sites. The recombinant MsCPK3 protein purified from E. coli was activated by Ca2+ and inhibited by calmodulin antagonist (W-7) in vitro phosphorylation assays. The expression of MsCPK3 gene increased in the early phase of the 2,4-D induced alfalfa somatic embryogenesis. Heat shock also activated this gene while kinetin, ABA and NaCl treatment did not result in MsCPK3 mRNA accumulation. The data presented suggest that the new alfalfa CPK differs in stress responses from the previously described homologues and in its potential involvement in hormone and stress-activated reprogramming of developmental pathways during somatic embryogenesis.