Molecular and biochemical characterization of the Capsicum annuum calcium-dependent protein kinase 3 (CaCDPK3) gene induced by abiotic and biotic stresses

The isolated full-length Capsicum annuum calcium-dependent protein kinase 3 (CaCDPK3) cDNA clone was selected from the chili pepper expressed sequence tag database (http://www.pdrc.re.kr/ks200201/ pepper.html). Phylogenetic analysis based on the deduced amino acid sequence of CaCDPK3 cDNA revealed significant sequence similarity to the winter squash ( Cucurbita maxima) CmCPK2 gene (81% identity). Genomic gel blot analysis disclosed that CaCDPK3 belongs to a multigene family in the pepper genome. CaCDPK3 expression was root tissue-specific, as shown by Northern blot data. The gene was rapidly induced in response to various osmotic stress factors and exogenous abscisic acid application in pepper leaves. Moreover, CaCDPK3 RNA expression was induced by an incompatible pathogen and by plant defense-related chemicals such as ethephon, salicylic acid and jasmonic acid. The biochemical properties of CaCDPK3 were investigated using a CaCDPK3 and glutathione S-transferase (GST) fusion protein. The recombinant proteins retained calcium-binding ability, and displayed autophosphorylation activity in vitro in a calcium-dependent manner. Further transient-expression studies showed that CaCDPK3 fused with soluble modified green fluorescent protein (smGFP) localized to the cytosol in chili pepper protoplasts. We propose that CaCDPK3 is implicated in biotic and abiotic stresses in pepper plants.