Genome-Wide Identification and Characterization of Calcium-Dependent Protein Kinase (CDPK) and CDPK-Related Kinase (CRK) Gene Families in Medicago truncatula

Abstract

Calcium-dependent protein kinase (CDPK or CPK) and CDPK-related kinase (CRK) play an important role in plant growth, development, and adaptation to environmental stresses. However, their gene families had been yet inadequately investigated in <i>Medicago truncatula</i>. In this study, six <i>MtCRK</i> genes were computationally identified, they were classified into five groups with <i>MtCDPKs</i> based on phylogenetic relationships. Six pairs of segmental duplications were observed in <i>MtCDPK</i> and <i>MtCRK</i> genes and the <i>Ka/Ks</i> ratio, an indicator of selection pressure, was below 0.310, indicating that these gene pairs underwent strong purifying selection. <i>Cis</i>-acting elements of morphogenesis, multiple hormone responses, and abiotic stresses were predicted in the promoter region. The spatial expression of <i>MtCDPKs</i> and <i>MtCRKs</i> displays diversity. The expression of <i>MtCDPKs</i> and <i>MtCRKs</i> could be regulated by various stresses. MtCDPK4, 14, 16, 22, and MtCRK6 harbor both N-myristoylation site and palmitoylation site and were anchored on plasma membrane, while MtCDPK7, 9, and 15 contain no or only one N-acylation site and were distributed in cytosol and nucleus, suggesting that the N-terminal acylation sites play a key role in subcellular localization of MtCDPKs and MtCRKs. In summary, comprehensive characterization of <i>MtCDPKs</i> and <i>MtCRKs</i> provide a subset of candidate genes for further functional analysis and genetic improvement against drought, cold, salt and biotic stress.