Genome-wide identification and expression analysis of calcium‑dependent protein kinase and its related kinase gene families in melon (Cucumis melo L.)

The calcium-dependent protein kinase (CDPK) is a ser/thr protein kinase that plays vital roles in plant growth, development, and responses to multiple stresses. Despite an important member of the stress responsive gene family, little is known about the evolutionary history and expression patterns of CDPK genes in melon. Herein, a total of 18 CDPK genes and 7 CDPK-related protein kinases (CRK) genes were identified in the melon genome via bioinformatic analysis, which were unevenly distributed across eleven chromosomes with an apparent exception for chromosome 3. Comparative syntenic analysis between Cucumis melo L. and Arabidopsis thaliana revealed that 13 CmCDPKs and 19 AtCPKs existed in 20 corresponding syntenic blocks. In addition, based on gene structure and phylogenetic analyses, all CmCDPKs were divided into four groups (CDPK I-IV) and CmCRKs clustered into one group (CRK I). Interestingly, group CDPK IV was clearly distinct from the other three CDPK groups, but clustered with CRK I on the phylogenetic tree, implying their origination from a common ancestor. Furthermore, CmCDPKand CmCRK genes were differentially expressed in response to various stimuli, such as biotic stress (Podosphaera xanthii), abiotic stress (salt and cold), and hormone (abscisic acid) treatment. To our knowledge, this is the first report on CDPK and CRK gene families in melon, which provides a basic foundation for functional characterizations of CmCDPK and CmCRK genes in the future.