Genome-Wide Identification and Characterization of CIPK Family and Analysis Responses to Various Stresses in Apple (Malus domestica)

In the CIPK family, the CBL-interacting protein kinases have shown crucial roles in hormone signaling transduction, and response to abiotic stress in plant developmental processes. The CIPK family is characterized by conserved NAF/FISL (Asn-Ala-Phe) and PPI (protein-phosphatase interaction) domains in the C-terminus. However, little data has been reported about the CIPK family in apple. A total of 34 MdCIPK genes were identified from the apple genome in this study and were later divided into two groups according to the CIPK domains, characterized by gene structure and chromosomal distribution, and then mapped onto 17 chromosomes. All MdCIPK genes were expressed in the four apple tissues (leaf, root, flower, and fruit). In addition, the MdCIPK gene expression profile showed that five members among them revealed enhanced expression during the pollen tube growth stages. The MdCIPK4 was the most expressive during the entire fruit development stages. Under stress conditions 21 MdCIPK genes transcript levels were up-regulated in response to fungal and salt treatments. This suggested the possible features of these genes' response to stresses in apples. Our findings provide a new insight about the roles of CIPK genes in apples, which could contribute to the cloning and functional analysis of CIPK genes in the future.