Characteristics of ZjCIPKs and ZjbHLH74-ZjCIPK5 regulated cold tolerance in jujube.

CIPKs are kind of serine/threonine (Ser/Thr) protein kinases which play important roles in response to biotic and abiotic stresses, and in plant growth and development. However, CIPKs in jujube (Ziziphus jujuba Mill.) had limited information, especially regarding their response to cold stress. In the current study, a total of 18 ZjCIPKs were identified in jujube genome which unevenly distributed on seven chromosomes. Conserved motif and gene structural analysis depicted them with conserved DEGLSA and APE motifs and similar structures. Phylogenetic analysis indicated that CIPKs were classified into five subgroups (I-V). In addition, three pairs of ZjCIPKs exhibited tandem duplication while the segmental duplication of ZjCIPKs was not identified. Study on the cis-acting elements indicted that stress or hormone related cis-acting elements were distributed unevenly on ZjCIPKs promoters and most ZjCIPKs were down- or up-regulated by the cold stress. VIGS induced silencing of ZjCIPK5 decreased the cold tolerance of sour jujube. Subcellular location analysis showed ZjCIPK5 located in nucleus. Moreover, transcription factor ZjbHLH74 which was induced at 6 h under cold stress could interact with the promoter of ZjCIPK5 to regulate jujube cold tolerance. These findings provided insights to a molecular basis of CIPK5 in jujube cold tolerance breeding for future.