Characterization and tissue-specific as well as heat-stress expression analysis of CBL-interacting protein kinase genes in Dimocarpus longan Lour

The CBL-interacting protein kinase (CIPK) gene family plays important roles in plant growth, development, and responses to abiotic stresses. To date, the CIPKs have been extensively identified and characterized in various plants. However, there have been few studies on CIPKs in Dimocarpus longan Lour (D. longan). In this study we identified eight putative CIPKs in D. longan (DlCIPKs) according to RNA-seq data. The physicochemical properties, subcellular localization, conserved motifs, phylogenetic relationships, glycosylation and phosphorylation sites, and gene ontology annotation were analyzed using bioinformatics tools. The tissue-specific and heat-stress-responsive expressions were systematically investigated as well. Ten motifs widely maintained by DlCIPKs were identified. All eight DlCIPKs identified from D. longan and the 50 CIPKs selected from Zea mays, Oryza sativa, Sorghum bicolor, Vitis vinifera, Populus trichocarpa, and Arabidopsis thaliana were categorized together into seven groups; group 7 was the largest and contained 20 CIPKs. Localizations of these eight DlCIPKs were predicted in the plasma membrane, cytoplasm, chloroplast thylakoid membrane, or nucleus and were predicted to differ. All eight DlCIPKs were predicted to be phosphorylated but with different numbers of phosphorylation sites. The quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed that among the eight DlCIPKs, only DlCIPK1, DlCIPK5, and DlCIPK8 were differently expressed; notably, between root and leaf tissues. All eight DlCIPKs responded to heat treatments. The expressions of DlCIPK1, DlCIPK4, DlCIPK5, and DlCIPK6 in D. longan leaves were upregulated to the maximum level after 1 h of heat treatment. In contrast, the expression levels of DlCIPK2, DlCIPK3, DlCIPK7, and DlCIPK8 increased significantly after 4 h of heat treatment. The results of this study will enrich our knowledge of DlCIPKs and establish a foundation for enhancing tolerance to abiotic stresses through genetic engineering in D. longan.