Insight into the CBL and CIPK gene families in pecan (Carya illinoinensis): identification, evolution and expression patterns in drought response.

BACKGROUND

Calcium (Ca) serves as a ubiquitous second messenger and plays a pivotal role in signal transduction. Calcineurin B-like proteins (CBLs) are plant-specific Ca sensors that interact with CBL-interacting protein kinases (CIPKs) to transmit Ca signals. CBL-CIPK complexes have been reported to play pivotal roles in plant development and response to drought stress; however, limited information is available about the CBL and CIPK genes in pecan, an important nut crop.

RESULTS

In the present study, a total of 9 CBL and 30 CIPK genes were identified from the pecan genome and divided into four and five clades based on phylogeny, respectively. Gene structure and distribution of conserved sequence motif analysis suggested that family members in the same clade commonly exhibited similar exon-intron structures and motif compositions. The segmental duplication events contributed largely to the expansion of pecan CBL and CIPK gene families, and Ka/Ks values revealed that all of them experienced strong negative selection. Phylogenetic analysis of CIPK proteins from 14 plant species revealed that CIPKs in the intron-poor clade originated in seed plants. Tissue-specific expression profiles of CiCBLs and CiCIPKs were analysed, presenting functional diversity. Expression profiles derived from RNA-Seq revealed distinct expression patterns of CiCBLs and CiCIPKs under drought treatment in pecan. Moreover, coexpression network analysis helped to elucidate the relationships between these genes and identify potential candidates for the regulation of drought response, which were verified by qRT-PCR analysis.

CONCLUSIONS

The characterization and analysis of CBL and CIPK genes in pecan genome could provide a basis for further functional analysis of CiCBLs and CiCIPKs in the drought stress response of pecan.