Genome-wide analysis of calcium-dependent protein kinase (CDPK) family and functional characterization of TaCDPK25-U in response to drought stress in wheat

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Calcium (Ca2+)-dependent protein kinase (CDPK) is one kind of biomacromolecule that can not only act as the unique Ca2+ sensors for the increase and decrease of calcium concentrations, but also as an effector for calcium signaling. It plays a vital role in regulating plant growth and development as well as stress responses. Although it has been extensively characterized in many plants, the importance of CDPK family in wheat is not well studied to date. In this study, a total of 85, 57, 27, and 27 CDPKs were identified in Triticum aestivum (T. aestivum), Triticum dicoccoides (T. dicoccoides), Triticum urartu (T. urartu) and Aegilops tauschii (A. tauschii), respectively, and grouped them into four phylogenetic subclades. Then, the gene structure, protein domains, conserved motifs and cis-acting elements of them were comprehensively investigated. Synteny analysis demonstrated that segmental duplication events and polyploidization contributed to the expansion of TaCDPK family. Furthermore, the tissue-specific as well as stress-responsive candidates were detected based on RNA-seq analysis. Results showed that under drought stress, TaCDPK25-U was induced to transcribe two alternative spliced isoforms (TaCDPK25-U-AS1 and TaCDPK25-U-AS2), which displayed differential expression levels and different subcellular localization. Finally, over-expression of TaCDPK25-U-AS1 or TaCDPK25-U-AS2 enhanced the drought tolerance in Arabidopsis thaliana (A. thaliana). Additionally, the expression of TaCDPK25-U-AS2 was demonstrated to be positively regulated by TaDREB3 to improve drought tolerance in vivo and in vitro. This study laid the foundation to better understand the evolution and function of CDPK family in wheat.