Genome-wide analysis of CBL and CIPK gene families in bermudagrass reveals the CdCIPK29-A1 as a stem growth angle regulator.

Key message: Genome-wide analysis of CBL and CIPK gene family was conducted in bermudagrass while a functional role in stem growth angle regulation was established for CdCIPK29-A1 via the generation of molecularly modified Arabidopsis plants. Calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs) are plant-specific Ca²⁺ sensors and effectors which mediate diverse Ca²⁺ signaling transduction pathways in plant growth, development, and stress responses. However, the functions of CBLs and CIPKs in bermudagrass (Cynodon dactylon L.), a widely planted warm-season turfgrass species with great economic value, remain poorly understood. In this study, a total of 33 CdCBL and 81 CdCIPK genes were identified in the bermudagrass genome, and were clustered in three and five groups according to their phylogenetic relationships, respectively. In line with their sequence divergence, different groups of CdCBL and CdCIPK genes exhibited different gene structures and expression patterns. Systematic yeast two-hybrid screening indicated that 27 CdCBL-CdCIPK complexes could be formed from 290 putative CdCBL and CdCIPK protein pairs. Among the CdCIPK proteins, CdCIPK29-A1 was found to interact with up to four CdCBL proteins. The CdCIPK29-A1 gene was preferentially expressed in the stolon internode of bermudagrass plants and the CdCIPK29-A1 protein was located to the cytoplasm. The expression of CdCIPK29-A1 in molecularly modified Arabidopsis thaliana (Arabidopsis) plants further indicated that CdCIPK29-A1 could regulate the stem growth angle and gravitropism possibly through modulating the starch metabolism in stem endodermal cells. These results not only established a solid foundation to explore the Ca²⁺ signaling transduction pathways in bermudagrass but also provided new insight into the function of CBL-CIPK complex in plant gravitropic response and stem growth angle regulation.