Evolution and functional diversification of CDK genes in bivalves: insights from Chlamys nobilis under biotic and...

Cyclin-dependent kinases (CDKs) are key regulators of cell cycle progression and transcriptional control, and play critical roles in stress responses. However, systematic studies and functional characterizations of the CDK gene family in bivalve mollusks remain scarce. In this study, a total of 409 CDK genes were identified from 34 bivalve species. Phylogenetic analysis assigned these genes to 13 highly conserved clades. Notably, CDK9 gene duplication events were detected in most of these species, collectively highlighting the evolutionary conservation and diversification of this gene family. For the noble scallop Chlamys nobilis, 14 CnCDK members were identified. Tissue expression profiling revealed that most CnCDK genes were highly expressed in gonads, mucosal tissues, and hemocytes, indicating their potential roles in gametogenesis and local immune regulation. Expression profiling following low-temperature stress and Vibrio parahaemolyticus exposure showed that multiple CnCDK members exhibited significant temporal expression changes under both stress conditions, suggesting that members of this gene family are widely involved in responses to biotic and abiotic stresses. Furthermore, CnCDK9a and CnCDK9b exhibited divergent tissue expression patterns but shared similar expression profiles under stress challenges, suggesting that they may have undergone regulatory subfunctionalization. This study systematically dissects the evolutionary characteristics and spatiotemporal expression regulatory patterns of the CDK gene family in bivalves, and provides a critical foundation for in-depth understanding of CDK functions in bivalve development, environmental adaptation, and stress-resistant breeding.