CDKD

CDKd, short for cyclin-dependent kinase delta, is a designation used for a subgroup of plant serine/threonine kinases that function as CDK-activating kinases (CAKs). In Arabidopsis thaliana, three paralogs have been identified: CDKd1, CDKd2, and CDKd3.

CDKd proteins form a CAK complex with Cyclin H and MAT1. As CAKs, they phosphorylate the activation loop, or T-loop, of other CDKs, enabling their catalytic activity and promoting cell cycle progression.

In addition to CDK activation, CDKd activity has been linked to transcriptional regulation through phosphorylation of the RNA polymerase II C-terminal domain, linking cell cycle control to transcription initiation and elongation.

Expression of CDKd genes is broad, with overlapping yet distinct patterns in developing tissues. Genetic analyses indicate partial redundancy among CDKd1–CDKd3, and higher-order mutants often exhibit more pronounced developmental defects, including altered growth and meristem function.

CDKd genes are part of a conserved CAK lineage in eukaryotes, with plants showing unique regulatory features compared to other kingdoms. See also cyclin-dependent kinase, CDK-activating kinase, Cyclin H, and MAT1.