Arabidopsis cyclin-dependent kinase C2 interacts with HDA15 and is involved in far-red light-mediated hypocotyl cell elongation

Histone deacetylases (HDAs) regulate many aspects of plant development and responses to environmental changes. Previous studies have demonstrated that the Arabidopsis histone deacetylase HDA15 is a positive regulator in far-red (FR) light-mediated inhibition of hypocotyl elongation. Furthermore, HDA15 can be phosphorylated and its enzymatic activity is negatively regulated by phosphorylation. However, the kinases that can phosphorylate HDA15 are still unknown. Cyclin-dependent kinases (CDKs) are a large family of serine/threonine protein kinases and have been identified as major regulators of the cell cycle and transcription. In this study, we show that the cyclin-dependent kinase CDKC2 interacts with HDA15 both in vitro and in vivo. In vitro kinase assays show that CDKC2 phosphorylates HDA15. Genetic evidence suggests that HDA15 acts downstream of CDKC2 in hypocotyl elongation under FR light. Furthermore, HDA15 and CDKC2 function synergistically in the regulation of FR-mediated cell elongation. The expression of cell wall organization- and auxin signaling-related genes under FR light is increased in hda15 and cdkc2/hda15 mutants. Taken together, our study indicates that CDKC2 can phosphorylate HDA15 and plays an important role in FR light-regulated hypocotyl elongation.