A Plant-specific Cyclin-dependent Kinase Is Involved in the Control of G2/M Progression in Plants*

Cyclin-dependent kinases (CDKs) control the key transitions in the eukaryotic cell cycle. All the CDKs known to control G2/M progression in yeast and animals are distinguished by the characteristic PSTAIRE motif in their cyclin-binding domain and are closely related. Higher plants contain in addition a number of more divergent non-PSTAIRE CDKs with still obscure functions. We show that a plant-specific type of non-PSTAIRE CDKs is involved in the control of the G2/M progression. In synchronized tobacco BY-2 cells, the corresponding protein, accumulated in a cell cycle-regulated fashion, peaking at the G2/M transition. The associated histone H1 kinase activity reached a maximum in mitosis and required a yet unidentified subunit to be fully active. Down-regulation of the associated kinase activity in transgenic tobacco plants using a dominant-negative mutation delayed G2/M transition. These results provide the first evidence that non-PSTAIRE CDKs are involved in the control of the G2/M progression in plants.