A plant-specific cyclin-dependent kinase is involved in the control of G(2)/M progression in plants

Cyclin-dependent kinases (CDKs) control the key transitions in the eukaryot ic cell cycle. All the CDKs known to control G(2)/M progression in yeast an d animals are distinguished by the characteristic PSTAIRE motif in their cy clin-binding domain and are closely related. Higher plants contain in addit ion a number of more divergent non-PSTAIRE CDKs with still obscure function s. We show that a plant-specific type of non-PSTAIRE CDKs is involved in th e control of the G(2)/M progression. In synchronized tobacco BY-2 cells, th e corresponding protein, accumulated in a cell cycle-regulated fashion, pea king at the G(2)/M transition. The associated histone HI kinase activity re ached a maximum in mitosis and required a yet unidentified subunit to be fu lly active. Down-regulation of the associated kinase activity in transgenic tobacco plants using a dominant-negative mutation delayed G(2)/M transitio n. These results provide the first evidence that non-PSTAIRE CDKs are invol ved in the control of the G(2)/M progression in plants.