Cell cycle control

Cell division in plants serves to subdivide space in the expanding organism rather than to supply cellular building blocks, as it does in animals. Despite these contrasting developmental contexts, transitions through and between stages of the mitotic cell cycle are controlled in both kingdoms by related families of cyclin-dependent kinases (CDKs) and their regulatory subunits (cyclins). Passage of animal cells through the G1 and S phases of the cycle is controlled by complexes of CDKs, cyclins, transcription factors, tumor supressor proteins, and inhibitor proteins. None of these complexes has been identified in plants. Most plant cell cycle regulators characterized to date resemble those active in the G2-M transition in yeast and animal cells, although biochemical demonstrations of their roles in plants are lacking. Also awaiting elucidation in plant systems are the essential connections between CDK-cyclin activities and hormonal or developmental signals.