Peter Casteels

The Arabidopsis Cks1At protein binds the cyclin-dependent kinases Cdc2aAt and Cdc2bAt

In Arabidopsis, two cyclin‐dependent kinases (CDK), Cdc2aAt and Cdc2bAt, have been described. Here, we have used the yeast two‐hybrid system to identify Arabidopsis proteins interacting with Cdc2aAt. Three different clones were isolated, one of which encodes a Suc1/Cks1 homologue. The functionality of the Arabidopsis Suc1/Cks1 homologue, designed Cks1At, was demonstrated by its ability to rescue the temperature‐sensitive cdc2‐L7 strain of fission yeast at low and intermediate expression levels. In contrast, high cks1At expression levels inhibited cell division in both mutant and wild‐type yeast strains. Cks1At binds both Cdc2aAt and Cdc2bAt in vivo and in vitro. Furthermore, we demonstrate that the fission yeast Suc1 binds Cdc2aAt but only weakly Cdc2bAt, whereas the human CksHs1 associated exclusively with Cdc2aAt.

Regulation of cyclin-dependent kinases in Arabidopsis thaliana.

In plants, different families of cyclin-dependent kinases (CDKs) and cyclins have been identified, indicating that also in plants the progression through the cell cycle is regulated by CDKs. In all eukaryotes, CDKs exert their activity through well-controlled phosphorylations of specific substrates on serine/threonine residues. Such post-translational modifications are universal mechanisms in signal transduction pathways. They allow the organism to differentiate, regulate growth and/or adapt to environmental changes, the latter being crucial for plants because of their sedentary life-style. This adaptation might explain the occurrence of a special CDK type with plant-specific features. This review focuses on the involvement of plant CDKs in different phases of the cell cycle in Arabidopsis thaliana and outlines their regulation by binding to other proteins, and by phosphorylation and dephosphorylation.