Seminars

Cyclin-dependent kinases are the central regulators of the cell cycle and as such key to growth, development and reproduction. The function of CDKs is in general conserved from yeast to plants and for example, expression of CDKA;1, the plant Cdk1 homolog, can complement yeast cdc2 or cdc28 mutants. In addition, recent studies have shown that the molecular mechanistics of CDK are conserved across kingdoms, e.g. the requirement for activation of CDKs through phosphorylation of a conserved Thr residue in their T-loop. In contrast to the conserved enzymatic function, the regulatory network of their action appears to have undergone dramatic changes during two billion years of eukaryotic evolution. Through extensive studies in yeast and humans, a comprehensive picture of CDK function has been revealed. We are interested in the properties of the network architecture of CDK action to understand general principles of cellular organization and coordination of the cell cycle with development as well as environmental conditions. In the first part of our presentation, given by Arp Schnittger, we will show our recent advances in establishing a genetic framework of cell cycle control in plants. Focus will be here on the core cell cycle control machinery comprising CDKs, cyclins, and CDK inhibitors. To decipher the function of these regulators, we use female and male gametophyte development. In the second part of the talk, presented by Hirofumi Harashima, we will present our recent attempts to understand what processes and in which order are regulated by CDK–cyclin complexes. To identify CDKA;1 substrates in Arabidopsis we follow different complementary approaches that are providing a growing list of CDKA;1 substrates, including a large number of plant specific substrates.  A comparison of CDK substrates from plants with substrates known from animals and yeast allows a view onto the evolutionary dynamics of the CDK network action and first conclusion is that the pattern of phosphorylation sites is very fast evolving.