Control of meiotic progression through cyclin-dependent kinase complexes in Arabidopsis thaliana ; Kontrolle der meiotischen Progression durch Cyclin-abhängige Kinase-Komplexe in Arabidopsis thaliana

Precise control of cell cycle progression is of key importance in maintaining genome stability in dividing cells. The cell cycle consists of a faithful order of events coordinating chromosome dynamics with cytoskeleton behavior to achieve cell growth and the formation of new daughter cells. In sexually reproducing organisms a special type of cell division, i.e. meiosis, is needed to keep the cellular DNA content stable over generations. In meiosis, a single round of DNA replication is followed by two rounds of chromosome segregation events, which result in a reduction of the genomic content by half. After meiosis, gametes can be formed which fuse in the process of fertilization to restore the original DNA amount in the offspring. Any deviations from normal meiosis could impair gamete function and thus compromise the future progeny. Hence, the control of the meiotic cell cycle program is of fundamental interest. Major regulators of cell cycle progression are cyclin-dependent kinase complexes. In this study I could show that the Arabidopsis central cell cycle regulator CDKA;1 together with the cyclin co-factor CYCB3;1 are key regulators of the microtubule cytoskeleton in meiosis. For full CDKA;1 activity, not only cyclin binding but also phosphorylation by Cdk-activating kinases (CAKs), i.e CDKD kinases is required. Combination of CAK mutants with a weak loss-of-function mutant in CDKA;1 revealed a plethora of phenotypes, including defects in chromosome segregation and microtubule organization during meiosis. Interestingly, a moderate reduction of CDKA;1 activity converted the simultaneous cytokinesis normally seen at the end of male meiosis in Arabidopsis into a successive cytokinesis as found in maize and other monocotyledonous species, where two cell division events, i.e. after meiosis I and after meiosis II occur. Additionally, live cell imaging upon treatment with the microtubule depolymerizing drug oryzalin revealed a novel function of CYCB3;1 in organizing microtubule arrays during meiosis. I was further ...