DNA double-strand break-induced endoreduplication and downregulation of B-type cyclin-dependent kinases

Genome integrity is continuously threatened by external stress or by errors in DNA replication, thus a response to DNA damage is essential for survival and continuous growth of plants. To prevent DNA-damaged cells from proliferating, plants may provoke the DNA damage checkpoint, but its regulatory mechanisms remain unknown.<br>In plants, A- and B-type cyclin-dependent kinases (CDKA and CDKB) are assumed to mainly control the cell cycle progression. CDKB is further classified into two subtypes, CDKB1 and CDKB2. CDKA can complements the yeast cdc2/cdc28p mutant, while CDKB cannot, suggesting that CDKB is a plant-specific type of CDK. <br>Recently, we found that the protein degradation of CDKB2 is enhanced in response to DNA double-strand breaks (DSBs).We also found that DSBs trigger transition to the endocycle, leading to endoreduplication, in Arabidopsis. These results promoted us to speculate that CDKB2 degradation may be involved in switching from the mitotic cell cycle to the endocycle in response to DSBs. To answer this question, we are investigating the ploidy distribution of Arabidopsis cultured cells that are knocked-down for the expression of CDKB1 and/or CDKB2.