Abstract
Cyclins are known as one of the most important regulators of the eukaryotic cell cycle. In our initial studies using synchronized cultures of tobacco BY2 cells, we identified cis element called MSA (M phase-specific activator) that is necessary and sufficient for activation of promoters from cyclin B genes. Beside the cyclin B genes, many other G2/M phase-specific genes are under the transcriptional control mediated by the MSA elements. A group of c-Myb-like transcription factors bind to the MSA motifs and regulate promoter activities of G2/M phase-specific genes in tobacco. We are currently analyzing Arabidopsis knockout mutants in which c-Myb-like genes are disrupted in various combinations. A double knockout mutation for two related c-Myb-like genes caused severe defects in nuclear division, division plane determination, and cytokinesis. The results of our reverse genetic studies of the c-Myb-like genes are consistent with their roles in transcriptional regulation at the G2/M in BY2 cells.
