Abstract
Most of G2/M phase-specific genes contain a common cis-acting element (MSA element) in their upstream regions, which binds with the R1R2R3-Myb proteins that act as transcriptional activators or repressors. Two R1R2R3-Myb genes, MYB3R1 and MYB3R4, encode structurally closely related transcriptional activators in Arabidopsis thaliana. The myb3r1 myb3r4 double mutant shows decreased expression of the G2/M-phase-sepcific genes and various developmental abnormalities that are caused by incomplete cytokinesis. To identify the novel factors that are involved in transcriptional activation of G2/M phase-specific genes, we performed a phenotypical enhancer screen of the loss-of-function myb3r4 mutant that shows weak cytokenetic defects, and obtained several enhancer mutants. In addition, we found that a polymorphism in the wild-type Landsberg erecta accession significantly enhances the defective cytokinesis of the myb3r4 null mutant. We are currently isolating the gene whose Landsberg allele is responsible for the phenotypical enhancement by a positional cloning approach.
