Abstract
During plant development, regulation of cell proliferation is considered to be mediated through cell cycle regulators in each cell. However, the mechanisms of such regulation are still poorly understood. Transcription of a group of G2/M phase-specific genes is regulated by a common cis-acting element and the R1R2R3-Myb transcription factors that bind to the element. Arabidopsis contains 5 genes encoding R1R2R3-Myb proteins, which can be divided into 3 groups (A-type, B-type and C-type) based on their primary structures. When two C-type Myb genes are doubly inactivated by T-DNA insertions, mRNA levels of various G2/M phase-specific genes are elevated. This up-regulation was more pronounced in developmentally old leaves with low cell division activities than in young leaves with high cell division activities. Our results suggest that C-type Myb proteins may down-regulate G2/M phase-specific genes and thereby inactivate cell proliferation during development of plant organs.
