Expression data from Arabidopsis myb3r mutants

Temporal and spatial regulation of cell division is central for generating multicellular organs with predictable sizes and shapes. However, it remains largely unclear how genes with mitotic functions are transcriptionally regulated during organogenesis in plants. Here, we showed that a group of R1R2R3-Myb transcription factors are responsible for developmentally controlled downregulation of variety of mitotic genes in Arabidopsis. Loss of their functions resulted in elevated expression of mitotic genes in quiescent cells including those underwent terminal differentiation. Concomitantly, their mutations enhanced cell division activities in various aspects of plant development, generating organs with increased sizes and irregular architectures. In addition, we showed that this type of R1R2R3-Myb proteins are required for oscillated expression of G2/M-specfiic genes, most likely by inhibiting transcription outside of G2/M in the cell cycle. Our finding uncovered a novel plant-specific mechanism in which scheduled expression of G2/M-specific genes may require their global repression both in the cell cycle and during development. Seedlings (9d-old) or leaves (5d or 15d-old) of the wild type or myb3r mutants were sampled for RNA extraction and hybridization on Affymetrix microarrays.