Abstract
Transcription of a set of G2/M phase-specific genes is regulated by a common mechanism which involves promoter element called MSA (M-specific activator) and a group of Myb transcription factors related to mammalian c-Myb. Tobacco c-Myb like transcription factors, NtmybA1, NtmybA2, and NtmybB, bind to and modulate the activity of the MSA element. In transient expression assay, NtmybA1 and A2 function as transcriptional activators, and NtmybB functions as a competitive repressor. Here we analyzed in vivo functions of these Ntmyb genes by generating overexpression lines and suppression lines in BY2 cells, hairy roots, and tobacco plants. Overexpression and suppression of Ntmyb genes affect growth rate, DNA content, and cell size. The observed phenotypes of the transgenic lines support our model in which balance between Myb activator and repressor control MSA-mediated transcription, thus regulating cell cycle progression during the G2/M.
