Conservation and diversification of three-repeat Myb transcription factors in plants

The Myb family of transcription factors is characterized by the presence of a conserved DNA-binding domain called the Myb domain, which typically contains two or three imperfect repeat sequences. Within this family, Myb proteins containing three repeat motifs are evolutionarily conserved and have important roles in the cell cycle. Vertebrates have three Myb proteins, c-Myb, A-Myb, and B-Myb, all of which contain three repeats and are proposed to have a role at the G1/S transition. In plants, Myb proteins with three repeats are encoded by genes in a small subfamily within the large Myb gene family, most of which encode for Myb proteins with only two repeats. We have shown that Myb proteins with three repeats have an important role at the G2/M in tobacco, by regulating transcription of cyclin B genes and many other genes that are expressed at a similar time in the cell cycle. In this review, we summarize current knowledge on structure, function, and regulation of the plant Myb factors with three repeats, and discuss their conserved and divergent features in comparison with animal counterparts.