c‐MYB oncogene‐like genes encoding three MYB repeats occur in all major plant lineages

Summary Since the identification of the first plant MYB‐like protein, the Zea mays factor C1, the number of MYB‐related genes described has greatly increased. All of the more than 150 plant MYB‐like proteins known so far contain either two or only one sequence‐related helix‐turn‐helix motif in their DNA‐binding domain. Animal c‐MYB genes contain three such helix‐turn‐helix motif‐encoding repeats (R1R2R3 class genes). It has therefore been concluded that R2R3‐MYB genes are the plant equivalents of c‐MYB and that there are significant differences in the basic structure of MYB genes of plants and animals. Here, we describe expressed R1R2R3‐MYB genes from Physcomitrella patens and Arabidopsis thaliana, designated PpMYB3R‐1 and AtMYB3R‐1. The amino acid sequences of their DNA‐binding domains show high similarity to those of animal MYB factors, and less similarity to R2R3‐MYB proteins from plants. In addition, R1R2R3‐MYB genes were identified in different plant evolutionary lineages including mosses, ferns and monocots. Our data show that a DNA‐binding domain consisting of three MYB repeats existed before the divergence of the animal and plant lineages. R1R2R3‐MYB genes may have a conserved function in eukaryotes, and R2R3‐MYB genes may predominantly regulate plant‐specific processes which evolved during plant speciation.