Maize R2R3 Myb genes: Sequence analysis reveals amplification in the higher plants

Transcription factors containing the Myb-homologous DNA-binding domain are widely found in eukaryotes. In plants, R2R3 Myb-domain proteins are involve d in the control of form and metabolism. The Arabidopsis genome harbors >10 0 R2R3 Myb genes, but few have been found in monocots, animals, and fungi. Using RT-PCR from different maize organs, we cloned 480 fragments correspon ding to a 42-44 residue-long sequence spanning the region between the conse rved DNA-recognition helices (Myb(BRH)) Of R2R3 Myb domains. We determined that maize expresses >80 different R2R3 Myb genes, and evolutionary distanc es among maize Myb(BRH) sequences indicate that most of the amplification o f the R2R3 Myb gene family occurred after the origin of land plants but pri or to the separation of monocots and dicots. In addition, evidence is provi ded for the very recent duplication of particular classes of R2R3 Myb genes in the grasses. Together, these findings render a novel line of evidence f or the amplification of the R2R3 MyB gene family in the early history of la nd plants and suggest that maize provides a possible model system to examin e the hypothesis that the expansion of Myb genes is associated with the reg ulation of novel plant cellular functions.