Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2002
Publication Date: 2/1/2003
Citation: DIAS, A.P., BRAUN, E.L., MCMULLEN, M.D., GROTEWOLD, E. RECENTLY DEVELOPED MAIZE R2R3 MYB GENES PROVIDE EVIDENCE FOR DISTINCT MECHANISMS OF EVOLUTIONARY DIVERGENCE AFTER DUPLICATION. PLANT PHYSIOLOGY. 2003. v. 131. p. 610-620. Interpretive Summary: Genes that encode regulatory proteins serve to control many developmental and secondary metabolism pathways in higher plants. As opposed to animals and other systems where there are only a handful of such genes, they number in the 100's in higher plants. To understand the evolution of new traits in plants, including crop plants, it is essential to define the roles of these genes and the traits they control. One approach is an evolutionary approach. How within higher plants does one gene family expand from a few genes to hundreds of genes? In this paper, we demonstrate that selection occurs on both conserved and rapidly evolving regions of the regulatory protein. This result indicates that both the conserved and rapidly evolving protein domains are defining function. This result is significant to scientists attempting to define the mechanism by which individual regulatory proteins control agronomic traits.
Technical Abstract: R2R3 Myb genes are widely distributed in higher plants and comprise one of the largest known families of regulatory proteins. We provide an evolutionary framework that helps explain the origin of the plant-specific R2R3 Myb genes from widely distributed R1R2R3 Myb genes, through a series of well-established steps. To understand the routes of sequence divergence that followed Myb gene duplication, we supplemented the information available on the recently duplicated maize R2R3 Myb genes (C1/Pl1 and P1/P2) by cloning and characterizing ZmMyb-IF35 and ZmMyb-IF25. These two genes correspond to the recently expanded P-to-A group of maize R1R2 Myb genes. Our analyses indicate that some recently duplicated Myb gene pairs display substantial differences in the numbers of synonymous substitutions that have accumulated in the conserved MYB domain and the divergent C-terminal regions. Thus, differences in the accumulation of substitutions during evolution can explain, in part, the rapid divergence of C-terminal regions for these proteins. Contrary to previous studies, we show that the divergent C-termini of these R2R3 MYB proteins are subject to purifying selection.