Recently Duplicated Maize R2R3 Myb Genes Provide Evidence for Distinct Mechanisms of Evolutionary Divergence after Duplication

Abstract

, Missouri 65211 (M.D.M.) R2R3 Myb genes are widely distributed in the higher plants and comprise one of the largest known families of regulatory proteins. Here, 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 recently duplicated maize (Zea mays) 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 R2R3 Myb genes. Although the origins of C1/Pl1 and ZmMyb-IF35/ZmMyb-IF25 are associated with the segmental allotetraploid origin of the maize genome, other gene duplication events also shaped the P-to-A clade. 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 in some cases. Contrary to previous studies, we show that the divergent C termini of these R2R3 MYB proteins are subject to purifying selection. Our results provide an in-depth analysis of the sequence divergence for some recently duplicated R2R3 Myb genes, yielding important information on general patterns of evolution for this large family of plant regulatory genes.

MYB98 Positively Regulates a Battery of Synergid-Expressed Genes Encoding Filiform Apparatus–Localized Proteins

“…R2R3-MYB proteins are thought to function as transcription factors because they contain a structurally conserved DNA binding domain referred to as the Myb domain. Consistent with this, many R2R3-MYB proteins have been shown to function in transcriptional regulation (Stracke et al, 2001;Dias et al, 2003). Here, we show that MYB98 is localized to the nuclei of the synergid cells ( Figures 1A and 1B) and is required for the expression of a battery of genes in the synergid cells (Figure 3).…”

GRASSIUS: A Platform for Comparative Regulatory Genomics across the Grasses

“…These trends may reflect the expansion/contraction of individual families in a particular taxon. The recent amplification of R2R3-MYB regulators during the radiation of the grasses (Dias et al, 2003) provides one possible mechanism for the expansion of particular families. Contraction could be associated with gene loss (Bennetzen, 2007) or domain loss, a phenomenon that has also been reported for MYB domains (Braun and Grotewold, 2001).…”

The Arabidopsis R2R3 MYB Proteins FOUR LIPS and MYB88 Restrict Divisions Late in the Stomatal Cell Lineage

“…Each MYB repeat usually contains three regularly spaced and highly conserved Trp residues (Figure 7). Two likely events during the evolution and proliferation of plant R2R3 MYB proteins were a substitution of a Phe for the first Trp in the R3 MYB repeat and then the insertion of a specific Leu (Dias et al, 2003). R2R3 MYB proteins that lack the Leu insertion are considered atypical.…”