Background: The MYB superfamily constitutes one of the most abundant groups of transcription factors described in plants. Nevertheless, their functions appear to be highly diverse and remain rather unclear. To date, no genome-wide characterization of this gene family has been conducted in a legume species. Here we report the first genome-wide analysis of the whole MYB superfamily in a legume species, soybean (Glycine max), including the gene structures, phylogeny, chromosome locations, conserved motifs, and expression patterns, as well as a comparative genomic analysis with Arabidopsis. Results: A total of 244 R2R3-MYB genes were identified and further classified into 48 subfamilies based on a phylogenetic comparative analysis with their putative orthologs, showed both gene loss and duplication events. The phylogenetic analysis showed that most characterized MYB genes with similar functions are clustered in the same subfamily, together with the identification of orthologs by synteny analysis, functional conservation among subgroups of MYB genes was strongly indicated. The phylogenetic relationships of each subgroup of MYB genes were well supported by the highly conserved intron/exon structures and motifs outside the MYB domain. Synonymous nucleotide substitution (d _N/d _S) analysis showed that the soybean MYB DNA-binding domain is under strong negative selection. The chromosome distribution pattern strongly indicated that genome-wide segmental and tandem duplication contribute to the expansion of soybean MYB genes. In addition, we found that ~ 4% of soybean R2R3-MYB genes had undergone alternative splicing events, producing a variety of transcripts from a single gene, which illustrated the extremely high complexity of transcriptome regulation. Comparative expression profile analysis of R2R3-MYB genes in soybean and Arabidopsis revealed that MYB genes play conserved and various roles in plants, which is indicative of a divergence in function. Conclusions: In this study we identified the largest MYB gene family in plants known to date. Our findings indicate that members of this large gene family may be involved in different plant biological processes, some of which may be potentially involved in legume-specific nodulation. Our comparative genomics analysis provides a solid foundation for future functional dissection of this family gene.

Brassica napus (2n = 4x = 38, AACC) is an important allopolyploid crop derived from interspecific crosses between Brassica rapa (2n = 2x = 20, AA) and Brassica oleracea (2n = 2x = 18, CC). However, no truly wild B. napus populations are known; its origin and improvement processes remain unclear. Here, we resequence 588 B. napus accessions. We uncover that the A subgenome may evolve from the ancestor of European turnip and the C subgenome may evolve from the common ancestor of kohlrabi, cauliflower, broccoli, and Chinese kale. Additionally, winter oilseed may be the original form of B. napus. Subgenome-specific selection of defense-response genes has contributed to environmental adaptation after formation of the species, whereas asymmetrical subgenomic selection has led to ecotype change. By integrating genome-wide association studies, selection signals, and transcriptome analyses, we identify genes associated with improved stress tolerance, oil content, seed quality, and ecotype improvement. They are candidates for further functional characterization and genetic improvement of B. napus.

MYB proteins comprise a large family of plant transcription factors, members of which perform a variety of functions in plant biological processes. To date, no genome-wide characterization of this gene family has been conducted in maize (Zea mays). In the present study, we performed a comprehensive computational analysis, to yield a complete overview of the R2R3-MYB gene family in maize, including the phylogeny, expression patterns, and also its structural and functional characteristics. The MYB gene structure in maize and Arabidopsis were highly conserved, indicating that they were originally compact in size. Subgroup-specific conserved motifs outside the MYB domain may reflect functional conservation. The genome distribution strongly supports the hypothesis that segmental and tandem duplication contribute to the expansion of maize MYB genes. We also performed an updated and comprehensive classification of the R2R3-MYB gene families in maize and other plant species. The result revealed that the functions were conserved between maize MYB genes and their putative orthologs, demonstrating the origin and evolutionary diversification of plant MYB genes. Species-specific groups/subgroups may evolve or be lost during evolution, resulting in functional divergence. Expression profile study indicated that maize R2R3-MYB genes exhibit a variety of expression patterns, suggesting diverse functions. Furthermore, computational prediction potential targets of maize microRNAs (miRNAs) revealed that miR159, miR319, and miR160 may be implicated in regulating maize R2R3-MYB genes, suggesting roles of these miRNAs in post-transcriptional regulation and transcription networks. Our comparative analysis of R2R3-MYB genes in maize confirm and extend the sequence and functional characteristics of this gene family, and will facilitate future functional analysis of the MYB gene family in maize.

R2R3-MYB genes (R2R3-MYBs) form one of the largest transcription factor gene families in the plant kingdom, with substantial structural and functional diversity. However, the evolutionary processes leading to this amazing functional diversity have not yet been clearly established. Recently developed genomic and classical molecular technologies have provided detailed insights into the evolutionary relationships and functions of plant R2R3-MYBs. Here, we review recent genome-level and functional analyses of plant R2R3-MYBs, with an emphasis on their evolution and functional diversification. In land plants, this gene family underwent a large expansion by whole genome duplications and small-scale duplications. Along with this population explosion, a series of functionally conserved or lineage-specific subfamilies/groups arose with roles in three major plant-specific biological processes: development and cell differentiation, specialized metabolism, and biotic and abiotic stresses. The rapid expansion and functional diversification of plant R2R3-MYBs are highly consistent with the increasing complexity of angiosperms. In particular, recently derived R2R3-MYBs with three highly homologous intron patterns (a, b, and c) are disproportionately related to specialized metabolism and have become the predominant subfamilies in land plant genomes. The evolution of plant R2R3-MYBs is an active area of research, and further studies are expected to improve our understanding of the evolution and functional diversification of this gene family.

MYBgenes are widely distributed in higher plants and comprise one of the largest transcription factors, which are characterized by the presence of a highly conserved MYB domain at their N-termini....