Evolution of the R2R3-MYB gene family in six Rosaceae species and expression in woodland strawberry

R2R3-MYB gene family play important roles in plants development, metabolism, and responses to various biotic and abiotic stresses. In this study, 838 R2R3-MYB genes were identified from six Rosaceae species, including 105 in woodland strawberry (Fragaria vesca), 173 in European pear (Pyrus communis), 219 in apple (Malus domestica), 121 in peach (Prunus persica), 121 in Chinese rose (Rosa chinensis), and 99 in black raspberry (Rubus occidentalis). All R2R3-MYB genes in the six Rosaceae species were clustered into 51 species-specific duplicated clades with 109 genes and 50 lineage-specific duplicated clades with 242 genes according to phylogenetic analysis. R2R3-MYB genes were distributed on all chromosomes in each of the six species, with a small amount of tandem duplication events. The proportion of tandem repeat genes ranged from 0 to 25.1%. The R2R3-MYB protein was conserved in a clade and likely to share similar functions. The distribution of Ks showed the duplication times of R2R3-MYB genes in six Rosaceae species. Furthermore, most of the R2R3-MYB genes had Ka/Ks values less than 1, which indicated they were driven by purifying selection during the evolutionary processes. The GO term enrichment analysis revealed that R2R3-MYB genes in strawberry and black raspberry were more divergent than in other Rosaceae species. Analysis of transcriptomes of 42 different tissues and development stages of woodland strawberry showed that high expression levels of R2R3-MYB suggested that the R2R3-MYB genes in strawberry played a key role in growth and development of both vegetative tissues and fruits. The strawberry R2R3-MYB genes in sub-group of S1, S2, S11, S20, and S22 had high expression levels both in young leaves (YL) and old leaves (OL) strawberry tissues under drought treatments.