Molecular evolution analysis of MYB5 in Brassicaceae with specific focus on seed coat color of Brassica napus

Abstract

Background MYB transcription factors are splay a vital role in plant biology, with previous research highlighting the significant impact of the R2R3-MYB-like transcription factor MYB5 on seed mucilage biosynthesis, trichome branching, and seed coat development. However, there is a dearth of studies investigating its role in the regulation of proanthocyanidin (PA) biosynthesis. Results In this study, a total of 51 MYB5 homologous genes were identified across 31 species belonging to the Brassicaceae family, with particular emphasis on Brassica napus for subsequent investigation. Through phylogenetic analysis, these genes were categorized into four distinct subclasses. Protein sequence similarity and identity analysis demonstrated a high degree of conservation of MYB5 among species within the Brassicaceae family. Additionally, the examination of selection pressure revealed that MYB5 predominantly underwent purifying selection during its evolutionary history, as indicated by the Ka/Ks values of all MYB5 homologous gene pairs being less than one. Notably, we observed a higher rate of non-synonymous mutations in orthologous genes compared to paralogous genes, and the Ka/Ks value displayed a stronger correlation with Ka. In B. napus, an examination of expression patterns in five tissues revealed that MYB5 exhibited particularly high expression in the black seed coat. The findings from the WGCNA demonstrated a robust correlation between MYB5 and BAN(ANR) associated with PA biosynthesis in the black seed coat, providing further evidence of their close association and co-expression. Furthermore, the results obtained from of the analysis of protein interaction networks offer supplementary support for the proposition that MYB5 possesses the capability to interact with transcriptional regulatory proteins, specifically TT8 and TT2, alongside catalytic enzymes implicated in the synthesis of PAs, thereby making a contribution to the biosynthesis of PAs. These findings imply a plausible and significant correlation between the nuique expression pattern of MYB5 and the pigmentation of rapeseed coats. Nevertheless, additional research endeavors are imperative to authenticate and substantiate these findings. Conclusions This study offers valuable insights into the genetic evolution of Brassicaceae plants, thereby serving as a significant reference for the genetic enhancement of Brassicaceae seed coat color.