Genome-Wide Identification of R2R3-MYB Transcription Factors: Discovery of a "Dual-Function" Regulator of Gypenoside and Flavonol Biosynthesis in .

The gene family participates in several plant physiological processes, especially the regulation of the biosynthesis of secondary metabolites. However, little is known about the functions of genes in (), a traditional Chinese medicinal herb that is an excellent source of gypenosides (a class of triterpenoid saponins) and flavonoids. In this study, a systematic genome-wide analysis of the gene family was performed using the recently sequenced genome. In total, 87 genes were identified and subsequently divided into 32 subgroups based on phylogenetic analysis. The analysis was based on conserved exon-intron structures and motif compositions within the same subgroup. Collinearity analysis demonstrated that segmental duplication events were majorly responsible for the expansion of the gene family, and Ka/Ks analysis indicated that the majority of the duplicated genes underwent purifying selection. A combination of transcriptome analysis and quantitative reverse transcriptase-PCR (qRT-PCR) confirmed that myeloblastosis 81 () along with genes encoding gypenoside and flavonol biosynthetic enzymes exhibited similar expression patterns in different tissues and responses to methyl jasmonate (MeJA). Moreover, GpMYB81 could bind to the promoters of farnesyl pyrophosphate synthase 1 () and chalcone synthase (), the key structural genes of gypenoside and flavonol biosynthesis, respectively, and activate their expression. Altogether, this study highlights a novel transcriptional regulatory mechanism that suggests that GpMYB81 acts as a "dual-function" regulator of gypenoside and flavonol biosynthesis in .