CsRAB, a R2R3-MYB transcription factor from purple tea (Camellia sinensis), positively regulates anthocyanin biosynthesis

In tea (<i>Camellia sinensis</i>), anthocyanins are important secondary metabolites that are linked to leaf color. Anthocyanin biosynthesis is a complex biological process, in which multiple genes including structural and regulatory genes are involved. Here, we describe the cloning and characterizing of a new R2R3-MYB transcription factor gene, <i>CsRAB</i>, isolated from purple tea variety '<i>Hongfei</i>'. Consistent with its predicted role as a transcription factor, the CsRAB protein localized to nuclei when expressed in onion (<i>Allium cepa</i>) epidermal cell. A dual-luciferase reporter assay demonstrated that CsRAB acts as a transcriptional activator <i>in vivo</i>. <i>CsRAB</i> overexpression in <i>Arabidopsis</i> seedlings led to higher expression levels of anthocyanin biosynthesis-related genes, and consequently, purple stems and higher anthocyanin contents were exhibited in overexpressing lines compared to wild type. The results indicated that <i>CsRAB</i> plays critical roles in positively regulating anthocyanins biosynthesis in tea plants.