A Scutellaria baicalensis R2R3-MYB gene, SbMYB8, regulates flavonoid biosynthesis and improves drought stress tolerance in transgenic tobacco

R2R3-MYB proteins are involved in the primary and secondary metabolism, developmental processes and the responses to biotic and abiotic stresses. Little is known about the functions of R2R3-MYB proteins in Scutellaria baicalensis Georgi which is a traditional Chinese medicinal plants. In this study, the function of a S. baicalensis R2R3-MYB protein, SbMYB8, was investigated. SbMYB8 had similar expression pattern with SbC4H and SbCHS in ABA-treated S. baicalensis, indicating that SbMYB8 might be involved in the flavonoid metabolism. SbMYB8 protein could bind to the GmMYB92 BS3 sequence of SbCHS promoter region, regulating the expression of SbCHS. The SbMYB8 protein was localized to the nucleus where it activated transcription. The transgenic tobacco plants over-expressing SbMYB8 had higher caffeoylquinic acid contents, compared to that in wild type plants. Overexpression of SbMYB8 also changed the expression level of some flavonoid biosynthesis-related genes. It was found that overexpression of SbMYB8 can improve stress tolerance of transgenic plants, and can alter the activity and expression levels of some antioxidant enzymes. These results indicate that SbMYB8 plays important roles in flavonoid biosynthesis and stress tolerance of plant.