Tartary Buckwheat FtMYB31 Gene Encoding an R2R3-MYB Transcription Factor Enhances Flavonoid Accumulation in Tobacco

The R2R3-MYB transcription factors play an important role in regulating secondary metabolism biosynthesis and abiotic stress in plants. In this article, we report the identification of the transcription factor gene, FtMYB31, from the popular Eurasian crop tartary buckwheat (Fagopyrum tataricum) that enhances accumulation of the nutritionally beneficial compound rutin in transgenic tobacco leaves. The FtMYB31 complete cDNA coding sequence was isolated from the leaves of tartary buckwheat, and multiple protein sequence alignments and conserved domain analysis showed it contained a typical R2R3 MYB domain. Subcellular location experiments showed the FtMYB31 protein is localized in nucleus. The phylogenetic tree clustered FtMYB31 with VvMYBPA1 from Vitis vinifera, and AtMYB123 from Arabidopsis thaliana, belonging to the Subgroup 5 cluster. Comparison by qRT-PCR of FtMYB31 transcripts and those from rutin synthesis-related genes showed a relationship between FtMYB31, Ft4CL, and FtUFGT transcripts and rutin content in different tissues of F. tataricum, with correlation coefficients of − 0.68, 0.69, and 0.47, respectively. Transgenic experiments indicated that FtMYB31 upregulated CHS, F3H, and FLS genes in transgenic tobacco and enhanced the accumulation of rutin and total flavonols. These results suggest that FtMYB31 encodes an R2R3-MYB transcription factor that positively regulates flavonol biosynthesis in tartary buckwheat and tobacco and is a possible target for genetically modifying tartary buckwheat to enhance the content of beneficial compounds such as rutin.