Identification and expression analysis of BrTT8 during anthocyanin biosynthesis and exposure to abiotic stress in turnip (Brassica rapa subsp. rapa 'Tsuda')

Transparent Testa 8 (TT8) is an important transcription factor in regulatory networks controlling development, metabolism and stress responses in plants. However, their molecular mechanism associated with anthocyanin biosynthesis in turnip remains largely unknown. In this study, BrTT8 (HQ337791) was isolated from 'Tsuda' turnip. A quantitative PCR analysis found the highest expression of BrTT8 in the red root epidermis of turnip and revealed that BrTT8 expression exhibited tissue specificity. BrTT8 expression in swollen hypocotyls was induced by UV-A light. A yeast two-hybrid assay revealed that BrMYB75 (HQ337792), a member of the set of R2R3-myb/bHLH complexes that regulate anthocyanin biosynthesis in plants, was localized in the nucleus and interacted with BrTT8. The transcript abundance of BrMYB75 in swollen hypocotyls increased after treatment with UV-A light. The cotransformation of BrTT8 and BrMYB75 in tomato led to enhanced anthocyanin biosynthesis. These results suggest that BrTT8, as a key transcription factor, might play a crucial role in UV-A-induced anthocyanin biosynthesis and also reveal that the BrTT8 gene is regulated by abiotic stresses, such as high- and low-temperature, hormone, osmotic and salt stresses.