MtGSTF7, activated by the MYB transcription factor LAP1, specifically participates in anthocyanin accumulation in Medicago truncatula

Abstract Anthocyanins and proanthocyanins are two end-products of the flavonoid biosynthesis pathway. They are believed to be synthesized on the ER, and then sequestered into the vacuole. In Arabidopsis thaliana, AtTT19 is necessary for both anthocyanin and PA accumulation. Here, we found that MtGSTF7, a homolog of AtTT19, is essential for anthocyanin accumulation but not required for PA accumulation in Medicago truncatula. MtGSTF7 was induced by the anthocyanin regulator LAP1 and its tissue expression pattern was correlated with anthocyanin deposition in M. truncatula. Tnt1-insertional mutants of MtGSTF7 lost anthocyanin accumulation in vegetative organs, and introducing a genomic fragment of MtGSTF7 could completely complement the mutant phenotypes. Additionally, the accumulation of anthocyanins induced by LAP1 was significantly blocked in mtgstf7 mutants. Yeast-one-hybridization and dual-luciferase reporter assays revealed that LAP1 could bind to the MtGSTF7 promoter to activate its expression. Ectopic expression of MtGSTF7 in tt19 mutants could rescue their anthocyanin deficiency, but not their PA defect. Furthermore, PA accumulation was not affected in the mtgstf7 mutants. Taken together, our results show that the mechanism of anthocyanin and PA accumulation in M. truncatula is different from that in A. thaliana, and provide a new target gene for engineering anthocyanins in plants.