Glutathione transferase MaGST1 mediates anthocyanin accumulation and influences flower color in grape hyacinth

Anthocyanins are biosynthesized in the endoplasmic reticulum and stored in vacuoles, and glutathione S -transferase (GST) plays a key role in anthocyanin accumulation. However, little is known about the mechanism of the role of GST in this process. We identified a prominent candidate gene, MaGST1 , which is highly expressed during the full-bloom stage, in grape hyacinth. MaGST1 rescued the phenotype of the anthocyanin biosynthesis-deficient mutant tt19 , indicating that MaGST1 functions in anthocyanin transport. MaGST1 -RNAi transgenic petals were generated by stable genetic transformation. We found that MaGST1 -RNAi inhibited the accumulation of anthocyanin in petals. Interestingly, in vitro experiments revealed that recombinant MaGST1 increased the water solubilities of cyanidin (Cya), delphinidin 3- O -glucoside (Dp3G), and petunidin 3- O -glucoside (Pt3G). Compared with Dp3G and Pt3G, Cya significantly suppressed the quenching of the intrinsic tryptophan fluorescence of MaGST1 to a lower level, indicating that MaGST1 has a greater affinity for Cya than for Dp3G and Pt3G. Site-directed mutagenesis and anthocyanin water solubility assays revealed that MaGST1 primarily binds to anthocyanin via Ser-68. Furthermore, yeast one-hybrid, dual-luciferase, and GUS staining assays revealed that MaGST1 expression is positively regulated by MaMybA. In summary, our findings reveal the molecular mechanism of anthocyanin transport mediated by MaGST1.