The RGL2a-TCP46-MYB1 module regulates GA-mediated anthocyanin biosynthesis in apple

Gibberellin (GA) inhibits anthocyanin biosynthesis, but the mechanism by which GA regulates anthocyanin accumulation is still not fully understood. Teosinte branched1/cycloidea/proliferating (TCP) transcription factor MdTCP46 is a positive regulator of anthocyanin biosynthesis in apple, which acts by recruiting MdMYB1, a core anthocyanin regulator, and activating its transcriptional activity. In this study, we found that MdTCP46 was responsive to the GA signaling at the transcriptional level. GA treatment inhibited the transcription of MdTCP46, while the expression of the MdTCP46 promoter was induced by paclobutrazol (PAC), an inhibitor of GA biosynthesis. Anthocyanin accumulation assays in apple fruits and callus showed that MdTCP46 played a negative role in GA-inhibited anthocyanin biosynthesis. Molecular biochemical assays indicated that MdTCP46 interacted with the DELLA protein MdRGL2a, a GA repressor responsible for anthocyanin biosynthesis in apple. MdRGL2a played a synergistic role in MdTCP46-promoted anthocyanin biosynthesis by enhancing the interaction between MdTCP46 and MdMYB1. Taken together, these results reveal that the RGL2a-TCP46-MYB1 module plays an important role in GA-mediated anthocyanin biosynthesis in apple. The discovery of the RGL2a-TCP46-MYB1 module is helpful to enrich the anthocyanin transcriptional regulatory network and provide reference for further study of GA signaling pathway.