StMYB3 controls anthocyanin biosynthesis in potato via its dual regulatory role on StAN2

Anthocyanins are a class of water-soluble flavonoid pigments that play crucial roles in plant physiology and human health. Their biosynthesis is regulated by the MYB-bHLH-WD40 transcriptional complex, in which MYB transcription factors serve as the key determinants. However, the function of repressor-type MYBs in tuber crops such as potato remains poorly understood. Here we show that the R2R3-MYB transcription factor StMYB3 acts as a repressor of anthocyanin biosynthesis in potato. Transient-expression assays revealed that co-expression of StMYB3 with StAN2 (an R2R3 MYB activator) markedly reduced anthocyanin accumulation in leaves, and tuber skins of StMYB3-over-expressing lines exhibited a significant decrease in anthocyanin content. Mechanistic analyses demonstrate that both StMYB3 and StAN2 interact with StAN1 (an anthocyanin related bHLH). StMYB3 not only suppresses the StAN2-mediated transcriptional activation of anthocyanin biosynthesis genes (StCHS, StF3H, StF3'5'H, and StGST) but also directly represses the promoter activity of bHLH transcription factor StAN1. Moreover, StMYB3 and StAN2 form a mutually reinforcing positive-feedback loop at the transcriptional level. These results uncovers a StMYB3-StAN1-StAN2 regulatory module whose dynamics, driven by competition and bidirectional feedback, precisely control anthocyanin accumulation. This finding provides a reference for breeding potatoes with high anthocyanin content.