FaMYB6-like negatively regulates FaMYB10-induced anthocyanin accumulation during strawberry fruit ripening

Abstract

Anthocyanins are one of the essential compounds affecting the quality of strawberry fruit. Several R2R3-MYB transcription factors have been well characterized as the anthocyanin activators in strawberry. However, we still lack valuable information on how R2R3-MYB repressors regulate strawberry anthocyanin accumulation. Here, we cloned a novel R2R3-MYB gene, FaMYB6-like, and characterized its repressive role during anthocyanin accumulation. FaMYB6-like encodes a nuclear localization protein, which was clustered into the FaMYB1-like type repressor clade in phylogenetic analysis. FaMYB6-like showed high expressions in anthocyanin-accumulating fruit and low transcript abundance in flowers, vegetative tissues, and early development stages of fruit. Transient overexpression of FaMYB6L-like repressed the expression of anthocyanin biosynthetic and transport genes, and reduced anthocyanin content in postharvest strawberry fruit. Transgenic tobacco lines overexpressing FaMYB6-like displayed a reduction in petal pigmentation. Overexpression of FaMYB6L-like in white-fleshed strawberry inhibited anthocyanin accumulation induced by FaMYB10. Protein interaction and promoter activation assays revealed that FaMYB6-like repressed the activation of target gene promoters by FaMYB10-FabHLH3 activation complex via its interaction with FabHLH3. Additionally, FaMYB6-like promoter activity can be activated by FaMYB10-FabHLH3 complex. Taken together, our study revealed that FaMYB6-like acted as a transcriptional repressor involved in an ‘activator-and-repressor’ feedback regulation mechanism for maintaining the balance of anthocyanin concentrations.