Epigenetic mechanisms underlie anthocyanin homeostasis via R2R3-MYB-mediated transcriptional repression

Abstract

Anthocyanins play vital roles in plant physiology and offer human health benefits. Anthocyanin homeostasis is coordinately regulated by MYB activators and repressors. However, the molecular mechanisms behind the inhibitory roles of MYB repressors and their interplay with MYB activators remain to be fully determined. Here, we report that PpMYB308A, an R2R3-MYB repressor from peach, acts as an anthocyanin brake. PpMYB308A was capable of binding to DNA, and it competed with PpMYB10.1 for binding MBS cis-elements. PpMYB308A has an EAR motif at the C-terminus that could form a repressor complex with the co-repressors, TOPLESS protein PpTPL and histone deacetylase PpHDA6, to induce histone deacetylation at the promoter of target genes, thereby exerting active repressive function. PpMYB308A was able to bind the promoter of target genes, both directly by itself and indirectly by incorporating into the MYB-bHLH-WD10 (MBW) complex, to execute the EAR motif-mediated transcriptional repression. These results uncover an epigenetic mechanism behind the regulation of anthocyanin biosynthesis by R2R3-MYB repressors. Additionally, PpMYB10.1, the master regulator of anthocyanin biosynthesis in peach, could activate transcription of PpMYB308A, thereby forming a negative feedback loop to fine-tune anthocyanin accumulation.