The NAC activator, MdNAC77L, regulates anthocyanin accumulation in red flesh apple

Anthocyanin is widely acknowledged as a crucial component contributing to apple fruit quality. However, research on the influence of NAC transcription factors on anthocyanin accumulation in red flesh apple is limited. In this study, a NAC transcription factor MdNAC77L was identified as highly related to the change of anthocyanin content, based on a combined anthocyanin metabolome and transcriptome analysis. Overexpression of MdNAC77L significantly increased the accumulation of anthocyanin in both apple and strawberry fruits, along with the expression of several anthocyanin-related enzymes. Molecular-level analyses demonstrated that MdNAC77L was directly combined with the promoters of three pivotal enzymes (dihydroflavonol 4-reductase, anthocyanin synthase, and UDP-flavonoid glucosyltransferase) of anthocyanin biosynthetic pathway. We found that ABA strongly induced the expression of MdNAC77L , which activated the expression of three downstream target genes. In addition, MdNAC77L showed higher transcript accumulation in flesh with lower anthocyanin content than that in red peel. We revealed the new core factor, MdNAC77L , involved in anthocyanin accumulation in apple red flesh. This research provides a fresh perspective on the intricate regulatory mechanisms governing anthocyanin biosynthesis in red-fleshed apples.