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.

中文翻译：

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NAC 激活剂 MdNAC77L 调节红肉苹果中花青素的积累


花青素被广泛认为是影响苹果果实品质的关键成分。然而，关于 NAC 转录因子对红肉苹果花青素积累影响的研究有限。在本研究中，基于花青素代谢组和转录组的组合分析，确定 NAC 转录因子 MdNAC77L 与花青素含量的变化高度相关。过表达 MdNAC77L 显著增加了苹果和草莓果实中花青素的积累，以及几种花青素相关酶的表达。分子水平分析表明，MdNAC77L 与花青素生物合成途径的 3 种关键酶 （二氢黄酮 4-还原酶、花青素合酶和 UDP-类黄酮葡萄糖基转移酶） 的启动子直接结合。我们发现 ABA 强烈诱导 MdNAC77L 的表达，从而激活 3 个下游靶基因的表达。此外，MdNAC77L 在花青素含量较低的果肉中的转录本积累高于红皮。我们揭示了参与苹果红果肉花青素积累的新核心因子 MdNAC77L。这项研究为控制红肉苹果花青素生物合成的复杂调控机制提供了新的视角。