Anthocyanin pigments contribute to plant coloration and are valuable sources of antioxidants in the human diet as components of fruits and vegetables. Their production is known to be induced by light in apple fruit (Malus domestica); however, the underlying molecular mechanism responsible for early-stage light-induced anthocyanin biosynthesis remains unclear. Here, we identified an ethylene response factor (ERF) protein, ERF109, involved in light-induced anthocyanin biosynthesis and found that it promotes coloration by directly binding to anthocyanin-related gene promoters. Promoter::β-glucuronidase reporter analysis and Hi-C sequencing showed that a long noncoding RNA, MdLNC499, located nearby MdERF109, induces the expression of MdERF109. A W-box cis-element in the MdLNC499 promoter was found to be regulated by a transcription factor, MdWRKY1. Transient expression in apple fruit and stable transformation of apple calli allowed us to reconstruct a MdWRKY1–MdLNC499–MdERF109 transcriptional cascade in which MdWRKY1 is activated by light to increase the transcription of MdLNC499, which in turn induces MdERF109. The MdERF109 protein induces the expression of anthocyanin-related genes and the accumulation of anthocyanins in the early stages of apple coloration. Our results provide a platform for better understanding the various regulatory mechanisms involved in light-induced apple fruit coloration.

中文翻译：

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长链非编码 RNA MdLNC499 桥接 MdWRKY1 和 MdERF109 调节苹果果实中早期光诱导花青素积累的功能

花青素色素有助于植物着色，并且是人类饮食中作为水果和蔬菜成分的抗氧化剂的宝贵来源。已知它们的生产是由苹果果实（Malus domestica）中的光诱导的；然而，负责早期光诱导花青素生物合成的潜在分子机制仍不清楚。在这里，我们鉴定了一种乙烯反应因子 (ERF) 蛋白 ERF109，它参与光诱导的花青素生物合成，并发现它通过直接与花青素相关基因启动子结合来促进着色。启动子::β-葡萄糖醛酸酶报告基因分析和 Hi-C 测序表明，位于 MdERF109 附近的长链非编码 RNA MdLNC499 可诱导 MdERF109 的表达。发现 MdLNC499 启动子中的 W-box 顺式元件受转录因子 MdWRKY1 的调节。苹果果实中的瞬时表达和苹果愈伤组织的稳定转化使我们能够重建 MdWRKY1–MdLNC499–MdERF109 转录级联，其中 MdWRKY1 被光激活以增加 MdLNC499 的转录，进而诱导 MdERF109。MdERF109蛋白在苹果着色早期诱导花青素相关基因的表达和花青素的积累。我们的研究结果为更好地理解光诱导苹果果实着色所涉及的各种调节机制提供了一个平台。MdERF109蛋白在苹果着色早期诱导花青素相关基因的表达和花青素的积累。我们的研究结果为更好地理解光诱导苹果果实着色所涉及的各种调节机制提供了一个平台。MdERF109蛋白在苹果着色早期诱导花青素相关基因的表达和花青素的积累。我们的研究结果为更好地理解光诱导苹果果实着色所涉及的各种调节机制提供了一个平台。