Ultraviolet-B (UV-B) radiation promotes anthocyanin synthesis in many plants. Although several transcription factors promote anthocyanin synthesis in response to UV-B radiation, the underlying mechanism remains unclear. In this study, the MdWRKY72 transcription factor gene was isolated from the 'Taishanzaoxia' apple genome. Quantitative real-time PCR analyses revealed that the genes encoding enzymes and transcription factors involved in the anthocyanin synthesis pathway (MdANS, MdDFR, MdUFGT, and MdMYB1) were more highly expressed in MdWRKY72-overexpressing transgenic calli than in the wild-type 'Orin' apple calli. The results indicated that MdWRKY72 increases anthocyanin synthesis in transgenic calli exposed to UV-B radiation. The results of a gel shift assay and chromatin immunoprecipitation proved that MdWRKY72 promotes MdMYB1 expression indirectly by binding to a W-box element in the MdHY5 promoter and directly by binding to a W-box element in the MdMYB1 promoter. Thus, MdWRKY72 increases anthocyanin synthesis via direct and indirect mechanisms. These findings may be useful for elucidating the molecular mechanism underlying UV-B-induced anthocyanin synthesis mediated by MdWRKY72.

中文翻译：

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紫外线B诱导的MdWRKY72表达促进苹果花青素合成

紫外线-B (UV-B) 辐射可促进许多植物中的花青素合成。尽管有几种转录因子可促进花青素合成以响应 UV-B 辐射，但其潜在机制仍不清楚。本研究从'泰山早下'苹果基因组中分离得到MdWRKY72转录因子基因。定量实时 PCR 分析显示，编码参与花青素合成途径的酶和转录因子（MdANS、MdDFR、MdUFGT 和 MdMYB1）的基因在过表达 MdWRKY72 的转基因愈伤组织中比在野生型“Orin”中表达更高苹果愈伤组织。结果表明，MdWRKY72 增加了暴露于 UV-B 辐射的转基因愈伤组织中的花青素合成。凝胶位移测定和染色质免疫沉淀的结果证明 MdWRKY72 通过与 MdHY5 启动子中的 W-box 元件结合并直接与 MdMYB1 启动子中的 W-box 元件结合来间接促进 MdMYB1 表达。因此，MdWRKY72 通过直接和间接机制增加花青素的合成。这些发现可能有助于阐明 MdWRKY72 介导的 UV-B 诱导花青素合成的分子机制。