Dry fig is a traditional healthy snack and has important economic value in a number of Mediterranean and Middle Eastern countries. Cultivars with no anthocyanin accumulation in the fruit peel are preferred for dry fig production. R2R3-MYB transcription factors have promotive or repressive regulatory roles in plant anthocyanin biosynthesis. In this study, 113 R2R3-MYB genes were identified in Ficus carica, 3 of which were assigned to the S4 subfamily of flavonoid-biosynthesis repressors. FcMYB57 was further recruited as a candidate anthocyanin-biosynthesis repressor based on its sequence features and expression, which was significantly negatively correlated with that of anthocyanin-biosynthesis structural genes. Transient overexpression of FcMYB57 in strawberry totally inhibited fruit pigmentation and significantly increased fruit firmness. The metabolomic analysis confirmed a significant reduction in the contents of cyanidin-3-O-glucoside and pelargonidin-3-O-glucoside, as well as other flavonoids, and transmission electron microscopy revealed an increment in cell-wall thickness. Transcriptome analysis showed downregulation of anthocyanin-biosynthesis structural genes and upregulation of genes related to xylan synthesis. Yeast one-hybrid and dual luciferase assays demonstrated a negative regulatory effect of FcMYB57 on the promoter of FcUFGT3 (UDP glucose-flavonoid 3-O-glcosyl-transferase). Yeast two-hybrid assay showed that FcMYB57 does not interact with FcbHLH42, 3, 14, MYC2, or FcTTG1, all of which have a previously identified or predicted role in flavonoid biosynthesis, however, interaction was detected with FcTPL (Topless), suggesting that FcMYB57 serves as an active repressor of anthocyanin biosynthesis. This is the first identification of an anthocyanin-biosynthesis repressor in fig, with a possible role in fig fruit quality.

中文翻译：

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R2R3-MYB 阻遏蛋白亚家族分析确定 FcMYB57 是榕树果实中花青素生物合成的负调节因子


无花果干是一种传统的健康零食，在许多地中海和中东国家具有重要的经济价值。果皮中没有花青素积累的栽培品种是干无花果生产的首选。R2R3-MYB 转录因子在植物花青素生物合成中具有促进或抑制调节作用。在这项研究中，在榕树中鉴定出 113 个 R2R3-MYB 基因，其中 3 个被归入类黄酮生物合成抑制因子的 S4 亚家族。根据 FcMYB57 的序列特征和表达，进一步招募 FcMYB57 作为候选花青素生物合成抑制因子，与花青素生物合成结构基因呈显著负相关。FcMYB57 在草莓中的瞬时过表达完全抑制了果实色素沉着，显著提高了果实的硬度。代谢组学分析证实，矢车菊素-3-O-葡萄糖苷和天竺葵素-3-O-葡萄糖苷以及其他类黄酮的含量显著降低，透射电子显微镜显示细胞壁厚度增加。转录组分析显示花青素生物合成结构基因下调，木聚糖合成相关基因上调。酵母单杂交和双荧光素酶测定表明 FcMYB57 对 FcUFGT3 启动子 （UDP 葡萄糖-类黄酮 3-O-glcosyl-转移酶） 的负调节作用。酵母双杂交测定显示，FcMYB57 不与 FcbHLH42、3、14、MYC2 或 FcTTG1 相互作用，所有这些都在类黄酮生物合成中具有先前确定或预测的作用，然而，检测到与 FcTPL （Topless） 的相互作用，表明 FcMYB57 是花青素生物合成的活性抑制因子。 这是首次在无花果中鉴定出花青素-生物合成抑制因子，可能在无花果果实质量中发挥作用。