Flavonoids have a major contribution to the fruit quality in cultivated strawberries and are regulated by MYB, bHLH and WD40 transcriptional factors. We reported here the identification of the FaMYB5, an R2R3-MYB transcription factor, which positively regulated the accumulation of anthocyanins and proanthocyanidins through the trans-activation of the F3'H and LAR. The strawberry FaEGL3 and FaLWD1/FaLWD1-like interact with the R2R3-FaMYB5 to form an MYB-bHLH-WD40 complex (MBW), enhancing the regulatory efficiency. The R2R3-FaMYB5 was constitutively expressed in various tissues and in fruits of different developmental stages, which was strikingly contrasting to the fruit-specific expression patterns of FaMYB10. Meanwhile, R2R3-FaMYB5 failed to promote a stable accumulation of anthocyanin glycosides in the mature fruits of the myb10 mutant, mainly due to the suppressed expression of TT19. The R2R3-FaMYB5 was regulated by an antisense long noncoding RNA lncRNA-myb5. Additionally, the R2R3-FaMYB5 protein could interact with FaBT2 and was degraded through the ubiquitin/26 S proteasome pathway. Transcriptome and metabolome data showed that R2R3-FaMYB5 enhanced the gene expression and the metabolite accumulation involved in the flavonoid, phenylpropanoid and lignin biosynthesis pathways. Collectively, we conclude that the FaMYB5 is an R2R3-MYB activator involved in the composition of MBW, which positively regulates the biosynthesis of anthocyanin and proanthocyanidin. These findings provided new insights into the molecular mechanisms that regulate flavonoids in strawberry fruits.

中文翻译：

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一种新型 R2R3-MYB 转录因子 FaMYB5 正向调节栽培草莓 (Fragaria × ananassa) 中花青素和原花青素的生物合成

类黄酮对栽培草莓的果实品质有重要贡献，并受 MYB、bHLH 和 WD40 转录因子调控。我们在此报道了 FaMYB5 的鉴定，这是一种 R2R3-MYB 转录因子，它通过 F3'H 和LAR的反式激活正向调节花青素和原花青素的积累。草莓 FaEGL3 和 FaLWD1/FaLWD1-like 与 R2R3-FaMYB5 相互作用形成 MYB-bHLH-WD40 复合物 (MBW)，从而提高调控效率。R2R3 -FaMYB5在各种组织和不同发育阶段的果实中组成型表达，这与FaMYB10的果实特异性表达模式形成鲜明对比. 同时，R2R3-FaMYB5 未能促进myb10突变体成熟果实中花青素苷的稳定积累，这主要是由于TT19的表达受到抑制。R2R3 -FaMYB5受反义长链非编码 RNA lncRNA-myb5调控. 此外，R2R3-FaMYB5 蛋白可以与 FaBT2 相互作用，并通过泛素/26 S 蛋白酶体途径被降解。转录组和代谢组数据显示，R2R3-FaMYB5 增强了类黄酮、苯丙烷和木质素生物合成途径中涉及的基因表达和代谢物积累。总的来说，我们得出结论，FaMYB5 是一种参与 MBW 组成的 R2R3-MYB 激活剂，它正向调节花青素和原花青素的生物合成。这些发现为草莓果实中黄酮类化合物的调节分子机制提供了新的见解。