Anthocyanin accumulation is transcriptionally regulated by the MYB-bHLH-WD40 complex. Light is indispensable for anthocyanin accumulation, and light-inducible MYB and HY5 were considered to promote anthocyanin accumulation in many fruits. Whether and how light-inducible bHLH transcription factor and HY5 regulate anthocyanin synthesis in strawberry is unknown. In this study, we identified a bHLH transcription factor, FvbHLH9, which was induced by light as well as FvHY5, and found that similar to FvHY5, the transient overexpression and interference FvbHLH9 in strawberry fruits can promote and decrease anthocyanin accumulation, respectively, indicating FvbHLH9 functions as a positive regulator of anthocyanin biosynthesis. Furthermore, we confirmed that both FvHY5 and FvbHLH9 specifically bind to the promoter region of some key enzyme genes, including FvDFR, and the expression of FvDFR was activated through the heterodimer formation between FvHY5 and FvbHLH9. Finally, we confirmed that FvbHLH9 promoted anthocyanin accumulation is dependent on HY5-bHLH heterodimer in Arabidopsis. Our findings provide insights into a mechanism involving the synergistic regulation of light-dependent coloration and anthocyanin biosynthesis via HY5-bHLH heterodimer formed by the interaction of FvHY5 with FvbHLH9 in strawberry fruits.

中文翻译：

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FvbHLH9通过在草莓果实中形成HY5-bHLH9转录复合体而充当花色苷生物合成的正调节剂。

花青素的积累受MYB-bHLH-WD40复合物的转录调控。光对于花色苷的积累是必不可少的，并且认为光诱导性MYB和HY5可以促进许多水果中的花色苷的积累。光诱导的bHLH转录因子和HY5是否以及如何调节草莓中的花色苷合成尚不清楚。在这项研究中，我们鉴定了由光以及FvHY5诱导的bHLH转录因子FvbHLH9，发现与FvHY5相似，草莓果实中的瞬时过表达和干扰FvbHLH9可以分别促进和减少花色素苷的积累，表明FvbHLH9作为花青素生物合成的正调节剂。此外，我们确认FvHY5和FvbHLH9都与某些关键酶基因的启动子区域特异性结合，包括FvDFR，并且FvDFR的表达通过FvHY5和FvbHLH9之间的异二聚体形成而被激活。最后，我们证实FvbHLH9促进花色苷积累取决于拟南芥中的HY5-bHLH异二聚体。我们的发现为涉及草莓果实中由FvHY5与FvbHLH9相互作用形成的HY5-bHLH异二聚体通过光调节着色和花色苷生物合成的协同调控机制提供了见解。