A light responsive transcription factor CsbHLH89 positively regulates anthocyanidin synthesis in tea (Camellia sinensis)

Abstract

Anthocyanins are a class of secondary metabolites with rich physiological functions and many benefits for the human body. Although there have been numerous reports on anthocyanin synthesis in tea plants, the mechanism by which bHLH transcription factors regulate anthocyanin synthesis in tea plants is still unclear. In this study, we identified CsbHLH89, a basic helix–loop–helix (bHLH) transcription factor that is located in the nucleus and cytoplasm and has transcriptional activation activity. CsbHLH89 directly binds to G-box elements and activates the CsCHS, CsFLS, and CsDFR promoters in vitro and in vivo. Further experiments demonstrated that CsbHLH89 could be involved in the synthesis of tea plant anthocyanins as homodimers or heterodimers. Our research results show that CsbHLH89 can positively regulate anthocyanin synthesis in tea. In addition, it was found that CsHY5, a light signal transduction factor, could bind to the promoter of CsbHLH89 to indirectly promote anthocyanin accumulation. Silencing of CsHY5 and CsbHLH89 by antisense oligonucleotide, respectively, revealed that the expression of structural genes and transcription factors were down-regulated. Shading treatment of tea plants revealed a significant reduction in anthocyanin content and down-regulation of the expression of genes involved in anthocyanin synthesis. Our research provides new insight into the regulatory network of anthocyanin synthesis in tea and a new strategy for breeding rich anthocyanin.