FvbHLH9 Interacts With FvHY5 To Regulate Anthocyanin Synthesis In Strawberry Fruits

Anthocyanin synthesis is regulated not only by internal genes but also by external environmental factors.As the most important environmental factor in protected cultivation,light environment often becomes the limiting factor for strawberry production.Insufficient light will cause strawberries on the market to be light in color but not sweet in taste.At present,there is little research on the regulation mechanism of light signal on strawberry anthocyanin biosynthesis.It is well known that anthocyanin accumulation is regulated by transcription of MYB-b HLH-WD40 complex.Light is indispensable to anthocyanin accumulation.Light-inducible transcription factors MYB and HY5 are believed to promote anthocyanin accumulation in many fruits.Whether and how light-induced b HLH transcription factor and HY5 regulate strawberry anthocyanin synthesis is unclear.In this study,after dark and light treatment of wild diploid strawberry Rugen,it was found that light signal can obviously promote anthocyanin accumulation and expression of key enzyme genes,and light signal also induces expression of transcription factor Fvb HLH9 and positive regulatory factor of light signal Fv HY5.In this study,we found that Fvb HLH9 is similar to Fv HY5,transient overexpression and interference of Fvb HLH9 in strawberry fruits can promote and reduce anthocyanin accumulation respectively,indicating that Fvb HLH9 acts as a positive regulator of anthocyanin biosynthesis.The results of yeast-one-hybrid assay showed that Fv HY5 and Fvb HLH9 could specifically bind to the promoter of anthocyanin synthesis key enzyme gene DFR,and there was a direct protein interaction between Fv HY5 and Fvb HLH9,and the Dual-LUC assay showed that Fv DFR expression was activated by the formation of Fv HY5 and Fvb HLH9 heterodimers.Finally,we confirmed that Fvb HLH9 promotes anthocyanin accumulation in Arabidopsis thaliana depending on HY5-b HLH heterodimer.Our findings provide a mechanism for the synergistic regulation of light-dependent coloration and anthocyanin biosynthesis by the HY5-b HLH heterodimer formed by the interaction of Fv HY5 and Fvb HLH9 in strawberry fruits.