Abstract

Apples (Malus domestica) are rich in flavonols, and 5-aminolevulinic acid (ALA) plays an important role in the regulation of plant flavonoid metabolism. To date, the underlying mechanism of ALA promoting flavonol accumulation is unclear. Flavonol synthase (FLS) is a key enzyme in flavonol biosynthesis. In this study, we found that ALA could enhance the promoter activity ofMdFLS1in the ‘Fuji’ apple and improve its expression. WithMdFLS1as bait, we screened a novel transcription factor MdSCL8 by the Yeast One-Hybrid (Y1H) system from the apple cDNA library which we previously constructed. Using luciferase reporter assay and transient GUS activity assay, we verified that MdSCL8 inhibits the activity ofMdFLS1promoter and hindersMdFLS1expression, thus reducing flavonol accumulation in apple. ALA significantly inhibitedMdSCL8expression. Therefore, ALA promoted the expression ofMdFLS1and the consequent flavonol accumulation probably by down-regulating MdSCL8. We also found that ALA significantly enhanced the gene expression of MdMYB22 and MdHY5, two positive regulators ofMdFLS. We further demonstrated that MdMYB22 interacts with MdHY5, but neither of them interacts with MdSCL8. Taken together, our data suggest MdSCL8 as a novel regulator ofMdFLS1and provide important insights into mechanisms of ALA-induced flavonol accumulation in apples.Keywords:ALA;apple;flavonol;MdFLS1;MdSCL8