FaABI3 regulates flavonoids accumulation in strawberries by activating FaFLS1

To investigate the regulation of flavonoids metabolism in strawberry during ripening, the transcription factor (TF) FaABI3 was isolated and characterized. In strawberry, quercetin, myricetin and quercetin 3-O-glucoside were the major flavonol substances during development, while during ripening, kaempferol and kaempferol 3-O-glucoside accumulated. A positive correlation was observed between the content of quercetin and quercetin 3-O-glucoside and the expression of FaF3’H1 and FaF3’5’H, respectively. Kaempferol and kaempferol 3-O-glucoside contents were positively correlated with FaF3H1, FaF3H2, FaFLS1, and FaF3GT7 expression. Yeast one-hybrid analysis and dual-luciferase assay established FaABI3 as an activator of the promoter of flavonol synthase 1 (FLS1). Analysis of amino acid sequence suggested that FaABI3 belonged to the B3 family. Furthermore, transient silencing of FaABI3 in strawberry down-regulated FaF3’H3, FaFLS1, FaFLS3, FaF3GT3, and FaF3GT7, up-regulated FaF3’5’H, FaF3H2, and FaF3GT6, and regulated the accumulation of flavonoids. In summary, FaFLS1 was transcriptionally regulated by FaABI3, which acted as a regulator of flavonoids metabolism in strawberry.