Overexpression of a Freesia hybrida flavonoid 3-O-glycosyltransferase gene, Fh3GT1, enhances transcription of key anthocyanin genes and accumulation of anthocyanin and flavonol in transgenic petunia (Petunia hybrida)

UDP glucose flavonoid 3-O-glycosyltransferase(3GT) is a key enzyme in biosynthesis of stable anthocyanins, which are generally required for flower coloration. Fh3GT1, a cDNA encoding the 3GT from Freesia hybrida, was overexpressed in Petunia hybrida to investigate the influence on flavonoid accumulation. Flowers of transgenic petunia showed color alteration from white to pink and were subjected to further analysis by HPLC-ESI-MS. The results indicated that overexpression of Fh3GT1 resulted in evident increase of cyanidin, peonidin, and kaempferol content in transgenic flowers, whereas the content of quercetin increased slightly. Expressions of endogenous flavonoid biosynthetic pathway genes in transgenic flowers were analyzed by real-time qPCR. The results showed that transcript levels of PhCHS, PhCHI, PhF3H, and Ph3GT were significantly upregulated. Meanwhile, overexpression of Fh3GT1 also led to enhanced expression of AN1 (bHLH) and MYBx (R3MYB) genes, as the mRNA levels of other transcription factors remained constant in control and overexpression lines. Thus, Fh3GT1 overexpression increased the accumulation of anthocyanins and flavonols by modulating the expressions of various flavonoid biosynthesis genes in flowers of transgenic petunia. These results also suggest that Fh3GT1 is a key gene involved in anthocyanin and flavonol biosynthesis and should serve as a useful candidate to modify the components of flavonoid in other plants.