Characterization and functional analysis of RdDFR1 regulation on flower color formation in Rhododendron delavayi.

Rhododendron delavayi is a popular ornamental plant with globular flowers noted for their bright red color, but very limited studies have been reported on its flower color formation. In this study, we successfully isolated a novel DFR gene (RdDFR1) from red flowers of Rhododendron delavayi. Multiple sequence alignments revealed that RdDFR1 had the conserved NADP and substrate binding domain, and was classified into Asn-type DFR. Meanwhile, quantitative real-time PCR analysis showed that transcript levels of RdDFR1 matched the accumulation patterns of anthocyanins during flower development, hinting its potential role involved in anthocyanin biosynthesis. Then in vitro enzymatic analysis indicated that recombinant RdDFR1 protein could catalyze the production of leucoanthocyanidins from dihydroquercetin and dihydromyricetin. Furthermore, the in planta assay, using Arabidopsis thaliana dfr mutant (tt3-1) and tobacco, displayed that RdDFR1 transgenes recovered the defective proanthocyanidin and anthocyanin biosynthesis at seed coats, hypocotyl as well as cotyledon, and altered the flowers color of tobacco from pale pink to dark pink which demonstrated its function as dihydroflavonol 4-reductase in vivo. In summary, our findings suggest that RdDFR1 plays a crucial role in the biosynthesis of anthocyanin and will also make a contribution to understand the mechanisms of flower color formation in Rhododendron delavayi.