Chalcone-Synthase-Encoding <i>RdCHS1</i> Is Involved in Flavonoid Biosynthesis in <i>Rhododendron delavayi</i>

Flower color is an important ornamental feature that is often modulated by the contents of flavonoids. Chalcone synthase is the first key enzyme in the biosynthesis of flavonoids, but little is known about the role of <i>R. delavayi</i> CHS in flavonoid biosynthesis. In this paper, three <i>CHS</i> genes (<i>RdCHS1-3</i>) were successfully cloned from <i>R. delavayi</i> flowers. According to multiple sequence alignment and a phylogenetic analysis, only RdCHS1 contained all the highly conserved and important residues, which was classified into the cluster of bona fide CHSs. RdCHS1 was then subjected to further functional analysis. Real-time PCR analysis revealed that the transcripts of <i>RdCHS1</i> were the highest in the leaves and lowest in the roots; this did not match the anthocyanin accumulation patterns during flower development. Biochemical characterization displayed that RdCHS1 could catalyze <i>p</i>-coumaroyl-CoA and malonyl-CoA molecules to produce naringenin chalcone. The physiological function of <i>RdCHS1</i> was checked in <i>Arabidopsis</i> mutants and tobacco, and the results showed that <i>RdCHS1</i> transgenes could recover the color phenotypes of the <i>tt4</i> mutant and caused the tobacco flower color to change from pink to dark pink through modulating the expressions of endogenous structural and regulatory genes in the tobacco. All these results demonstrate that RdCHS1 fulfills the function of a bona fide CHS and contributes to flavonoid biosynthesis in <i>R. delavayi</i>.