Molecular characterization of a chalcone synthase gene RhCHS from Rhododendron × hybridum Hort

Chalcone synthase (CHS) plays a vital role in anthocyanin biosynthesis pathway, which is associated with petal color of flower. To date, lots of CHS genes have been obtained from plants, while few were from Rhododendron genus. In this study we got a new CHS gene named RhCHS (MW358095) from Rhododendron × hybridum Hort. It had a 2040 bp coding region consisting of two exons and one intron. By using the deduced RhCHS protein as a query sequence, 15 CHS homologous family genes with sequence similarity from 60% to 98%, designated as RgCHS-D(x), were retrieved from the genome assembly of Rhododendron griersonianum (RGv1.1) by TBlastN. 12 CHS family genes were found locating in No.9 chromosome arranged in clusters, while only 3 of them exhibited in No.1, 2, and 8 chromosomes, respectively. The results revealed gene duplication of CHS in evolutionary process. Multiple alignment of the deduced amino acid sequence of RhCHS showed high similarity of the active site, the catalytic residue, and the signature motif, the conserved characteristics of which were also exhibited in the tertiary structure prediction of the RhCHS, as well as the phylogenetic tree, all these demonstrated the RhCHS belonging to the type III PKS superfamily. HPLC-MS/MS of flower petals detected the total concentration of CC, DC, and PelC. These anthocyanidins showed an overall increasing trend during the flowering period and reached the peak in the full-blooming stage, which was consistence with the changeable rule of RhCHS expression level. The promoter, which was 1507 bp exhibiting high β-glucuronidase (GUS) staining activity, was predicted containing many cis-acting elements, especially light and transcription factor such as bHLH, MYB, WRKY, Dof, and ERF. In short, this study may provide the help to Rhododendron × hybridum Hort. not only in the mechanism research of petals color exhibition, but also in molecular breeding of CHS practice value.