Flower color alteration in the liliaceous ornamental Tricyrtis sp. by RNA interference-mediated suppression of the chalcone synthase gene

Chalcone synthase (CHS) is the key enzyme in an early stage of the flavonoid biosynthetic pathway. In the present study, a full-length cDNA clone for CHS was isolated from flower tepals of the liliaceous ornamental Tricyrtis sp., in which tepals have many reddish-purple spots resulting from accumulation of cyanidin derivatives. The deduced amino acid sequence of the isolated cDNA clone, designated TrCHS1 (accession number AB478624 in the GenBank/EMBL/DDBJ databases), shows 79.4–91.4% identity with those of previously reported CHS genes. An RNA interference (RNAi) construct targeting TrCHS1 was introduced by Agrobacterium-mediated transformation in order to alter the flower color of Tricyrtis sp. Seven transgenic plants that produced flowers could be classified into three types according to flower color phenotype: one transgenic plant had tepals with as many reddish-purple spots as non-transgenic plants (Type I); one had tepals with reduced numbers of reddish-purple spots (Type II); and five had completely white tepals without any spots (Type III). High-performance liquid chromatography analysis showed that tepals of Type III transgenic plants did not accumulate detectable amounts of anthocyanidins. In addition, TrCHS1 mRNA levels in tepals of Type II and Type III transgenic plants decreased substantially compared with non-transgenic plants, as determined by quantitative real-time reverse transcription–polymerase chain reaction analysis. Our results indicate the validity of RNAi suppression of the flavonoid biosynthetic pathway genes for flower color alteration in Tricyrtis sp. To the best of our knowledge, this is the first report on flower color alteration by genetic transformation in monocotyledonous ornamentals.