RNAi suppression of the anthocyanidin synthase gene in Torenia hybrida yields white flowers with higher frequency and better stability than antisense and sense suppression

Down-regulation of a target gene in a target crop is fundamentally important to generate useful transgenic plants through genetic engineering.The knockout of a gene by homologous recombination has been reported for a few plant species, including rice (Terada et al. 2002), but it is not yet a practical choice for most plant species.Post-transcriptional gene silencing (PTGS) is a widely used technique to suppress a target gene.Antisense and sense suppression, which are types of PTGS, have been reported for many plant species.The frequency of phenotypic changes by antisense and sense suppression in transgenic plants is less than 1% to 40%, respectively (Tanaka and Mason 2003).More recently, the transcription of double-strand RNA was shown to effectively down-regulate a gene (up to 96%; Hamilton et al. 1998; Waterhouse et al. 1998).Flower color comes mainly from anthocyanins, a color class of flavonoids.All structural genes leading to anthocyanidins in the pathway have been cloned from many plants (Tanaka et al. 2005).Some of these genes have been used to generate white flowers from color flowers through antisense or sense suppression.Antisense and sense suppression were described in petunia using the chalcone synthase (CHS) gene (van der Krol 1988 and Napoli et al. 1990, respectively).