Abstract
Aurones are a class of flavonoid derivatives, and confers bright yellow coloration to flower in some ornamental plants such as Antirrhinum majus. An Antirrhinum polyphenol oxidase homolog, aureusidin synthase (AmAS1), catalyzes synthesis of aurones from chalcones. However, transgenic plants overexpressing AmAS1 gene alone failed to produce aurones and yellow color flowers. Here we have revealed that a novel Antirrhinum chalcone 4'-glucosyltransferase (Am4'CGT) provide chalcone 4'-glucoside to AmAS1 and that Am4'CGT plays a critical role for aurone biosynthesis. Overxpression of Am4'CGT and AmAS1 genes is sufficient to produce aureusidin 6-glucoside in transgenic torenia. Furthermore, overexpression of Am4'CGT and, AmAS1 and simultaneous RNAi of anthocyanin biosynthetic genes result in bright yellow flower accumulating aureusidin 6-glucoside. This is the first report of successful generation of clear yellow flowers with genetic engineering. Subcellular localization study of Am4'CGT and AmAS1 strongly suggests that chalcone 4'-glucoside is synthesized in cytosol and is transported to vacuole.
