Ectopic expression of snapdragon transcription factors facilitates the identification of genes encoding enzymes of anthocyanin decoration in tomato.

Given the potential health benefits of polyphenolic compounds in the diet, there is a growing interest in the generation of food crops enriched with health-protective flavonoids. We undertook a series of metabolite analyses of tomatoes ectopically expressing the Delila and Rosea1 transcription factor genes from snapdragon, paying particular attention to changes in phenylpropanoids compared to controls. These analyses revealed multiple changes including depletion of rutin and naringenin-chalcone, enhanced levels of anthocyanins and phenylacylated flavonol derivatives. We isolated and characterised the chemical structures of the two most abundant anthocyanins which were shown by nuclear magnetic resonance spectroscopy to be delphinidin-3-(4'''-O-trans-p-coumaroyl)-rutinoside-5-O-glucoside and petunidin-3-(4'''-O-trans-p-coumaroyl)-rutinoside-5-O-glucoside. By performing RNA sequencing on both the purple fruit and wild type fruit we collected important information concerning the relative expression of both structural and transcription factor genes. Integrative analysis of the transcript and metabolite datasets provided compelling evidence of the nature of all genes involved in anthocyanin biosynthesis including those encoding species-specific anthocyanin decoration enzymes. One gene, SlFdAT1 (Solyc12g088170), predicted to encode a flavonoid-3-O-rutinoside-4'''-phenylacyltransferase was characterized by assays of recombinant protein and overexpression assays in tobacco. The combined data are discussed in the context of both our current understanding of phenylpropanoid metabolism in Solanaceous species, and evolution of flavonoid decorating enzymes and their transcriptional networks in different plant species