Flavonoid metabolism and gene expression in developing olive (Olea europaea L.) fruit

The expression pattern of six genes (phenylalanine-ammonia-lyase, PAL, chalcone synthase, CHS, flavanone 3-hydroxylase, F3H, dihydroflavonol 4-reductase, DFR, anthocyanidin synthase, ANS, UDP-glucose-flavonoid 3-O-glucosyltransferase, UFGT) was studied, together with the accumulation of total flavonoids and anthocyanins in developing olive (Olea europaea L.) fruit. Flavonoid concentration showed the highest values in young fruit whereas anthocyanins accumulated at ripening, in particular in epicarp tissue, concurrently with an up-regulation of UFGT. PAL, CHS, F3H, and UFGT were expressed at the early stages of fruit development when DFR and ANS transcripts were not detected. DFR was induced in the epicarp at the onset of ripening and color change, while ANS transcripts were extremely abundant at a more advanced stage. A coordinated up-regulation of the genes involved in the last steps of anthocyanin biosynthesis was observed in ripe olives. These results suggest that DFR and ANS, together with UFGT, might represent key elements in the regulation of anthocyanin biosynthesis in olives, and that the expression pattern of these two genes could be used to monitor, at the molecular level, the evolution of ripening in fruits of this species.