Anthocyaninless Cultivars of Sweet Orange Lack to Express the UDP-Glucose Flavonoid 3-O-Glucosyl Transferase

Abstract

In this study we isolated the partial cDNA clone of three enzymes active in the late steps of anthocyanins biosynthetic pathway such as DFR, ANS and UFGT from Citrus sinensis (L) Osbeck. The predicted aminoacids sequences shared very high identity values ranging from 77 % for DFR (Pyrus communis, Malus domestica), to 86 % for ANS (Vitis vinifera) with homologous available protein sequences. Only the UFGT sequence showed lower identity value (59 %), but this finding is in accordance with data obtained for other enzymes belonging to the plant glucosyl transferase superfamily. The expression of CHS, CHI, F3OH, DFR, ANS and UFGT was also investigated in both coloured and uncoloured oranges juice vesicles. Transcripts encoding the enzymes involved in the earlier reactions have been detected in either blood and blonde oranges by RT-PCR. Conversely, considerable difference emerged in the case of the later gene ufgt which was totally unexpressed in blonde oranges juice vesicles probably determining the lack of anthocyanins production in all blonde orange cultivars analysed.