Isolation and characterization of a flavonoid 3 '-hydroxylase cDNA clone corresponding to the Ht1 locus of Petunia hybrida

We have isolated a cDNA clone that corresponds to the Ht? locus of petunia which controls the hydroxylation of dihydrokaempferol to dihydroquercetin a nd of naringenin to eriodictyol by the action of flavonoid 3'-hydroxylase ( F3'H). The cDNA encodes a 512 amino acid polypeptide with regions of simila rity to petunia flavonoid 3',5'-hydroxylases (F3'5'H). Both F3'H and F3'5'H are cytochromes P450 and are key enzymes in the flavonoid pathway leading to the production of the coloured anthocyanins. The F3'H transcript is most abundant in petals from flowers at an early stage of development and level s decline as the flower matures. Transcripts are also detected in the ovari es, sepals, peduncles, stems and anthers of the petunia plant. No or very r educed levels of transcripts are detected in ht1/ht1 lines. This is the fir st report of isolation of a F3'H cDNA clone from any species.