Gibberellic acid regulates flavonoid 3′,5′-hydroxylase gene transcription in the corolla ofGentiana scabra

The flavonoid 3′,5′-hydroxylase (F3′,5′H) gene is in the NADPH-Cytochrome P450 reductase family. A partial F3′,5′H cDNA was cloned by RT-PCR from corollas ofGentiana scabra. Activity of F3′,5′H was observed during flower development, and activity was highest at the stage prior to flower opening. The enzyme activity was increased with the addition of SO μM gibberellic acid (GA3) immediately prior to flower opening. Western blot analysis showed that purified F3′,5′H protein fromG. scabra was cross-reacted with rabbit anti-Gentiana triflora NADPH-Cyt P450 reductase antibodies. Only one 80 to 82 kDa protein was detected by western blot analysis of fresh microsomal extracts. The enzyme activity was not distinctly changed by adding 50 μM GA3 to corollas. Therefore, we conclude that GA3 controls the expression of the F3′,5′H gene at the transcriptional level, not at the translational level.