Molecular cloning of the flavanone 3β-hydroxylase gene (FHT) from carnation (Dianthus caryophyllus) and analysis of stable and unstable FHT mutants.

Using a cDNA encoding the flavanone 3β-hydroxylase (FHT) from Dianthus caryophyllus (carnation) as a probe, we isolated the FHT gene from a genomic library. Sequence analysis revealed that the FHT gene consists of three exons and two introns. Two putative light-regulated elements were identified in the promoter region by sequence comparison. Southern blot analysis indicated that a single copy of the FHT gene is in the plant genome. Furthermore, a stable and an unstable FHT mutant of D. caryophyllus, both showing almost no FHT activity, were analyzed by Southern, Northern and Western blotting. It turned out that the FHT gene is present in both mutants, but no protein was detectable in the mutant flowers. FHT mRNA in amounts comparable to that found in the wildtype is present in flowers of the stable mutant, indicating a block in translation, but not in flowers of the unstable mutant, indicating a block in transcription. The translational block of the FHT mRNA of the stable mutant was demonstrated by in vitro translation of total flower mRNA followed by the specific measurement of FHT activity.