ANALYSIS OF FLAVANONE 3-HYDROXYLASE IN ARABIDOPSIS SEEDLINGS - COORDINATE REGULATION WITH CHALCONE SYNTHASE AND CHALCONE ISOMERASE

A genomic clone encoding flavanone 5-hydroxylase (F3H) was isolated fr om Arabidopsis thaliana. The deduced amino acid sequence is 72 to 94% identical to all previously reported F3H proteins. Low-stringency DNA blot analysis indicated that F3H is encoded by a single gene in Arabid opsis. The F3H locus was mapped to the bottom of chromosome 3 and ther efore does not correspond to any of the 13 flavonoid-deficient transpa rent testa mutants for which a map position is known. Analysis of gene expression in etiolated seedlings exposed to white light and in two p utative regulatory mutants, ttg and tt8, demonstrated that the Arabido psis F3H gene is coordinately expressed with chalcone synthase and cha lcone isomerase in seedlings, whereas dihydroflavonol reductase expres sion is controlled by distinct regulatory mechanisms. The F3H gene may represent a pivotal point in the regulation of flavonoid biosynthesis because its expression is coordinated with different subsets of genes in different plant species.