title: Biochemical and genetic characterization of Arabidopsis flavanone 3beta-hydroxylase.
abstract: Flavanone 3beta-hydroxylase (F3H; EC 1.14.11.9) is a 2-oxoglutarate dependent dioxygenase that catalyzes the synthesis of dihydrokaempferol, the common precursor for three major classes of 3-hydroxy flavonoids, the flavonols, anthocyanins, and proanthocyanidins. This enzyme also competes for flux into the 3-deoxy flavonoid branch pathway in some species. F3H genes are increasingly being used, often together with genes encoding other enzymes, to engineer flavonoid synthesis in microbes and plants. Although putative F3H genes have been cloned in a large number of plant species, only a handful have been functionally characterized. Here we describe the biochemical properties of the Arabidopsis thaliana F3H (AtF3H) enzyme and confirm the activities of gene products from four other plant species previously identified as having high homology to F3H. We have also investigated the surprising "leaky" phenotype of AtF3H mutant alleles, uncovering evidence that two related flavonoid enzymes, flavonol synthase (EC 1.14.11.23) and anthocyanidin synthase (EC 1.14.11.19), can partially compensate for F3H in vivo. These experiments further indicate that the absence of F3H in these lines enables the synthesis of uncommon 3-deoxy flavonoids in the Arabidopsis seed coat.
authors.affiliation: Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Daniel K
authors.initials: DK
authors.lastname: Owens
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Crosby
authors.forename: Justin
authors.initials: J
authors.lastname: Runac
authors.forename: Brad A
authors.initials: BA
authors.lastname: Howard
authors.forename: Brenda S J
authors.initials: BS
authors.lastname: Winkel
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D001483:Base Sequence; D002851:Chromatography, High Pressure Liquid; D017931:DNA Primers; D005419:Flavonoids / Q000378:metabolism*; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D005419:Flavonoids; D006899:Mixed Function Oxygenases; C048797:flavanone 3-dioxygenase