title: Redirection of flavonoid biosynthesis through the down-regulation of an anthocyanidin glucosyltransferase in ripening strawberry fruit.
abstract: Strawberry (Fragaria x ananassa) fruit contains several anthocyanins that give the ripe fruits their attractive red color. The enzyme that catalyzes the formation of the first stable intermediate in the anthocyanin pathway is anthocyanidin-3-O-glucosyltransferase. A putative glycosyltransferase sequence (FaGT1) was cloned from a strawberry fruit cDNA library and the recombinant FaGT1 transferred UDP-glucose to anthocyanidins and, to a lesser extent, flavonols, generating the respective 3-O-glucosides. Quantitative polymerase chain reaction revealed that transcripts of FaGT1 were almost undetectable in green fruits, but gene expression increased dramatically in both turning and ripe red fruit, corresponding closely to the accumulation of anthocyanins during fruit ripening. The expression of FaGT1 is fruit associated and negatively regulated by auxin. To elucidate the in planta function of FaGT1, Agrobacterium tumefaciens cells harboring an intron-hairpin construct of a partial FaGT1 sequence were injected into midsized ripening fruits. In about one-third of the injected fruits, this led to significant down-regulation of FaGT1 transcript levels that corresponded to reduced concentrations of anthocyanin pigments in ripe strawberry fruits. In contrast, significant levels of epiafzelechin--formed by anthocyanidin reductase (ANR) from pelargonidin--were identified in FaGT1-silenced fruits, indicating competition of FaGT1 and FaANR for the common anthocyanidin substrate. Thus, FaGT1 represents an important branching-point enzyme because it is channeling the flavonoid pathway to anthocyanins. These results demonstrate a method to redirect the anthocyanin biosynthesis into flavan-3-ol production to increase the levels of bioactive natural products or modify pigments in plant tissues.
authors.affiliation: Biomolecular Food Technology, Technical University Munich, 85354 Freising, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Griesser
authors.forename: Thomas
authors.initials: T
authors.lastname: Hoffmann
authors.forename: Mari Luz
authors.initials: ML
authors.lastname: Bellido
authors.forename: Carlo
authors.initials: C
authors.lastname: Rosati
authors.forename: Barbara
authors.initials: B
authors.lastname: Fink
authors.forename: Robert
authors.initials: R
authors.lastname: Kurtzer
authors.forename: Asaph
authors.initials: A
authors.lastname: Aharoni
authors.forename: Juan
authors.initials: J
authors.lastname: Muñoz-Blanco
authors.forename: Wilfried
authors.initials: W
authors.lastname: Schwab
mesh_terms: D002853:Chromatography, Liquid; D017931:DNA Primers; D015536:Down-Regulation; D005419:Flavonoids / Q000096:biosynthesis*; D031985:Fragaria / Q000201:enzymology* / Q000235:genetics; D020868:Gene Silencing; D017343:Genes, Plant; D005964:Glucosyltransferases / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D017931:DNA Primers; D005419:Flavonoids; D005964:Glucosyltransferases; C118149:UDP-glucose anthocyanin 5-O-glucosyltransferase