title: Glucosylation of 4-Hydroxy-2,5-Dimethyl-3(2H)-Furanone, the Key Strawberry Flavor Compound in Strawberry Fruit.
abstract: Strawberries emit hundreds of different volatiles, but only a dozen, including the key compound HDMF [4-hydroxy-2,5-dimethyl-3(2H)-furanone] contribute to the flavor of the fruit. However, during ripening, a considerable amount of HDMF is metabolized to the flavorless HDMF β-d-glucoside. Here, we functionally characterize nine ripening-related UGTs (UDP-glucosyltransferases) in Fragaria that function in the glucosylation of volatile metabolites by comprehensive biochemical analyses. Some UGTs showed a rather broad substrate tolerance and glucosylated a range of aroma compounds in vitro, whereas others had a more limited substrate spectrum. The allelic UGT71K3a and b proteins and to a lesser extent UGT73B24, UGT71W2, and UGT73B23 catalyzed the glucosylation of HDMF and its structural homolog 2(or 5)-ethyl-4-hydroxy-5(or 2)-methyl-3(2H)-furanone. Site-directed mutagenesis to introduce single K458R, D445E, D343E, and V383A mutations and a double G433A/I434V mutation led to enhanced HDMF glucosylation activity compared to the wild-type enzymes. In contrast, a single mutation in the center of the plant secondary product glycosyltransferase box (A389V) reduced the enzymatic activity. Down-regulation of UGT71K3 transcript expression in strawberry receptacles led to a significant reduction in the level of HDMF-glucoside and a smaller decline in HDMF-glucoside-malonate compared with the level in control fruits. These results provide the foundation for improvement of strawberry flavor and the biotechnological production of HDMF-glucoside.
authors.affiliation: Biotechnology of Natural Products, Technische Universität München, Liesel-Beckmann-Str.1, 85354 Freising, Germany.
authors.forename: Chuankui
authors.identifier: 0000-0002-7852-1194
authors.initials: C
authors.lastname: Song
authors.affiliation: Biotechnology of Natural Products, Technische Universität München, Liesel-Beckmann-Str.1, 85354 Freising, Germany.
authors.forename: Xiaotong
authors.initials: X
authors.lastname: Hong
authors.affiliation: Biotechnology of Natural Products, Technische Universität München, Liesel-Beckmann-Str.1, 85354 Freising, Germany.
authors.forename: Shuai
authors.initials: S
authors.lastname: Zhao
authors.affiliation: Biotechnology of Natural Products, Technische Universität München, Liesel-Beckmann-Str.1, 85354 Freising, Germany.
authors.forename: Jingyi
authors.initials: J
authors.lastname: Liu
authors.affiliation: Biotechnology of Natural Products, Technische Universität München, Liesel-Beckmann-Str.1, 85354 Freising, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Schulenburg
authors.affiliation: Biotechnology of Natural Products, Technische Universität München, Liesel-Beckmann-Str.1, 85354 Freising, Germany.
authors.forename: Fong-Chin
authors.initials: FC
authors.lastname: Huang
authors.affiliation: Biotechnology of Natural Products, Technische Universität München, Liesel-Beckmann-Str.1, 85354 Freising, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Franz-Oberdorf
authors.affiliation: Biotechnology of Natural Products, Technische Universität München, Liesel-Beckmann-Str.1, 85354 Freising, Germany wilfried.schwab@tum.de.
authors.forename: Wilfried
authors.identifier: 0000-0002-9753-3967
authors.initials: W
authors.lastname: Schwab
mesh_terms: D015536:Down-Regulation; D057075:Enzyme Assays; D004926:Escherichia coli / Q000235:genetics; D005421:Flavoring Agents / Q000737:chemistry*; D031985:Fragaria / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D005638:Fruit / Q000201:enzymology* / Q000378:metabolism*; D005663:Furans / Q000737:chemistry / Q000378:metabolism*; D015870:Gene Expression; D017343:Genes, Plant; D005822:Genetic Vectors; D005960:Glucosides / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D005421:Flavoring Agents; D005663:Furans; D005960:Glucosides; D010940:Plant Proteins; D011994:Recombinant Proteins; C058427:furaneol; D005964:Glucosyltransferases