title: Genetic analysis of the biosynthesis of 2-methoxy-3-isobutylpyrazine, a major grape-derived aroma compound impacting wine quality.
abstract: Methoxypyrazines (MPs) are strongly odorant volatile molecules with vegetable-like fragrances that are widespread in plants. Some grapevine (Vitis vinifera) varieties accumulate significant amounts of MPs, including 2-methoxy-3-isobutylpyrazine (IBMP), which is the major MP in grape berries. MPs are of particular importance in white Sauvignon Blanc wines. The typicality of these wines relies on a fine balance between the pea pod, capsicum character of MPs and the passion fruit/grapefruit character due to volatile thiols. Although MPs play a crucial role in Sauvignon varietal aromas, excessive concentrations of these powerful odorants alter wine quality and reduce consumer acceptance, particularly in red wines. The last step of IBMP biosynthesis has been proposed to involve the methoxylation of the nonvolatile precursor 2-hydroxy-3-isobutylpyrazine to give rise to the highly volatile IBMP. In this work, we have used a quantitative trait loci approach to investigate the genetic bases of IBMP biosynthesis. This has led to the identification of two previously uncharacterized S-adenosyl-methionine-dependent O-methyltransferase genes, termed VvOMT3 and VvOMT4. Functional characterization of these two O-methyltransferases showed that the VvOMT3 protein was highly specific and efficient for 2-hydroxy-3-isobutylpyrazine methylation. Based on its differential expression in high- and low-MP-producing grapevine varieties, we propose that VvOMT3 is a key gene for IBMP biosynthesis in grapevine.
authors.affiliation: Université de Bordeaux and Institut National de la Recherche Agronomique, Institut des Sciences de la Vigne et du Vin, Ecophysiologie et Génomique Fonctionnelle de la Vigne, Unité Mixte de Recherche 1287, F-33140 Villenave d'Ornon, France.
authors.forename: Sabine
authors.initials: S
authors.lastname: Guillaumie
authors.forename: Andrea
authors.initials: A
authors.lastname: Ilg
authors.forename: Stéphane
authors.initials: S
authors.lastname: Réty
authors.forename: Maxime
authors.initials: M
authors.lastname: Brette
authors.forename: Claudine
authors.initials: C
authors.lastname: Trossat-Magnin
authors.forename: Stéphane
authors.initials: S
authors.lastname: Decroocq
authors.forename: Céline
authors.initials: C
authors.lastname: Léon
authors.forename: Céline
authors.initials: C
authors.lastname: Keime
authors.forename: Tao
authors.initials: T
authors.lastname: Ye
authors.forename: Raymonde
authors.initials: R
authors.lastname: Baltenweck-Guyot
authors.forename: Patricia
authors.initials: P
authors.lastname: Claudel
authors.forename: Louis
authors.initials: L
authors.lastname: Bordenave
authors.forename: Sandra
authors.initials: S
authors.lastname: Vanbrabant
authors.forename: Eric
authors.initials: E
authors.lastname: Duchêne
authors.forename: Serge
authors.initials: S
authors.lastname: Delrot
authors.forename: Philippe
authors.initials: P
authors.lastname: Darriet
authors.forename: Philippe
authors.initials: P
authors.lastname: Hugueney
authors.forename: Eric
authors.initials: E
authors.lastname: Gomès
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D063427:Food Quality; D018506:Gene Expression Regulation, Plant; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009812:Odorants; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011487:Protein Conformation; D011719:Pyrazines / Q000378:metabolism*; D040641:Quantitative Trait Loci; D017386:Sequence Homology, Amino Acid; D027843:Vitis / Q000235:genetics* / Q000378:metabolism*; D014920:Wine
chemical_list: D010940:Plant Proteins; D011719:Pyrazines; D008780:Methyltransferases; C034376:2-isobutyl-3-methoxypyrazine