Two O-methyltransferases involved in the biosynthesis of methoxypyrazines: grape-derived aroma compounds important to wine flavour

Abstract

Methoxypyrazines (MPs) are volatile, grape-derived aroma compounds that contribute to the distinct herbaceous characters of some wines. Although the full pathway leading to MP production has not been elucidated, there is strong evidence that the final step involves the methylation of non-volatile hydroxypyrazine (HP) precursors. Two cDNA encoding O-methyltransferases (OMTs) that have homology to an enzyme previously purified and shown to catalyse the methylation of HPs were isolated from Cabernet Sauvignon. Recombinant protein from the cDNAs (VvOMT1 and VvOMT2) was produced in E. coli and activity assays demonstrated that both encode OMTs able to methylate HPs to produce MPs, however both showed greatest activity against the flavonol quercetin. VvOMT1 has higher catalytic activity against isobutyl hydroxypyrazine compared to isopropyl hydroxypyrazine, whereas the converse is true for VvOMT2. The timing of the expression of VvOMT1 in the skin and the flesh of developing Cabernet Sauvignon grape berries was associated with the period of MP accumulation in these tissues, while VvOMT2 expression was greatest in roots, which were found to contain high levels of MPs. The MP composition of these tissues also reflects the relative levels of expression of these genes and their substrate preference. The identification of genes responsible for MP production in grapevine will help in understanding the effect of different viticultural and environmental factors on MP accumulation.

Changes of 3-Alkyl-2-methoxypyrazines in Developing Cabernet Sauvignon (Vitis vinifera) and Zuoshanyi (Vitis amurensis Rupr.) Grapes from North China

“…This trend was in good agreement with that described in previous reports (Ryona et al, 2008;Dunlevy et al, 2010). Similar levels of IBMP were observed in Cabernet Sauvignon grapes from the Huailai and Changli areas, and their highest contents were 129.9 ng/L and 130.6 ng/l respectively.…”

“…In Vitis vinifera grapes, MPs accumulate at pre-véraison and then decrease markedly until maturity (Ryona et al, 2008;Dunlevy et al, 2010). The contents of MPs in grapes are affected by cluster light exposure, yield, irrigation condition, vine training, plantation density, seasonal temperature, vineyard altitude and soil (Hashizume & Samuta, 1999;De Boubée et al, 2000;Chapman et al, 2004;Sala et al, 2004Sala et al, , 2005Belancic & Agosin, 2007;Falcão et al, 2007;Ryona et al, 2008;Dunlevy et al, 2009).…”

A lignan O-methyltransferase catalyzing the regioselective methylation of matairesinol in Carthamus tinctorius

“…Alignment of the predicted amino acid sequences of CtOMT2 (CtMROMT), CtOMT3 (CtFOMT), CtCAldOMT1, and related OMTs. SAM-biding motifs A, B, and C (Joshi and Chiang 1998); and regions I, II, III, IV, and V are domains conserved among plant OMTs (Dunlevy et al 2010).…”

A new <i>O</i>-methyltransferase for monolignol synthesis in <i>Carthamus tinctorius</i>

“…The cDNA (DDBJ accession number, AB980250) encodes a polypeptide of 367 amino acids, which is shown in Figure 2 together with other selected OMTs including CtCAldOMT1, CtMROMT, CtFOMT, Forsythia koreana MROMT (FkMROMT) (Ragamustari et al 2014), and M. sativa isoflavone OMT. The Sadenosyl-L-methionine (SAM)-binding motifs A, B, and C (Joshi and Chiang 1998); and domains I, II, III, IV, and V that are conserved among plant OMTs (Dunlevy et al 2010) were present in CtAAOMT (Figure 2). Phylogenetic analysis, which was conducted as previously Umezawa et al 2013) (Figure 3) indicated that the CtAAOMT showed 55% identity to FkMROMT, while it exhibited 49-53% identity to (Dunlevy et al 2010).…”

“…The Sadenosyl-L-methionine (SAM)-binding motifs A, B, and C (Joshi and Chiang 1998); and domains I, II, III, IV, and V that are conserved among plant OMTs (Dunlevy et al 2010) were present in CtAAOMT (Figure 2). Phylogenetic analysis, which was conducted as previously Umezawa et al 2013) (Figure 3) indicated that the CtAAOMT showed 55% identity to FkMROMT, while it exhibited 49-53% identity to (Dunlevy et al 2010). #, Catalytic residues; *, SAM binding residues; S, Substrate binding residues of Medicago sativa isoflavone OMT (MsIOMT, AAC49927) as determined by Zubieta et al (2001).…”