The yeast IRC7 gene encodes a β-lyase responsible for production of the varietal thiol 4-mercapto-4-methylpentan-2-one in wine

Genomic Insights into the Saccharomyces sensu stricto Complex

“…The IRC7 gene encodes a b-lyase that is responsible for the release of volatile thiols that are especially important during winemaking (Thibon et al 2008;Roncoroni et al 2011). While the genomes of all strains of S. cerevisiae, including S288c, appear to contain IRC7, a highly diverse homolog of this gene (88% DNA identity to S288c IRC7) was identified in the human clinical isolate YJM540.…”

“…While the genomes of all strains of S. cerevisiae, including S288c, appear to contain IRC7, a highly diverse homolog of this gene (88% DNA identity to S288c IRC7) was identified in the human clinical isolate YJM540. This new IRC7-family member was subsequently shown to be highly active at thiol release, providing YJM450 with the ability to produce enhanced levels of these aroma compounds compared to other yeast strains (Roncoroni et al 2011). Subsequent genome sequencing has identified this ortholog in only one other strain of S. cerevisiae (Y10), isolated from coconut in the Philippines.…”

“…During its initial characterization, this divergent ortholog was suggested to have been introgressed from S. paradoxus. However, given that this gene has been identified only in one strain of S. paradoxus (UWOPS91-917.1 isolated in Hawaii), the actual origin of this particular version of IRC7 may lie outside of both of these species or be a result of rapid sequence divergence of the common S. cerevisiae gene (Liti et al 2009;Roncoroni et al 2011).…”

Synthetic genome engineering forging new frontiers for wine yeast

“…Examples include strains that produce wines with lower alcohol levels; [46][47][48][49][50][51][52][53][54][55] mutants that limit the production of unwanted hydrogen-sulfide off-flavors and volatile acidy; [56][57][58] and strains that produce desirable esters, [59,60] terpenes, [61] and thiols ( Figure 18). [62][63][64][65][66][67][68][69][70] Efforts are also underway to express the a-guaiene-2-oxidase from grapevine in S. cerevisiae, thereby equipping wine yeast to transform grapederived a-guaiene to the sought-after spicy aroma compound of Shiraz wine, rotundone. [71][72][73] Several of these improved wine strains were patented but, so far, only two GM strains have been cleared by regulators in the USA and Canada for commercialization.…”

“…IRC7-expressing strains release more volatile thiols during fermentation, thereby producing wine with more fruity characters. [64] Valuable genomic insights were also gained into the Saccharomyces sensu stricto clade, comprising the S. cerevisiae complex (consisting of clearly defined "pure" lineages based strictly around geographic or industrial limits, and mosaic strains that appear to be the result of outcrossing between multiple pure lineages), and seven distinct Saccharomyces species (S. arboricolus, S. cariocanus, S. eubayanus, S. kudriavzevii, S. mikatae, S. paradoxus, and S. uvarum). [87] As an example, genomic comparisons revealed that the thiol-releasing wine yeast, VIN7, has an allotriploid hybrid genome with S. cerevisiae and S. kudriavzevii origins.…”