Maltotriose consumption by hybridSaccharomyces pastorianusis heterotic and results from regulatory cross-talk between parental sub-genomes
Authors: Brouwers Nick , Brickwedde Anja , Gorter de Vries Arthur R. , van den Broek Marcel , Weening Susan M. , van den Eijnden Lieke , Diderich Jasper A. , Bai Feng-Yan , Pronk Jack T. , Daran Jean-Marc G. 
Published: June 2019

S. pastorianusstrains are hybrids ofS. cerevisiaeandS. eubayanusthat have been domesticated for several centuries in lager-beer brewing environments. As sequences and structures ofS. pastorianusgenomes are being resolved, molecular mechanisms and evolutionary origin of several industrially relevant phenotypes remain unknown. This study investigates how maltotriose metabolism, a key feature in brewing, may have arisen in earlyS. eubayanus × S. cerevisiaehybrids. To address this question, we generated a near-complete genome assembly of HimalayanS. eubayanusstrains of the Holarctic subclade. This group of strains have been proposed to be the origin of theS. eubayanussubgenome of currentS. pastorianusstrains. The HimalayanS. eubayanusgenomes harbored several copies of aSeAGT1α-oligoglucoside transporter gene with high sequence identity to genes encountered inS. pastorianus. Although HimalayanS. eubayanusstrains are unable to grown on maltose and maltotriose, their maltose-hydrolase andSeMALT1andSeAGT1maltose-transporter genes complemented the corresponding null mutants ofS. cerevisiae. Expression, in a HimalayanS. eubayanusstrain, of a functionalS. cerevisiaemaltose-metabolism regulator gene (MALx3) enabled growth on oligoglucosides. The hypothesis that the maltotriose-positive phenotype inS. pastorianusis a result of heterosis was experimentally tested by constructing aS. cerevisiae×S. eubayanuslaboratory hybrid with a complement of maltose-metabolism genes that resembles that of currentS. pastorianusstrains. The ability of this hybrid to consume maltotriose in brewer’s wort demonstrated regulatory cross talk between sub-genomes and thereby validated this hypothesis. These results provide experimental evidence of the evolutionary origin of an essential phenotype of lager-brewing strains and valuable knowledge for industrial exploitation of laboratory-madeS. pastorianus-like hybrids.

Importance

S.pastorianus, aS.cerevisiaeXS.eubayanushybrid, is used for production of lager beer, the most produced alcoholic beverage worldwide It emerged by spontaneous hybridization and have colonized early lager-brewing processes. Despite accumulation and analysis of genome sequencing data ofS.pastorianusparental genomes, the genetic blueprint of industrially relevant phenotypes remains unknown. Assimilation of wort abundant sugar maltotriose has been postulated to be inherited fromS.cerevisiaeparent. Here, we demonstrate that although AsianS.eubayanusisolates harbor a functional maltotriose transporterSeAGT1gene, they are unable to grow on α-oligoglucosides, but expression ofS. cerevisaeregulatorScMAL13was sufficient to restore growth on trisaccharides. We hypothesized thatS. pastorianusmaltotriose phenotype results from regulatory interaction betweenS.cerevisaemaltose transcription activator and the promoter ofSeAGT1. We experimentally confirmed the heterotic nature of the phenotype and thus this results provide experimental evidence of the evolutionary origin of an essential phenotype of lager-brewing strains.