Himalayan Saccharomyces eubayanus Genome Sequences Reveal Genetic Markers Explaining Heterotic Maltotriose Consumption by Saccharomyces pastorianus Hybrids

strains are hybrids of and that have been domesticated for centuries in lager beer brewing environments. As sequences and structures of genomes are being resolved, molecular mechanisms and evolutionary origins of several industrially relevant phenotypes remain unknown. This study investigates how maltotriose metabolism, a key feature in brewing, may have arisen in early × hybrids. To address this question, we generated a nearly complete genome assembly of Himalayan strains of the Holarctic subclade. This group of strains has been proposed to be the subgenome origin of current strains. The Himalayan genomes harbored several copies of an ( ) α-oligoglucoside transporter gene with high sequence identity to genes encountered in Although Himalayan strains cannot grow on maltose and maltotriose, their maltose-hydrolase and and maltose transporter genes complemented the corresponding null mutants of Expression, in Himalayan of a functional maltose metabolism regulator gene ( ) enabled growth on oligoglucosides. The hypothesis that the maltotriose-positive phenotype in is a result of heterosis was experimentally tested by constructing an × laboratory hybrid with a complement of maltose metabolism genes that resembles that of current strains. The ability of this hybrid to consume maltotriose in brewer's wort demonstrated regulatory cross talk between subgenomes and thereby validated this hypothesis. These results support experimentally the new postulated hypothesis on the evolutionary origin of an essential phenotype of lager brewing strains and valuable knowledge for industrial exploitation of laboratory-made -like hybrids. , an × hybrid, is used for production of lager beer, the most produced alcoholic beverage worldwide. It emerged by spontaneous hybridization and colonized early lager brewing processes. Despite accumulation and analysis of genome sequencing data of parental genomes, the genetic blueprint of industrially relevant phenotypes remains unresolved. Assimilation of maltotriose, an abundant sugar in wort, has been postulated to be inherited from the parent. Here, we demonstrate that although Asian isolates harbor a functional maltotriose transporter gene, they are unable to grow on α-oligoglucosides, but expression of regulator ( ) was sufficient to restore growth on trisaccharides. We hypothesized that the maltotriose phenotype results from regulatory interaction between maltose transcription activator and the promoter of We experimentally confirmed t