Paper ID: 61
Trinity College Dublin (Ireland)
Saccharomyces pastorianus (lager yeasts) are interspecies hybrids of Saccharomyces cerevisiae and Saccharomyces eubayanus and are classified as Group I and II, based on DNA content and chromosome structure. Recombination events between the parental chromosomes have created a novel set of hybrid chromosomes. Most recombination sites are intragenic, giving rise to a unique set of hybrid genes composed of part S. eubayanus and part S. cerevisiae sequences. In addition to hybrid genes, S. pastorianus encodes for several “orphan” genes, which are conserved in industrial strains of S. cerevisiae only, but for which no known homologues exist in either prokaryotic or eukaryotic species. Such hybrid and orphan genes, if functional, can potentially influence the biochemical, physiological and phenotypic landscape of lager yeasts.
Several hybrid alleles of the gene YGL173C (XRN1) are found in lager yeasts and Group I and II lager yeasts co-express different XRN1 alleles. XRN1 encodes for a 5’ to 3’ exoribonuclease that is required for mRNA degradation in the cell. Given its central role in RNA metabolism, we hypothesise that the co-expression of allelic variants of XRN1 may significantly impact the steady state pool of mRNAs and thus the protein landscape of lager yeasts.
The XRN1 genes, in the same combinations as found in the Group I and II lager yeasts, were cloned into S. cerevisiae Δxrn1. RNAseq data reveals that the co-expression of different allelic variants of XRN1 significantly alters the suite of mRNAs found in the cell. Recapitulating the XRN1 composition of Group I and Group II lager yeasts leads to the differential stabilisation of mRNAs encoding for proteins involved in amino acid metabolism and plasma membrane composition, pathways that significantly influence the fermentation and flavour properties of beer.
A role for the orphan gene “HYPO”, encoding a hypothetical open reading frame, is also being investigated. The expressed protein is located at the plasma membrane where it forms distinct patches. Mass spectrophotometric analysis of HYPO-associated proteins suggests a role for HYPO is stress responses in lager yeasts.