Comprehensive polymorphism survey elucidates population structure of Saccharomyces cerevisiae

Abstract

Baker's yeast, Saccharomyces cerevisiae, is one of the best studied model organisms, and has been associated with human activity for thousands of years. Two papers published in the 19 March 2009 issue of Nature provide a picture of its population structure and its relationship with other yeasts. Liti et al. compare genome variation in S. cerevisiae isolates with its closest wild cousin, S. paradoxus, which has never been associated with human activity. They find that variation in S. paradoxus closely follows geographic borders; S. cerevisiae shows less differentiation, consistent with opportunities for cross-breeding, rather than a few distinct domestication events, as the main human influence. Schacherer et al. compare 63 S. cerevisiae isolates from different ecological niches and geographic locations. They find evidence for genetic differentiation of three distinct subgroups based on where the strains were isolated: from vineyards, sake and related fermentations and lab strains. Their data support the hypothesis that these three groups represent separate domestication events, and that S. cerevisiae as a whole is not domesticated. This study provides a nucleotide-level survey of genome variation in 63 Saccharomyces cerevisiae strains sampled from different ecological niches and geographical locations. The analysis of genome-wide patterns of the nucleotide polymorphism and deletion variants discovered lays the foundation for genome-wide association studies in yeast. Comprehensive identification of polymorphisms among individuals within a species is essential both for studying the genetic basis of phenotypic differences and for elucidating the evolutionary history of the species. Large-scale polymorphism surveys have recently been reported for human1, mouse2 and Arabidopsis thaliana3. Here we report a nucleotide-level survey of genomic variation in a diverse collection of 63 Saccharomyces cerevisiae strains sampled from different ecological niches (beer, bread, vineyards, immunocompromised individuals, various fermentations and nature) and from locations on different continents. We hybridized genomic DNA from each strain to whole-genome tiling microarrays and detected 1.89 million single nucleotide polymorphisms, which were grouped into 101,343 distinct segregating sites. We also identified 3,985 deletion events of length >200 base pairs among the surveyed strains. We analysed the genome-wide patterns of nucleotide polymorphism and deletion variants, and measured the extent of linkage disequilibrium in S. cerevisiae. These results and the polymorphism resource we have generated lay the foundation for genome-wide association studies in yeast. We also examined the population structure of S. cerevisiae, providing support for multiple domestication events as well as insight into the origins of pathogenic strains.