Polygenic analysis of high osmotolerance in Saccharomyces cerevisiae

The main objective of our research is to investigate the molecular basis of superior osmotolerance in Saccharomyces cerevisiae and to identify unique mutations in the causative genes that are responsible for superior fermentation performance under very high gravity fermentation. We employed pooled-segregant whole-genome sequence analysis, a technology for efficient polygenic analysis of complex traits developed in our laboratory. For that purpose, a haploid segregant of an osmotolerant yeast strain with the best superior phenotype has been crossed with a haploid segregant from an unrelated industrial strain with a comparatively inferior phenotype. The diploid hybrid has been sporulated and about 30 segregants with the superior phenotype have been selected to construct the superior pool. About 30 segregants were also randomly selected regardless of their phenotype to construct the unselected pool. Pooled genomic DNA extraction was performed for both pools separately and submitted to custom whole-genome sequence analysis. The two parent strains have also been sent for sequencing to determine all SNPs. The variant frequency of the SNPs in the pool has been used to map the QTLs containing the causative mutations in the genome. Several clear QTLs with different strength have been identified in this way. This is followed by the application of reciprocal hemizygosity analysis to identify the causative gene(s) with the responsible mutation in the mapped loci. Finally the identified causative mutations will be introduced in to industrial strains to improve the very high gravity bioethanol fermentation performance.