Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Most traits of industrial importance in yeast and other industrial microorganisms are polygenic traits, i.e. traits determined by multiple genes together. Genetic analysis of such polygenic, usually quantitative traits remains an important challenge. High ethanol tolerance is a complex trait. It is an exquisite characteristic of S. cerevisiae and is of prime importance in first- and second-generation industrial bioethanol production. It has a major effect on yield and productivity because it affects the fermentation rate, the attenuation of the sugar, the maximal final ethanol titer and strongly influences sensitivity to other stress factors. Up to now, ethanol tolerance has only been analyzed in laboratory yeast strains with moderate ethanol tolerance. The genetic basis of the much higher ethanol tolerance in natural and industrial yeast strains is unknown. We have applied pooled-segregant whole-genome sequence analysis to map all Quantitative Trait Loci (QTL) determining high ethanol tolerance. We crossed a highly ethanol tolerant segregant of a Brazilian bioethanol production strain with a laboratory strain with moderate ethanol tolerance. We identified all QTL (Quantitative Trait Loci) that determine tolerance to 16% and 17% ethanol. We fine-mapped two major QTL and identified all causative genes in these QTL affecting high ethanol tolerance. These are the first causative genes involved in high ethanol tolerance in yeast and they are different from those required for the low ethanol tolerance of lab strains. This work shows that pooled segregant sequencing is a promising, powerful technology for analysis of complex traits of industrial importance in yeast.