Adaptive oxidative stress in yeast Saccharomyces cerevisiae: interslope genetic divergence in ‘Evolution Canyon’

Abstract

We investigated the adaptation to oxidative stress by Saccharomyces cerevisiae strains existing in spatial proximity but in contrasting climatic niches, by monitoring gene expression responses in the entire S. cerevisiae genome. Strains were isolated from different locations along a microclimatic gradient at ‘Evolution Canyon’ (EC), Mt Carmel, Israel. Selected were 17 strains from the canyon's ‘African’ south-facing slope (SFS), characterized by xeric conditions and high irradiation, 19 from the ‘European’ north-facing slope (NFS), characterized by mesic conditions and low irradiation, and six strains from the valley bottom. We wished to test a hypothesis assuming that S. cerevisiae strains found in EC locations characterized by either high or low intrinsic stress, such as light, temperature, UV light, and/or a radical oxygen burden, might be confined to niches due to genetic differences reflected in their transcript profiles. Survival and recovery for three different stresses, NaCl, H2O2, and mannitol, was tested. H2O2-sensitive strains included the laboratory strain S150-2B and most strains from the NFS. A correlation between peroxide tolerance, the SFS, and sunny niches within slopes was statistically supported. Salinity tolerance segregated with peroxide tolerance in most strains. Analysis using a S. cerevisiae genome array and hierarchical clustering of regulated transcripts indicated maximum linkage of expression profiles between strains that showed the same phenotypic stress response. In addition to genes for functionally unknown open reading frames, genes commonly up-regulated in tolerant strains in response to H2O2, but not up-regulated in sensitive strains, were related to protein synthesis, cell wall biosynthesis, fatty acid metabolism, and amino acid biosynthesis. In contrast, genes induced only in sensitive strains identified oxidative stress-related functions, sugar permeases, heat-shock proteins, and genes for functions in oxidative phosphorylation. In conclusion, oxidative stress emerged as the primary determinant of niche differences.