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Evolution of S. cerevisiae - S. bayanus Interspecific Hybrids

ABSTRACT: Hybrid progeny can enjoy increased fitness and stress tolerance relative to their ancestral species, a phenomenon known as hybrid vigor. Though this phenomenon has been documented throughout the Eukarya, evolution of hybrid populations has yet to be explored experimentally in the lab. To fill this knowledge gap we created a pool of Saccharomyces cerevisiae and S. bayanus homoploid and aneuploid hybrids, and then investigated how selection in the form of incrementally increased temperature or ethanol impacted hybrid genome structure and adaptation. During 500 generations of continuous ammonia-limited, glucose-sufficient culture, temperature was raised from 25C to 46??C. This selection invariably resulted in nearly-complete loss of the S. bayanus genome, although the dynamics of genome loss differed among independent replicates. Temperature-evolved isolates were significantly more thermal tolerant and exhibited greater phenotypic plasticity than parental species and founding hybrids. By contrast, when the same hybrid pool was subjected to increases in exogenous ethanol from 0% to 14%, selection favored euploid S. cerevisiae x S. bayanus hybrids. Ethanol-evolved isolates exhibited significantly greater ethanol tolerance relative only to S. bayanus and one of the founding hybrids tested. Adaptation to thermal and ethanol stress manifested as heritable changes in cell wall structure demonstrated by resistance to zymolyase or micafungin treatment. This is the first study to show experimentally that the fate of interspecific hybrids critically depends on the type of selection they encounter during the course of evolution.

ORGANISM(S): Saccharomyces bayanus Saccharomyces bayanus x Saccharomyces cerevisiae Saccharomyces cerevisiae

PROVIDER: GSE24479 | GEO | 2012/08/01

SECONDARY ACCESSION(S): PRJNA132509

REPOSITORIES: GEO

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Project description:Hybrid progeny can enjoy increased fitness and stress tolerance relative to their ancestral species, a phenomenon known as hybrid vigor. Though this phenomenon has been documented throughout the Eukarya, evolution of hybrid populations has yet to be explored experimentally in the lab. To fill this knowledge gap we created a pool of Saccharomyces cerevisiae and S. bayanus homoploid and aneuploid hybrids, and then investigated how selection in the form of incrementally increased temperature or ethanol impacted hybrid genome structure and adaptation. During 500 generations of continuous ammonia-limited, glucose-sufficient culture, temperature was raised from 25C to 46??C. This selection invariably resulted in nearly-complete loss of the S. bayanus genome, although the dynamics of genome loss differed among independent replicates. Temperature-evolved isolates were significantly more thermal tolerant and exhibited greater phenotypic plasticity than parental species and founding hybrids. By contrast, when the same hybrid pool was subjected to increases in exogenous ethanol from 0% to 14%, selection favored euploid S. cerevisiae x S. bayanus hybrids. Ethanol-evolved isolates exhibited significantly greater ethanol tolerance relative only to S. bayanus and one of the founding hybrids tested. Adaptation to thermal and ethanol stress manifested as heritable changes in cell wall structure demonstrated by resistance to zymolyase or micafungin treatment. This is the first study to show experimentally that the fate of interspecific hybrids critically depends on the type of selection they encounter during the course of evolution. Array-CGH was performed on the S. cerevisiae parent strain CEN.PK (GSY2160), the S. bayanus parent strain CBS7001 (GSY2161) and on the F1 interspecific hybrid resulting from mating the 2 parents (GSY2168). Additionally, three rare viable spores obtained after sporulation of the F1 were assayed by array-CGH (F2a, F2b, F2c). A large pool of F2 spores (and probably some number of F1 hybrid cells) were subjected to gradually increasing temperatures, in three independent vessels, with populations sampled at various generation times. Likewise, the same pool was used to found populations in an additional three independent vessels, which were then subjected to gradually increasing ethanol concentrations (at constant temperature). Array-CGH was performed on three different clones from each of the three temperature vessels at the final 500 generation time point (T500 clones). Biological replicates of the T500 clones were performed (T500-new). Two self-self array-CGH hybridization controls were also performed (self-control). Array-CGH was performed on one clone from each of the three ethanol vessels taken at the 400 generation timepoint (EtOH400gen clones).

Project description:Reproductive barriers perform a vital role during speciation1. Hybrid weakness, the poor development of hybrids compared to their parents, hinders gene exchange between different species at the postzygotic stage2,3. The molecular and evolutionary mechanisms of hybrid weakness are poorly understood2. Here, we report that two incompatible dominant loci (Hwi1 and Hwi2) involving three genes determine the high temperature-dependent expression of hybrid weakness in interspecific hybrids of rice. Hwi1 comprises two indispensable wild rice (Oryza rufipogon)-specific leucine-rich repeat receptor-like kinase (LRR-RLK) genes, 25L1 and 25L2, for inducing hybrid weakness, and the genes possibly undergo balancing selection. Hwi2, a rare allele that is predominantly distributed in indica rice (Oryza sativa), encodes a secreted putative subtilisin-like protease. Functional analysis indicated that pyramiding of Hwi1 and Hwi2 activates the autoimmune response in the basal nodes of hybrids, interrupting root formation and then impairing shoot growth, likely due to immune signal is transmitted from the basal nodes to the above-ground parts. Considering the nature of RLK activity of Hwi1 and the protease activity of Hwi2, we propose that a certain endogenous signaling molecule produced by Hwi2 is perceived by Hwi1 to activate autoimmunity through ligand-receptor signal transduction. These findings bring new insights into our understanding of reproductive isolation and may benefit rice breeding to maximally utilize invaluable genes from wild rice. We conducted microarray analysis to unravel the global changes in gene expression of a pair of NILs (nearly isogenic lines). Plants were cultivated at constant 20°C for 20 days and then shifted to constant 30°C conditions. The basal nodes of NIL(Hwi1) and NIL(hwi1) were harvested immediately before the temperature shift (set as the 0 point) or at 3, 7 or 15 days after the shift. Three biological replicates (each comprising basal nodes from 15–20 individuals) were used for each time point.

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Evolution of S. cerevisiae - S. bayanus Interspecific Hybrids

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