Differential paralog divergence modulates evolutionary outcomes in yeast

Abstract

2Evolutionary outcomes depend not only on the selective forces acting upon a species, but 3 also on the genetic background. However, large timescales and uncertain historical 4 selection pressures can make it difficult to discern such important background differences 5 between species. Experimental evolution is one tool to compare evolutionary potential of 6 known genotypes in a controlled environment. Here we utilized a highly reproducible 7 evolutionary adaptation in Saccharomyces cerevisiae to investigate whether other yeast 8 species would adopt similar evolutionary trajectories. We evolved populations of S. 9 cerevisiae, S. paradoxus, S. mikatae, S. uvarum, and interspecific hybrids between S. 1 0 uvarum and S. cerevisiae for ~200-500 generations in sulfate-limited continuous culture. 1 1 Wild-type S. cerevisiae cultures invariably amplify the high affinity sulfate transporter 1 2 gene, SUL1. However, while amplification of the SUL1 locus was detected in S. 1 3 paradoxus and S. mikatae populations, S. uvarum cultures instead selected for 1 4amplification of the paralog, SUL2. We measured the relative fitness of strains bearing 1 5 deletions and amplifications of both SUL genes from different species, confirming that, 1 6 converse to S. cerevisiae, S. uvarum SUL2 contributes more to fitness in sulfate limitation 1 7 than S. uvarum SUL1. By measuring the fitness and gene expression of chimeric 1 8 promoter-ORF constructs, we were able to delineate the cause of this differential fitness 1 9 hold at 95°C for 4 min, followed by 50 cycles of 10 sec at 95°C and 45 sec at 56°C. The

Experimental evolution reveals favored adaptive routes to cell aggregation in yeast

“…There is evidence that strain background contributes significantly to the likelihood of evolving flocculation in chemostat experiments. Saccharomyces uvarum, a budding yeast related to S. cerevisiae and often used in interspecific hybrid studies, has only Ty4 elements in its genome (Liti et al 2005), and evolves flocculation more slowly than S. cerevisiae in chemostat experiments (Heil et al 2017;Sanchez et al 2017). Not only do different species of yeast have different Ty element burdens, natural isolates of S. cerevisiae also provide strain-specific differences in Ty element burden (Dunn et al 2012;Bleykasten-Grosshans et al 2013), and a reservoir of variation in evolutionary potential that will be useful in future evolution experiments for studying flocculation and other complex traits.…”