Role ofcis,trans, and inbreeding effects on meiotic recombination inSaccharomyces cerevisiae
Authors: Raffoux Xavier , Bourge Mickael , Dumas Fabrice , Martin Olivier C. , Falque Matthieu 
Published: July 2018

Meiotic recombination is a major driver of genome evolution by creating new genetic combinations. To probe the factors driving variability of meiotic recombination, we used a high-throughput method to measure recombination rates in 26S. cerevisiaestrains from different geographic origins and habitats. Fourteen intervals were monitored for each strain, covering chromosomes VI and XI entirely, and part of chromosome I. We found an average number of crossovers per chromosome ranging between 1.0 and 9.5 across strains (“domesticated” or not), which is higher than the average between 0.5 and 1.5 found in most organisms. In the different intervals analyzed, recombination showed up to 9-fold variation across strains but global recombination landscapes along chromosomes varied less. We also built an incomplete diallel experiment to measure recombination rates in one region of chromosome XI in 10 different crosses involving five parental strains. Our overall results indicate that recombination rate is increasingly positively correlated with sequence similarity between homologs (i) in DSB rich regions within intervals, (ii) in entire intervals, and (iii) at the whole genome scale. Therefore, these correlations cannot be explained bycis-effects only. In addition, by using a quantitative genetics analysis, we identified an inbreeding effect that reduces recombination rate in homozygous genotypes while other interaction effects (specific combining ability) or additive effects (general combining ability) are found to be weak. Finally, we measured significant crossover interference in some strains, and interference intensity was positively correlated with crossover number.

Author Summary

Meiosis is a key process for sexually reproducing organisms by producing gametes with a halved set of genetic material. An essential step of meiosis is the formation of crossovers which are reciprocal exchanges of genetic material between chromosomes inherited from both parents. Crossovers ensure proper chromosome segregation and thus viable gametes. They also create novel genetic diversity which contributes to evolution and permits genetic improvement of agriculturally important species. Most living organisms produce between one and three crossovers per chromosome, and tight regulatory mechanisms control the number of crossovers and their distribution along chromosomes. In spite of their potential importance for biotechnological applications, such mechanisms are still poorly understood.

Using a high throughput method based on fluorescent markers, we investigated the diversity of recombination in the budding yeast Saccharomyces cerevisiae. We observed up to 9-fold differences in numbers of crossovers across hybrids obtained by crossing different strains with a common tester, and this variation was correlated with the degree of DNA sequence similarity between homologous chromosomes. By also investigating homozygotes, we conclude that on the one hand too much sequence divergence impairs recombination in distantly-related hybrids, and on the other hand complete homozygosity is also associated with lower numbers of crossovers.