Saccharomyces cerevisiae x Saccharomyces kudriavzevii VIN7 genome analysis

Ancient events of polyploidy have been linked to huge evolutionary leaps in the tree of life, while increasing evidence show that newly established polyploids have adaptive advantages in certain stress condition compared to relatives with lower ploidy. The genus Saccharomyces is a good model for studying such events, as it contains an ancient whole genome duplication event and many sequenced Saccharomyces cerevisiae are, evolutionary speaking, newly formed polyploids. Many polyploids have unstable genomes and go through large genome erosions, however, it is still unknown what mechanisms governance this reduction. Here we sequenced and studied the commercial S. cerevisiae x S. kudriavzevii hybrid strain: VIN7. The most singular observation is that the genome is highly unstable and drastic genomic alterations were observed in only a few generations, leading to a widening of the phenotypic landscape. To better understand what leads to the loss of certain chromosomes in the population, we look for genetic features of the genes, such as physical interactions, complexes, epistatic interactions and stress responding genes, which could have beneficial or detrimental effects on the cell if their dosage is altered by a chromosomal copy number variation. The three chromosomes lost in our VIN7 population showed different patterns, indicating that multiple factors could explain the mechanism behind chromosomal loss. However, one common feature for two out of the three chromosomes is that they are among the smallest. We hypothesis that small chromosomes alter more frequently their copy number as a low number of genes are affected, meaning it is a by-product of genome instability, which might be the chief driving force of the adaptability and genome architecture of this hybrid.