Genome instability and chromosomal rearrangements in a heterothallic wine yeast

Abstract

Wine strains of Saccharomyces cerevisiae are usually homothallic diploids and show chromosome length polymorphism. We describe the analysis of a heterothallic strain heterozygous for the mating types a and alpha. Surveying cultures of the strain, we found a remarkable degree of heterogeneity in ploidy and in electrophoretic karyotype. The CHEF analysis of tetrads and dyads revealed an enormous variability of band patterns hampering the analysis of chromosome segregation. We propose that the instability of ploidy and chromosome polymorphism might be due to heterothallism that precludes the process "genome renewal" (MORTIMER et al. 1994) by selfdiploidization of spore clones.

Diversity, variability and fast adaptive evolution of the wine yeast (Saccharomyces cerevisiae) genome—a review

“…The haploid products (spores) of meiosis have only single copies of each chromosome and, if they undergo autodiploidisation, produce homozygous diploid clones with two identical sets of chromosomes (Mortimer et al 1994). A consequence of this process is that karyotypically unstable strains produce karyotypically (more) stable meiotic products (Miklos et al 1997;Carro and Pina 2001). If the sporulating wine strain was heterozygous for deleterious mutations, its meiotic progeny will contain segregants with poor enological properties and segregants that received favourable sets of alleles (see above).…”

“…Thus, meiotic segregation of karyotypes is quite common in natural wine yeasts (e.g. Miklos et al 1996Miklos et al , 1997Budroni et al 2000;Puig et al 2000;Carro and Pina 2001;Sipiczki et al 2004;Marullo et al 2004Marullo et al , 2007. Low sporulation efficiency and low spore viability (also referred to as low fertility) hampers meiotic segregation and renders the genome more stable.…”

“…Longo and Vezinhet 1993;Schütz and Gafner 1993;Nadal et al 1996). The presence of multiple subpopulations may account for the increased number of bands and the heterogeneous brightness of bands in karyotypes of the cultures (Miklos et al 1997). The brighter bands represent chromosomes present in all (or in the larger) subpopulations whereas the fainter bands correspond to chromosomes that are present only in minor subpopulations.…”

“…The brighter bands represent chromosomes present in all (or in the larger) subpopulations whereas the fainter bands correspond to chromosomes that are present only in minor subpopulations. These subpopulations can be identified and separated by plating samples of the culture onto an agar medium and selecting individual colonies that show different karyotypes, usually containing fewer but uniformly bright bands (Longo and Vezinhet 1993;Miklos et al 1996Miklos et al , 1997. The rate of chromosome rearrangement events is highly variable in various strains.…”

Genetic Instability of Heterozygous, Hybrid, Natural Wine Yeasts

“…In S. cerevisiae, genetic instability is associated with a high rate of loss of heterozygosity (LOH), chromosome size changes, and the appearance of spontaneous recessive homozygous mutants (14). Although the genetic instability of yeasts has been analyzed in detail in recent years (1,4,5,9,19,24,26), little is known about the causes of this instability or the suppression mechanisms in genetically stable cells (reviewed by Kolodner et al [14]). More than 50 genes (many of them involved in DNA recombination, S-phase checkpoints, and telomere maintenance) have been implicated in the maintenance of S. cerevisiae genome stability (14).…”