Effects of oxidative stress on mitotic recombination and genomic stability in yeast after 20 passages

Oxidative stress is a common factor threatening genomic stability in almost all aerobic organisms. Using a yeast screening system, we measured the frequency of mitotic recombination was greatly elevated after H2O2 treatment. H2O2 was able to break chromatid directly in G1 synchronized cells and homologous recombination was induced to repair DNA double stand breaks at S/G2 phase. By whole genome SNP microarray and sequencing, the patterns of H2O2 induced loss of heterozygosity (LOH; gene conversion and crossover), chromosomal rearrangement, and aneuploidy changes were revealed. LOH events were the most common genomic alterations induced by H2O2 and were randomly distributed throughout the genome. To allow accumulation of recombination events, 30 JSC25-1-derived isolated colonies were independently treated with H2O2 (100 mM) for 20 passages. In each passage, cells were treated with 100 mM H2O2 for 1 h, washed, and then plated on YPD medium to form colonies. After 20 sequential treatments of H2O2, 30 JSC25-1-derived mutants (named as HOS1-30) from the last treatment were examined by whole genome SNP microarrays.