Oxidative stress tolerance of a spore clone isolated from Shirakami kodama yeast depends on altered regulation of Msn2 leading to enhanced expression of ROS-degrading enzymes

We analyzed the stress response in a spore clone from Shirakami kodama yeast, Saccharomyces cerevisiae, with an exceptional high tolerance to oxidative stress. The levels of reactive oxygen species (ROS) in this clone were very low, whereas the genes for superoxide dismutase (SOD2) and catalase (CTT1) were highly expressed and those enzymes also had high activities even under non-stress conditions. Both genes are regulated by general stress-responsive transcription factors Msn2 and Msn4, and Yap1, a transcription factor required for oxidative stress tolerance, and the removal of Msn2 or Yap1 caused a significant decrease in CTT1-expression. Under non-stress conditions, Msn2 was ~3.6-fold more abundant in the nucleus of the spore clone compared with a laboratory strain, whereas the nuclear abundance of Yap1 remained unchanged. Thus, a high tolerance to oxidative stress in this spore clone results from a high expression of ROS-degrading enzymes by the abundant accumulation of Msn2 in the nucleus. We found that oxidative stress caused by the presence of furfural did not impair fermentation by this strain, which could make it attractive for ethanol production from lignocellulosic biomass.