The Effects Of Ploidy Changes On Phenotypes And Gene Expression Of Saccharomyces Cerevisiae

To discover the effects of increased ploidy on the phenotypes, phsyology, and transcriptom of yeast cells, diploid, triploid and tetraploid yeast strains were constructed from a haploid Sacchromyces cerevisiae strain CEN-H through mating-type altering and mating. The increased ploidy of the diploid, triploid and tetraploid strains was confirmed by flow cytomesty and karyotype analysis. Growth, tolerance to multiple stresses, ethanol fermentation performances, physiological and biochemical properties, and RNA-seqs of these four strains were then analyzed in this study.Using scanning electron microscope (SEM) we found the yeast cell with increased ploidy showed a larger cell volume and a more number of bud scar. A negative relationship was also observed between ploidy and growth rate in YPD. Distinct tolerances to environmental factors or inhibitors (including high temperature, hyperosmosis, low pH, ethanol, formic acid, acetic acid, lactic acid, furfural,5-HMF, vanilline, H2O2, CUSO4, NaAsO2, fluconazole and carbendazim) were observed among the haploid, diploid, triploid and tetraploid strains. The yeast cell with more chromosomes had a better tolerance to vanilline, CuSO4, and fluconazole. Instead, the tolerance to lactic acid and carbendazim were decreased gradually in the four strains. The diploid yeast cell was more resistant to stress of furfural,5-HMF, NaAsO2,8% ethanol and 42? than other three strains. However, under the stresses of formic acid, H2O2 and hyperosmosis, the triploid yeast cell showed best tolerance. Interestingly, the four strains also showed different ethanol fermentation performances under different conditions. The fermentation rate was affected with the increase of diploidy in YPD medium of 20% glucose, but the diploid and triploid strains produced more ethanol at the end of fermentation. The triploid strain was the fastest one to finish ethanol fermentation in the present of inhibitors from cellulosic hydrolysates, but the ethanol yields of four strains were similar. The yeast strains with different numbers of chromosome sets showed various physiological attributes. For example, the intracellular trehalose contents of haploid and triploid were more than those in diploid and tetraploid strains; and the triploid strain had highest activities of SOD and CAT. RNA-seqs of four strains suggested that the genes relating to the processes of translation, ribosome biogenesis and gene expression were ploidy-induced; and the expression levels of the genes involved in response to stress were ploidy-repressed. Although the different contents of trehalose and ergosterol had a strong correlation with the different expression levels of genes among the four strains, some other physiological attributs could not been explained simply by gene expression at mRNA levels.