Coenzyme Q (CoQ) is an essential factor for aerobic growth and oxidative phosphorylation in the electron transport system. The biosynthetic pathway for CoQ has been proposed mainly from biochemical and genetic analyses of Escherichia coli and Saccharomyces cerevisiae; however, the biosynthetic pathway in higher eukaryotes has been explored in only a limited number of studies. We previously reported the roles of several genes involved in CoQ synthesis in the fission yeast Schizosaccharomyces pombe. Here, we expand these findings by identifying ten genes (dps1, dlp1, ppt1, and coq3–9) that are required for CoQ synthesis. CoQ10-deficient S. pombe coq deletion strains were generated and characterized. All mutant fission yeast strains were sensitive to oxidative stress, produced a large amount of sulfide, required an antioxidant to grow on minimal medium, and did not survive at the stationary phase. To compare the biosynthetic pathway of CoQ in fission yeast with that in higher eukaryotes, the ability of CoQ biosynthetic genes from humans and plants (Arabidopsis thaliana) to functionally complement the S. pombe coq deletion strains was determined. With the exception of COQ9, expression of all other human and plant COQ genes recovered CoQ10 production by the fission yeast coq deletion strains, although the addition of a mitochondrial targeting sequence was required for human COQ3 and COQ7, as well as A. thaliana COQ6. In summary, this study describes the functional conservation of CoQ biosynthetic genes between yeasts, humans, and plants.

Fungal cell walls are medically important since they represent a drug target site for antifungal medication. So far there is no method to directly visualize structurally similar cell wall components such as α-glucan, β-glucan and mannan with high specificity, especially in a label-free manner. In this study, we have developed a Raman spectroscopy based molecular imaging method and combined multivariate curve resolution analysis to enable detection and visualization of multiple polysaccharide components simultaneously at the single cell level. Our results show that vegetative cell and ascus walls are made up of both α- and β-glucans while spore wall is exclusively made of α-glucan. Co-localization studies reveal the absence of mannans in ascus wall but are distributed primarily in spores. Such detailed picture is believed to further enhance our understanding of the dynamic spore wall architecture, eventually leading to advancements in drug discovery and development in the near future.

In response to osmotic stress, proline is accumulated in many bacterial and plant cells. During various stresses, the yeast Saccharomyces cerevisiae induces glycerol or trehalose synthesis, but the fluctuations in gene expression and intracellular levels of proline in yeast are not yet well understood. We previously found that proline protects yeast cells from damage by freezing, oxidative, or ethanol stress. In this study, we examined the relationships between the gene expression profiles and intracellular contents of glycerol, trehalose, and proline under stress conditions. When yeast cells were exposed to 1 M sorbitol stress, the expression of GPD1 encoding glycerol-3-phosphate dehydrogenase is induced, leading to glycerol accumulation. In contrast, in the presence of 9% ethanol, the rapid induction of TPS2 encoding trehalose-6-phosphate phosphatase resulted in trehalose accumulation. We found that intracellular proline levels did not increase immediately after addition of sorbitol or ethanol. However, the expressions of genes involved in proline synthesis and degradation did not change during exposure to these stresses. It appears that the elevated proline levels are due primarily to an increase in proline uptake from a nutrient medium caused by the induction of PUT4. These results suggest that S. cerevisiae cells do not accumulate proline in response to sorbitol or ethanol stress different from other organisms.

During fermentation processes, Saccharomyces cerevisiae cells are exposed to multiple stresses, including a high concentration of ethanol that represents toxicity through intracellular reactive oxygen species (ROS) generation. We previously reported that proline protected yeast cells from damage caused by various stresses, such as freezing and ethanol. As an anti-oxidant, proline is suggested to scavenge intracellular ROS. In this study, we examined the role of intracellular proline during ethanol treatment in S. cerevisiae strains that accumulate different concentrations of proline. When cultured in YPD medium, there was a significant accumulation of proline in the put1 mutant strain, which is deficient in proline oxidase, in the stationary phase. Expression of the mutant PRO1 gene, which encodes the γ-glutamyl kinase variant (Asp154Asn or Ile150Thr) with desensitization to feedback inhibition by proline in the put1 mutant strain, showed a prominent increase in proline content as compared with that of the wild-type strain. The oxidation level was clearly increased in wild-type cells after exposure to ethanol, indicating that the generation of ROS occurred. Interestingly, proline accumulation significantly reduces the ROS level and increases the survival rate of yeast cells in the stationary phase under ethanol stress conditions. However, there was not a clear correlation between proline content and survival rate in yeast cells. An appropriate level of intracellular proline in yeast might be important for its stress-protective effect. Hence, the engineering of proline metabolism could be promising for breeding stress-tolerant industrial yeast strains.

Coenzyme Q (CoQ) is essential for mitochondrial respiration and as a cofactor for sulfide quinone reductase. Schizosaccharomyces pombe produces a human-type CoQ. Here, we analyzed CoQ in other fission yeast species. S. cryophilus and S. octosporus produce CoQ. S. japonicus produces low levels of CoQ, although all necessary genes for CoQ synthesis have been identified in its genome. We expressed three genes (dps1, dlp1, and ppt1) for CoQ synthesis from S. japonicus in the corresponding S. pombe mutants, and confirmed that they were functional. S. japonicus had very low levels of oxygen consumption and was essentially respiration defective, probably due to mitochondrial dysfunction. S. japonicus grows well on minimal medium during anaerobic culture, indicating that it acquires sufficient energy by fermentation. S. japonicus produces comparable levels of ethanol under both normal and elevated temperature (42 °C) conditions, at which S. pombe is not able to grow.