Functional relevance of water and glycerol channels in Saccharomyces cerevisiae

Activation of CWI pathway through high hydrostatic pressure, enhancing glycerol efflux via the aquaglyceroporin Fps1 in Saccharomyces cerevisiae

The fungal cell wall is the initial barrier for the fungi against diverse external stresses, such as osmolarity changes, harmful drugs, and mechanical injuries. This study explores the roles of osmoregulation and the cell-wall integrity (CWI) pathway in response to high hydrostatic pressure in the yeast Saccharomyces cerevisiae. We demonstrate the roles of the transmembrane mechanosensor Wsc1 and aquaglyceroporin Fps1 in a general mechanism to maintain cell growth under high-pressure regimes. The promotion of water influx into cells at 25 MPa, as evident by an increase in cell volume and a loss of the plasma membrane eisosome structure, activates the CWI pathway through the function of Wsc1. Phosphorylation of Slt2, the downstream mitogen-activated protein kinase, was increased at 25 MPa. Glycerol efflux increases via Fps1 phosphorylation, which is initiated by downstream components of the CWI pathway, and contributes to the reduction in intracellular osmolarity under high pressure. The elucidation of the mechanisms underlying adaptation to high pressure through the well-established CWI pathway could potentially translate to mammalian cells and provide novel insights into cellular mechanosensation.

Evolutionary Overview of Aquaporin Superfamily

Aquaporins (AQPs) are present not only in three domains of life, bacteria, eukaryotes, and archaea, but also in viruses. With the accumulating arrays of AQP superfamily, the evolutional relationship has attracted much attention with multiple publications on "the genome-wide identification and phylogenetic analysis" of AQP superfamily. A pair of NPA boxes forming a pore is highly conserved throughout the evolution and renders key residues for the classification of AQP superfamily into four groups: AQP1-like, AQP3-like, AQP8-like, and AQP11-like. The complexity of AQP family has mostly been achieved in nematodes and subsequent evolution has been directed toward increasing the number of AQPs through whole-genome duplications (WGDs) to extend the tissue specific expression and regulation. The discovery of the intracellular AQP (iAQP: AQP8-like and AQP11-like) and substrate transports by the plasma membrane AQP (pAQP: AQP1-like and AQP3-like) have accelerated the AQP research much more toward the transport of substrates with complex profiles. This evolutionary overview based on a simple classification of AQPs into four subfamilies will provide putative structural, functional, and localization information and insights into the role of AQP as well as clues to understand the complex diversity of AQP superfamily.

TOR complex 2 is a master regulator of plasma membrane homeostasis

As first demonstrated in budding yeast (Saccharomyces cerevisiae), all eukaryotic cells contain two, distinct multi-component protein kinase complexes that each harbor the TOR (Target Of Rapamycin) polypeptide as the catalytic subunit. These ensembles, dubbed TORC1 and TORC2, function as universal, centrally important sensors, integrators, and controllers of eukaryotic cell growth and homeostasis. TORC1, activated on the cytosolic surface of the lysosome (or, in yeast, on the cytosolic surface of the vacuole), has emerged as a primary nutrient sensor that promotes cellular biosynthesis and suppresses autophagy. TORC2, located primarily at the plasma membrane, plays a major role in maintaining the proper levels and bilayer distribution of all plasma membrane components (sphingolipids, glycerophospholipids, sterols, and integral membrane proteins). This article surveys what we have learned about signaling via the TORC2 complex, largely through studies conducted in S. cerevisiae. In this yeast, conditions that challenge plasma membrane integrity can, depending on the nature of the stress, stimulate or inhibit TORC2, resulting in, respectively, up-regulation or down-regulation of the phosphorylation and thus the activity of its essential downstream effector the AGC family protein kinase Ypk1. Through the ensuing effect on the efficiency with which Ypk1 phosphorylates multiple substrates that control diverse processes, membrane homeostasis is maintained. Thus, the major focus here is on TORC2, Ypk1, and the multifarious targets of Ypk1 and how the functions of these substrates are regulated by their Ypk1-mediated phosphorylation, with emphasis on recent advances in our understanding of these processes.

Genomic Adaptations of Saccharomyces Genus to Wine Niche

Wine yeast have been exposed to harsh conditions for millennia, which have led to adaptive evolutionary strategies. Thus, wine yeasts from Saccharomyces genus are considered an interesting and highly valuable model to study human-drive domestication processes. The rise of whole-genome sequencing technologies together with new long reads platforms has provided new understanding about the population structure and the evolution of wine yeasts. Population genomics studies have indicated domestication fingerprints in wine yeast, including nucleotide variations, chromosomal rearrangements, horizontal gene transfer or hybridization, among others. These genetic changes contribute to genetically and phenotypically distinct strains. This review will summarize and discuss recent research on evolutionary trajectories of wine yeasts, highlighting the domestication hallmarks identified in this group of yeast.

Comparative Analysis of Arsenic Transport and Tolerance Mechanisms: Evolution from Prokaryote to Higher Plants

Arsenic (As) is a toxic metalloid for all living organisms and can cause serious harm to humans. Arsenic is also toxic to plants. To alleviate As toxicity, all living organisms (from prokaryotes to higher plants) have evolved comprehensive mechanisms to reduce cytosolic As concentration through the set of As transporters localized at the plasma and tonoplast membranes, which operate either in arsenite As(III) extrusion out of cells (via ArsB, ACR3, and aquaporins) or by sequestering arsenic into vacuoles (by ABC transporters). In addition, a special arsenate resistance mechanism found in some bacterial systems has evolved in an As hyperaccumulating fern Pteris vittata, which involves transforming arsenate As(V) to an As(V) phosphoglycerate derivative by a glyceraldehyde 3-phosphate dehydrogenase and transporting this complex by an efflux transporter. In the present review, we summarize the evolution of these arsenic resistance mechanisms from prokaryotes to eukaryotes and discuss future approaches that could be utilized to better understand and improve As resistance mechanisms in plants.

Effect of glucose levels on carbon flow rate, antioxidant status, and enzyme activity of yeast during fermentation

BACKGROUND

The physiological metabolism of yeast has a significant impact on the quality of fermentation products. The present study aimed to investigate yeast metabolism in response to a changing glucose content environment, especially in fermentation products, as well as the change of carbon flow rate, antioxidant status, and yeast enzyme activity.

RESULTS

Yeast in a 0 g L^-1 glucose level was subjected to carbon starvation stress, cell growth retardation and cell proliferation was significantly inadequate; in the logarithmic growth stage of yeast, at a 30 g L^-1 glucose level, the carbon source mainly flowed to tricarboxylic acid cycle and pentose phosphate metabolism, cell division, proliferation, and increased cell growth. In later logarithmic growth period and stable period, carbon flowed into glycerol and trehalose metabolism, to cope with the environmental stress; yeast in 60 and 150 g L^-1 glucose levels faced high glucose stress at the beginning, the content of reactive oxygen increased, malondialdehyde content increased, cell damage was reduced through the regulation of superoxide dismutase and catalase enzyme activities, and most of the carbon flowed into the metabolic pathway of ethanol, glycerol, and trehalose to cope with high glucose stress, the pentose phosphate pathway showed a large late influx, and NADPH also started to increase rapidly after 24 h.

CONCLUSION

Yeast was stressed in a high-sugar environment and ensured the activity of yeast by preferentially increasing the metabolic intensity of trehalose, glycerol, and glycolytic metabolism, weakening tricarboxylic acid metabolism, and first weakening and then increasing pentose phosphate metabolism. © 2022 Society of Chemical Industry.

The role of the glycerol transporter channel Fps1p in cellular proteostasis during enhanced proteotoxic stress

In response to osmotic shock, the components of high-osmolarity glycerol (HOG) pathway regulate the level of intracellular glycerol in yeast and ensure cell survival. Glycerol is a compatible solute and a stabiliser of proteins. Its role in maintaining proteostasis is less explored. We show that mild stress in the form of dietary restriction leads to increased glycerol level which increases cell viability. However, dietary restriction coupled with protein aggregation decreases intracellular glycerol level and attenuates cell viability. The transcript level of FPS1, the glycerol transporter channel, remains unchanged. However, its activity is altered under enhanced proteotoxic stress. Our results provide evidence for a probable role of the Fps1p channel in the cellular proteostasis network. KEY POINTS: • Dietary restriction led to increased accumulation of glycerol in Fps1-deleted yeast cells. • This led to lower protein aggregation in these cells. • Increased production of glycerol under dietary restriction was not linked to increased level of Fps1.

Screening and Genetic Network Analysis of Genes Involved in Freezing and Thawing Resistance in DaMDHAR-Expressing Saccharomyces cerevisiae Using Gene Expression Profiling

The cryoprotection of cell activity is a key determinant in frozen-dough technology. Although several factors that contribute to freezing tolerance have been reported, the mechanism underlying the manner in which yeast cells respond to freezing and thawing (FT) stress is not well established. Therefore, the present study demonstrated the relationship between DaMDHAR encoding monodehydroascorbate reductase from Antarctic hairgrass Deschampsia antarctica and stress tolerance to repeated FT cycles (FT2) in transgenic yeast Saccharomyces cerevisiae. DaMDHAR-expressing yeast (DM) cells identified by immunoblotting analysis showed high tolerance to FT stress conditions, thereby causing lower damage for yeast cells than wild-type (WT) cells with empty vector alone. To detect FT2 tolerance-associated genes, 3′-quant RNA sequencing was employed using mRNA isolated from DM and WT cells exposed to FT (FT2) conditions. Approximately 332 genes showed ≥2-fold changes in DM cells and were classified into various groups according to their gene expression. The expressions of the changed genes were further confirmed using western blot analysis and biochemical assay. The upregulated expression of 197 genes was associated with pentose phosphate pathway, NADP metabolic process, metal ion homeostasis, sulfate assimilation, β-alanine metabolism, glycerol synthesis, and integral component of mitochondrial and plasma membrane (PM) in DM cells under FT2 stress, whereas the expression of the remaining 135 genes was partially related to protein processing, selenocompound metabolism, cell cycle arrest, oxidative phosphorylation, and α-glucoside transport under the same condition. With regard to transcription factors in DM cells, MSN4 and CIN5 were activated, but MSN2 and MGA1 were not. Regarding antioxidant systems and protein kinases in DM cells under FT stress, CTT1, GTO, GEX1, and YOL024W were upregulated, whereas AIF1, COX2, and TRX3 were not. Gene activation represented by transcription factors and enzymatic antioxidants appears to be associated with FT2-stress tolerance in transgenic yeast cells. RCK1, MET14, and SIP18, but not YPK2, have been known to be involved in the protein kinase-mediated signalling pathway and glycogen synthesis. Moreover, SPI18 and HSP12 encoding hydrophilin in the PM were detected. Therefore, it was concluded that the genetic network via the change of gene expression levels of multiple genes contributing to the stabilization and functionality of the mitochondria and PM, not of a single gene, might be the crucial determinant for FT tolerance in DaMDAHR-expressing transgenic yeast. These findings provide a foundation for elucidating the DaMDHAR-dependent molecular mechanism of the complex functional resistance in the cellular response to FT stress.

Cryopreservation and the Freeze-Thaw Stress Response in Yeast

The ability of yeast to survive freezing and thawing is most frequently considered in the context of cryopreservation, a practical step in both industrial and research applications of these organisms. However, it also relates to an evolved ability to withstand freeze-thaw stress that is integrated with a larger network of survival responses. These responses vary between different strains and species of yeast according to the environments to which they are adapted, and the basis of this adaptation appears to be both conditioned and genetic in origin. This review article briefly touches upon common yeast cryopreservation methods and describes in detail what is known about the biochemical and genetic determinants of cell viability following freeze-thaw stress. While we focus on the budding yeast Saccharomyces cerevisiae, in which the freeze-thaw stress response is best understood, we also highlight the emerging diversity of yeast freeze-thaw responses as a manifestation of biodiversity among these organisms.

Analysis of nicotine-induced metabolic changes in Blakeslea trispora by GC-MS

Blakeslea trispora is a natural source of carotenoids, including β-carotene and lycopene, which have industrial applications. Therefore, classical selective breeding techniques have been applied to generate strains with increased productivity, and microencapsulated β-carotene preparation has been used in food industry (Li et al., 2019). In B. trispora, lycopene is synthesized via the mevalonate pathway (Venkateshwaran et al., 2015). Lycopene cyclase, which is one of the key enzymes in this pathway, is a bifunctional enzyme that can catalyze the cyclization of lycopene to produce β-carotene and exhibit phytoene synthase activity (He et al., 2017).

Comparative Metabolic Responses Induced by Pyridine and Imidazole in Blakeslea trispora

Lycopene cyclase needs to be inhibited by the blockers like pyridine or imidazole in the lycopene accumulation of Blakeslea trispora. This work investigated how pyridine and imidazole impacted the basal metabolism of B. trispora, the results helped us understand how they could affect the lycopene production and application, and see the metabolic risks from different inhibitors. In this study, the highest yield of lycopene with pyridine was obtained at 176 mg/L without amino acids supplement, and got more lycopene at 237 mg/L adding tyrosine, lysine, proline all together as 0.01 mol/L each in fermented broth. GC-MS and Principal Component Analysis (PCA) were used to find that amino acids, fatty acids, organic acids including phosphoric acid, carbon source and imidazole derivatives played the most important roles in lycopene fermentation with imidazole, differently, fatty acids, carbon source, and pyridine derivatives were more significant in the pyridine process and it was remarkable that the residual of both blockers' derivatives would bring the potential risks on applications of lycopene products. Predominantly, durene met 0.35 mg/g DCW with imidazole and piperidine formaldehyde attained 0.24 mg/g DCW with pyridine after the end of lycopene fermentations.

Hyperoxidation of mitochondrial peroxiredoxin limits H2 O2 -induced cell death in yeast

Hydrogen peroxide (H2 O2 ) plays important roles in cellular signaling, yet nonetheless is toxic at higher concentrations. Surprisingly, the mechanism(s) of cellular H2 O2 toxicity remain poorly understood. Here, we reveal an important role for mitochondrial 1-Cys peroxiredoxin from budding yeast, Prx1, in regulating H2 O2 -induced cell death. We show that Prx1 efficiently transfers oxidative equivalents from H2 O2 to the mitochondrial glutathione pool. Deletion of PRX1 abrogates glutathione oxidation and leads to a cytosolic adaptive response involving upregulation of the catalase, Ctt1. Both of these effects contribute to improved cell viability following an acute H2 O2 challenge. By replacing PRX1 with natural and engineered peroxiredoxin variants, we could predictably induce widely differing matrix glutathione responses to H2 O2 . Therefore, we demonstrated a key role for matrix glutathione oxidation in driving H2 O2 -induced cell death. Finally, we reveal that hyperoxidation of Prx1 serves as a switch-off mechanism to limit oxidation of matrix glutathione at high H2 O2 concentrations. This enables yeast cells to strike a fine balance between H2 O2 removal and limitation of matrix glutathione oxidation.

Mucor circinelloides Thrives inside the Phagosome through an Atf-Mediated Germination Pathway

Mucormycosis is an emerging fungal infection that is often lethal due to the ineffectiveness of current therapies. Here, we have studied the first stage of this infection-the germination of Mucor circinelloides spores inside phagocytic cells-from an integrated transcriptomic and functional perspective. A relevant fungal gene network is remodeled in response to phagocytosis, being enriched in crucial functions to survive and germinate inside the phagosome, such as nutritional adaptation and response to oxidative stress. Correspondingly, the phagocytic cells induced a specific proinflammatory and apoptotic response to the pathogenic strain. Deletion of fungal genes encoding putative transcription factors (atf1, atf2, and gcn4), extracellular proteins (chi1 and pps1), and an aquaporin (aqp1) revealed that these genes perform important roles in survival following phagocytosis, germination inside the phagosome, and virulence in mice. atf1 and atf2 play a major role in these pathogenic processes, since their mutants showed the strongest phenotypes and both genes control a complex gene network of secondarily regulated genes, including chi1 and aqp1 These new insights into the initial phase of mucormycosis define genetic regulators and molecular processes that could serve as pharmacological targets.IMPORTANCE Mucorales are a group of ancient saprophytic fungi that cause neglected infectious diseases collectively known as mucormycoses. The molecular processes underlying the establishment and progression of this disease are largely unknown. Our work presents a transcriptomic study to unveil the Mucor circinelloides genetic network triggered in fungal spores in response to phagocytosis by macrophages and the transcriptional response of the host cells. Functional characterization of differentially expressed fungal genes revealed three transcription factors and three extracellular proteins essential for the fungus to survive and germinate inside the phagosome and to cause disease in mice. Two of the transcription factors, highly similar to activating transcription factors (ATFs), coordinate a complex secondary gene response involved in pathogenesis. The significance of our research is in characterizing the initial stages that lead to evasion of the host innate immune response and, in consequence, the dissemination of the infection. This genetic study offers possible targets for novel antifungal drugs against these opportunistic human pathogens.

Extreme Osmotolerance and Halotolerance in Food-Relevant Yeasts and the Role of Glycerol-Dependent Cell Individuality

Osmotolerance or halotolerance are used to describe resistance to sugars and salt, or only salt, respectively. Here, a comprehensive screen of more than 600 different yeast isolates revealed that osmosensitive species were equally affected by NaCl and glucose. However, the relative toxicity of salt became increasingly prominent in more osmoresistant species. We confirmed that growth inhibition by glucose in a laboratory strain of Saccharomyces cerevisiae occurred at a lower water activity (A_w) than by salt (NaCl), and pre-growth in high levels of glucose or salt gave enhanced cross-resistance to either. Salt toxicity was largely due to osmotic stress but with an additive enhancement due to effects of the relevant cation. Almost all of the yeast isolates from the screen were also noted to exhibit hetero-resistance to both salt and sugar, whereby high concentrations restricted growth to a small minority of cells within the clonal populations. Rare resistant colonies required growth for up to 28 days to become visible. This cell individuality was more marked with salt than sugar, a possible further reflection of the ion toxicity effect. In both cases, heteroresistance in S. cerevisiae was strikingly dependent on the GPD1 gene product, important for glycerol synthesis. In contrast, a tps1Δ deletant impaired for trehalose showed altered MIC but no change in heteroresistance. Effects on heteroresistance were evident in chronic (but not acute) salt or glucose stress, particularly relevant to growth on low A_w foods. The study reports diverse osmotolerance and halotolerance phenotypes and heteroresistance across an extensive panel of yeast isolates, and indicates that Gpd1-dependent glycerol synthesis is a key determinant enabling growth of rare yeast subpopulations at low A_w, brought about by glucose and in particular salt.