Low ergosterol content in yeast adh1 mutant enhances chitin maldistribution and sensitivity to paraquat-induced oxidative stress

Roles of alcohol dehydrogenase 1 in the biological activities of Candida albicans

Candida albicans stands as the foremost prevalent human commensal pathogen and a significant contributor to nosocomial fungal infections. In the metabolism of C. albicans, alcohol dehydrogenase 1 (Adh1) is one of the important enzymes that converts acetaldehyde produced by pyruvate decarboxylation into ethanol at the end of glycolysis. Leveraging the foundational processes of alcoholic fermentation, Adh1 plays an active role in multiple biological phenomena, including biofilm formation, interactions between different species, the development of drug resistance, and the potential initiation of gastrointestinal cancer. Additionally, Adh1 within C. albicans has demonstrated associations with regulating the cell cycle, stress responses, and various intracellular states. Furthermore, Adh1 is extracellularly localized on the cell wall surface, where it plays roles in processes such as tissue invasion and host immune responses. Drawing from an analysis of ADH1 gene structure, expression patterns, and fundamental functions, this review elucidates the intricate connections between Adh1 and various biological processes within C. albicans, underscoring its potential implications for the prevention, diagnosis, and treatment of candidiasis.

Physiological and transcriptomic insights into sugar stress resistance in osmophilic yeast Zygosaccharomyces rouxii

The osmophilic yeast Zygosaccharomyces rouxii has attracted increasing attention for its ability to survive and grow in extremely high sugar environments. This trait determines its role in fermentation process and results in contamination in the food industry. However, the behavior of Z. rouxii in regulating cell metabolism to combat high sugar stress and the corresponding mechanism have not been completely elucidated. Here, the resistance strategies of Z. rouxii against high glucose stress were explored by physiological analysis at cell membrane level and transcriptomic analysis. Physiological analysis showed that under high glucose stress, colony transparency increased, cell volume decreased, which was accompanied by reduction in permeability and integrity of cell membrane and subsequent gradual recovering. Additionally, the proportion of ergosterol and unsaturated fatty acids in cell membrane significantly increased under high glucose stress. A comparison of transcriptome data showed that most of the obtained differentially expressed genes (DEGs) involved in ergosterol and linoleic acid synthesis pathways as well as cell wall integrity (CWI) and high osmolarity glycerol mitogen-activated protein kinase (HOG-MAPK) pathways, which was in line with the results of physiological data. Our results provided a theoretic basis to develop the process control for the production of high sugar foods.

Enhanced Expression of Alcohol Dehydrogenase I in Pichia pastoris Reduces the Content of Acetaldehyde in Wines

Acetaldehyde is an important carbonyl compound commonly detected in wines. A high concentration of acetaldehyde can affect the flavor of wines and result in adverse effects on human health. Alcohol dehydrogenase I (ADH1) in Saccharomyces cerevisiae catalyzes the reduction reaction of acetaldehyde into ethanol in the presence of cofactors, showing the potential to reduce the content of acetaldehyde in wines. In this study, ADH1 was successfully expressed in Pichia pastoris GS115 based on codon optimization. Then, the expression level of ADH1 was enhanced by replacing its promoter with optimized promoters and increasing the copy number of the expression cassette, with ADH1 being purified using nickel column affinity chromatography. The enzymatic activity of purified ADH1 reached 605.44 ± 44.30 U/mg. The results of the effect of ADH1 on the content of acetaldehyde in wine revealed that the acetaldehyde content of wine samples was reduced from 168.05 ± 0.55 to 113.17 ± 6.08 mg/L with the addition of 5 mM NADH and the catalysis of ADH1, and from 135.53 ± 4.08 to 52.89 ± 2.20 mg/L through cofactor regeneration. Our study provides a novel approach to reducing the content of acetaldehyde in wines through enzymatic catalysis.

Erg4 Is Involved in Ergosterol Biosynthesis, Conidiation and Stress Response in Penicillium expansum

erg4 is a key gene for ergosterol biosynthesis in filamentous fungi, but its function in Penicillium expansum remains unknown. Our results showed that P. expansum contains three erg4 genes, including erg4A, erg4B and erg4C. The expression levels of the three genes showed differences in the wild-type (WT) strain, and the expression level of erg4B was the highest, followed by erg4C. Deletion of erg4A, erg4B or erg4C in the WT strain revealed functional redundancy between them. Compared to the WT strain, erg4A, erg4B or erg4C knockout mutants reduced ergosterol levels, with erg4B deletion having the greatest effect. Furthermore, deletion of the three genes reduced sporulation of the strain, and Δerg4B and Δerg4C mutants showed defective spore morphology. In addition, Δerg4B and Δerg4C mutants were found to be more sensitive to cell wall integrity and oxidative stress. However, deletion of erg4A, erg4B or erg4C had no significant effect on colony diameter, spore germination rate, conidiophore structure of P. expansum or pathogenicity to apple fruit. Taken together, erg4A, erg4B and erg4C have redundant functions and are all involved in ergosterol synthesis and sporulation in P. expansum. In addition, erg4B and erg4C contribute to spore morphogenesis, cell wall integrity and response to oxidative stress in P. expansum.

Mevalonate kinase of Leishmania donovani protects parasite against oxidative stress by modulating ergosterol biosynthesis

Leishmaniasis comprises of a wide variety of diseases, caused by protozoan parasite belonging to the genus Leishmania. Leishmania parasites undergo different types of stress during their lifetime and have developed strategies to overcome this damage. Identifying the mechanistic approach used by the parasite in dealing with the stress is of immense importance for unfolding the survival strategy adopted by the parasite. Mevalonate kinase (MVK) is an important regulatory factor in the mevalonate pathway in both bacteria and eukaryotes. In this study, we explored the role of Leishmania donovani mevalonate kinase (LdMVK) in parasite survival under stress condition. Hydrogen peroxide (H₂O₂) and menadione, the two known oxidants were used to carry out the experiments. The MVK expression was found to be up regulated ∼2.1 fold and ∼2.3 fold under oxidative stress condition and under the effect of anti-Leishmania drug, AmBisome respectively. The cell viability declined under the effect of MVK inhibitor viz: vanadyl sulfate (VS). The level of intracellular ROS was also found to be increased under the effect of MVK inhibitor. To confirm the findings, LdMVK over expression (LdMVK OE) and LdMVK knockdown (LdMVK KD) parasites were generated. The level of ergosterol, an important component of plasma membrane in L. donovani, was observed and found to be reduced by nearly 60 % in LdMVK KD parasite and increased by nearly 30 % in LdMVK OE parasites as compared to wild type. However, the ergosterol content was found to be elevated under oxidative stress. Furthermore, LdMVK was also found to be associated with maintaining the plasma membrane integrity and also in preventing the peroxidation of cellular lipids when exposed to oxidative stress. The above data clearly suggests that MVK has a vital role in protecting the parasite from oxidative stress. These findings may also explore the contribution of LdMVK in drug unresponsiveness which may help in future rational drug designing for leishmaniasis.

Distinct Proteome Remodeling of Industrial Saccharomyces cerevisiae in Response to Prolonged Thermal Stress or Transient Heat Shock

To gain a deep understanding of yeast-cell response to heat stress, multiple laboratory strains have been intensively studied via genome-wide expression analysis for the mechanistic dissection of classical heat-shock response (HSR). However, robust industrial strains of Saccharomyces cerevisiae have hardly been explored in global analysis for elucidation of the mechanism of thermotolerant response (TR) during fermentation. Herein, we employed data-independent acquisition and sequential window acquisition of all theoretical mass spectra based proteomic workflows to characterize proteome remodeling of an industrial strain, ScY01, responding to prolonged thermal stress or transient heat shock. By comparing the proteomic signatures of ScY01 in TR versus HSR as well as the HSR of the industrial strain versus a laboratory strain, our study revealed disparate response mechanisms of ScY01 during thermotolerant growth or under heat shock. In addition, through proteomics data-mining for decoding transcription factor interaction networks followed by validation experiments, we uncovered the functions of two novel transcription factors, Mig1 and Srb2, in enhancing the thermotolerance of the industrial strain. This study has demonstrated that accurate and high-throughput quantitative proteomics not only provides new insights into the molecular basis for complex microbial phenotypes but also pinpoints upstream regulators that can be targeted for improving the desired traits of industrial microorganisms.

Development of a plasmid free CRISPR-Cas9 system for the genetic modification of Mucor circinelloides

Mucor circinelloides and other members of Mucorales are filamentous fungi, widely used as model organisms in basic and applied studies. Although genetic manipulation methods have been described for some Mucoral fungi, construction of stable integrative transformants by homologous recombination has remained a great challenge in these organisms. In the present study, a plasmid free CRISPR-Cas9 system was firstly developed for the genetic modification of a Mucoral fungus. The described method offers a rapid but robust tool to obtain mitotically stable mutants of M. circinelloides via targeted integration of the desired DNA. It does not require plasmid construction and its expression in the recipient organism. Instead, it involves the direct introduction of the guide RNA and the Cas9 enzyme and, in case of homology directed repair (HDR), the template DNA into the recipient strain. Efficiency of the method for non-homologous end joining (NHEJ) and HDR was tested by disrupting two different genes, i.e. carB encoding phytoene dehydrogenase and hmgR2 encoding 3-hydroxy-3-methylglutaryl-CoA reductase, of M. circinelloides. Both NHEJ and HDR resulted in stable gene disruption mutants. While NHEJ caused extensive deletions upstream from the protospacer adjacent motif, HDR assured the integration of the deletion cassette at the targeted site.

Recent Advances in Ergosterol Biosynthesis and Regulation Mechanisms in Saccharomyces cerevisiae

Ergosterol, an important component of the fungal cell membrane, is not only essential for fungal growth and development but also very important for adaptation to stress in fungi. Ergosterol is also a direct precursor for steroid drugs. The biosynthesis of ergosterol can be divided into three modules: mevalonate, farnesyl pyrophosphate (farnesyl-PP) and ergosterol biosynthesis. The regulation of ergosterol content is mainly achieved by feedback regulation of ergosterol synthase activity through transcription, translation and posttranslational modification. The synthesis of HMG-CoA, catalyzed by HMGR, is a major metabolic check point in ergosterol biosynthesis. Excessive sterols can be subsequently stored in lipid droplets or secreted into the extracellular milieu by esterification or acetylation to avoid toxic effects. As sterols are insoluble, the intracellular transport of ergosterol in cells requires transporters. In recent years, great progress has been made in understanding ergosterol biosynthesis and its regulation in Saccharomyces cerevisiae. However, few reviews have focused on these studies, especially the regulation of biosynthesis and intracellular transport. Therefore, this review summarizes recent research progress on the physiological functions, biosynthesis, regulation of biosynthesis and intracellular transportation of ergosterol in S. cerevisiae.

Tolerant and Susceptible Sesame Genotypes Reveal Waterlogging Stress Response Patterns

Waterlogging is a common adverse environmental condition that limits plant growth. Sesame (Sesamum indicum) is considered a drought-tolerant oil crop but is typically susceptible to harmful effects from waterlogging. The present study used comparative analysis to explore the waterlogging stress response associated with two sesame genotypes. The RNA-seq dataset generated during a time course of 0, 3, 9 and 15 h of waterlogging as well as 20 h post-drainage indicated that stress gradually suppressed the expression of sesame genes, with 9 h as the critical time point for the response of sesame to waterlogging stress. Of the 19,316 genes expressed during waterlogging, 72.1% were affected significantly. Sesame of both tolerant and susceptible genotypes showed decreased numbers of upregulated differentially expressed genes (DEGs) but increased numbers of downregulated DEGs at the onset of waterlogging. However, the tolerant-genotype sesame exhibited 25.5% more upregulated DEGs and 29.7% fewer downregulated DEGs than those of the susceptible-genotype strain between 3 and 15 h. The results indicated that the tolerant sesame displayed a more positive gene response to waterlogging. A total of 1,379 genes were significantly induced and commonly expressed in sesame under waterlogging conditions from 3 to 15 h regardless of tolerance level; of these genes, 98 are known homologous stress responsive genes, while the remaining 1,281 are newly reported here. This gene set may represent the core genes that function in response to waterlogging, including those related mainly to energy metabolism and phenylpropanoid biosynthesis. Furthermore, a set of 3,016 genes functioning in energy supply and cell repair or formation was activated in sesame recovery from waterlogging stress. A comparative analysis between sesame of the tolerant and susceptible genotypes revealed 66 genes that may be candidates for improving sesame tolerance to waterlogging. This study provided a comprehensive picture of the sesame gene expression pattern in response to waterlogging stress. These results will help dissect the mechanism of the sesame response to waterlogging and identify candidate genes to improve its tolerance.

Involvement of FgERG4 in ergosterol biosynthesis, vegetative differentiation and virulence in Fusarium graminearum

The ergosterol biosynthesis pathway is well understood in Saccharomyces cerevisiae, but currently little is known about the pathway in plant-pathogenic fungi. In this study, we characterized the Fusarium graminearum FgERG4 gene encoding sterol C-24 reductase, which catalyses the conversion of ergosta-5,7,22,24-tetraenol to ergosterol in the final step of ergosterol biosynthesis. The FgERG4 deletion mutant ΔFgErg4-2 failed to synthesize ergosterol. The mutant exhibited a significant decrease in mycelial growth and conidiation, and produced abnormal conidia. In addition, the mutant showed increased sensitivity to metal cations and to various cell stresses. Surprisingly, mycelia of ΔFgErg4-2 revealed increased resistance to cell wall-degrading enzymes. Fungicide sensitivity tests revealed that ΔFgErg4-2 showed increased resistance to various sterol biosynthesis inhibitors (SBIs), which is consistent with the over-expression of SBI target genes in the mutant. ΔFgErg4-2 was impaired dramatically in virulence, although it was able to successfully colonize flowering wheat head and tomato, which is in agreement with the observation that the mutant produces a significantly lower level of trichothecene mycotoxins than does the wild-type progenitor. All of these phenotypic defects of ΔFgErg4-2 were complemented by the reintroduction of a full-length FgERG4 gene. In addition, FgERG4 partially rescued the defect of ergosterol biosynthesis in the Saccharomyces cerevisiae ERG4 deletion mutant. Taken together, the results of this study indicate that FgERG4 plays a crucial role in ergosterol biosynthesis, vegetative differentiation and virulence in the filamentous fungus F. graminearum.

New rapid screening method for anti-aging compounds using budding yeast and identification of beauveriolide I as a potent active compound

The chronological lifespan (CLS) of budding yeast is a model for the aging of post-mitotic cells in higher eukaryotes. We report here the development of a new method to assess yeast CLS. The new assay is simple, convenient and labor-saving. We applied this new method to screen natural compounds isolated from mushrooms and discovered beauveriolide I as a potent anti-aging agent.

A network-based approach on elucidating the multi-faceted nature of chronological aging in S. cerevisiae

BACKGROUND

Cellular mechanisms leading to aging and therefore increasing susceptibility to age-related diseases are a central topic of research since aging is the ultimate, yet not understood mechanism of the fate of a cell. Studies with model organisms have been conducted to ellucidate these mechanisms, and chronological aging of yeast has been extensively used as a model for oxidative stress and aging of postmitotic tissues in higher eukaryotes.

METHODOLOGY/PRINCIPAL FINDINGS

The chronological aging network of yeast was reconstructed by integrating protein-protein interaction data with gene ontology terms. The reconstructed network was then statistically "tuned" based on the betweenness centrality values of the nodes to compensate for the computer automated method. Both the originally reconstructed and tuned networks were subjected to topological and modular analyses. Finally, an ultimate "heart" network was obtained via pooling the step specific key proteins, which resulted from the decomposition of the linear paths depicting several signaling routes in the tuned network.

CONCLUSIONS/SIGNIFICANCE

The reconstructed networks are of scale-free and hierarchical nature, following a power law model with γ  =  1.49. The results of modular and topological analyses verified that the tuning method was successful. The significantly enriched gene ontology terms of the modular analysis confirmed also that the multifactorial nature of chronological aging was captured by the tuned network. The interplay between various signaling pathways such as TOR, Akt/PKB and cAMP/Protein kinase A was summarized in the "heart" network originated from linear path analysis. The deletion of four genes, TCB3, SNA3, PST2 and YGR130C, was found to increase the chronological life span of yeast. The reconstructed networks can also give insight about the effect of other cellular machineries on chronological aging by targeting different signaling pathways in the linear path analysis, along with unraveling of novel proteins playing part in these pathways.