Small heat-shock protein Hsp9 has dual functions in stress adaptation and stress-induced G2-M checkpoint regulation via Cdc25 inactivation in Schizosaccharomyces pombe

Near-gapless genome and transcriptome analyses provide insights into fruiting body development in Lentinula edodes

Fruiting body development in macrofungi is an intensive research subject. In this study, high-quality genomes were assembled for two sexually compatible monokaryons from a heterokaryotic Lentinula edodes strain WX1, and variations in L. edodes genomes were analyzed. Specifically, differential gene expression and allele-specific expression (ASE) were analyzed using the two monokaryotic genomes and transcriptome data from four different stages of fruiting body development in WX1. Results revealed that after aeration, mycelia sensed cell wall stress, pheromones, and a decrease in CO2 concentration, leading to up-regulated expression in genes related to cell adhesion, cell wall remodeling, proteolysis, and lipid metabolism, which may promote primordium differentiation. Aquaporin genes and those related to proteolysis, mitosis, lipid, and carbohydrate metabolism may play important roles in primordium development, while genes related to tissue differentiation and sexual reproduction were active in fruiting body. Several essential genes for fruiting body development were allele-specifically expressed and the two nuclear types could synergistically regulate fruiting body development by dominantly expressing genes with different functions. ASE was probably induced by long terminal repeat-retrotransposons. Findings here contribute to the further understanding of the mechanism of fruiting body development in macrofungi.

Effects of rpl1001 Gene Deletion on Cell Division of Fission Yeast and Its Molecular Mechanism

The rpl1001 gene encodes 60S ribosomal protein L10, which is involved in intracellular protein synthesis and cell growth. However, it is not yet known whether it is involved in the regulation of cell mitosis dynamics. This study focuses on the growth, spore production, cell morphology, the dynamics of microtubules, chromosomes, actin, myosin, and mitochondria of fission yeast (Schizosaccharomyces pombe) to investigate the impact of rpl1001 deletion on cell mitosis. RNA-Seq and bioinformatics analyses were also used to reveal key genes, such as hsp16, mfm1 and isp3, and proteasome pathways. The results showed that rpl1001 deletion resulted in slow cell growth, abnormal spore production, altered cell morphology, and abnormal microtubule number and length during interphase. The cell dynamics of the rpl1001Δ strain showed that the formation of a monopolar spindle leads to abnormal chromosome segregation with increased rate of spindle elongation in anaphase of mitosis, decreased total time of division, prolonged formation time of actin and myosin loops, and increased expression of mitochondrial proteins. Analysis of the RNA-Seq sequencing results showed that the proteasome pathway, up-regulation of isp3, and down-regulation of mfm1 and mfm2 in the rpl1001Δ strain were the main factors underpinning the increased number of spore production. Also, in the rpl1001Δ strain, down-regulation of dis1 caused the abnormal microtubule and chromosome dynamics, and down-regulation of hsp16 and pgk1 were the key genes affecting the delay of actin ring and myosin ring formation. This study reveals the effect and molecular mechanism of rpl1001 gene deletion on cell division, which provides the scientific basis for further clarifying the function of the Rpl1001 protein in cell division.

The small heat shock protein Hsp12.1 has a major role in the stress response and virulence of Cryptococcus gattii

Cryptococcus gattii is one of the etiological agents of cryptococcosis. To achieve a successful infection, C. gattii cells must overcome the inhospitable host environment and deal with the highly specialized immune system and poor nutrients availability. Inside the host, C. gattii uses a diversified set of tools to maintain homeostasis and establish infection, such as the expression of remarkable and diverse heat shock proteins (Hsps). Grouped by molecular weight, little is known about the Hsp12 subset in pathogenic fungi. In this study, the function of the C. gattii HSP12.1 and HSP12.2 genes was characterized. Both genes were upregulated during murine infection and heat shock. The hsp12.1 Δ null mutant cells were sensitive to plasma membrane and oxidative stressors. Moreover, HSP12 deletion induced C. gattii reactive oxygen species (ROS) accumulation associated with a differential expression pattern of oxidative stress-responsive genes compared to the wild type strain. Apart from these findings, the deletion of the paralog gene HSP12.2 did not lead to any detectable phenotype. Additionally, the double-deletion mutant strain hsp12.1 Δ /hsp12.2 Δ presented a similar phenotype to the single-deletion mutant hsp12.1 Δ, suggesting a minor participation of Hsp12.2 in these processes. Furthermore, HSP12.1 disruption remarkably affected C. gattii virulence and phagocytosis by macrophages in an invertebrate model of infection, demonstrating its importance for C. gattii pathogenicity.

Sclerotinia sclerotiorum Response to Long Exposure to Glucosinolate Hydrolysis Products by Transcriptomic Approach

White mold disease, caused by the necrotrophic fungus Sclerotinia sclerotiorum, affects Brassica crops. Brassica crops produce a broad array of compounds, such as glucosinolates, which contribute to the defense against pathogens. From their hydrolysis, several products arise that have antimicrobial activity (GHPs) whose toxicity is structure dependent. S. sclerotiorum may overcome the toxic effect of moderate GHP concentrations after prolonged exposure to their action. Our objective was to identify the molecular mechanism underlying S. sclerotiorum response to long exposure to two chemically diverse GHPs: aliphatic GHP allyl-isothiocyanate (AITC) and indole GHP indol-3-carbinol (I3C). We found that the transcriptomic response is dependent on the type of GHP and on their initial target, involving cell membranes in the case of AITC or DNA in the case of I3C. Response mechanisms include the reorganization of chromatin, mediated by histone chaperones hip4 and cia1, ribosome synthesis controlled by the kinase-phosphatase pair aps1-ppn1, catabolism of proteins, ergosterol synthesis, and induction of detoxification systems. These mechanisms probably help S. sclerotiorum to grow and survive in an environment where GHPs are constantly produced by Brassica plants upon glucosinolate breakdown. IMPORTANCEBrassica species, including important vegetable crops, such as cabbage, cauliflower, or broccoli, or oil crops, such as rapeseed, produce specific chemical compounds useful to protect them against pests and pathogens. One of the most destructive Brassica diseases in temperate areas around the world is Sclerotinia stem rot, caused by the fungus Sclerotinia sclerotiorum. This is a generalist pathogen that causes disease over more than 400 plant species, being a serious threat to economically important crops worldwide, including potato, bean, soybean, and sunflower, among many others. Understanding the mechanisms utilized by pathogens to overcome specific plant defensive compounds can be useful to increase plant resistance. Our study demonstrated that Sclerotinia shows different adaptation mechanisms, including detoxification systems, to grow and survive when plant protective compounds are present.

Comparative transcriptome analysis of abnormal cap and healthy fruiting bodies of the edible mushroom Lentinula edodes

Lentinula edodes, a commercially important mushroom, is cultivated worldwide. Artificially cultivated L. edodes often present with abnormal symptoms in the fruiting body, which affect their commercial value and reduce production efficiency. In this study, we carried out a comparative transcriptome analysis of normal fruiting body pileus (LeNP), normal margin in abnormal fruiting body pileus (LeAPNM), and abnormal margin in abnormal fruiting body pileus (LeAPAM). Metabolic pathways such as those involved in transmembrane transport, ribosome production, tryptophan metabolism, arginine and proline metabolism, and the metabolism of other amino acids were significantly enriched in LeAPAM. F-box, short-chain dehydrogenases/reductases, the major facilitator superfamily, and the FMN_red superfamily are related to malformation in L. edodes. Genes encoding heat shock proteins, G protein, and β-1,3-glucanase in the GH5 family showed different expression patterns, suggesting that these genes are involved in the development of L. edodes fruiting bodies. In particular, CAZymes, which are involved in the development of cell walls in L. edodes, were highly expressed in LeAPAM. According to TEM observation, the cell wall of LeAPAM samples showed significant thickening compared to the other samples. These results suggested that cell wall anabolism in LeAPAM samples was more active than that in normal fruiting bodies, enhancing the environmental adaptability of the fungus. This study provides preliminary data for future research aimed at solving the phenomenon of abnormal fruiting bodies of L. edodes.

Aspergillus flavus NRRL 35739, a Poor Biocontrol Agent, May Have Increased Relative Expression of Stress Response Genes

Biocontrol of the mycotoxin aflatoxin utilizes non-aflatoxigenic strains of Aspergillus flavus, which have variable success rates as biocontrol agents. One non-aflatoxigenic strain, NRRL 35739, is a notably poor biocontrol agent. Its growth in artificial cultures and on peanut kernels was found to be slower than that of two aflatoxigenic strains, and NRRL 35739 exhibited less sporulation when grown on peanuts. The non-aflatoxigenic strain did not greatly prevent aflatoxin accumulation. Comparison of the transcriptomes of aflatoxigenic and non-aflatoxigenic A. flavus strains AF36, AF70, NRRL 3357, NRRL 35739, and WRRL 1519 indicated that strain NRRL 35739 had increased relative expression of six heat shock and stress response proteins, with the genes having relative read counts in NRRL 35739 that were 25 to 410 times more than in the other four strains. These preliminary findings tracked with current thought that aflatoxin biocontrol efficacy is related to the ability of a non-aflatoxigenic strain to out-compete aflatoxigenic ones. The slower growth of NRRL 35739 might be due to lower stress tolerance or overexpression of stress response(s). Further study of NRRL 35739 is needed to refine our understanding of the genetic basis of competitiveness among A. flavus strains.

Production of 3-hydroxypropionic acid via the malonyl-CoA pathway using recombinant fission yeast strains

3-Hydroxypropionic acid (3-HP) can be converted into derivatives such as acrylic acid, a source for producing super absorbent polymers. Although Escherichia coli has often been used for 3-HP production, it exhibits low tolerance to 3-HP. To circumvent this problem, we selected the fission yeast Schizosaccharomyces pombe as this microorganism has higher tolerance to 3-HP than E. coli. Therefore, we constructed S. pombe transformants overexpressing two genes, one encoding the S. pombe acetyl-CoA carboxylase (Cut6p) and the other encoding the malonyl-CoA reductase derived from Chloroflexus aurantiacus (CaMCR). To prevent the degradation of these expressed proteins, we employed an S. pombe protease-deficient strain. Moreover, to increase the cytosolic concentration of acetyl-CoA, we supplemented acetate to the medium, which improved 3-HP production. To further produce 3-HP by overexpressing Cut6p and CaMCR, we exploited the highly expressing S. pombe hsp9 promoter. Finally, culturing in high-density reached 3-HP production to 7.6 g/L at 31 h.

The Effect of Fermented Lingonberry Juice on Candida glabrata Intracellular Protein Expression

Lingonberries have a long traditional use in treating fungal infections on mucosal membranes, but very little is known about the exact antifungal mechanisms. We tested the effects of fermented lingonberry juice on Candida glabrata intracellular protein expression. A Candida glabrata clinical strain was grown in the presence of fermented lingonberry juice (FLJ). Also the effect of lowered pH was tested. Intracellular protein expression levels were analyzed by the 2D-DIGE method. Six proteins detected with ≥1.5-fold lowered expression levels from FLJ treated cells were further characterized with LC-MS/MS. Heat shock protein 9/12 and redoxin were identified with peptide coverage/scores of 68/129 and 21/26, respectively. Heat shock protein 9/12 had an oxidized methionine at position 56. We found no differences in protein expression levels at pH 3.5 compared to pH 7.6. These results demonstrate that FLJ exerts an intracellular stress response in Candida glabrata, plausibly impairing its ability to express proteins related to oxidative stress or maintaining cell wall integrity.

Screening Molecular Chaperones Similar to Small Heat Shock Proteins in Schizosaccharomyces pombe

To screen molecular chaperones similar to small heat shock proteins (sHsps), but without α-crystalline domain, heat-stable proteins from Schizosaccharomyces pombe were analyzed by 2-dimensional electrophoresis and matrix assisted laser desorption/ionization time-of-flight mass spectrometry. Sixteen proteins were identified, and four recombinant proteins, including cofilin, NTF2, pyridoxin biosynthesis protein (Snz1) and Wos2 that has an α-crystalline domain, were purified. Among these proteins, only Snz1 showed the anti-aggregation activity against thermal denaturation of citrate synthase. However, pre-heating of NTF2 and Wos2 at 70℃ for 30 min, efficiently prevented thermal aggregation of citrate synthase. These results indicate that Snz1 and NTF2 possess molecular chaperone activity similar to sHsps, even though there is no α-crystalline domain in their sequences.

Enhanced pathway efficiency of Saccharomyces cerevisiae by introducing thermo-tolerant devices

In this study, thermo-tolerant devices consisting of heat shock genes from thermophiles were designed and introduced into Saccharomyces cerevisiae for improving its thermo-tolerance. Among ten engineered thermo-tolerant yeasts, T.te-TTE2469, T.te-GroS2 and T.te-IbpA displayed over 25% increased cell density and 1.5-4-fold cell viability compared with the control. Physiological characteristics of thermo-tolerant strains revealed that better cell wall integrity, higher trehalose content and enhanced metabolic energy were preserved by thermo-tolerant devices. Engineered thermo-tolerant strain was used to investigate the impact of thermo-tolerant device on pathway efficiency by introducing β-amyrin synthesis pathway, showed 28.1% increased β-amyrin titer, 28-35°C broadened growth temperature range and 72h shortened fermentation period. The results indicated that implanting heat shock proteins from thermophiles to S. cerevisiae would be an efficient approach to improve its thermo-tolerance.

Development of episomal vectors carrying a nourseothricin-resistance marker for use in minimal media for Schizosaccharomyces pombe

In the post-genomic era, an immediate challenge is to assign biological functions to novel proteins encoded by the genome. This challenge requires the use of a simple organism as a genetic tool and a range of new high-throughput techniques. Schizosacchromyces pombe is a powerful model organism used to investigate disease-related genes and provides useful tools for the functional analysis of heterologous genes. To expand the current array of experimental tools, we constructed two series of Sz. pombe expression vectors, i.e. general and Gateway vectors, containing nourseothricin-resistance markers. Vectors carrying nourseothricin-resistance markers possess advantages in that they do not limit the parental strains with auxotrophic mutations with respect to availability for use in clone selection and can be used together with vectors carrying nutrient markers in minimal media. We modified the pSLF173, pSLF273 and pSLF373 vectors carrying a triple haemagglutinin epitope (3×HA) and an Ura4 marker. The vectors described here contain the nmt1 promoter with three different episomal expression strengths for proteins fused with 3×HA, EGFP or DsRed at the N-terminus. These vectors represent an important contribution to the genome-wide investigation of multiple heterologous genes and for functional and genetic analysis of novel human genes.