General control nonderepressible 4 activates the transcription of trehalose phosphorylase to improve trehalose production and abiotic stress tolerance in Ganoderma lucidum

Trehalose plays an important role in enhancing abiotic stress tolerance. Although studies have reported the induction of trehalose by adverse environments, the molecular mechanism underlying its induction in fungi is unclear. In fungi, the trehalose phosphorylase (TreP) catalyzes the reversible reaction of trehalose formation. Here, we found that the carbon and nitrogen metabolism integrated transcription factor, general control nonderepressible 4 (GCN4) directly binds to the promoter of TreP in Ganoderma lucidum. GCN4 up-regulates the transcription and protein levels of TreP, leading to enhanced trehalose synthase activity and trehalose accumulation. A reduced abundance of GCN4 alleviated the low-nitrogen induced increase in Trep and trehalose contents. As a result, knockdown of both GCN4 and TreP leads to a reduction in the trehalose content and growth inhibition of mycelia, especially under low-nitrogen conditions. Furthermore, in addition to nitrogen deficiency, both high temperature and drought treatments increase the transcription and protein levels of GCN4 and TreP. The GCN4 or TreP knockdown strains are hypersensitive to heat stress and drought, while exogenous trehalose treatment enhances the mycelial growth under stressful conditions. Together, our results revealed that the GCN4-TreP module promotes trehalose accumulation in response to abiotic stresses to improve the stress tolerance of G. lucidum, and highlighted the pivotal role of GCN4 in integrating metabolic adaptation to environmental stresses.

Genomic evidence of symbiotic adaptations in fungus-associated bacteria

Fungi harbor diverse bacteria that engage in various relationships. While these relationships potentially influence fungal functioning, their underlying genetic mechanisms remain unexplored. Here, we aimed to elucidate the key genomic features of fungus-associated bacteria (FaB) by comparing 163 FaB genomes to 1,048 bacterial genomes from other hosts and habitats. Our analyses revealed several distinctive genomic features of FaB. We found that FaB are enriched in carbohydrate transport/metabolism- and motility-related genes, suggesting an adaptation for utilizing complex fungal carbon sources. They are also enriched in genes targeting fungal biomass, likely reflecting their role in recycling and rebuilding fungal structures. Additionally, FaB associated with plant-mutualistic fungi possess a wider array of carbon-acquisition enzymes specific to fungal and plant substrates compared to those residing with saprotrophic fungi. These unique genomic features highlight FaB' potential as key players in fungal nutrient acquisition and decomposition, ultimately influencing plant-fungal symbiosis and ecosystem functioning.

Lessons on fruiting body morphogenesis from genomes and transcriptomes of Agaricomycetes

Fruiting bodies (sporocarps, sporophores or basidiomata) of mushroom-forming fungi (Agaricomycetes) are among the most complex structures produced by fungi. Unlike vegetative hyphae, fruiting bodies grow determinately and follow a genetically encoded developmental program that orchestrates their growth, tissue differentiation and sexual sporulation. In spite of more than a century of research, our understanding of the molecular details of fruiting body morphogenesis is still limited and a general synthesis on the genetics of this complex process is lacking. In this paper, we aim at a comprehensive identification of conserved genes related to fruiting body morphogenesis and distil novel functional hypotheses for functionally poorly characterised ones. As a result of this analysis, we report 921 conserved developmentally expressed gene families, only a few dozens of which have previously been reported to be involved in fruiting body development. Based on literature data, conserved expression patterns and functional annotations, we provide hypotheses on the potential role of these gene families in fruiting body development, yielding the most complete description of molecular processes in fruiting body morphogenesis to date. We discuss genes related to the initiation of fruiting, differentiation, growth, cell surface and cell wall, defence, transcriptional regulation as well as signal transduction. Based on these data we derive a general model of fruiting body development, which includes an early, proliferative phase that is mostly concerned with laying out the mushroom body plan (via cell division and differentiation), and a second phase of growth via cell expansion as well as meiotic events and sporulation. Altogether, our discussions cover 1 480 genes of Coprinopsis cinerea, and their orthologs in Agaricus bisporus, Cyclocybe aegerita, Armillaria ostoyae, Auriculariopsis ampla, Laccaria bicolor, Lentinula edodes, Lentinus tigrinus, Mycena kentingensis, Phanerochaete chrysosporium, Pleurotus ostreatus, and Schizophyllum commune, providing functional hypotheses for ~10 % of genes in the genomes of these species. Although experimental evidence for the role of these genes will need to be established in the future, our data provide a roadmap for guiding functional analyses of fruiting related genes in the Agaricomycetes. We anticipate that the gene compendium presented here, combined with developments in functional genomics approaches will contribute to uncovering the genetic bases of one of the most spectacular multicellular developmental processes in fungi. Citation: Nagy LG, Vonk PJ, Künzler M, Földi C, Virágh M, Ohm RA, Hennicke F, Bálint B, Csernetics Á, Hegedüs B, Hou Z, Liu XB, Nan S, M. Pareek M, Sahu N, Szathmári B, Varga T, Wu W, Yang X, Merényi Z (2023). Lessons on fruiting body morphogenesis from genomes and transcriptomes of Agaricomycetes. Studies in Mycology 104: 1-85. doi: 10.3114/sim.2022.104.01.

Heat stress in macrofungi: effects and response mechanisms

Temperature is one of the key factors that affects the growth and development of macrofungi. Heat stress not only negatively affects the morphology and growth rate of macrofungi, but also destroys cell structures and influences cell metabolism. Due to loosed structure of cell walls and increased membrane fluidity, which caused by heat stress, the outflow of intracellular nutrients makes macrofungi more vulnerable to invasion by pathogens. Macrofungi accumulate reactive oxygen species (ROS), Ca²⁺, and nitric oxide (NO) when heat-stressed, which transmit and amplify the heat stimulation signal through intracellular signal transduction pathways. Through regulation of some transcription factors including heat response factors (HSFs), POZCP26 and MYB, macrofungi respond to heat stress by different mechanisms. In this paper, we present mechanisms used by macrofungi to adapt and survive under heat stress conditions, including antioxidant defense systems that eliminate the excess ROS, increase in trehalose levels that prevent enzymes and proteins deformation, and stabilize cell structures and heat shock proteins (HSPs) that repair damaged proteins and synthesis of auxins, which increase the activity of antioxidant enzymes. All of these help macrofungi resist and adapt to heat stress. KEY POINTS: • The effects of heat stress on macrofungal growth and development were described. • The respond mechanisms to heat stress in macrofungi were summarized. • The further research directions of heat stress in macrofungi were discussed.

Label-Free Comparative Proteomics Analysis Revealed Heat Stress Responsive Mechanism in Hypsizygus marmoreus

Heat stress is an important adverse environmental stress that influences the growth and development of Hypsizygus marmoreus (white var.). However, the molecular basis of heat stress response in H. marmoreus remains poorly understood. In this study, label-free comparative proteomic technique was applied to investigate global protein expression profile of H. marmoreus mycelia under heat stress. Confocal laser scanning microscope observation revealed that mycelia underwent autolysis and apoptosis under heat stress. Autolysis was mediated by upregulating the expression of cell wall degradation enzymes and inhibiting cell wall synthesis enzymes, and apoptosis might be induced by ROS and activation of caspases. TBARS analysis indicated that ROS was accumulated in H. marmoreus mycelia under heat stress. H. marmoreus induced antioxidant defense system by upregulating the expression of catalases, superoxide dismutases and peroxidases to prevent oxidative damage. MAPK cascade was found to be involved in heat stress signal transduction. The stress signal induced a ubiquitous defense response: inducible expression of different kinds of heat shock proteins. Trehalose synthesis enzymes were also upregulated, suggesting the accumulation of stress protector trehalose under heat stress. Besides, upregulated proteasome was identified, which could prevented the accumulation of non-functional misfolding proteins. To satisfy ATP depletion in heat response cellular processes, such as ROS scavenging, and protein folding and synthesis, enzymes involved in energy production (carbon metabolism and ATP synthesis) system were upregulated under heat stress. Taken together, these findings improve our understanding of the molecular mechanisms underlying the response of heat stress in H. marmoreus.

Antimicrobial activity, chemical composition and cytotoxicity of Lentinus crinitus basidiocarp

Lentinus crinitus (L.) Fr. (Basidiomycota: Polyporales) is a wild mushroom with several biotechnological applications; however, there are few studies on its chemical composition and antimicrobial activity. Therefore, this study aims to evaluate the chemical composition, cytotoxicity, and antimicrobial activity of L. crinitus basidiocarp. For that, its nutritional value (AOAC procedures) and its composition in some hydrophilic and lipophilic compounds (chromatographic techniques) were assessed. Moreover, the potential hepatotoxic effects were evaluated using a primary cell culture obtained from porcine liver, and its growth inhibitory capacity was also evaluated against four human tumour cell lines (spectrophotometric assays). The antimicrobial activity was evaluated by microdilution against eight bacteria and fungi. The basidiocarp has a high content of carbohydrates and, therefore, a relatively high energetic value. It is also rich in soluble sugars, β-tocopherol, phenolic acids, mainly p-hydroxybenzoic acid, and organic acids, mainly malic acid. L. crinitus did not show cytotoxicity in non-tumour cells, but it did not inhibit the growth of human tumour cell lines either. The basidiocarp has a wide antimicrobial activity, inhibiting the growth of different species of bacteria and fungi. It showed minimum bactericidal and fungicidal concentration values similar to or lower than those verified by commercial antibiotics or food additives used as preservatives. The antimicrobial activity was more evident against Listeria monocytogenes, Salmonella enterica, and Penicillium ochrochloron, followed by Aspergillus ochraceus and Trichoderma viride, when compared to the controls. The results obtained in this study showed that L. crinitus basidiocarp has great potential to be used by the industry without toxicity risks.

Heat shock protein 70 (HmHsp70) from Hypsizygus marmoreus confers thermotolerance to tobacco

The 70-kD heat shock proteins (Hsp70s) have been proved to be important for stress tolerance and protein folding and unfolding in almost all organisms. However, the functions of Hsp70s in mushroom are not well understood. In the present study, a hsp70 gene from Hypsizygus marmoreus, hmhsp70, was cloned and transferred to tobacco (Nicotiana tabacum) to evaluate its function in thermotolerance. Sequence alignments and phylogenetic analysis revealed that HmHsp70 may be located in the mitochondria region. qPCR analysis revealed that the transcription level of hmhsp70 in H. marmoreus mycelia increased after heat shock treatment in high temperature (42 °C) compared with untreated mycelia (at 25 °C). Transgenic tobaccos expressing hmhsp70 gene showed enhanced resistance to lethal temperature compared with the wild type (WT) plants. Nearly 30% of the transgenic tobaccos survived after treated at a high temperature (50 °C and 52 °C for 4 h); however, almost all the WT tobaccos died after treated at 50 °C and no WT tobacco survived after heat shock at 52 °C. This study firstly showed the function of a hsp70 gene from H. marmoreus.

Glucose Utilization in the Regulation of Chitin Synthesis in Brown Planthopper

Glucose-6-phosphatase (G6Pase) and hexokinase (HK) are two key enzymes in the glycolysis and gluconeogenesis pathways, which catalyze the synthesis and degradation of glucose in insects, respectively. G6Pase and HK play an important role in insect growth by regulating the metabolism of glucose, leading to the efficient metabolism of other macromolecules. However, it is unclear whether these genes could be investigated for pest control through their actions on chitin metabolism. We studied the potential functions of G6Pase and HK genes in the regulation of chitin metabolism pathways by RNAi technology. Interference with G6Pase expression did not affect trehalose and chitin metabolism pathways in brown planthopper, Nilaparvata lugens (Stål). However, knockdown of the HK gene resulted in a significant decrease of expression of genes associated with the trehalose metabolic pathway but had no significant effect on trehalase activity, trehalose content, or glucogen content. Additionally, HK knockdown resulting in downregulation of the genes involved in chitin metabolism in the brown planthopper. These insects also showed wing deformities and difficulty in molting to varying degrees. We suggest that the silencing of HK expression directly inhibited the decomposition of glucose, leading to impaired chitin synthesis.

MAL62 Overexpression Enhances Freezing Tolerance of Baker's Yeast in Lean Dough by Enhancing Tps1 Activity and Maltose Metabolism

Trehalose plays a crucial role in response to freezing stress in baker's yeast. MAL62, a gene involved in the adenosine diphosphoglucose-dependent trehalose synthesis pathway, can increase trehalose content. However, the difference between MAL62-related trehalose synthesis and traditional uridine diphosphoglucose-dependent trehalose synthesis is not well-understood. MAL62 overexpression showed less effect in enhancing intracellular trehalose compared to TPS1 overexpression. However, MAL62 overexpression elicited trehalose synthesis before fermentation with enhanced maltose metabolism and had a similar effect on cell viability after freezing. Furthermore, MAL62 and TPS1 overexpression in the NTH1 deletion background further strengthened freezing tolerance and improved leavening ability. Our results suggest that the enhancement in freezing tolerance by MAL62 overexpression may involve multiple pathways rather than simply enhancing trehalose synthesis. The results reveal valuable insights into the relationship between maltose metabolism and freezing tolerance and may help to develop better yeast strains for enhancing fermentation characteristics of frozen dough.

Trehalose induced by reactive oxygen species relieved the radial growth defects of Pleurotus ostreatus under heat stress

Trehalose is a nonreducing disaccharide, and it plays an intracellular protective role in organisms under various stress conditions. In this study, the trehalose synthesis and its protective role in Pleurotus ostreatus were investigated. As a signal in metabolic regulation, reactive oxygen species (ROS) accumulated in the mycelia of P. ostreatus under heat stress (HS). Furthermore, mycelial growth was significantly inhibited, and the malondialdehyde (MDA) level significantly increased under HS. First, exogenous addition of H₂O₂ inhibited mycelial growth and elevated the MDA level, while N-acetyl cysteine (NAC) and vitamin C (VC) reduced the MDA level and recovered mycelial growth under HS by scavenging ROS. These results indicated that the mycelial radial growth defect under HS might be partly caused by ROS accumulation. Second, adding NAC and VC to the media resulted in rescued trehalose accumulation, which indicated that ROS has an effect on inducing trehalose synthesis. Third, the mycelial growth was recovered by addition of trehalose to the media after HS, and the MDA level was reduced. This effect was further verified by the overexpression of genes for trehalose-6-phosphate synthase (TPS) and neutral trehalase (NTH), which led to increased and reduced trehalose content, respectively. In addition, adding validamycin A (NTH inhibitor) to the media promoted trehalose accumulation and the recovered mycelial growth after HS. In conclusion, trehalose production was partly induced by ROS accumulation in the mycelia under HS, and the accumulated trehalose could promote the recovery of growth after HS, partly by reducing the MDA level in the mycelia.

Involvement of trehalose-6-phosphate synthase in innate immunity of Musca domestica

Trehalose-6-phosphate synthase (TPS) is responsible for synthesizing trehalose, which is prevalent in crustaceans and insects as blood-sugar. In this paper, a TPS gene from Musca domestica(MdTPS)has been cloned and characterized. MdTPS promoter was analyzed, and its transcriptional activity was verified in vitro by Sf9 cell. Quantitative RT-PCR analysis revealed that the MdTPS transcription was up-regulated following bacterial challenge by Escherichia coli or Staphylococcus aureus. Meanwhile, trehalose is accumulated in larvae upon bacterial challenge. Significantly increased mortality can be observed in MdTPS depleted (RNA interference, RNAi) larvae under bacterial infection. Interestingly, feeding trehalose led to increasing trehalose content in larvae, and the effects of RNAi targeting MdTPS on host survival against bacterial challenge was partly counteracted. Taken together, these results suggest that MdTPS acts as an inducible anti-stress gene that takes part in immune defense in M. domestica via synthesizing its product trehalose.

Gene expression related to trehalose metabolism and its effect on Volvariella volvacea under low temperature stress

The mechanism of the low temperature autolysis of Volvariella volvacea (V. volvacea) has not been thoroughly explained, and trehalose is one of the most important osmolytes in the resistance of fungi to adversity. The present study used the low temperature sensitive V. volvacea strain V23 and the low temperature tolerant strain VH3 as test materials. Intracellular trehalose contents under low temperature stress in the two strains were measured by high performance liquid chromatography (HPLC). Quantitative real-time PCR (qPCR) analysis was carried out to study the transcriptional expression differences of enzymes related to trehalose metabolism. And trehalose solution was exogenously added during the cultivation of fruit bodies of V. volvacea. The effect of exogenous trehalose solution on the anti-hypothermia of fruit bodies was studied by evaluating the sensory changes under low temperature storage after harvest. The results showed that the intracellular trehalose content in VH3 was higher than that in V23 under low temperature stress. In the first 2 h of low temperature stress, the expression of trehalose-6-phosphate phosphatase (TPP) gene involved in trehalose synthesis decreased, while the expression of trehalose phosphorylase (TP) gene increased. The expression of TPP gene was almost unchanged in VH3, but it decreased dramatically in V23 at 4 h of low temperature stress. The expression levels of TPP and TP genes in VH3 was significantly higher than that in V23 from 6 h to 8 h of low temperature stress. TP gene may be a crucial gene of trehalose metabolism, which was more inclined to synthesize trehalose during low temperature stress. In addition, the sensory traits of V. volvacea fruit bodies stored at 4 °C were significantly improved by the application of exogenous trehalose compared with the controls. Thus, trehalose could help V. volvacea in response to low temperature stress and high content of it may be one of the reasons that why VH3 strain was more tolerant to the low temperature stress than V23 strain.

Genome-Wide Characterization and Expression Analyses of Pleurotus ostreatus MYB Transcription Factors during Developmental Stages and under Heat Stress Based on de novo Sequenced Genome

Pleurotus ostreatus is a commercially grown mushroom species in China. However, studies on the mechanisms of the fruiting body development and stress response of P. ostreatus are still at a primary stage. In this study, we report the entire genome sequence of P. ostreatus CCMSSC03989. Then, we performed comprehensive genome-wide characterization and expression analysis of the MYB transcription factor family during a series of developmental stages and under the condition of heat stress. A 34.76 Mb genome was obtained through next-generation sequencing (NGS) and Bionano optical mapping approaches. The genome has a scaffold N50 of 1.1 Mb and contains 10.11% repeats, and 10,936 gene models were predicted. A total of 20 MYB genes (PoMYB) were identified across the genome, and the full-length open reading frames were isolated. The PoMYBs were classified into 1 repeat (1R), 2R, and 3R-MYB groups according to their MYB domain repeat numbers, and 3R-MYBs possessed relatively more introns than 1R and 2R-MYBs. Based on phylogenetic analysis, the PoMYBs were divided into four groups and showed close relationships with the MYB genes of plants and fungi. RNA-sequencing (RNA-Seq) and quantitative PCR (qPCR) analyses revealed that PoMYB expression showed stage-specific patterns in reproductive stages and could be induced by heat stress. The P. ostreatus draft genome will promote genome-wide analysis, and our study of PoMYBs will promote further functional analysis of MYB genes in mushrooms.

Trehalose Contributes to Gamma-Linolenic Acid Accumulation in Cunninghamella echinulata Based on de Novo Transcriptomic and Lipidomic Analyses

Gamma-linolenic acid (GLA) is essential for the well-being of humans and other animals. People may lack GLA because of aging or diseases, and thus, dietary supplements or medical reagents containing GLA-enriched lipids are in demand. Cunninghamella echinulata is a potential GLA-producing strain. Interestingly, we found that the GLA content of C. echinulata FR3 was up to 21% (proportion of total lipids) when trehalose was used as a carbon source, significantly higher than the 13% found when glucose was used. Trehalose is quite common and can be accumulated in microorganisms under stress conditions. However, little information is available regarding the role of trehalose in GLA synthesis and accumulation. Our study aimed to understand how the metabolism of C. echinulata responds to trehalose as a carbon source for GLA and lipid biosynthesis. We profiled the major sugars, fatty acids, phospholipids, and gene transcripts of C. echinulata FR3 grown in trehalose medium with glucose as a control by de novo transcriptomics, lipidomics, and other methods. The results showed that trehalose could influence the expression of desaturases and that the GLA proportion increased because of delta-6 desaturase upregulation. The increased GLA was transferred to the extracellular environment through the active PI ion channel, which prefers polyunsaturated acyl chains. At the same time, trehalose might prevent GLA from peroxidation by forming a trehalose-polyunsaturated fatty acid (PUFA) complex. Our study provides new insights into the functions of trehalose in GLA accumulation.

Invertebrate Trehalose-6-Phosphate Synthase Gene: Genetic Architecture, Biochemistry, Physiological Function, and Potential Applications

The non-reducing disaccharide trehalose is widely distributed among various organisms. It plays a crucial role as an instant source of energy, being the major blood sugar in insects. In addition, it helps countering abiotic stresses. Trehalose synthesis in insects and other invertebrates is thought to occur via the trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) pathways. In many insects, the TPP gene has not been identified, whereas multiple TPS genes that encode proteins harboring TPS/OtsA and TPP/OtsB conserved domains have been found and cloned in the same species. The function of the TPS gene in insects and other invertebrates has not been reviewed in depth, and the available information is quite fragmented. The present review discusses the current understanding of the trehalose synthesis pathway, TPS genetic architecture, biochemistry, physiological function, and potential sensitivity to insecticides. We note the variability in the number of TPS genes in different invertebrate species, consider whether trehalose synthesis may rely only on the TPS gene, and discuss the results of in vitro TPS overexpression experiment. Tissue expression profile and developmental characteristics of the TPS gene indicate that it is important in energy production, growth and development, metamorphosis, stress recovery, chitin synthesis, insect flight, and other biological processes. We highlight the molecular and biochemical properties of insect TPS that make it a suitable target of potential pest control inhibitors. The application of trehalose synthesis inhibitors is a promising direction in insect pest control because vertebrates do not synthesize trehalose; therefore, TPS inhibitors would be relatively safe for humans and higher animals, making them ideal insecticidal agents without off-target effects.

Gene cloning, expression, and characterization of trehalose-6-phosphate synthase from Pleurotus ostreatus

Trehalose-6-phosphate synthase (TPS; EC2.4.1.15) catalyzes the first step in trehalose synthesis, which involves transfer of glucose from uridine diphosphate glucose (UDPG) to glucose 6-phosphate (G6P) to form trehalose-6-phosphate. To determine the gene and enzymatic characteristics of TPS in Pleurotus ostreatus, we cloned and sequenced the cDNA of PoTPS1, which contains a 1665 bp open reading frame that encodes a 554-amino acid protein with a predicted molecular weight of 62.01 kDa. This gene was expressed in Escherichia coli BL21 and then the recombinant protein was purified and characterized. Results showed that the optimum pH and temperature for the recombinant PoTPS1 were 7.4 and 30 °C, respectively; the K_m value against G6P and UDPG were 0.14 and 0.17 mM, respectively, and the V_max and K_cat values were 91.86 nkat/g and 5.89 s^-1 , respectively. Trehalose content was as high as 158.88 mg g^-1 dry weight after heat treatment at 40 °C for 15 h, which was consistent with highest TPS1 activity at that time point. This result indicated that PoTPS1 was responsible for trehalose synthesis in P. ostreatus.