Hydrogen-rich water mediates redox regulation of the antioxidant system, mycelial regeneration and fruiting body development in Hypsizygus marmoreus

Low-Molecular-Weight Peptides Prepared from Hypsizygus marmoreus Exhibit Strong Antioxidant and Antibacterial Activities

Hypsizygus marmoreus has abundant proteins and is a potential source for the development of bioactive peptides. However, currently, the research on the bioactive components of H. marmoreus mainly focuses on polysaccharides, and there is no relevant research on the preparation of bioactive peptides. In this article, an ultrasound-assisted extraction method was used to extract proteins from H. marmoreus, and then, four peptides with different molecular weight ranges were prepared through protease hydrolysis and molecular classification. The antioxidant and antibacterial activities were also studied. Under the optimal conditions, the extraction rate of H. marmoreus proteins was 53.6%. Trypsin exhibited the highest hydrolysis rate of H. marmoreus proteins. The optimal parameters for enzymatic hydrolysis were a substrate concentration of 3.7%, enzyme addition of 5700 U/g, pH value of 7, extraction temperature of 55 °C, and time of 3.3 h. Under these conditions, the peptide yield was 59.7%. The four types of H. marmoreus peptides were prepared by molecular weight grading. Among them, peptides with low molecular weight (<1 kDa) had stronger antioxidant and antibacterial activities. This study provides a theoretical basis for the efficient preparation of H. marmoreus peptides and the development of antioxidant and antibacterial peptide products.

Potential of silicon-rich biochar (Sichar) amendment to control crop pests and pathogens in agroecosystems: A review

We reviewed the potential of silicon (Si)-rich biochars (sichars) as crop amendments for pest and pathogen control. The main pathosystems that emerged from our systematic literature search were bacterial wilt on solanaceous crops (mainly tomato, pepper, tobacco and eggplant), piercing-sucking hemipteran pests and soil-borne fungi on gramineous crops (mainly rice and wheat), and parasitic nematodes on other crops. The major pest and pathogen mitigation pathways identified were: i) Si-based physical barriers; ii) Induction of plant defenses; iii) Enhancement of plant-beneficial/pathogen-antagonistic soil microflora in the case of root nematodes; iv) Alteration of soil physical-chemical properties resulting in Eh-pH conditions unfavorable to root nematodes; v) Alteration of soil physical-chemical properties resulting in Eh-pH, bulk density and/or water holding capacity favorable to plant growth and resulting tolerance to necrotrophic pathogens; vi) Increased Si uptake resulting in reduced plant quality, owing to reduced nitrogen intake towards some hemi-biotrophic pests or pathogens. Our review highlighted synergies between pathways and tradeoffs between others, depending, inter alia, on: i) crop type (notably whether Si-accumulating or not); ii) pest/pathogen type (e.g. below-ground/root-damaging vs above-ground/aerial part-damaging; "biotrophic" vs "necrotrophic" sensu lato, and corresponding systemic resistance pathways; thriving Eh-pH spectrum; etc.); iii) soil type. Our review also stressed the need for further research on: i) the contribution of Si and other physical-chemical characteristics of biochars (including potential antagonistic effects); ii) the pyrolysis process to a) optimize Si availability in the soil and its uptake by the crop and b) to minimize formation of harmful compounds e.g. cristobalite; iii) on the optimal form of biochar, e.g. Si-nano particles on the surface of the biochar, micron-sized biochar-based compound fertilizer vs larger biochar porous matrices.

Comparative transcriptome analysis on candidate genes associated with fruiting body growth and development in Lyophyllum decastes

Lyophyllum decastes is a mushroom that is highly regarded for its culinary and medicinal properties. Its delectable taste and texture make it a popular choice for consumption. To gain a deeper understanding of the molecular mechanisms involved in the development of the fruiting body of L. decastes, we used RNA sequencing to conduct a comparative transcriptome analysis. The analysis encompassed various developmental stages, including the vegetative mycelium, primordial initiation, young fruiting body, medium-size fruiting body, and mature fruiting body stages. A range of 40.1 to 60.6 million clean reads were obtained, and de novo assembly generated 15,451 unigenes with an average length of 1,462.68 bp. Functional annotation of transcriptomes matched 76.84% of the unigenes to known proteins available in at least one database. The gene expression analysis revealed a significant number of differentially expressed genes (DEGs) between each stage. These genes were annotated and subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses. Highly differentially expressed unigenes were also identified, including those that encode extracellular enzymes, transcription factors, and signaling pathways. The accuracy of the RNA-Seq and DEG analyses was validated using quantitative PCR. Enzyme activity analysis experiments demonstrated that the extracellular enzymes exhibited significant differences across different developmental stages. This study provides valuable insights into the molecular mechanisms that underlie the development of the fruiting body in L. decastes.

Successive mycelial subculturing decreased lignocellulase activity and increased ROS accumulation in Volvariella volvacea

Strain degradation is a common problem in many artificially-cultivated edible mushrooms. As a fungus with poor tolerance to low-temperature, Volvariella volvacea cannot delay its degradation by long-term low temperature storage like other fungi, so its degradation is particularly severe, which hinders industrial applications. Periodic mycelial subculture is a common storage method for V. volvacea, but excessive subculturing can also lead to strain degeneration. After 20 months of continuous subculturing every 3 days, V. volvacea strains S1–S20 were obtained, and their characteristics throughout the subculture process were analyzed. With increasing number of subculture, the growth rate, mycelial biomass, the number of fruiting bodies and biological efficiency gradually decreased while the production cycle and the time to primordium formation was lengthened. Strains S13–S20, obtained after 13–20 months of mycelial subculturing, also lacked the ability to produce fruiting bodies during cultivation experiments. Determination of reactive oxygen species (ROS) content as well as enzyme activity showed that decreased lignocellulase activity, along with excessive accumulation of ROS, was concomitant with the subculture-associated degeneration of V. volvacea. Reverse transcription polymerase chain reaction (RT-PCR) was eventually used to analyze the gene expression for lignocellulase and antioxidant enzymes in subcultured V. volvacea strains, with the results found to be consistent with prior observations regarding enzyme activities. These findings could form the basis of further studies on the degeneration mechanism of V. volvacea and other fungi.

Identification and profiling of the community structure and potential function of bacteria from the fruiting bodies of Sanghuangporus vaninii

Sanghuangporus sp., a medicinal and edible homologous macrofungus known as 'forest gold', which has good effects on antitumor, hypolipidemia and the treatment of gynecological diseases. However, the natural resources of fruiting body are on the verge of depletion due to its long growth cycle and over exploitation. The growth and metabolism of macrofungi are known to depend on the diverse bacterial community. Here, we characterized the diversity and potential function of bacteria inhabiting in the fruiting body of the most widely applied S. vaninii using a combination method of high-throughput sequencing with pure culturing for the first time, and tested the biological activities of bacterial isolates, of which Illumina NovaSeq provided a more comprehensive results on the bacterial community structure. Total 33 phyla, 82 classes, 195 orders, 355 families, 601 genera and 679 species were identified in the fruiting body, and our results revealed that the community was predominated by the common Proteobacteria, Gammaproteobacteria, Burkholderiales, Methylophilaceae (partly consistent with pure-culturing findings), and was dominated by the genera of distinctive Methylotenera and Methylomonas (yet-uncultured taxa). Simultaneously, the functional analysis showed that companion bacteria were involved in the pathways of carbohydrate transport and metabolism, metabolism of terpenoids and polyketides, cell wall/membrane/envelope biogenesis, etc. Hence, it was inferred that bacteria associated with fruiting body may have the potential to adjust the growth, development and active metabolite production of host S. vaninii combined with the tested results of indole-3-acetic acid and total antioxidant capacity. Altogether, this report first provided new findings which can be inspiring for further in-depth studies to exploit bioactive microbial resources for increased production of Sanghuangporus, as well as to explore the relationship between medicinal macrofungi and their associated endophytes.

Transcriptomic analysis of Stropharia rugosoannulata reveals carbohydrate metabolism and cold resistance mechanisms under low-temperature stress

Low temperature is an important environmental factor that restricts the growth of Stropharia rugosoannulata; however, the molecular mechanisms underlying S. rugosoannulata responses to low-temperature stress are largely unknown. In this study, we performed a transcriptome analysis of a high-sensitivity strain (DQ-1) and low-sensitivity strain (DQ-3) under low-temperature stress. The liquid hyphae of S. rugosoannulata treated at 25 °C and 10 °C were analyzed by RNA-Seq, and a total of 9499 differentially expressed genes (DEGs) were identified. GO and KEGG enrichment analyses showed that these genes were enriched in "xenobiotic biodegradation and metabolism", "carbohydrate metabolism", "lipid metabolism" and "oxidoreductase activity". Further research found that carbohydrate enzyme (AA, GH, CE, and GT) genes were downregulated more significantly in DQ-1 than DQ-3 and several cellulase activities were also reduced to a greater extent. Moreover, the CAT1, CAT2, GR, and POD genes and more heat shock protein genes (HSP20, HSP78 and sHSP) were upregulated in the two strains after low-temperature stress, and the GPX gene and more heat shock protein genes were upregulated in DQ-3. In addition, the enzyme activity and qRT-PCR results showed trends similar to those of the RNA-Seq results. This result indicates that low-temperature stress reduces the expression of different AA, GH, CE, and GT enzyme genes and reduces the secretion of cellulase, thereby reducing the carbohydrate metabolism process and mycelial growth of S. rugosoannulata. Moreover, the expression levels of different types of antioxidant enzymes and heat shock proteins are also crucial for S. rugosoannulata to resist low-temperature stress. In short, this study will provide a basis for further research on important signaling pathways, gene functions and variety breeding of S. rugosoannulata related to low-temperature stress.

The Importance of Nitric Oxide as the Molecular Basis of the Hydrogen Gas Fumigation-Induced Alleviation of Cd Stress on Ganoderma lucidum

Whether or not hydrogen gas (H₂) can reduce cadmium (Cd) toxicity in Ganoderma lucidum has remained largely unknown. Here, we report that Cd-induced growth inhibition in G. lucidum was significantly alleviated by H₂ fumigation or hydrogen-rich water (HRW), evaluated by lower oxidative damage and Cd accumulation. Moreover, the amelioration effects of H₂ fumigation were better than of HRW in an optimum concentration of H₂ under our experimental conditions. Further results showed that H₂-alleviated growth inhibition in G. lucidum was accompanied by increased nitric oxide (NO) level and nitrate reductase (NR) activity under Cd stress. On the other hand, the mitigation effects were reversed after removing endogenous NO with its scavenger cPTIO or inhibiting H₂-induced NR activity with sodium tungstate. The role of NO in H₂-alleviated growth inhibition under Cd stress was proved to be achieved through a restoration of redox balance, an increase in cysteine and proline contents, and a reduction in Cd accumulation. In summary, these results clearly revealed that NR-dependent NO might be involved in the H₂-alleviated Cd toxicity in G. lucidum through rebuilding redox homeostasis, increasing cysteine and proline levels, and reducing Cd accumulation. These findings may open a new window for H₂ application in Cd-stressed economically important fungi.

Genetic and functional analysis of the Zn(II)2Cys6 transcription factor HADA-1 in Hypsizygus marmoreus

Zn(II)₂Cys₆ transcription factors are critical for the reproductive growth and sexual development of fungi, but their roles in Basidiomycota remain unclear. In this study, the Hypsizygus marmoreus gene hada-1 was shown to encode a Zn(II)₂Cys₆ transcription factor, the growth rate of mycelia was decreased, hyphae were angulated, and fruiting body development was hindered in the hada-1-silenced strains. In addition, mitochondrial stability was lost, and the mitochondria morphologies changed from oval shaped to dumbbell or linear shaped in the silenced strains. Regarding mitochondrial instability, the mitochondrial complex II, III, and V activities and adenosine triphosphate content were significantly decreased. At the same time, the activities of the carbohydrate metabolism-related enzymes glucose-6-plosphatase, glucose dehydrogenase, and laccase were significantly decreased, which might have resulted in the reduction of carbon metabolism. Furthermore, hada-1 was shown to regulate the reactive oxygen species (ROS) level; compared with the wild-type (WT) strain, the silenced mycelia exhibited higher ROS contents and were more sensitive to oxidative stress. Taken together, these results indicate that, as a global regulator, hada-1 plays crucial roles in mycelial growth, fruiting body development, carbon metabolism, mitochondrial stability, and oxidative stress in the basidiomycete H. marmoreus. KEY POINTS: • Zn(II)₂Cys₆ transcription factor, mitochondrial stability, fruiting body development.

The functions of glutathione peroxidase in ROS homeostasis and fruiting body development in Hypsizygus marmoreus

Glutathione peroxidase (GPX) is one of the most important antioxidant enzymes for maintaining reactive oxygen species (ROS) homeostasis. Although studies on fungi have suggested many important physiological functions of GPX, few studies have examined the role of this enzyme in Basidiomycetes, particularly its functions in fruiting body developmental processes. In the present study, GPX-silenced (GPxi) strains were obtained by using RNA interference. The GPxi strains of Hypsizygus marmoreus showed defects in mycelial growth and fruiting body development. In addition, the results indicated essential roles of GPX in controlling ROS homeostasis by regulating intracellular H₂O₂ levels, maintaining GSH/GSSG balance, and promoting antioxidant enzyme activity. Furthermore, lignocellulose enzyme activity levels were reduced and the mitochondrial phenotype and mitochondrial complex activity levels were changed in the H. marmoreus GPxi strains, possibly in response to impediments to mycelial growth and fruiting body development. These findings indicate that ROS homeostasis has a complex influence on growth, fruiting body development, GSH/GSSG balance, and carbon metabolism in H. marmoreus.Key points• ROS balance, energy metabolism, fruiting development.

Exogenous l-ascorbic acid regulates the antioxidant system to increase the regeneration of damaged mycelia and induce the development of fruiting bodies in Hypsizygus marmoreus

Hypsizygus marmoreus is an important commercial edible fungus, but the lack of basic studies on this fungus has hindered further development of its commercial value. In this study, we found that the treatment of damaged vegetative mycelia with 1 mM l-ascorbic acid (ASA) significantly increased the antioxidant enzyme activities (GPX, GR, CAT and SOD) and antioxidant contents (GSH and ASA) and reduced the ROS levels (H₂O₂ and O₂^-) in mechanically damaged mycelia. Additionally, this treatment increased mycelial biomass. At the reproductive stage, our results demonstrated that the treatment of damaged H. marmoreus mycelia with 2.24 mM ASA significantly increased the antioxidant enzyme activities (GPX, GR, GST, TRXR and CAT), endogenous ASA contents and GSH/GSSG ratios in different developmental stages and significantly decreased the MDA and H₂O₂ contents. Furthermore, this study showed that the expression levels of the antioxidant enzyme genes were consistent with the enzyme activities. Damaged mycelia treated with ASA regenerated 2-3 d earlier than the control group and showed significantly enhanced fruiting body production. These results suggested that exogenous ASA regulated mycelia intracellular ASA content to increase mycelial antioxidant abilities, induce the regeneration of damaged mycelia and regulate the development of fruiting bodies in H. marmoreus.

Comparative transcriptome analysis revealed genes involved in the fruiting body development of Ophiocordyceps sinensis

Ophiocordyceps sinensis is a highly valued fungus that has been used as traditional Asian medicine. This fungus is one of the most important sources of income for the nomadic populations of the Tibetan Plateau. With global warming and excessive collection, the wild O. sinensis resources declined dramatically. The cultivation of O. sinensis hasn’t been fully operational due to the unclear genetic basis of the fruiting body development. Here, our study conducted pairwise comparisons between transcriptomes acquired from different growth stages of O. sinensis including asexual mycelium (CM), developing fruiting body (DF) and mature fruiting body (FB). All RNA-Seq reads were aligned to the genome of O. sinensis CO18 prior to comparative analyses. Cluster analysis showed that the expression profiles of FB and DF were highly similar compared to CM. Alternative splicing analysis (AS) revealed that the stage-specific splicing genes may have important functions in the development of fruiting body. Functional enrichment analyses showed that differentially expressed genes (DEGs) were enriched in protein synthesis and baseline metabolism during fruiting body development, indicating that more protein and energy might be required for fruiting body development. In addition, some fruiting body development-associated genes impacted by ecological factors were up-regulated in FB samples, such as the nucleoside diphosphate kinase gene (ndk), β subunit of the fatty acid synthase gene (cel-2) and the superoxide dismutase gene (sod). Moreover, the expression levels of several cytoskeletons genes were significantly altered during all these growth stages, suggesting that these genes play crucial roles in both vegetative growth and the fruiting body development. Quantitative PCR (qPCR) was used to validate the gene expression profile and the results supported the accuracy of the RNA-Seq and DEGs analysis. Our study offers a novel perspective to understand the underlying growth stage-specific molecular differences and the biology of O. sinensis fruiting body development.