Ostreolysin enhances fruiting initiation in the oyster mushroom (Pleurotus ostreatus)

Assembly dynamics and structure of an aegerolysin, ostreolysin A6

Ostreolysin A6 (OlyA6) is an oyster mushroom-derived membrane-binding protein that, upon recruitment of its partner protein, pleurotolysin B, forms a cytolytic membrane pore complex. OlyA6 itself is not cytolytic but has been reported to exhibit pro-apoptotic activities in cell culture. Here we report the formation dynamics and the structure of OlyA6 assembly on a lipid membrane containing an OlyA6 high-affinity receptor, ceramide phosphoethanolamine, and cholesterol. High-speed atomic force microscopy revealed the reorganization of OlyA6 dimers from initial random surface coverage to 2D protein crystals composed of hexameric OlyA6 repeat units. Crystal growth took place predominantly in the longitudinal direction by the association of OlyA6 dimers, forming a hexameric unit cell. Molecular-level examination of the OlyA6 crystal elucidated the arrangement of dimers within the unit cell and the structure of the dimer that recruits pleurotolysin B for pore formation.

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.

Identification of Key Regulatory Pathways of Basidiocarp Formation in Pleurotus spp. Using Modeling, Simulation and System Biology Studies

Pleurotus (Oyster mushroom) is an important cultivated edible mushroom across the world. It has several therapeutic effects as it contains various useful bio-molecules. The cultivation and crop management of these basidiomycete fungi depends on many extrinsic and intrinsic factors such as substrate composition, growing environment, enzymatic properties, and the genetic makeup, etc. Moreover, for efficient crop production, a comprehensive understanding of the fundamental properties viz. intrinsic–extrinsic factors and genotype-environment interaction analysis is required. The present study explores the basidiocarp formation biology in Pleurotus mushroom using an in silico response to the environmental factors and involvement of the major regulatory genes. The predictive model developed in this study indicates involvement of the key regulatory pathways in the pinhead to fruit body development process. Notably, the major regulatory pathways involved in the conversion of mycelium aggregation to pinhead formation and White Collar protein (PoWC1) binding flavin-chromophore (FAD) to activate respiratory enzymes. Overall, cell differentiation and higher expression of respiratory enzymes are the two important steps for basidiocarp formation. PoWC1 and pofst genes were participate in the structural changes process. Besides this, the PoWC1 gene is also involved in the respiratory requirement, while the OLYA6 gene is the triggering point of fruiting. The findings of the present study could be utilized to understand the detailed mechanism associated with the basidiocarp formation and to cultivate mushrooms at a sustainable level.

Towards Understanding the Function of Aegerolysins

Aegerolysins are remarkable proteins. They are distributed over the tree of life, being relatively widespread in bacteria and fungi, but also present in some insects, plants, protozoa, and viruses. Despite their abundance in cells of certain developmental stages and their presence in secretomes, only a few aegerolysins have been studied in detail. Their function, in particular, is intriguing. Here, we summarize previously published findings on the distribution, molecular interactions, and function of these versatile aegerolysins. They have very diverse protein sequences but a common fold. The machine learning approach of the AlphaFold2 algorithm, which incorporates physical and biological knowledge of protein structures and multisequence alignments, provides us new insights into the aegerolysins and their pore-forming partners, complemented by additional genomic support. We hypothesize that aegerolysins are involved in the mechanisms of competitive exclusion in the niche.

Identification of hydrophobin genes and their physiological functions related to growth and development in Pleurotus ostreatus

Hydrophobins are small secreted proteins with important physiological functions and potential applications. Here, Pleurotus ostreatus hydrophobin genes were systematically analyzed: they were characterized, classified, and their expression profiles and gene functions were explored. In total, 40 P. ostreatus hydrophobin genes were found and showed genetic diversity, of which 15 were newly identified. The hydrophobin protein sequences were diverse but all contained eight cysteine residues with a conserved spacing pattern, and 33 of them were class I hydrophobins. The expression profile analyses showed that Vmh3 and Hydph20 were abundant in monokaryotic and dikaryotic mycelia, whereas Hydph17, Po.hyd16, Hydph8 were specifically expressed in monokaryotic mycelia and Po.hyd10 were specific in dikaryotic mycelia. Furthermore, Vmh3, Hydph20, Po.hyd7, and Po.hyd10 were abundant when dikaryotic mycelia cultivated on PDA, which are different from on substrate (Vmh2, Vmh3, Hydph7, Po.hyd3, Po.hyd7, Po.hyd9); Hydph12, POH1, and Po.hyd4 can be induced by natural light and cold stimulation during development from mycelia to primordia; Vmh3, FBH1, Hydph12, Po.hyd1-Po.hyd5, and Po.hyd8 were highly expressed in primordia and young fruiting bodies; Hydph12, Po.hyd1, Po.hyd4, and Po.hyd5 were specifically expressed in pilei. In addition, RNAi transformants of FBH1 exhibited slower growth rates and had fewer primordia and fruiting bodies, which suggests FBH1 affects the growth rate and primordia formation of P. ostreatus. Therefore, P. ostreatus hydrophobin genes belong to a large family and are temporally and spatially expressed to meet the developmental needs of mushroom.

Aegerolysins from the fungal genus Pleurotus - Bioinsecticidal proteins with multiple potential applications

The aegerolysin proteins ostreolysin A6, pleurotolysin A2 and erylysin A are produced by mushrooms of the genus Pleurotus. These aegerolysins can interact specifically with sphingolipid-enriched membranes. In particular, they strongly bind insect cells and to artificial lipid membranes that contain physiologically relevant concentrations of the main invertebrate-specific sphingolipid, ceramide phosphoethanolamine. Moreover, the aegerolysins permeabilise these membranes when combined with their protein partner pleurotolysin B, which contains a membrane-attack-complex/perforin domain. These aegerolysin/ pleurotolysin B complexes show strong and selective toxicity towards western corn rootworm larvae and adults and Colorado potato beetle larvae. Their insecticidal activities arise through aegerolysin binding to ceramide phosphoethanolamine in the insect midgut. This mode of membrane binding is different from those described for similar aegerolysin-based complexes of bacterial origin (e.g., Cry34Ab1/Cry35Ab1), or other Bacillus thuringiensis proteinaceous crystal toxins, which associate with protein receptors. The ability of Pleurotus aegerolysins to specifically interact with sphingolipid-enriched domains in mammalian cells can be further exploited to visualize lipid rafts in living cells, and to treat certain types of tumours and metabolic disorders. Finally, these proteins can strongly enhance fruiting initiation of P. ostreatus even when applied externally. In this review, we summarise the current knowledge of the potential biotechnological and biomedical applications of the Pleurotus aegerolysins, either alone or when complexed with pleurotolysin B, with special emphasis on their bioinsecticidal effects.

Genetic improvement in Pleurotus (oyster mushroom): a review

Pleurotus is an important genus comprising several edible species of great commercial significance. These species are grown all across the world. The production areas of Pleurotus mainly belong to the Asian part and are gaining wide popularity across the globe owing to their promising nutritional gains. The demand for improved strains with high productivity has also been rising. The genetic improvement in Pleurotus started with a simple selection technique, which later utilized hybridization (intraspecific, interspecific and intergeneric) and mutation breeding. The traits such as productivity, sporelessness and quality improvement are important objectives on which most of the works have been done so far. However, new generation approaches such as molecular breeding, genetic transformation and genome editing techniques also added pace to the present improvement process. Hitherto, seven species of Pleurotus have been sequenced and a sizable data has been generated that can be used in further breeding programs. This paper discusses and summarizes various research findings on genetic improvement of Pleurotus and gives an outlook for future breeding programs.

The genome sequence of the commercially cultivated mushroom Agrocybe aegerita reveals a conserved repertoire of fruiting-related genes and a versatile suite of biopolymer-degrading enzymes

BACKGROUND

Agrocybe aegerita is an agaricomycete fungus with typical mushroom features, which is commercially cultivated for its culinary use. In nature, it is a saprotrophic or facultative pathogenic fungus causing a white-rot of hardwood in forests of warm and mild climate. The ease of cultivation and fructification on solidified media as well as its archetypal mushroom fruit body morphology render A. aegerita a well-suited model for investigating mushroom developmental biology.

RESULTS

Here, the genome of the species is reported and analysed with respect to carbohydrate active genes and genes known to play a role during fruit body formation. In terms of fruit body development, our analyses revealed a conserved repertoire of fruiting-related genes, which corresponds well to the archetypal fruit body morphology of this mushroom. For some genes involved in fruit body formation, paralogisation was observed, but not all fruit body maturation-associated genes known from other agaricomycetes seem to be conserved in the genome sequence of A. aegerita. In terms of lytic enzymes, our analyses suggest a versatile arsenal of biopolymer-degrading enzymes that likely account for the flexible life style of this species. Regarding the amount of genes encoding CAZymes relevant for lignin degradation, A. aegerita shows more similarity to white-rot fungi than to litter decomposers, including 18 genes coding for unspecific peroxygenases and three dye-decolourising peroxidase genes expanding its lignocellulolytic machinery.

CONCLUSIONS

The genome resource will be useful for developing strategies towards genetic manipulation of A. aegerita, which will subsequently allow functional genetics approaches to elucidate fundamentals of fruiting and vegetative growth including lignocellulolysis.

A Sphingosine-type cerebroside in Clavicorona pyxidata induce fruit body formation

Clavicorona pyxidata is a wild edible and medicinal mushroom that is rich in bioactive natural products and has thus been extensively used as traditional medicine in China. The present study has determined that the organic crude extract prepared from a fermented culture of C. pyxidata imparted auto-inhibitory effects on mycelial growth and then induced the formation of fruiting bodies. By monitoring bioactivity, one compound was isolated via successive chromatography over silica gel, Sephadex LH-20, and Cl8-reversed phase silica gel and was identified as a known sphingosine-type cerebroside by nuclear magnetic resonance (NMR) and physicochemical data, namely, (4E, 8E)-N-D-2'-hydroxypalmitoyl-1-O-β-D-glucopyranosyl-9-methyl-4,8-sphingadienine. The application of this cerebroside at a concentration of 200 μg/disc paper resulted in the inhibition of aerial hyphal growth of C. pyxidata. The findings of the present study indicated that this C. pyxidata cerebroside is a fruiting body-inducing substance (FIS).

Tea waste: an effective and economic substrate for oyster mushroom cultivation

BACKGROUND

Tea waste is the residue that remains after tea leaves have been extracted by hot water to obtain water-soluble components. The waste contains a re-usable energy substrate and nutrients which may pollute the environment if they are not dealt with appropriately. Other agricultural wastes have been widely studied as substrates for cultivating mushrooms. In the present study, we cultivated oyster mushroom using tea waste as substrate. To study the feasibility of re-using it, tea waste was added to the substrate at different ratios in different experimental groups. Three mushroom strains (39, 71 and YOU) were compared and evaluated. Mycelia growth rate, yield, biological efficiency and growth duration were measured.

RESULTS

Substrates with different tea waste ratios showed different growth and yield performance. The substrate containing 40-60% of tea waste resulted in the highest yield.

CONCLUSION

Tea waste could be used as an effective and economic substrate for oyster mushroom cultivation. This study also provided a useful way of dealing with massive amounts of tea waste.

Comparative Analysis of Sporulating and Spore-Deficient Strains of Agrocybe salicacola Based on the Transcriptome Sequences

The large number of spores produced by edible mushrooms cause many problems, including causing lung disease, depleting natural genetic diversity, and reduced quality of fruiting bodies. Obtaining spore-deficient strains and understanding the underlying molecular mechanisms of such strains are important for breeding work. In this study, we crossed monokaryotic strains isolated from the edible fungi Agrocybe salicacola to obtain three spore-deficient strains with losses of the sterigmata on the surface of the lamella. A mating test revealed that recessive alleles distributed in some strains might control sterigmata development during the mitotic or meiotic phases. Transcriptome analysis revealed that the majority of the genes involved in DNA mismatch repair, base excision repair, and homologous recombination exhibited down-regulated expression patterns in the mutant fruiting bodies. Five genetic fragments, which were highly similar to the GTP-cyclohydrolase encoding gene, the DNA repair gene rad 8, and cell wall integrity and stress response component-encoding genes, were all expressed exclusively in the wild-type strains; these findings provide important information for the study of the spore development of edible fungi.

Fungal aegerolysin-like proteins: distribution, activities, and applications

The aegerolysin protein family (from aegerolysin of the mushroom Agrocybe aegerita) comprises proteins of ∼15-20 kDa from various eukaryotic and bacterial taxa. Aegerolysins are inconsistently distributed among fungal species, and variable numbers of homologs have been reported for species within the same genus. As such noncore proteins, without a member of a protein family in each of the sequenced fungi, they can give insight into different species-specific processes. Some aegerolysins have been reported to be hemolytically active against mammalian erythrocytes. However, some function as bi-component proteins that have membrane activity in concert with another protein that contains a membrane attack complex/perforin domain. The function of most of aegerolysins is unknown, although some have been suggested to have a role in development of the organism. Potential biotechnological applications of aegerolysins are already evident, despite the limited scientific knowledge available at present. Some mushroom aegerolysins, for example, can be used as markers to detect and label specific membrane lipids. Others can be used as biomarkers of fungal exposure, where their genes can serve as targets for detection of fungi and their progression during infectious diseases. Antibodies against aegerolysins can also be raised as immuno-diagnostic tools. Aegerolysins have been shown to serve as a species determination tool for fungal phytopathogen isolates in terms of some closely related species, where commonly used internal transcribed spacer barcoding has failed. Moreover, strong promoters that regulate aegerolysin genes can promote secretion of heterologous proteins from fungi and have been successfully applied in simultaneous multi-gene expression techniques.

Fungal hemolysins

Hemolysins are a class of proteins defined by their ability to lyse red cells but have been described to exhibit pleiotropic functions. These proteins have been extensively studied in bacteria and more recently in fungi. Within the last decade, a number of studies have characterized fungal hemolysins and revealed a fascinating yet diverse group of proteins. The purpose of this review is to provide a synopsis of the known fungal hemolysins with an emphasis on those belonging to the aegerolysin protein family. New insight and perspective into fungal hemolysins in biotechnology and health are additionally presented.

Development of monoclonal antibodies to recombinant terrelysin and characterization of expression in Aspergillus terreus

Aspergillus terreus is an emerging pathogen that mostly affects immunocompromised patients, causing infections that are often difficult to manage therapeutically. Current diagnostic strategies are limited to the detection of fungal growth using radiological methods or biopsy, which often does not enable species-specific identification. There is thus a critical need for diagnostic techniques to enable early and specific identification of the causative agent. In this study, we describe monoclonal antibodies (mAbs) developed to a previously described recombinant form of the haemolysin terrelysin. Sixteen hybridomas of various IgG isotypes were generated to the recombinant protein, of which seven demonstrated reactivity to the native protein in hyphal extracts. Cross-reactivity analysis using hyphal extracts from 29 fungal species, including 12 Aspergillus species and five strains of A. terreus, showed that three mAbs (13G10, 15B5 and 10G4) were A. terreus-specific. Epitope analysis demonstrated mAbs 13G10 and 10G4 recognize the same epitope, PSNEFE, while mAb 15B5 recognizes the epitope LYEGQFHS. Time-course studies showed that terrelysin expression was highest during early hyphal growth and dramatically decreased after mycelial expansion. Immunolocalization studies demonstrated that terrelysin was not only localized within the cytoplasm of hyphae but appeared to be more abundant at the hyphal tip. These findings were confirmed in cultures grown at room temperature as well as at 37 °C. Additionally, terrelysin was detected in the supernatant of A. terreus cultures. These observations suggest that terrelysin may be a candidate biomarker for A. terreus infection.

Characterization of recombinant terrelysin, a hemolysin of Aspergillus terreus

Fungal hemolysins are potential virulence factors. Some fungal hemolysins belong to the aegerolysin protein family that includes cytolysins capable of lysing erythrocytes and other cells. Here, we describe a hemolysin from Aspergillus terreus called terrelysin. We used the genome sequence database to identify the terrelysin sequence based on homology with other known aegerolysins. Aspergillus terreus mRNA was isolated, transcribed to cDNA and the open reading frame for terrelysin amplified by PCR using specific primers. Using the pASK-IBA6 cloning vector, we produced recombinant terrelysin (rTerrelysin) as a fusion product in Escherichia coli. The recombinant protein was purified and using MALDI-TOF MS determined to have a mass of 16,428 Da. Circular dichroism analysis suggests the secondary structure of the protein to be predominantly β-sheet. Results from thermal denaturation of rTerrelysin show that the protein maintained the β-sheet confirmation up to 65°C. Polyclonal antibody to rTerrelysin recognized a protein of approximately 16.5 kDa in mycelial extracts from A. terreus.

Early development of Moniliophthora perniciosa basidiomata and developmentally regulated genes

BACKGROUND

The hemibiotrophic fungus Moniliophthora perniciosa is the causal agent of Witches' broom, a disease of Theobroma cacao. The pathogen life cycle ends with the production of basidiocarps in dead tissues of the infected host. This structure generates millions of basidiospores that reinfect young tissues of the same or other plants. A deeper understanding of the mechanisms underlying the sexual phase of this fungus may help develop chemical, biological or genetic strategies to control the disease.

RESULTS

Mycelium was morphologically analyzed prior to emergence of basidiomata by stereomicroscopy, light microscopy and scanning electron microscopy. The morphological changes in the mycelium before fructification show a pattern similar to other members of the order Agaricales. Changes and appearance of hyphae forming a surface layer by fusion were correlated with primordia emergence. The stages of hyphal nodules, aggregation, initial primordium and differentiated primordium were detected. The morphological analysis also allowed conclusions on morphogenetic aspects. To analyze the genes involved in basidiomata development, the expression of some selected EST genes from a non-normalized cDNA library, representative of the fruiting stage of M. perniciosa, was evaluated. A macroarray analysis was performed with 192 selected clones and hybridized with two distinct RNA pools extracted from mycelium in different phases of basidiomata formation. This analysis showed two groups of up and down-regulated genes in primordial phases of mycelia. Hydrophobin coding, glucose transporter, Rho-GEF, Rheb, extensin precursor and cytochrome p450 monooxygenase genes were grouped among the up-regulated. In the down-regulated group relevant genes clustered coding calmodulin, lanosterol 14 alpha demethylase and PIM1. In addition, 12 genes with more detailed expression profiles were analyzed by RT-qPCR. One aegerolysin gene had a peak of expression in mycelium with primordia and a second in basidiomata, confirming their distinctiveness. The number of transcripts of the gene for plerototolysin B increased in reddish-pink mycelium and indicated an activation of the initial basidiomata production even at this culturing stage. Expression of the glucose transporter gene increased in mycelium after the stress, coinciding with a decrease of adenylate cyclase gene transcription. This indicated that nutrient uptake can be an important signal to trigger fruiting in this fungus.

CONCLUSION

The identification of genes with increased expression in this phase of the life cycle of M. perniciosa opens up new possibilities of controlling fungus spread as well as of genetic studies of biological processes that lead to basidiomycete fruiting. This is the first comparative morphologic study of the early development both in vivo and in vitro of M. perniciosa basidiomata and the first description of genes expressed at this stage of the fungal life cycle.

Aegerolysins: structure, function, and putative biological role

Aegerolysins, discovered in fungi, bacteria and plants, are highly similar proteins with interesting biological properties. Certain aegerolysins possess antitumoral, antiproliferative, and antibacterial activities. Further possible medicinal applications include their use in the prevention of atherosclerosis, or as vaccines. Additional biotechnological value of fungal aegerolysins lies in their involvement in development, which could improve cultivation of commercially important edible mushrooms. Besides, new insights on microheterogeneity of raft-like membrane domains could be gained by using aegerolysins as specific markers in cell and molecular biology. Although the exact function of aegerolysins in their producing organisms remains to be explained, they are biochemically well characterized all-beta structured proteins sharing the following common features: low isoelectric points, similar molecular weights (15-17 kDa), and stability in a wide pH range.