A lectin-mediated resistance of higher fungi against predators and parasites

Snowball: a novel gene family required for developmental patterning of fruiting bodies of mushroom-forming fungi (Agaricomycetes)

The morphogenesis of sexual fruiting bodies of fungi is a complex process determined by a genetically encoded program. Fruiting bodies reached the highest complexity levels in the Agaricomycetes; yet, the underlying genetics is currently poorly known. In this work, we functionally characterized a highly conserved gene termed snb1, whose expression level increases rapidly during fruiting body initiation. According to phylogenetic analyses, orthologs of snb1 are present in almost all agaricomycetes and may represent a novel conserved gene family that plays a substantial role in fruiting body development. We disrupted snb1 using CRISPR/Cas9 in the agaricomycete model organism Coprinopsis cinerea. snb1 deletion mutants formed unique, snowball-shaped, rudimentary fruiting bodies that could not differentiate caps, stipes, and lamellae. We took advantage of this phenotype to study fruiting body differentiation using RNA-Seq analyses. This revealed differentially regulated genes and gene families that, based on wild-type RNA-Seq data, were upregulated early during development and showed tissue-specific expression, suggesting a potential role in differentiation. Taken together, the novel gene family of snb1 and the differentially expressed genes in the snb1 mutants provide valuable insights into the complex mechanisms underlying developmental patterning in the Agaricomycetes.

IMPORTANCE

Fruiting bodies of mushroom-forming fungi (Agaricomycetes) are complex multicellular structures, with a spatially and temporally integrated developmental program that is, however, currently poorly known. In this study, we present a novel, conserved gene family, Snowball (snb), termed after the unique, differentiation-less fruiting body morphology of snb1 knockout strains in the model mushroom Coprinopsis cinerea. snb is a gene of unknown function that is highly conserved among agaricomycetes and encodes a protein of unknown function. A comparative transcriptomic analysis of the early developmental stages of differentiated wild-type and non-differentiated mutant fruiting bodies revealed conserved differentially expressed genes which may be related to tissue differentiation and developmental patterning fruiting body development.

het-B allorecognition in Podospora anserina is determined by pseudo-allelic interaction of genes encoding a HET and lectin fold domain protein and a PII-like protein

Filamentous fungi display allorecognition genes that trigger regulated cell death (RCD) when strains of unlike genotype fuse. Podospora anserina is one of several model species for the study of this allorecognition process termed heterokaryon or vegetative incompatibility. Incompatibility restricts transmission of mycoviruses between isolates. In P. anserina, genetic analyses have identified nine incompatibility loci, termed het loci. Here we set out to clone the genes controlling het-B incompatibility. het-B displays two incompatible alleles, het-B1 and het-B2. We find that the het-B locus encompasses two adjacent genes, Bh and Bp that exist as highly divergent allelic variants (Bh1/Bh2 and Bp1/Bp2) in the incompatible haplotypes. Bh encodes a protein with an N-terminal HET domain, a cell death inducing domain bearing homology to Toll/interleukin-1 receptor (TIR) domains and a C-terminal domain with a predicted lectin fold. The Bp product is homologous to PII-like proteins, a family of small trimeric proteins acting as sensors of adenine nucleotides in bacteria. We show that although the het-B system appears genetically allelic, incompatibility is in fact determined by the non-allelic Bh1/Bp2 interaction while the reciprocal Bh2/Bp1 interaction plays no role in incompatibility. The highly divergent C-terminal lectin fold domain of BH determines recognition specificity. Population studies and genome analyses indicate that het-B is under balancing selection with trans-species polymorphism, highlighting the evolutionary significance of the two incompatible haplotypes. In addition to emphasizing anew the central role of TIR-like HET domains in fungal RCD, this study identifies novel players in fungal allorecognition and completes the characterization of the entire het gene set in that species.

A Comprehensive Review on Euphorbiaceae lectins: Structural and Biological Perspectives

Euphorbiaceae, also known as the spurge family, is a large group of flowering plants. Despite being tropical natives, they are now widespread. Due to its medicinal and commercial importance, this family of plants attracted a lot of attention in the scientific community. The distinctive characteristic of the family is production of milky latex, which is a rich source of several lectins, the proteins that bind carbohydrates. Although their function is unclear, they are believed to defend plants against damaging phytopathogenic microorganisms, insects, and predatory animals. Additionally, they serve as crucial metabolic regulators under a variety of stressors. Detection, separation, purification, and characterization of lectins from the Euphorbiaceae family - mostly from the latex of plants - began over 40 years ago. This effort produced over 35 original research papers that were published. However, no systematic review that compiles these published data has been presented yet. This review summarizes and describes several procedures and protocols employed for extraction and purification of lectins belonging to this family. Physicochemical properties and biological activities of the lectins, along with their medicinal and pharmacological properties, have also been analyzed. Additionally, using examples of ricin and ricin agglutinin, we have structurally analyzed characteristics of the lectin known as Ribosome Inactivating Protein Type II (RIP-Type II) that belongs to this family. We anticipate that this review article will offer a useful compendium of information on this important family of lectins, show the scientists involved in lectin research the gaps in our knowledge, and offer insights for future research.

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.

A lectin gene is involved in the defense of Pleurotus ostreatus against the mite predator Tyrophagus putrescentiae

The storage mite, Tyrophagus putrescentiae, found worldwide in many habitats, is an important pest of edible mushrooms. Excessive chemical spraying for pest control has been linked to environmental pollution, health risks, insecticide resistance development, and food safety. Host resistance can be sustainable and cost-effective and provide effective and economical pest control. Previous studies have reported that the oyster mushroom Pleurotus ostreatus has evolved effective defense mechanisms against T. putrescentiae attack, but the underlying mechanism remains unclear. Here we report that a lectin gene from P. ostreatus mycelia, Polec2, induced fungal resistance to mite grazing. Polec2 belongs to a galectin-like lectin classification, encoding a protein with β-sandwith-fold domain. Overexpression of Polec2 in P. ostreatus led to activation of the reactive oxygen species (ROS)/mitogen-activated protein kinases (MAPKs) signaling pathway, salicylic acid (SA), and jasmonate (JA) biosynthesis. The activation resulted in bursts of antioxidant activities of catalases (CAT), peroxidases (POD), superoxide dismutases (SOD), and increased production of SA, JA, jasmonic acid-isoleucine (JA-Ile) and jasmonic acid methyl ester (MeJA), accompanied by reduced T. putrescentiae feeding and suppressed its population. We also provide an overview of the phylogenetic distribution of lectins across 22 fungal genomes. Our findings shed light on the molecular mechanisms of P. ostreatus' defense against the mite predator and will be useful in investigating the molecular basis of fungi-fungivory interactions and gene mining for pest-resistance genes.

Coprinopsis cinerea Galectin CGL1 Induces Apoptosis and Inhibits Tumor Growth in Colorectal Cancer Cells

Mushroom galectins are promising anticancer agents for their low IC50 values against cancer cells in vitro. In this study, two Coprinopsis cinerea galectins, CGL1 and CGL2, were heterologously expressed, and their biochemistry properties and anticancer effects were evaluated. The purified galectins were thermostable at neutral pH conditions. They both existed as tetramers and shared a high affinity towards lactose. CGL1 and CGL2 strongly inhibited the cell viability of many cancer cell lines, including three colorectal cancer cells, in a dose-dependent manner by inducing mitochondria-mediated caspase-dependent apoptosis. Furthermore, CGL1 exhibited higher apoptosis-inducing ability and cytotoxicity than CGL2. In vivo cell viability experiments based on two xenograft mouse models showed that CGL1 had a more substantial inhibitory effect than CGL2 on HCT116 tumor growth (p < 0.0001), whereas only CGL1 inhibited DLD1 tumor growth (p < 0.01). This is the first study to evaluate the anti-colorectal cancer effect of mushroom lectins in vivo, and our results showed that CGL1 is a potent agent for colorectal cancer treatment.

Toxin-Producing Endosymbionts Shield Pathogenic Fungus against Micropredators

The fungus Rhizopus microsporus harbors a bacterial endosymbiont (Mycetohabitans rhizoxinica) for the production of the antimitotic toxin rhizoxin. Although rhizoxin is the causative agent of rice seedling blight, the toxinogenic bacterial-fungal alliance is, not restricted to the plant disease. It has been detected in numerous environmental isolates from geographically distinct sites covering all five continents, thus raising questions regarding the ecological role of rhizoxin beyond rice seedling blight. Here, we show that rhizoxin serves the fungal host in fending off protozoan and metazoan predators. Fluorescence microscopy and coculture experiments with the fungivorous amoeba Protostelium aurantium revealed that ingestion of R. microsporus spores is toxic to P. aurantium. This amoebicidal effect is caused by the dominant bacterial rhizoxin congener rhizoxin S2, which is also lethal toward the model nematode Caenorhabditis elegans. By combining stereomicroscopy, automated image analysis, and quantification of nematode movement, we show that the fungivorous nematode Aphelenchus avenae actively feeds on R. microsporus that is lacking endosymbionts, whereas worms coincubated with symbiotic R. microsporus are significantly less lively. This study uncovers an unexpected ecological role of rhizoxin as shield against micropredators. This finding suggests that predators may function as an evolutionary driving force to maintain toxin-producing endosymbionts in nonpathogenic fungi.

Mycorrhiza-induced mycocypins of Laccaria bicolor are potent protease inhibitors with nematotoxic and collembola antifeedant activity

Fungivory of mycorrhizal hyphae has a significant impact on fungal fitness and, by extension, on nutrient transfer between fungi and host plants in natural ecosystems. Mycorrhizal fungi have therefore evolved an arsenal of chemical compounds that are hypothesized to protect the hyphal tissues from being eaten, such as the protease inhibitors mycocypins. The genome of the ectomycorrhizal fungus Laccaria bicolor has an unusually high number of mycocypin-encoding genes. We have characterized the evolution of this class of proteins, identified those induced by symbiosis with a host plant and characterized the biochemical properties of two upregulated L. bicolor mycocypins. More than half of L. bicolor mycocypin-encoding genes are differentially expressed during symbiosis or fruiting body formation. We show that two L. bicolor mycocypins that are strongly induced during symbiosis are cysteine protease inhibitors and exhibit similar but distinct localization in fungal tissues at different developmental stages and during interaction with a host plant. Moreover, we show that these L. bicolor mycocypins have toxic and feeding deterrent effect on nematodes and collembolans, respectively. Therefore, L. bicolor mycocypins may be part of a mechanism by which this species deters grazing by different members of the soil food web.

Genomic and proteomic analysis of Tausonia pullulans reveals a key role for a GH15 glucoamylase in starch hydrolysis

Basidiomycetous yeasts remain an almost unexplored source of enzymes with great potential in several industries. Tausonia pullulans (Tremellomycetes) is a psychrotolerant yeast with several extracellular enzymatic activities reported, although the responsible genes are not known. We performed the genomic sequencing, assembly and annotation of T. pullulans strain CRUB 1754 (Perito Moreno glacier, Argentina), a gene survey of carbohydrate-active enzymes (CAZymes), and analyzed its secretome by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) after growth in glucose (GLU) or starch (STA) as main carbon sources. T. pullulans has 7210 predicted genes, 3.6% being CAZymes. When compared to other Tremellomycetes, it contains a high number of CAZy domains, and in particular higher quantities of glucoamylases (GH15), pectinolytic enzymes (GH28) and lignocellulose decay enzymes (GH7). When the secretome of T. pullulans was analyzed experimentally after growth in starch or glucose, 98 proteins were identified. The 60% of total spectral counts belonged to GHs, oxidoreductases and to other CAZymes. A 65 kDa glucoamylase of family GH15 (TpGA1) showed the highest fold change (tenfold increase in starch). This enzyme contains a conserved active site and showed extensive N-glycosylation. This study increases the knowledge on the extracellular hydrolytic enzymes of basidiomycetous yeasts and, in particular, establishes T. pullulans as a potential source of carbohydrate-active enzymes. KEY POINTS: • Tausonia pullulans genome harbors a high number of genes coding for CAZymes. • Among CAZy domains/families, the glycoside hydrolases are the most abundant. • Secretome analysis in glucose or starch as main C sources identified 98 proteins. • A 65 kDa GH15 glucoamylase showed the highest fold increase upon culture in starch.

Structure-function relationship of a novel fucoside-binding fruiting body lectin from Coprinopsis cinerea exhibiting nematotoxic activity

Lectins are non-immunoglobulin-type proteins that bind to specific carbohydrate epitopes and play important roles in intra- and inter-organismic interactions. Here, we describe a novel fucose-specific lectin, termed CML1, which we identified from fruiting body extracts of Coprinopsis cinerea. For further characterization, the coding sequence for CML1 was cloned and heterologously expressed in Escherichia coli. Feeding of CML1-producing bacteria inhibited larval development of the bacterivorous nematode Caenorhabditis tropicalis, but not of C. elegans. The crystal structure of the recombinant protein in its apo-form and in complex with H type I or Lewis A blood group antigens was determined by X-ray crystallography. The protein folds as a sandwich of 2 antiparallel β-sheets and forms hexamers resulting from a trimer of dimers. The hexameric arrangement was confirmed by small-angle X-ray scattering (SAXS). One carbohydrate-binding site per protomer was found at the dimer interface with both protomers contributing to ligand binding, resulting in a hexavalent lectin. In terms of lectin activity of recombinant CML1, substitution of the carbohydrate-interacting residues His54, Asn55, Trp94, and Arg114 by Ala abolished carbohydrate-binding and nematotoxicity. Although no similarities to any characterized lectin were found, sequence alignments identified many non-characterized agaricomycete proteins. These results suggest that CML1 is the founding member of a novel family of fucoside-binding lectins involved in the defense of agaricomycete fruiting bodies against predation by fungivorous nematodes.

Cocaprins, β-Trefoil Fold Inhibitors of Cysteine and Aspartic Proteases from Coprinopsis cinerea

We introduce a new family of fungal protease inhibitors with β-trefoil fold from the mushroom Coprinopsis cinerea, named cocaprins, which inhibit both cysteine and aspartic proteases. Two cocaprin-encoding genes are differentially expressed in fungal tissues. One is highly transcribed in vegetative mycelium and the other in the stipes of mature fruiting bodies. Cocaprins are small proteins (15 kDa) with acidic isoelectric points that form dimers. The three-dimensional structure of cocaprin 1 showed similarity to fungal β-trefoil lectins. Cocaprins inhibit plant C1 family cysteine proteases with Ki in the micromolar range, but do not inhibit the C13 family protease legumain, which distinguishes them from mycocypins. Cocaprins also inhibit the aspartic protease pepsin with Ki in the low micromolar range. Mutagenesis revealed that the β2-β3 loop is involved in the inhibition of cysteine proteases and that the inhibitory reactive sites for aspartic and cysteine proteases are located at different positions on the protein. Their biological function is thought to be the regulation of endogenous proteolytic activities or in defense against fungal antagonists. Cocaprins are the first characterized aspartic protease inhibitors with β-trefoil fold from fungi, and demonstrate the incredible plasticity of loop functionalization in fungal proteins with β-trefoil fold.

Injection into and extraction from single fungal cells

The direct delivery of molecules and the sampling of endogenous compounds into and from living cells provide powerful means to modulate and study cellular functions. Intracellular injection and extraction remain challenging for fungal cells that possess a cell wall. The most common methods for intracellular delivery into fungi rely on the initial degradation of the cell wall to generate protoplasts, a step that represents a major bottleneck in terms of time, efficiency, standardization, and cell viability. Here, we show that fluidic force microscopy enables the injection of solutions and cytoplasmic fluid extraction into and out of individual fungal cells, including unicellular model yeasts and multicellular filamentous fungi. The approach is strain- and cargo-independent and opens new opportunities for manipulating and analyzing fungi. We also perturb individual hyphal compartments within intact mycelial networks to study the cellular response at the single cell level.

Guillaume-Gentil et al. describe a method that employs a modified AFM tip for selectively sampling from and injecting into individual fungal cells of differing morphology. The authors describe extensive modifications on their system previously used for mammalian cells to overcome many of the challenges associated with working on single fungal cells.

The fucose-specific lectin gene AOL_s00054g276 affects trap formation and nematocidal activity of the nematophagous fungus Arthrobotrys oligospora

Nematode-trapping fungi are natural enemies of nematodes in nature. Arthrobotrys oligospora, a typical nematode-trapping fungus with a clear genetic background, can capture and infect nematodes by forming adhesive three-dimensional networks. Lectins, a class of glycoproteins containing glycosyl-specific recognition domains, play an important role in biological recognition. However, the fucose-specific lectins have rarely been studied regarding the process of preying on nematodes. In this study, we characterized the biological role of the fucose-specific lectin encoding gene AOL_s00054g276 (g276) in A. oligospora. The gene g276 was first deleted based on homologous recombination, then the phenotype and nematocidal activity of the Δg276 mutant was evaluated. The results showed that the deletion of gene g276 delayed trap formation and weakened its nematocidal activity; however, mycelial growth, conidia production, conidial germination rates, and adaption to environmental stresses were not affected. Our results suggest that the fucose-specific lectin encoding gene g276 might be associated with the morphogenesis of this fungus, and its deletion resulted in a significantly low density of three-dimensional traps (P < 0.05) and a significantly low nematode-tapping efficiency (P < 0.001). These findings provide a basis for further elucidating the mechanism of A. oligospora preying on nematodes and lay a foundation for the development and utilization of fungal-derived lectins for nematode control in future.

Drosophila attack inhibits hyphal regeneration and defense mechanisms activation for the fungus Trichoderma atroviride

The capability to respond to wounding is a process shared by organisms of different kingdoms that can result in the regeneration of whole-body parts or lost structures or organs. Filamentous fungi constitute a rich food source that ensures survival and reproduction of their predators and are therefore continuously exposed to mechanical damage. Nevertheless, our understanding of how fungi respond to wounding and predators is scarce. Fungi like plants and animals respond to injury recognizing Damage- and Microbe-Associated Molecular Patterns (DAMPs/MAMPs) that activate Ca2+ and Mitogen-Activated Protein Kinase dependent signaling for the activation of defense mechanisms. During herbivory, plants, in addition to activating pathways related to injury, activate specific responses to combat their predators. Using a transcriptional approach, we studied the capacity of the filamentous fungus Trichoderma atroviride to activate specific responses to injury and attack by different arthropods. Attack by Drosophila melanogaster inhibited the transcriptional activation of genes required for hyphal regeneration, and the fungal innate immune and chemical defense responses. We also provide mechanistic insight of this inhibition involving components of the D. melanogaster salivary glands that repress the expression of a set of genes and block hyphal regeneration.

Bacterial endosymbionts protect beneficial soil fungus from nematode attack

Soil is a complex and competitive environment, forcing its inhabitants to develop strategies against competitors, predators, and pathogens. Identifying and understanding the molecular mechanisms has translational value for medicine, ecology, and agriculture. In this study, we show that a member of important soil-dwelling fungi (Mortierella) forms a tight alliance with toxin-producing bacteria (Mycoavidus) that live within the fungal hyphae and protect their host from nematode attack. This discovery is relevant since Mortierella species correlate with healthy soils and are used as plant growth–promoting fungi in agriculture. Unraveling an ecological role for fungal endosymbionts in Mortierella, our results contribute to the understanding of a mainspring in fungal–endobacterial symbioses and open the possibility for the development of new biocontrol agents.

Fungi of the genus Mortierella occur ubiquitously in soils where they play pivotal roles in carbon cycling, xenobiont degradation, and promoting plant growth. These important fungi are, however, threatened by micropredators such as fungivorous nematodes, and yet little is known about their protective tactics. We report that Mortierella verticillata NRRL 6337 harbors a bacterial endosymbiont that efficiently shields its host from nematode attacks with anthelmintic metabolites. Microscopic investigation and 16S ribosomal DNA analysis revealed that a previously overlooked bacterial symbiont belonging to the genus Mycoavidus dwells in M. verticillata hyphae. Metabolic profiling of the wild-type fungus and a symbiont-free strain obtained by antibiotic treatment as well as genome analyses revealed that highly cytotoxic macrolactones (CJ-12,950 and CJ-13,357, syn. necroxime C and D), initially thought to be metabolites of the soil-inhabiting fungus, are actually biosynthesized by the endosymbiont. According to comparative genomics, the symbiont belongs to a new species (Candidatus Mycoavidus necroximicus) with 12% of its 2.2 Mb genome dedicated to natural product biosynthesis, including the modular polyketide-nonribosomal peptide synthetase for necroxime assembly. Using Caenorhabditis elegans and the fungivorous nematode Aphelenchus avenae as test strains, we show that necroximes exert highly potent anthelmintic activities. Effective host protection was demonstrated in cocultures of nematodes with symbiotic and chemically complemented aposymbiotic fungal strains. Image analysis and mathematical quantification of nematode movement enabled evaluation of the potency. Our work describes a relevant role for endofungal bacteria in protecting fungi against mycophagous nematodes.

Marasmius oreades agglutinin enhances resistance of Arabidopsis against plant-parasitic nematodes and a herbivorous insect

BACKGROUND

Plant-parasitic nematodes and herbivorous insects have a significant negative impact on global crop production. A successful approach to protect crops from these pests is the in planta expression of nematotoxic or entomotoxic proteins such as crystal proteins from Bacillus thuringiensis (Bt) or plant lectins. However, the efficacy of this approach is threatened by emergence of resistance in nematode and insect populations to these proteins. To solve this problem, novel nematotoxic and entomotoxic proteins are needed. During the last two decades, several cytoplasmic lectins from mushrooms with nematicidal and insecticidal activity have been characterized. In this study, we tested the potential of Marasmius oreades agglutinin (MOA) to furnish Arabidopsis plants with resistance towards three economically important crop pests: the two plant-parasitic nematodes Heterodera schachtii and Meloidogyne incognita and the herbivorous diamondback moth Plutella xylostella.

RESULTS

The expression of MOA does not affect plant growth under axenic conditions which is an essential parameter in the engineering of genetically modified crops. The transgenic Arabidopsis lines showed nearly complete resistance to H. schachtii, in that the number of female and male nematodes per cm root was reduced by 86-91 % and 43-93 % compared to WT, respectively. M. incognita proved to be less susceptible to the MOA protein in that 18-25 % and 26-35 % less galls and nematode egg masses, respectively, were observed in the transgenic lines. Larvae of the herbivorous P. xylostella foraging on MOA-expression lines showed a lower relative mass gain (22-38 %) and survival rate (15-24 %) than those feeding on WT plants.

CONCLUSIONS

The results of our in planta experiments reveal a robust nematicidal and insecticidal activity of the fungal lectin MOA against important agricultural pests which may be exploited for crop protection.

Cytoplasmic Lipases-A Novel Class of Fungal Defense Proteins Against Nematodes

Fungi are an attractive food source for predators such as fungivorous nematodes. Several fungal defense proteins and their protective mechanisms against nematodes have been described. Many of these proteins are lectins which are stored in the cytoplasm of the fungal cells and bind to specific glycan epitopes in the digestive tract of the nematode upon ingestion. Here, we studied two novel nematotoxic proteins with lipase domains from the model mushroom Coprinopsis cinerea. These cytoplasmically localized proteins were found to be induced in the vegetative mycelium of C. cinerea upon challenge with fungivorous nematode Aphelenchus avenae. The proteins showed nematotoxicity when heterologously expressed in E. coli and fed to several bacterivorous nematodes. Site-specific mutagenesis of predicted catalytic residues eliminated the in-vitro lipase activity of the proteins and significantly reduced their nematotoxicity, indicating the importance of the lipase activity for the nematotoxicity of these proteins. Our results suggest that cytoplasmic lipases constitute a novel class of fungal defense proteins against predatory nematodes. These findings improve our understanding of fungal defense mechanisms against predators and may find applications in the control of parasitic nematodes in agriculture and medicine.

Expression of a Fungal Lectin in Arabidopsis Enhances Plant Growth and Resistance Toward Microbial Pathogens and a Plant-Parasitic Nematode

Coprinopsis cinerea lectin 2 (CCL2) is a fucoside-binding lectin from the basidiomycete C. cinerea that is toxic to the bacterivorous nematode Caenorhabditis elegans as well as animal-parasitic and fungivorous nematodes. We expressed CCL2 in Arabidopsis to assess its protective potential toward plant-parasitic nematodes. Our results demonstrate that expression of CCL2 enhances host resistance against the cyst nematode Heterodera schachtii. Surprisingly, CCL2-expressing plants were also more resistant to fungal pathogens including Botrytis cinerea, and the phytopathogenic bacterium Pseudomonas syringae. In addition, CCL2 expression positively affected plant growth indicating that CCL2 has the potential to improve two important agricultural parameters namely biomass production and general disease resistance. The mechanism of the CCL2-mediated enhancement of plant disease resistance depended on fucoside-binding by CCL2 as transgenic plants expressing a mutant version of CCL2 (Y92A), compromised in fucoside-binding, exhibited wild type (WT) disease susceptibility. The protective effect of CCL2 did not seem to be direct as the lectin showed no growth-inhibition toward B. cinerea in in vitro assays. We detected, however, a significantly enhanced transcriptional induction of plant defense genes in CCL2- but not CCL2-Y92A-expressing lines in response to infection with B. cinerea compared to WT plants. This study demonstrates a potential of fungal defense lectins in plant protection beyond their use as toxins.

Structural insights into the fungi-nematodes interaction mediated by fucose-specific lectin AofleA from Arthrobotrys oligospora

Fungal lectin can bind specific carbohydrate structures of the host and work in recognition and adhesion or as a toxic factor. AofleA, as a fucose-specific lectin from widely studied nematode predatory fungus Arthrobotrys oligospora, possibly plays a key role in the event of capturing nematodes, but the mechanism remains unknown. Here we report the crystal structure of AofleA, which exists as a homodimer with each subunit folds as a six-bladed β-propeller. Our structural and biological results revealed that three of the six putative binding sites of AofleA had fucose-binding abilities. In addition, we found that AofleA could bind to the pharynx and intestine of the nematode in a fucose-binding-dependent manner. Our results facilitate the understanding of the mechanism that fucose-specific lectin mediates fungi-nematodes interaction, and provide structural information for the development of potential applications of AofleA.

Ricin B-like lectin orthologues from two mushrooms, Hericium erinaceus and Stereum hirsutum, enable recognition of highly fucosylated N-glycans

The mushroom Hericium erinaceus contains isolectins, including the ricin B-like lectin HEL1 and the core 1 O-glycan-binding lectin HEL2. Recombinant HEL2 reportedly binds O-linked glycans, but recombinant HEL1 (rHEL1) has not been characterized. HEL1 and Stereum hirsutum lectin (SHL1) orthologues, which contain the typical (QxW)₃ ricin-B like motif, were evaluated. Interestingly, under non-denaturing conditions, recombinant SHL1 (rSHL1) existed as a trimer and exhibited agglutination activity, whereas rHEL1 existed as a monomer with no agglutination activity. The hemagglutination activity of rSHL1 was inhibited by N-linked glycoprotein transferrin. A glycan-array analysis revealed that the two recombinant lectins had different binding intensities toward fucosylated N-glycans harboring fucose-α(1,2) galactose or fucose-α(1,4) N-acetylglucosamine. Isothermal calorimetry showed that compared with rHEL1, rSHL1 interacted more strongly with transferrin, a fucosylated glycoprotein, than with other fucosylated disaccharide glycoconjugates. Finally, rSHL1 and rHEL1 were comparable in their ability to detect highly fucosylated N-glycans within glycoproteins on the surface of SW1116 human colorectal carcinoma cells. Therefore, these ricin B-like lectins might enable detection of highly fucosylated glycoepitopes on cancer cells for diagnostic applications.

CNL-Clitocybe nebularis Lectin-The Fungal GalNAcβ1-4GlcNAc-Binding Lectin

Clitocybe nebularis lectin (CNL) is present in fruiting bodies of clouded agaric along with several similar isolectins that are all small and stable proteins. It is a beta-trefoil type lectin forming homodimers that are essential for its functionality. It binds specifically N,N′-diacetyllactosediamine (GalNAcβ1-4GlcNAc, LacDiNac) and human blood group A determinant-containing glycan epitopes. Its most probable function is to defend fruiting bodies against predators and parasites. In addition, an endogenous regulatory function is possible for CNL, as indicated by its interaction with fungal protease inhibitors sharing the beta-trefoil fold. CNL is toxic to insects, nematodes and amoebae, as well as to leukemic T-cell lines. Bivalent carbohydrate binding is essential for the toxicity of CNL, against both invertebrates and cancer-derived cell lines. In addition, CNL exhibits potent immunostimulation of human dendritic cells, resulting in a strong T helper cell type 1 response. Based on its unique characteristics, CNL is a promising candidate for applications in human and veterinary medicine as well as in agriculture, for plant protection.

Heterologous Production and Functional Characterization of Ageritin, a Novel Type of Ribotoxin Highly Expressed during Fruiting of the Edible Mushroom Agrocybe aegerita

Fungi produce various defense proteins against antagonists, including ribotoxins. These toxins cleave a single phosphodiester bond within the universally conserved sarcin-ricin loop of ribosomes and inhibit protein biosynthesis. Here, we report on the structure and function of ageritin, a previously reported ribotoxin from the edible mushroom Agrocybe aegerita The amino acid sequence of ageritin was derived from cDNA isolated from the dikaryon A. aegerita AAE-3 and lacks, according to in silico prediction, a signal peptide for classical secretion, predicting a cytoplasmic localization of the protein. The calculated molecular weight of the protein is slightly higher than the one reported for native ageritin. The A. aegerita ageritin-encoding gene, AaeAGT1, is highly induced during fruiting, and toxicity assays with AaeAGT1 heterologously expressed in Escherichia coli showed a strong toxicity against Aedes aegypti larvae yet not against nematodes. The activity of recombinant A. aegerita ageritin toward rabbit ribosomes was confirmed in vitro Mutagenesis studies revealed a correlation between in vivo and in vitro activities, indicating that entomotoxicity is mediated by ribonucleolytic cleavage. The strong larvicidal activity of ageritin makes this protein a promising candidate for novel biopesticide development.IMPORTANCE Our results suggest a pronounced organismal specificity of a protein toxin with a very conserved intracellular molecular target. The molecular details of the toxin-target interaction will provide important insight into the mechanism of action of protein toxins and the ribosome. This insight might be exploited to develop novel bioinsecticides.

Nucleocytoplasmic O-glycosylation in protists

O-Glycosylation is an increasingly recognized modification of intracellular proteins in all kingdoms of life, and its occurrence in protists has been investigated to understand its evolution and its roles in the virulence of unicellular pathogens. We focus here on two kinds of glycoregulation found in unicellular eukaryotes: one is a simple O-fucose modification of dozens if not hundreds of Ser/Thr-rich proteins, and the other a complex pentasaccharide devoted to a single protein associated with oxygen sensing and the assembly of polyubiquitin chains. These modifications are not required for life but contingently modulate biological processes in the social amoeba Dictyostelium and the human pathogen Toxoplasma gondii, and likely occur in diverse unicellular protists. O-Glycosylation that is co-localized in the cytoplasm allows for glycoregulation over the entire life of the protein, contrary to the secretory pathway where glycosylation usually occurs before its delivery to its site of function. Here, we interpret cellular roles of nucleocytoplasmic glycans in terms of current evidence for their effects on the conformation and dynamics of protist proteins, to serve as a guide for future studies to examine their broader significance.

The different morphologies of yeast and filamentous fungi trigger distinct killing and feeding mechanisms in a fungivorous amoeba

Size and diverse morphologies pose a primary challenge for phagocytes such as innate immune cells and predatory amoebae when encountering fungal prey. Although filamentous fungi can escape phagocytic killing by pure physical constraints, unicellular spores and yeasts can mask molecular surface patterns or arrest phagocytic processing. Here, we show that the fungivorous amoeba Protostelium aurantium was able to adjust its killing and feeding mechanisms to these different cell shapes. Yeast-like fungi from the major fungal groups of basidiomycetes and ascomycetes were readily internalized by phagocytosis, except for the human pathogen Candida albicans whose mannoprotein coat was essential to escape recognition by the amoeba. Dormant spores of the filamentous fungus Aspergillus fumigatus also remained unrecognized, but swelling and the onset of germination induced internalization and intracellular killing by the amoeba. Mature hyphae of A. fumigatus were mostly attacked from the hyphal tip and killed by an actin-mediated invasion of fungal filaments. Our results demonstrate that predatory pressure imposed by amoebae in natural environments selects for distinct survival strategies in yeast and filamentous fungi but commonly targets the fungal cell wall as a crucial molecular pattern associated to prey and pathogens.

Combining microfluidics and RNA-sequencing to assess the inducible defensome of a mushroom against nematodes

BACKGROUND

Fungi are an attractive source of nutrients for predators. As part of their defense, some fungi are able to induce the production of anti-predator protein toxins in response to predation. A previous study on the interaction of the model mushroom Coprinopsis cinerea by the fungivorous nematode Aphelenchus avenae on agar plates has shown that the this fungal defense response is most pronounced in the part of the mycelium that is in direct contact with the nematode. Hence, we hypothesized that, for a comprehensive characterization of this defense response, an experimental setup that maximizes the zone of direct interaction between the fungal mycelium and the nematode, was needed.

RESULTS

In this study, we conducted a transcriptome analysis of C. cinerea vegetative mycelium upon challenge with A. avenae using a tailor-made microfluidic device. The device was designed such that the interaction between the fungus and the nematode was confined to a specific area and that the mycelium could be retrieved from this area for analysis. We took samples from the confrontation area after different time periods and extracted and sequenced the poly(A)+ RNA thereof. The identification of 1229 differentially expressed genes (DEGs) shows that this setup profoundly improved sensitivity over co-cultivation on agar plates where only 37 DEGs had been identified. The product of one of the most highly upregulated genes shows structural homology to bacterial pore-forming toxins, and revealed strong toxicity to various bacterivorous nematodes. In addition, bacteria associated with the fungivorous nematode A. avenae were profiled with 16S rRNA deep sequencing. Similar to the bacterivorous and plant-feeding nematodes, Proteobacteria and Bacteroidetes were the most dominant phyla in A. avenae.

CONCLUSIONS

The use of a novel experimental setup for the investigation of the defense response of a fungal mycelium to predation by fungivorous nematodes resulted in the identification of a comprehensive set of DEGs and the discovery of a novel type of fungal defense protein against nematodes. The bacteria found to be associated with the fungivorous nematode are a possible explanation for the induction of some antibacterial defense proteins upon nematode challenge.

Remusatia vivipara lectin and Sclerotium rolfsii lectin interfere with the development and gall formation activity of Meloidogyne incognita in transgenic tomato

Root knot nematodes are serious threats to growth and yield of solaneous crops including tomato. In this study, a binary vector carrying Remusatia vivipara (rvl1) and Sclerotium rolfsii (srl1) lectin genes were introduced independently into Lycopersicon esculentum cv. Pusa Ruby via Agrobacterium tumefaciens for resistance against root knot nematode, Meloidogyne incognita. In total, one hundred and one rvl1 and srl1-transformed plants exhibiting kanamycin resistance were confirmed to carry transgenes as detected by polymerase chain reaction (PCR) with 4.59% transformation efficiency. Genetic analysis of T₁ progeny confirmed Mendelian segregation of the introduced genes. Three events each of rvl1 and srl1 transgenic tomato were randomly selected for further confirmation by Southern and TAIL-PCR analyses. All three events of srl1 transgenics showed single copy transgene, whereas two rvl1 transgenic events showed single copy of transgene, while remaining event showed two copies of transgenes. Site of integration obtained for rvl1 and srl1 transgenic events by TAIL-PCR revealed that all the three events of rvl1 and srl1 transgenics differed for their site of integration and insertion sites did not contain any predicted gene. Moreover, expression of the rvl1 and srl1 transgenes was detected by haemagglutination assay in all three events of rvl1 and srl1, but not in non-transgenic tomato plant. Homozygous progenies of these events were grown and inoculated with M. incognita. Development and reproduction of M. incognita was severely affected in transgenic tomato plants expressing RVL1 and SRL1 exhibiting the high levels of resistance compared to non-transgenic plants. Therefore, these transgenic lines demonstrate a promising potential for variety development of tomato lines with enhanced resistance against M. incognita.

N-glycomic Complexity in Anatomical Simplicity: Caenorhabditis elegans as a Non-model Nematode?

Caenorhabditis elegans is a genetically well-studied model nematode or "worm"; however, its N-glycomic complexity is actually baffling and still not completely unraveled. Some features of its N-glycans are, to date, unique and include bisecting galactose and up to five fucose residues associated with the asparagine-linked Man2-3GlcNAc2 core; the substitutions include galactosylation of fucose, fucosylation of galactose and methylation of mannose or fucose residues as well as phosphorylcholine on antennal (non-reducing) N-acetylglucosamine. Only some of these modifications are shared with various other nematodes, while others have yet to be detected in any other species. Thus, C. elegans can be used as a model for some aspects of N-glycan function, but its glycome is far from identical to those of other organisms and is actually far from simple. Possibly the challenges of its native environment, which differ from those of parasitic or necromenic species, led to an anatomically simple worm possessing a complex glycome.

The 'Amoeboid Predator-Fungal Animal Virulence' Hypothesis

The observation that some aspects of amoeba-fungal interactions resemble animal phagocytic cell-fungal interactions, together with the finding that amoeba passage can enhance the virulence of some pathogenic fungi, has stimulated interest in the amoeba as a model system for the study of fungal virulence. Amoeba provide a relatively easy and cheap model system where multiple variables can be controlled for the study of fungi-protozoal (amoeba) interactions. Consequently, there have been significant efforts to study fungal⁻amoeba interactions in the laboratory, which have already provided new insights into the origin of fungal virulence as well as suggested new avenues for experimentation. In this essay we review the available literature, which highlights the varied nature of amoeba-fungal interactions and suggests some unsolved questions that are potential areas for future investigation. Overall, results from multiple independent groups support the 'amoeboid predator⁻fungal animal virulence hypothesis', which posits that fungal cell predation by amoeba can select for traits that also function during animal infection to promote their survival and thus contribute to virulence.

Trichoderma atroviride from Predator to Prey: Role of the Mitogen-Activated Protein Kinase Tmk3 in Fungal Chemical Defense against Fungivory by Drosophila melanogaster Larvae

Fungi, like other organisms, have natural predators, including fungivorous nematodes and arthropods that use them as an important food source. Thus, they require mechanisms to detect and respond to injury. Trichoderma atroviride responds to mycelial injury by rapidly regenerating its hyphae and developing asexual reproduction structures. Whether this injury response is associated with attack by fungivorous insects is unknown. Therefore, determining the possible conservation of a defense mechanism to predation in T. atroviride and plants and elucidating the mechanisms involved in the establishment of this response is of major interest. Here, we describe the chemical response of T. atroviride to mechanical injury and fungivory and the role of a MAPK pathway in the regulation of this response.

The response to injury represents an important strategy for animals and plants to survive mechanical damage and predation. Plants respond to injury by activating a defense response that includes the production of an important variety of compounds that help them withstand predator attack and recover from mechanical injury (MI). Similarly, the filamentous fungus Trichoderma atroviride responds to MI by strongly modifying its transcriptional profile and producing asexual reproduction structures (conidia). Here, we analyzed whether the response to MI in T. atroviride is related to a possible predator defense mechanism from a metabolic perspective. We found that the production of specific groups of secondary metabolites increases in response to MI but is reduced after fungivory by Drosophila melanogaster larvae. We further show that fungivory results in repression of the expression of genes putatively involved in the regulation of secondary metabolite production in T. atroviride. Activation of secondary metabolite production appears to depend on the mitogen-activated protein kinase (MAPK) Tmk3. Interestingly, D. melanogaster larvae preferred to feed on a tmk3 gene replacement mutant rather than on the wild-type strain. Consumption of the mutant strain, however, resulted in increased larval mortality.

IMPORTANCE Fungi, like other organisms, have natural predators, including fungivorous nematodes and arthropods that use them as an important food source. Thus, they require mechanisms to detect and respond to injury. Trichoderma atroviride responds to mycelial injury by rapidly regenerating its hyphae and developing asexual reproduction structures. Whether this injury response is associated with attack by fungivorous insects is unknown. Therefore, determining the possible conservation of a defense mechanism to predation in T. atroviride and plants and elucidating the mechanisms involved in the establishment of this response is of major interest. Here, we describe the chemical response of T. atroviride to mechanical injury and fungivory and the role of a MAPK pathway in the regulation of this response.

Bidirectional Propagation of Signals and Nutrients in Fungal Networks via Specialized Hyphae

Intercellular distribution of nutrients and coordination of responses to internal and external cues via endogenous signaling molecules are hallmarks of multicellular organisms. Vegetative mycelia of multicellular fungi are syncytial networks of interconnected hyphae resulting from hyphal tip growth, branching, and fusion. Such mycelia can reach considerable dimensions and, thus, different parts can be exposed to quite different environmental conditions. Our knowledge about the mechanisms by which fungal mycelia can adjust nutrient gradients or coordinate their defense response to fungivores is scarce, in part due to limitations in technologies currently available for examining different parts of a mycelium over longer time periods at the microscopic level. Here, we combined a tailor-made microfluidic platform with time-lapse fluorescence microscopy to visualize the dynamic response of the vegetative mycelium of a basidiomycete to two different stimuli. The microfluidic platform allows simultaneous monitoring at both the colony and single-hypha level. We followed the dynamics of the distribution of a locally administered nutrient analog and the defense response to spatially confined predation by a fungivorous nematode. Although both responses of the mycelium were constrained locally, we observed long-distance propagation for both the nutrient analog and defense response in a subset of hyphae. This propagation along hyphae occurred in both acropetal and basipetal directions and, intriguingly, the direction was found to alternate every 3 hr in an individual hypha. These results suggest that multicellular fungi have, as of yet, undescribed mechanisms to coordinate the distribution of nutrients and their behavioral response upon attack by fungivores.

Toxicity of Potential Fungal Defense Proteins towards the Fungivorous Nematodes Aphelenchus avenae and Bursaphelenchus okinawaensis

Our results support the hypothesis that cytoplasmic proteins abundant in fungal fruiting bodies are involved in fungal resistance against predation. The toxicity of these proteins toward stylet-feeding nematodes, which are also capable of feeding on plants, and the abundance of these proteins in edible mushrooms, may open possible avenues for biological crop protection against parasitic nematodes, e.g., by expression of these proteins in crops.

Resistance of fungi to predation is thought to be mediated by toxic metabolites and proteins. Many of these fungal defense effectors are highly abundant in the fruiting body and not produced in the vegetative mycelium. The defense function of fruiting body-specific proteins, however, including cytoplasmically localized lectins and antinutritional proteins such as biotin-binding proteins, is mainly based on toxicity assays using bacteria as a heterologous expression system, with bacterivorous/omnivorous model organisms as predators. Here, we present an ecologically more relevant experimental setup to assess the toxicity of potential fungal defense proteins towards the fungivorous, stylet-feeding nematodes Aphelenchus avenae and Bursaphelenchus okinawaensis. As a heterologous expression host, we exploited the filamentous fungus Ashbya gossypii. Using this new system, we assessed the toxicity of six previously characterized, cytoplasmically localized, potential defense proteins from fruiting bodies of different fungal phyla against the two fungivorous nematodes. We found that all of the tested proteins were toxic against both nematodes, albeit to various degrees. The toxicity of these proteins against both fungivorous and bacterivorous nematodes suggests that their targets have been conserved between the different feeding groups of nematodes and that bacterivorous nematodes are valid model organisms to assess the nematotoxicity of potential fungal defense proteins.

IMPORTANCE Our results support the hypothesis that cytoplasmic proteins abundant in fungal fruiting bodies are involved in fungal resistance against predation. The toxicity of these proteins toward stylet-feeding nematodes, which are also capable of feeding on plants, and the abundance of these proteins in edible mushrooms, may open possible avenues for biological crop protection against parasitic nematodes, e.g., by expression of these proteins in crops.

Induction of antibacterial proteins and peptides in the coprophilous mushroom Coprinopsis cinerea in response to bacteria

Bacteria are the main nutritional competitors of saprophytic fungi during colonization of their ecological niches. This competition involves the mutual secretion of antimicrobials that kill or inhibit the growth of the competitor. Over the last years it has been demonstrated that fungi respond to the presence of bacteria with changes of their transcriptome, but the significance of these changes with respect to competition for nutrients is not clear as functional proof of the antibacterial activity of the induced gene products is often lacking. Here, we report the genome-wide transcriptional response of the coprophilous mushroom Coprinopsis cinerea to the bacteria Bacillus subtilis and Escherichia coli. The genes induced upon co-cultivation with each bacterium were highly overlapping, suggesting that the fungus uses a similar arsenal of effectors against Gram-positive and -negative bacteria. Intriguingly, the induced genes appeare to encode predominantly secreted peptides and proteins with predicted antibacterial activities, which was validated by comparative proteomics of the C. cinerea secretome. Induced members of two putative antibacterial peptide and protein families in C. cinerea, the cysteine-stabilized αβ-defensins (Csαβ-defensins) and the GH24-type lysozymes, were purified, and their antibacterial activity was confirmed. These results provide compelling evidence that fungi are able to recognize the presence of bacteria and respond with the expression of an arsenal of secreted antibacterial peptides and proteins.

Fungal Morphogenesis, from the Polarized Growth of Hyphae to Complex Reproduction and Infection Structures

Filamentous fungi constitute a large group of eukaryotic microorganisms that grow by forming simple tube-like hyphae that are capable of differentiating into more-complex morphological structures and distinct cell types. Hyphae form filamentous networks by extending at their tips while branching in subapical regions. Rapid tip elongation requires massive membrane insertion and extension of the rigid chitin-containing cell wall. This process is sustained by a continuous flow of secretory vesicles that depends on the coordinated action of the microtubule and actin cytoskeletons and the corresponding motors and associated proteins. Vesicles transport cell wall-synthesizing enzymes and accumulate in a special structure, the Spitzenkörper, before traveling further and fusing with the tip membrane. The place of vesicle fusion and growth direction are enabled and defined by the position of the Spitzenkörper, the so-called cell end markers, and other proteins involved in the exocytic process. Also important for tip extension is membrane recycling by endocytosis via early endosomes, which function as multipurpose transport vehicles for mRNA, septins, ribosomes, and peroxisomes. Cell integrity, hyphal branching, and morphogenesis are all processes that are largely dependent on vesicle and cytoskeleton dynamics. When hyphae differentiate structures for asexual or sexual reproduction or to mediate interspecies interactions, the hyphal basic cellular machinery may be reprogrammed through the synthesis of new proteins and/or the modification of protein activity. Although some transcriptional networks involved in such reprogramming of hyphae are well studied in several model filamentous fungi, clear connections between these networks and known determinants of hyphal morphogenesis are yet to be established.

Fungal genotype determines survival of Drosophila melanogaster when competing with Aspergillus nidulans

Fungi produce an astonishing variety of secondary metabolites, some of which belong to the most toxic compounds in the living world. Several fungal metabolites have anti-insecticidal properties which may yield advantages to the fungus in competition with insects for exploitation of environmental resources. Using the Drosophila melanogaster/Aspergillus nidulans ecological model system to assess secondary metabolite mutant genotypes, we find a major role for the veA allele in insect/fungal confrontations that exceeds the influence of other factors such as LaeA. VeA along with LaeA is a member of a transcriptional complex governing secondary metabolism in A. nidulans. However, historically a mutant veA allele, veA1 reduced in secondary metabolite output, has been used in many studies of this model organism. To test the significance of this allele in our system, Aspergillus nidulans veA wild type, veA1, ΔveA and ΔlaeA were evaluated in confrontation assays to analyze egg laying activity, and the survival rate of larvae. The veA1 genetic background led to a significant increase of larval survival. Adult flies were observed almost exclusively on veA1, ΔveA or ΔlaeA genetic backgrounds, suggesting a role for the velvet complex in insect/fungal interactions. This effect was most profound using the veA1 mutant. Hence, larval survival in confrontations is highly affected by the fungal genotype.

When green and red mycology meet: Impressions from an interdisciplinary forum on virulence mechanisms of phyto- and human-pathogenic fungi

Fungal infections pose a constant threat to plants and humans, but detailed knowledge about pathogenesis, immunity, or virulence is rather scarce. Due to the fact that a certain overlap in the armoury of infection exists between plant- and human-pathogenic fungi, an interdisciplinary forum was held in October 2016 at the Institute for Clinical Microbiology, Immunology and Hygiene in Erlangen under the organisational umbrella from two special interest groups of German microbial societies. Scientific exchange and intense discussion of this timely topic was fostered by bringing together renowned experts in their respective fields to present their thoughts and recent findings in the course of a plenary lecture and six themed sessions, accompanied by oral and poster contributions of young researchers. By targeting the topic of fungal virulence mechanisms from various angles and in the context of plant and human hosts, some common grounds and exciting perspectives could be deduced during this vibrant scientific event.

Effects of Lectins on initial attachment of cariogenic Streptococcus mutans

Oral bacteria initiate biofilm formation by attaching to tooth surfaces via an interaction of a lectin-like bacterial protein with carbohydrate chains on the pellicle. This study aimed to find naturally derived lectins that inhibit the initial attachment of a cariogenic bacterial species, Streptococcus mutans (S. mutans), to carbohydrate chains in saliva in vitro. Seventy kinds of lectins were screened for candidate motifs that inhibit the attachment of S. mutans ATCC 25175 to a saliva-coated culture plate. The inhibitory effect of the lectins on attachment of the S. mutans to the plates was quantified by crystal violet staining, and the biofilm was observed under a scanning electron microscope (SEM). Surface plasmon resonance (SPR) analysis was performed to examine the binding of S. mutans to carbohydrate chains and the binding of candidate lectins to carbohydrate chains, respectively. Moreover, binding assay between the biotinylated-lectins and the saliva components was conducted to measure the lectin binding. Lectins recognizing a salivary carbohydrate chain, Galβ1-3GalNAc, inhibited the binding of S. mutans to the plate. In particular, Agaricus bisporus agglutinin (ABA) markedly inhibited the binding. This inhibition was confirmed by SEM observation. SPR analysis indicated that S. mutans strongly binds to Galβ1-3GalNAc, and ABA binds to Galβ1-3GalNAc. Finally, the biotinylated Galβ1-3GalNAc-binding lectins including ABA demonstrated marked binding to the saliva components. These results suggest that ABA lectin inhibited the attachment of S. mutans to Galβ1-3GalNAc in saliva and ABA can be useful as a potent inhibitor for initial attachment of oral bacteria and biofilm formation.

Typhonium giganteum Lectin Exerts A Pro-Inflammatory Effect on RAW 264.7 via ROS and The NF-κB Signaling Pathway

Typhonii rhizoma, a widely used herb in traditional Chinese medicine, has acute irritating toxicity related to Typhonium giganteum lectin (TGL). TGL exhibits acute inflammatory effects, but the underlying molecular mechanisms are largely unknown. This paper is designed to assess the pro-inflammatory response of TGL on RAW 264.7 cells. RAW 264.7 treated with 6.25, 12.5, 25, and 50 µg/mL TGL showed elevated levels of inflammatory factors (TNF-α, IL-1β) and of p-IκB and p-p65, all dose-dependent, indicating that TGL had a substantial inflammatory effect and mobilized the nuclear factor-κB (NF-κB) pathway. All four TGL treatments also induced the up-regulation of reactive oxygen species (ROS) and cytosolic free Ca²⁺ and down-regulation of mitochondrial membrane potential (MMP). The production of cytokines and p-IκB, p-p65 were reduced by N-acetylcysteine (NAC), an ROS scavenger, which somewhat abrogated ROS production. The results showed the TGL-activated inflammatory signaling pathway NF-κB to be associated with the overproduction of ROS. Moreover, 50 μg/mL treatment with TGL led to cell apoptosis after 1 h and increased necrosis over time. These results provided potential molecular mechanisms for the observed inflammatory response to TGL including up-regulation of ROS and cytosolic free Ca²⁺, down-regulation of MMP, the mobilization of the NF-κB pathway, and the subsequent overproduction of pro-inflammatory factors resulting in apoptosis. Long-term stimulation with TGL resulted in strong toxic effects related to inflammation that induced necrosis in macrophages.

Lectins from Mycelia of Basidiomycetes

Lectins are proteins of a nonimmunoglobulin nature that are capable of specific recognition of and reversible binding to the carbohydrate moieties of complex carbohydrates, without altering the covalent structure of any of the recognized glycosyl ligands. They have a broad range of biological activities important for the functioning of the cell and the whole organism and, owing to the high specificity of reversible binding to carbohydrates, are valuable tools used widely in biology and medicine. Lectins can be produced by many living organisms, including basidiomycetes. Whereas lectins from the fruit bodies of basidiomycetes have been studied sufficiently well, mycelial lectins remain relatively unexplored. Here, we review and comparatively analyze what is currently known about lectins isolated from the vegetative mycelium of macrobasidiomycetes, including their localization, properties, and carbohydrate specificities. Particular attention is given to the physiological role of mycelial lectins in fungal growth and development.

Globally distributed root endophyte Phialocephala subalpina links pathogenic and saprophytic lifestyles

BACKGROUND

Whereas an increasing number of pathogenic and mutualistic ascomycetous species were sequenced in the past decade, species showing a seemingly neutral association such as root endophytes received less attention. In the present study, the genome of Phialocephala subalpina, the most frequent species of the Phialocephala fortinii s.l. - Acephala applanata species complex, was sequenced for insight in the genome structure and gene inventory of these wide-spread root endophytes.

RESULTS

The genome of P. subalpina was sequenced using Roche/454 GS FLX technology and a whole genome shotgun strategy. The assembly resulted in 205 scaffolds and a genome size of 69.7 Mb. The expanded genome size in P. subalpina was not due to the proliferation of transposable elements or other repeats, as is the case with other ascomycetous genomes. Instead, P. subalpina revealed an expanded gene inventory that includes 20,173 gene models. Comparative genome analysis of P. subalpina with 13 ascomycetes shows that P. subalpina uses a versatile gene inventory including genes specific for pathogens and saprophytes. Moreover, the gene inventory for carbohydrate active enzymes (CAZymes) was expanded including genes involved in degradation of biopolymers, such as pectin, hemicellulose, cellulose and lignin.

CONCLUSIONS

The analysis of a globally distributed root endophyte allowed detailed insights in the gene inventory and genome organization of a yet largely neglected group of organisms. We showed that the ubiquitous root endophyte P. subalpina has a broad gene inventory that links pathogenic and saprophytic lifestyles.

A Novel Fucose-binding Lectin from Photorhabdus luminescens (PLL) with an Unusual Heptabladed β-Propeller Tetrameric Structure

Photorhabdus luminescens is known for its symbiosis with the entomopathogenic nematode Heterorhabditis bacteriophora and its pathogenicity toward insect larvae. A hypothetical protein from P. luminescens was identified, purified from the native source, and characterized as an l-fucose-binding lectin, named P. luminescens lectin (PLL). Glycan array and biochemical characterization data revealed PLL to be specific toward l-fucose and the disaccharide glycan 3,6-O-Me₂-Glcβ1-4(2,3-O-Me₂)Rhaα-O-(p-C₆H₄)-OCH₂CH₂NH₂ PLL was discovered to be a homotetramer with an intersubunit disulfide bridge. The crystal structures of native and recombinant PLL revealed a seven-bladed β-propeller fold creating seven putative fucose-binding sites per monomer. The crystal structure of the recombinant PLL·l-fucose complex confirmed that at least three sites were fucose-binding. Moreover, the crystal structures indicated that some of the other sites are masked either by the tetrameric nature of the lectin or by incorporation of the C terminus of the lectin into one of these sites. PLL exhibited an ability to bind to insect hemocytes and the cuticular surface of a nematode, H. bacteriophora.

An Unusual Member of the Papain Superfamily: Mapping the Catalytic Cleft of the Marasmius oreades agglutinin (MOA) with a Caspase Inhibitor

Papain-like cysteine proteases (PLCPs) constitute the largest group of thiol-based protein degrading enzymes and are characterized by a highly conserved fold. They are found in bacteria, viruses, plants and animals and involved in a number of physiological and pathological processes, parasitic infections and host defense, making them interesting targets for drug design. The Marasmius oreades agglutinin (MOA) is a blood group B-specific fungal chimerolectin with calcium-dependent proteolytic activity. The proteolytic domain of MOA presents a unique structural arrangement, yet mimicking the main structural elements in known PLCPs. Here we present the X-ray crystal structure of MOA in complex with Z-VAD-fmk, an irreversible caspase inhibitor known to cross-react with PLCPs. The structural data allow modeling of the substrate binding geometry and mapping of the fundamental enzyme-substrate interactions. The new information consolidates MOA as a new, yet strongly atypical member of the papain superfamily. The reported complex is the first published structure of a PLCP in complex with the well characterized caspase inhibitor Z-VAD-fmk.

In Silico Study to Develop a Lectin-Like Protein from Mushroom Agaricus bisporus for Pharmaceutical Application

A lectin-like protein of unknown function designated as LSMT was recently discovered in the edible mushroom Agaricus bisporus. The protein shares high structural similarity to HA-33 from Clostridium botulinum (HA33) and Ricin-B-like lectin from the mushroom Clitocybe nebularis (CNL), which have been developed as drug carrier and anti-cancer, respectively. These homologous proteins display the ability to penetrate the intestinal epithelial cell monolayer, and are beneficial for oral administration. As the characteristics of LSMT are unknown, a structural study in silico was performed to assess its potential pharmaceutical application. The study suggested potential binding to target ligands such as HA-33 and CNL although the nature, specificity, capacity, mode, and strength may differ. Further molecular docking experiments suggest that interactions between the LSMT and tested ligands may take place. This finding indicates the possible use of the LSMT protein, initiating new research on its use for pharmaceutical purposes.

Soil-on-a-Chip: microfluidic platforms for environmental organismal studies

Soil is the habitat of countless organisms and encompasses an enormous variety of dynamic environmental conditions. While it is evident that a thorough understanding of how organisms interact with the soil environment may have substantial ecological and economical impact, current laboratory-based methods depend on reductionist approaches that are incapable of simulating natural diversity. The application of Lab-on-a-Chip or microfluidic technologies to organismal studies is an emerging field, where the unique benefits afforded by system miniaturisation offer new opportunities for the experimentalist. Indeed, precise spatiotemporal control over the microenvironments of soil organisms in combination with high-resolution imaging has the potential to provide an unprecedented view of biological events at the single-organism or single-cell level, which in turn opens up new avenues for environmental and organismal studies. Herein we review some of the most recent and interesting developments in microfluidic technologies for the study of soil organisms and their interactions with the environment. We discuss how so-called "Soil-on-a-Chip" technology has already contributed significantly to the study of bacteria, nematodes, fungi and plants, as well as inter-organismal interactions, by advancing experimental access and environmental control. Most crucially, we highlight where distinct advantages over traditional approaches exist and where novel biological insights will ensue.