The catalytic subunit of type 2A protein phosphatase negatively regulates conidiation and melanin biosynthesis in Setosphaeria turcica

Northern corn leaf blight caused by Setosphaeria turcica is a major fungal disease responsible for significant reductions in maize yield worldwide. Eukaryotic type 2A protein phosphatase (PP2A) influences growth and virulence in a number of pathogenic fungi, but little is known about its roles in S. turcica. Here, we functionally characterized S. turcica StPP2A-C, which encodes the catalytic C subunit of StPP2A. StPP2A-C deletion slowed colony growth, conidial germination, and appressorium formation but increased conidiation, melanin biosynthesis, glycerol content, and disease lesion size on maize. These effects were associated with expression changes in genes related to calcium signaling, conidiation, laccase activity, and melanin and glycerol biosynthesis, as well as changes in intra- and extracellular laccase activity. A pull-down screen for candidate StPP2A-c interactors revealed an interaction between StPP2A-c and StLac1. Theoretical modeling and yeast two-hybrid experiments confirmed that StPP2A-c interacted specifically with the copper ion binding domain of StLac1 and that Cys267 of StPP2A-c was required for this interaction. StPP2A-C expression thus appears to promote hyphal growth and reduce pathogenicity in S. turcica, at least in part by altering melanin synthesis and laccase activity; these insights may ultimately support the development of novel strategies for biological management of S. turcica.

Study on the virulence of Metarhizium anisopliae against Spodoptera frugiperda (J. E. Smith, 1797)

This study examined the impact of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) conidia on the eggs, larvae, pupae, and adults of Spodoptera frugiperda. The results showed that eggs, larvae, pupae, and adults exhibited mortality rates that were dependent on the dose. An increased amount of conidia (1.5 × 109 conidia/mL) was found to be toxic to larvae, pupae, and adults after 9 days of treatment, resulting in a 100% mortality rate in eggs, 98% in larvae, 76% in pupae, and 85% in adults. A study using earthworms as bioindicators found that after 3 days of exposure, M. anisopliae conidia did not cause any harmful effects on the earthworms. In contrast, the chemical treatment (positive control) resulted in 100% mortality at a concentration of 40 ppm. Histopathological studies showed that earthworm gut tissues treated with fungal conidia did not show significant differences compared with those of the negative control. The gut tissues of earthworms treated with monocrotophos exhibited significant damage, and notable differences were observed in the chemical treatment. The treatments with 70 and 100 µg/mL solutions of Eudrilus eugeniae epidermal mucus showed no fungal growth. An analysis of the enzymes at a biochemical level revealed a decrease in the levels of acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase in S. frugiperda larvae after exposure to fungal conidia. This study found that M. anisopliae is effective against S. frugiperda, highlighting the potential of this entomopathogenic fungus in controlling this agricultural insect pest.

Nucleoside Diphosphate Kinase FgNdpk Is Required for DON Production and Pathogenicity by Regulating the Growth and Toxisome Formation of Fusarium graminearum

Nucleoside diphosphate kinases (NDPKs) are nucleotide metabolism enzymes that play different physiological functions in different species. However, the roles of NDPK in phytopathogen and mycotoxin production are not well understood. In this study, we showed that Fusarium graminearum FgNdpk is important for vegetative growth, conidiation, sexual development, and pathogenicity. Furthermore, FgNdpk is required for deoxynivalenol (DON) production; deletion of FgNDPK downregulates the expression of DON biosynthesis genes and disrupts the formation of FgTri4-GFP-labeled toxisomes, while overexpression of FgNDPK significantly increases DON production. Interestingly, FgNdpk colocalizes with the DON biosynthesis proteins FgTri1 and FgTri4 in the toxisome, and coimmunoprecipitation (Co-IP) assays show that FgNdpk associates with FgTri1 and FgTri4 in vivo and regulates their localizations and expressions, respectively. Taken together, these data demonstrate that FgNdpk is important for vegetative growth, conidiation, and pathogenicity and acts as a key protein that regulates toxisome formation and DON biosynthesis in F. graminearum.

Regulation of sexual differentiation initiation in Schizosaccharomyces pombe

The fission yeast Schizosaccharomyces pombe is an excellent model organism to explore cellular events owing to rich tools in genetics, molecular biology, cellular biology, and biochemistry. Schizosaccharomyces pombe proliferates continuously when nutrients are abundant but arrests in G1 phase upon depletion of nutrients such as nitrogen and glucose. When cells of opposite mating types are present, cells conjugate, fuse, undergo meiosis, and finally form 4 spores. This sexual differentiation process in S. pombe has been studied extensively. To execute sexual differentiation, the glucose-sensing cAMP-PKA (cyclic adenosine monophosphate-protein kinase A) pathway, nitrogen-sensing TOR (target of rapamycin) pathway, and SAPK (stress-activating protein kinase) pathway are crucial, and the MAPK (mitogen-activating protein kinase) cascade is essential for pheromone sensing. These signals regulate ste11 at the transcriptional and translational levels, and Ste11 is modified in multiple ways. This review summarizes the initiation of sexual differentiation in S. pombe based on results I have helped to obtain, including the work of many excellent researchers.

The Gene vepN Regulated by Global Regulatory Factor veA That Affects Aflatoxin Production, Morphological Development and Pathogenicity in Aspergillus flavus

Velvet (VeA), a light-regulated protein that shuttles between the cytoplasm and the nucleus, serves as a key global regulator of secondary metabolism in various Aspergillus species and plays a pivotal role in controlling multiple developmental processes. The gene vepN was chosen for further investigation through CHIP-seq analysis due to significant alterations in its interaction with VeA under varying conditions. This gene (AFLA_006970) contains a Septin-type guanine nucleotide-binding (G) domain, which has not been previously reported in Aspergillus flavus (A. flavus). The functional role of vepN in A. flavus was elucidated through the creation of a gene knockout mutant and a gene overexpression strain using a well-established dual-crossover recombinational technique. A comparison between the wild type (WT) and the ΔvepN mutant revealed distinct differences in morphology, reproductive capacity, colonization efficiency, and aflatoxin production. The mutant displayed reduced growth rate; dispersion of conidial heads; impaired cell wall integrity; and decreased sclerotia formation, colonization capacity, and aflatoxin levels. Notably, ΔvepN exhibited complete growth inhibition under specific stress conditions, highlighting the essential role of vepN in A. flavus. This study provides evidence that vepN positively influences aflatoxin production, morphological development, and pathogenicity in A. flavus.

Mitochondrial Outer Membrane Translocase MoTom20 Modulates Mitochondrial Morphology and Is Important for Infectious Growth of the Rice Blast Fungus Magnaporthe oryzae

Mitochondria are highly dynamic organelles that constantly change their morphology to adapt to the cellular environment through fission and fusion, which is critical for a cell to maintain normal cellular functions. Despite the significance of this process in the development and pathogenicity of the rice blast fungus Magnaporthe oryzae, the underlying mechanism remains largely elusive. Here, we identified and characterized a mitochondrial outer membrane translocase, MoTom20, in M. oryzae. Targeted gene deletion revealed that MoTom20 plays an important role in vegetative growth, conidiogenesis, penetration, and infectious growth of M. oryzae. The growth rate, conidial production, appressorium turgor, and pathogenicity are decreased in the ΔMotom20 mutant compared with the wild-type and complemented strains. Further analysis revealed that MoTom20 localizes in mitochondrion and plays a key role in regulating mitochondrial fission and fusion balance, which is critical for infectious growth. Finally, we found that MoTom20 is involved in fatty-acid utilization, and its yeast homolog ScTom20 is able to rescue the defects of ΔMotom20 in mitochondrial morphology and pathogenicity. Overall, our data demonstrate that MoTom20 is a key regulator for mitochondrial morphology maintenance, which is important for infectious growth of the rice blast fungus M. oryzae. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Development of a Rapid Sporulation Method of Fusarium graminearum Using Liquid Cultivation

Fusarium graminearum is an important fungus causing a variety of maize diseases, including stalk rot, ear rot, and sheath rot. However, conidia of F. graminearum are not easily obtained under normal culture conditions, which seriously affects the identification and pathogenicity assessment of the isolates and screening of resistance sources. This study was undertaken to develop and utilize a rapid sporulation technique of F. graminearum using liquid cultivation, which could meet the needs of various tests. The results show that the optimum conditions for sporulation of F. graminearum were as follows: culture medium, 0.154 mol/liter of saline; temperature, 28 to 30°C; incubation time, 96 h; initial pH, 9 to 10; illumination, continuous ultraviolet light; and shaking speed, 150 rpm. Using this culture method, conidial concentration of tested F. graminearum strains can reach >1.5 × 10⁵ conidia/ml. Compared with the existing methods using mung bean and carboxylmethyl cellulose as matrix, saline is relatively inexpensive, and the culture process, relatively quick. Overall, this study provided a systematic, rapid, and simple method to obtain a large number of conidia of F. graminearum.

The pleiotropic functions of intracellular hydrophobins in aerial hyphae and fungal spores

Higher fungi can rapidly produce large numbers of spores suitable for aerial dispersal. The efficiency of the dispersal and spore resilience to abiotic stresses correlate with their hydrophobicity provided by the unique amphiphilic and superior surface-active proteins-hydrophobins (HFBs)-that self-assemble at hydrophobic/hydrophilic interfaces and thus modulate surface properties. Using the HFB-enriched mold Trichoderma (Hypocreales, Ascomycota) and the HFB-free yeast Pichia pastoris (Saccharomycetales, Ascomycota), we revealed that the rapid release of HFBs by aerial hyphae shortly prior to conidiation is associated with their intracellular accumulation in vacuoles and/or lipid-enriched organelles. The occasional internalization of the latter organelles in vacuoles can provide the hydrophobic/hydrophilic interface for the assembly of HFB layers and thus result in the formation of HFB-enriched vesicles and vacuolar multicisternal structures (VMSs) putatively lined up by HFBs. These HFB-enriched vesicles and VMSs can become fused in large tonoplast-like organelles or move to the periplasm for secretion. The tonoplast-like structures can contribute to the maintenance of turgor pressure in aerial hyphae supporting the erection of sporogenic structures (e.g., conidiophores) and provide intracellular force to squeeze out HFB-enriched vesicles and VMSs from the periplasm through the cell wall. We also show that the secretion of HFBs occurs prior to the conidiation and reveal that the even spore coating of HFBs deposited in the extracellular matrix requires microscopic water droplets that can be either guttated by the hyphae or obtained from the environment. Furthermore, we demonstrate that at least one HFB, HFB4 in T. guizhouense, is produced and secreted by wetted spores. We show that this protein possibly controls spore dormancy and contributes to the water sensing mechanism required for the detection of germination conditions. Thus, intracellular HFBs have a range of pleiotropic functions in aerial hyphae and spores and are essential for fungal development and fitness.

Propagation and characterization of viable arbuscular mycorrhizal fungal spores within maize plant (Zea mays L.)

BACKGROUND

The harmful effect of chemical fertilizer application on human health and the environment as a modern method of meeting the food demand of the increasing world population demands an urgent alternative that is environmentally friendly, which will pose no harm to human health and the environment. Arbuscular mycorrhizal fungi (AMF) are beneficial soil microorganisms that provide various ecological functions in increasing soil fertility and enhancing plant growth. This present study aimed to propagate, characterize and examine the effect of viable arbuscular mycorrhizal fungal spores on maize (Zea mays L) hosts using molecular methods. The propagation of AMF in the host plant using sterile soil and vermiculite was conducted in the greenhouse.

RESULT

The effect of AMF inoculation revealed a significant difference (P > 0.05) in maize growth, root colonization and AMF spore count when compared with the control. In all the parameters measured in this study, all the AMF spores propagated had a positive effect on the maize plant over the control, with the highest value mostly recorded in Rhizophagus irregularis AOB1. The molecular characterization of the spore using a specific universal primer for Glomeromycota established the success of the propagation process, which enhanced the classification of the AMF species into Rhizophagus irregularis OAB1, Glomus mosseae OAB2 and Paraglomus occultum OAB3.

CONCLUSION

This finding will be a starting point in producing arbuscular mycorrhizal inoculum as a biofertilizer to enhance plant growth promotion. © 2021 Society of Chemical Industry.

Inhibition of Aspergillus oryzae Mycelium Growth and Conidium Production by Irradiation with Light at Different Wavelengths and Intensities

Aspergillus oryzae is a safe filamentous fungus widely used in the food, medicine, and feed industries, but there is currently not enough research on the light response of A. oryzae. In this study, 12 different light conditions were set and A. oryzae GDMCC 3.31 was continuously irradiated for 72 h to investigate the effect of light on mycelial growth and conidium production. Specifically, each light condition was the combination of one light wavelength (475, 520, or 630 nm) and one light intensity (20, 40, 60, or 80 μmol photon m-2 s-1). The results show that mycelium growth was inhibited significantly by green light (wavelength of 520 nm and intensities of 20 and 60 μmol photon m-2 s-1) and blue light (wavelength of 475 nm and intensity of 80 μmol photon m-2 s-1). The production of conidia was suppressed only by blue light (wavelength of 475 nm and intensities of 40, 60, and 80 μmol photon m-2 s-1), and those levels of inhibition increased when the intensity of blue light increased. When the strain was irradiated by blue light (80 μmol photon m-2 s-1), the number of conidia was 57.4% less than that of the darkness group. However, within our set range of light intensities, A. oryzae GDMCC 3.31 was insensitive to red light (wavelength of 630 nm) in terms of mycelium growth and conidium production. Moreover, interaction effects between light wavelength and intensity were found to exist in terms of colony diameter and the number of conidia. This research investigated the light response of A. oryzae, which may provide a new method to regulate mixed strains in fermented foods by light. IMPORTANCE Studies on the monochromatic light response of Aspergillus nidulans and Neurospora crassa have gone deep into the molecular mechanism. However, research methods for the light response of A. oryzae remain in the use of white light sources. In this study, we first demonstrated that A. oryzae GDMCC 3.31 was sensitive to light wavelength and intensity. We have observed that blue light inhibited its growth and sporulation and the inhibitory effect increased with intensity. This research not only adds new content to the study of the photoreaction of Aspergillus but also brings new possibilities for the use of light to regulate mixed strains and ultimately improve the flavor quality of fermented foods.

BbWor1, a Regulator of Morphological Transition, Is Involved in Conidium-Hypha Switching, Blastospore Propagation, and Virulence in Beauveria bassiana

Morphological transition is an important adaptive mechanism in the host invasion process. Wor1 is a conserved fungal regulatory protein that controls the phenotypic switching and pathogenicity of Candida albicans. By modulating growth conditions, we simulated three models of Beauveria bassiana morphological transitions, including CTH (conidia to hyphae), HTC (hyphae to conidia), and BTB (blastospore to blastospore). Disruption of BbWor1 (an ortholog of Wor1) resulted in a distinct reduction in the time required for conidial germination (CTH), a significant increase in hyphal growth, and a decrease in the yield of conidia (HTC), indicating that BbWor1 positively controls conidium production and negatively regulates hyphal growth in conidium-hypha switching. Moreover, ΔBbWor1 prominently decreased blastospore yield, shortened the G0/G1 phase, and prolonged the G2/M phase under the BTB model. Importantly, BbWor1 contributed to conidium-hypha switching and blastospore propagation via different genetic pathways, and yeast one-hybrid testing demonstrated the necessity of BbWor1 to control the transcription of an allergen-like protein gene (BBA_02580) and a conidial wall protein gene (BBA_09998). Moreover, the dramatically weakened virulence of ΔBbWor1 was examined by immersion and injection methods. Our findings indicate that BbWor1 is a vital participant in morphological transition and pathogenicity in entomopathogenic fungi. IMPORTANCE As a well-known entomopathogenic fungus, Beauveria bassiana has a complex life cycle and involves transformations among single-cell conidia, blastospores, and filamentous hyphae. This study provides new insight into the regulation of the fungal cell morphological transitions by simulating three models. Our research identified BbWor1 as a core transcription factor of morphological differentiation that positively regulates the production of conidia and blastospores but negatively regulates hyphal growth. More importantly, BbWor1 affects fungal pathogenicity and the global transcription profiles within three models of growth stage transformation. The present study lays a foundation for the exploration of the transition mechanism of entomopathogenic fungi and provides material for the morphological study of fungi.

Homeobox Transcription Factors Are Required for Fungal Development and the Suppression of Host Defense Mechanisms in the Colletotrichum scovillei-Pepper Pathosystem

Colletotrichum scovillei, an ascomycete phytopathogenic fungus, is the main causal agent of serious yield losses of economic crops worldwide. The fungus causes anthracnose disease on several fruits, including peppers. However, little is known regarding the underlying molecular mechanisms involved in the development of anthracnose caused by this fungus. In an initial step toward understanding the development of anthracnose on pepper fruits, we retrieved 624 transcription factors (TFs) from the whole genome of C. scovillei and comparatively analyzed the entire repertoire of TFs among phytopathogenic fungi. Evolution and proliferation of members of the homeobox-like superfamily, including homeobox (HOX) TFs that regulate the development of eukaryotic organisms, were demonstrated in the genus Colletotrichum. C. scovillei was found to contain 10 HOX TF genes (CsHOX1 to CsHOX10), which were functionally characterized using deletion mutants of each CsHOX gene. Notably, CsHOX1 was identified as a pathogenicity factor required for the suppression of host defense mechanisms, which represents a new role for HOX TFs in pathogenic fungi. CsHOX2 and CsHOX7 were found to play essential roles in conidiation and appressorium development, respectively, in a stage-specific manner in C. scovillei. Our study provides a molecular basis for understanding the mechanisms associated with the development of anthracnose on fruits caused by C. scovillei, which will aid in the development of novel approaches for disease management. IMPORTANCE The ascomycete phytopathogenic fungus, Colletotrichum scovillei, causes serious yield loss on peppers. However, little is known about molecular mechanisms involved in the development of anthracnose caused by this fungus. We analyzed whole-genome sequences of C. scovillei and isolated 624 putative TFs, revealing the existence of 10 homeobox (HOX) transcription factor (TF) genes. We found that CsHOX1 is a pathogenicity factor required for the suppression of host defense mechanism, which represents a new role for HOX TFs in pathogenic fungi. We also found that CsHOX2 and CsHOX7 play essential roles in conidiation and appressorium development, respectively, in a stage-specific manner in C. scovillei. Our study contributes to understanding the mechanisms associated with the development of anthracnose on fruits caused by C. scovillei, which will aid for initiating novel approaches for disease management.

Antagonistic fungal enterotoxins intersect at multiple levels with host innate immune defences

Animals and plants need to defend themselves from pathogen attack. Their defences drive innovation in virulence mechanisms, leading to never-ending cycles of co-evolution in both hosts and pathogens. A full understanding of host immunity therefore requires examination of pathogen virulence strategies. Here, we take advantage of the well-studied innate immune system of Caenorhabditis elegans to dissect the action of two virulence factors from its natural fungal pathogen Drechmeria coniospora. We show that these two enterotoxins have strikingly different effects when expressed individually in the nematode epidermis. One is able to interfere with diverse aspects of host cell biology, altering vesicle trafficking and preventing the key STAT-like transcription factor STA-2 from activating defensive antimicrobial peptide gene expression. The second increases STA-2 levels in the nucleus, modifies the nucleolus, and, potentially as a consequence of a host surveillance mechanism, causes increased defence gene expression. Our results highlight the remarkably complex and potentially antagonistic mechanisms that come into play in the interaction between co-evolved hosts and pathogens.

Functional Analysis of Autophagy-Related Gene ATG12 in Potato Dry Rot Fungus Fusarium oxysporum

Autophagy is an intracellular process in all eukaryotes which is responsible for the degradation of cytoplasmic constituents, recycling of organelles, and recycling of proteins. It is an important cellular process responsible for the effective virulence of several pathogenic plant fungal strains, having critical impacts on important crop plants including potatoes. However, the detailed physiological mechanisms of autophagy involved in the infection biology of soil-borne pathogens in the potato crop needs to be investigated further. In this study, the autophagy-related gene, FoATG12, in potato dry rot fungus Fusarium oxysporum was investigated by means of target gene replacement and overexpression. The deletion mutant ∆FoATG12 showed reduction in conidial formation and exhibited impaired aerial hyphae. The FoATG12 affected the expression of genes involved in pathogenicity and vegetative growth, as well as on morphology features of the colony under stressors. It was found that the disease symptoms were delayed upon being inoculated by the deletion mutant of FoATG12 compared to the wild-type (WT) and overexpression (OE), while the deletion mutant showed the disease symptoms on tomato plants. The results confirmed the significant role of the autophagy-related ATG12 gene in the production of aerial hyphae and the effective virulence of F. oxysporum in the potato crop. The current findings provid an enhanced gene-level understanding of the autophagy-related virulence of F. oxysporum, which could be helpful in pathogen control research and could have vital impacts on the potato crop.

MdPR4, a pathogenesis-related protein in apple, is involved in chitin recognition and resistance response to apple replant disease pathogens

To maximize breeding and exploitation of disease resistance traits for managing apple replant disease (ARD), it is of great importance to understand the mechanisms of apple root resistance. Currently, little is known about the functions of the specific genes that confer resistance traits in apple root. In this study, molecular, biochemical, and genetic approaches allowed an in-depth understanding of the role of the MdPR4 gene in the defense response of apple root. The MdPR4 encoding gene showed upregulation following ARD pathogen inoculation in our previous transcriptome data. Subcellular localization analyses revealed that MdPR4 is localized on the plasma membrane, endoplasmic reticulum, and apoplast, which is mainly determined by its signal peptide. Molecular docking analysis between MdPR4 protein with chitin molecule and in vitro MdPR4 chitin affinity assay proved its chitin-binding ability, which provided evidence for its role in chitin-mediated immune responses. Purified MdPR4 protein and MdPR4 overexpressed apple callus inhibited spore germination and mycelial growth of ARD-related Fusarium spp. pathogens. These data support the conclusion that MdPR4 is a chitin-binding protein in apple vegetative tissues that may play an important role in defense activation in response to ARD pathogen infection.

Ecology of Diaporthe eres, the causal agent of hazelnut defects

Diaporthe eres has been recently reported as the causal agent of hazelnut defects, with characteristic brown spots on the kernels surface and internal fruit discoloration. Knowledge regarding the ecology of this fungus is poor but, is critical to support a rationale and effective hazelnut crop protection strategy. Therefore, a study was performed to describe and model the effect of different abiotic factors such as temperature (T, 5-35°C, step 5°C) and water activity (aw 0.83-0.99, step 0.03) regimes on D. eres mycelial growth, pycnidial conidiomata development and asexual spore production during a 60-day incubation period. Alpha conidia germination was tested in the same T range and at different relative humidities (RH = 94, 97 and 100%) over 48 h incubation period. Fungal growth was observed from the first visual observation; regarding pycnidia and cirrhi, their development started after 8 and 19 days of incubation, respectively and increased over time. The optimum T for growth was 20-25°C and for pycnidia and cirrhi development was 30°C; aw ≥ 0.98 was optimal for the tested steps of the fungal cycle. The best condition for conidial germination of D. eres was at 25°C with RH = 100%. Quantitative data obtained were fitted using non- linear regression functions (Bete, logistic and polynomial), which provided a very good fit of the biological process (R2 = 0.793-0.987). These functions could be the basis for the development of a predictive model for the infection of D. eres of hazelnuts.

Encephalitozoon cuniculi takes advantage of efferocytosis to evade the immune response

Microsporidia are recognized as opportunistic pathogens in individuals with immunodeficiencies, especially related to T cells. Although the activity of CD8+ T lymphocytes is essential to eliminate these pathogens, earlier studies have shown significant participation of macrophages at the beginning of the infection. Macrophages and other innate immunity cells play a critical role in activating the acquired immunity. After programmed cell death, the cell fragments or apoptotic bodies are cleared by phagocytic cells, a phenomenon known as efferocytosis. This process has been recognized as a way of evading immunity by intracellular pathogens. The present study evaluated the impact of efferocytosis of apoptotic cells either infected or not on macrophages and subsequently challenged with Encephalitozoon cuniculi microsporidia. Macrophages were obtained from the bone marrow monocytes from C57BL mice, pre-incubated with apoptotic Jurkat cells (ACs), and were further challenged with E. cuniculi spores. The same procedures were performed using the previously infected Jurkat cells (IACs) and challenged with E. cuniculi spores before macrophage pre-incubation. The average number of spores internalized by macrophages in phagocytosis was counted. Macrophage expression of CD40, CD206, CD80, CD86, and MHCII, as well as the cytokines released in the culture supernatants, was measured by flow cytometry. The ultrastructural study was performed to analyze the multiplication types of pathogens. Macrophages pre-incubated with ACs and challenged with E. cuniculi showed a higher percentage of phagocytosis and an average number of internalized spores. Moreover, the presence of stages of multiplication of the pathogen inside the macrophages, particularly after efferocytosis of infected apoptotic bodies, was observed. In addition, pre-incubation with ACs or IACs and/or challenge with the pathogen decreased the viability of macrophages, reflected as high percentages of apoptosis. The marked expression of CD206 and the release of large amounts of IL-10 and IL-6 indicated the polarization of macrophages to an M2 profile, compatible with efferocytosis and favorable for pathogen development. We concluded that the pathogen favored efferocytosis and polarized the macrophages to an M2 profile, allowing the survival and multiplication of E. cuniculi inside the macrophages and explaining the possibility of macrophages acting as Trojan horses in microsporidiosis.

A Heterogeneously Expressed Gene Family Modulates the Biofilm Architecture and Hypoxic Growth of Aspergillus fumigatus

The genus Aspergillus encompasses human pathogens such as Aspergillus fumigatus and industrial powerhouses such as Aspergillus niger In both cases, Aspergillus biofilms have consequences for infection outcomes and yields of economically important products. However, the molecular components influencing filamentous fungal biofilm development, structure, and function remain ill defined. Macroscopic colony morphology is an indicator of underlying biofilm architecture and fungal physiology. A hypoxia-locked colony morphotype of A. fumigatus has abundant colony furrows that coincide with a reduction in vertically oriented hyphae within biofilms and increased low oxygen growth and virulence. Investigation of this morphotype has led to the identification of the causative gene, biofilm architecture factor A (bafA), a small cryptic open reading frame within a subtelomeric gene cluster. BafA is sufficient to induce the hypoxia-locked colony morphology and biofilm architecture in A. fumigatus Analysis across a large population of A. fumigatus isolates identified a larger family of baf genes, all of which have the capacity to modulate hyphal architecture, biofilm development, and hypoxic growth. Furthermore, introduction of A. fumigatusbafA into A. niger is sufficient to generate the hypoxia-locked colony morphology, biofilm architecture, and increased hypoxic growth. Together, these data indicate the potential broad impacts of this previously uncharacterized family of small genes to modulate biofilm architecture and function in clinical and industrial settings.IMPORTANCE The manipulation of microbial biofilms in industrial and clinical applications remains a difficult task. The problem is particularly acute with regard to filamentous fungal biofilms for which molecular mechanisms of biofilm formation, maintenance, and function are only just being elucidated. Here, we describe a family of small genes heterogeneously expressed across Aspergillus fumigatus strains that are capable of modifying colony biofilm morphology and microscopic hyphal architecture. Specifically, these genes are implicated in the formation of a hypoxia-locked colony morphotype that is associated with increased virulence of A. fumigatus Synthetic introduction of these gene family members, here referred to as biofilm architecture factors, in both A. fumigatus and A. niger additionally modulates low oxygen growth and surface adherence. Thus, these genes are candidates for genetic manipulation of biofilm development in aspergilli.

Sub3 inhibits Aspergillus flavus growth by disrupting mitochondrial energy metabolism, and has potential biocontrol during peanut storage

BACKGROUND

Aspergillus flavus, a saprophytic fungus, is regularly detected in oil-enriched seeds. During colonization, this organism releases aflatoxins that pose a serious risk to food safety and human health. Therefore, an eco-friendly biological approach to inhibit the pathogen is desirable.

RESULTS

Experimental results indicated that A. flavus spores could not germinate in potato dextrose broth culture medium, when the concentration of Sub3 exceeded 0.15 g L^-1 . Morphological evaluation performed by flow cytometry and scanning electron microscopy indicated that spores were shrunken and pitted following Sub3 exposure. Physiological assessment using propidium iodide, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbocyanine iodide, 2,7-dichlorodihydrofluorescein diacetate and 4',6-diamidino-2-phenylindole staining revealed damaged cell membranes, decreased mitochondrial membrane potential, increased intracellular reactive oxygen species levels, and elevated large nuclear condensation and DNA fragmentation. Moreover, mitochondrial dehydrogenase activity was reduced by 29.42% and 45.48% after treatment with 0.1 and 0.15 g L^-1 Sub3, respectively. Additionally, colonization capacity in peanut was significantly decreased, and the number of spores on seeds treated with Sub3 was decreased by 26.86% (0.1 g L^-1 ) and 77.74% (0.15 g L^-1 ) compared with the control group.

CONCLUSION

Sub3 likely inhibits A. flavus by crossing the cell wall and targeting the cell membrane, disrupting mitochondrial energy metabolism, and inducing DNA damage, leading to spore death. Thus, Sub3 may provide a useful biocontrol strategy to control A. flavus growth in peanuts. © 2020 Society of Chemical Industry.

Synthetic antimicrobial agents inhibit aflatoxin production

Antimicrobial peptides (AMPs) are biologically active molecules that can eradicate bacteria by destroying the bacterial membrane structure, causing the bacteria to rupture. However, little is known about the extent and effect of AMPs on filamentous fungi. In this study, we synthesized small molecular polypeptides by an inexpensive heat conjugation approach and examined their effects on the growth of Aspergillus flavus and its secondary metabolism. The antimicrobial agents significantly inhibited aflatoxin production, conidiation, and sclerotia formation in A. flavus. Furthermore, we found that the expression of aflatoxin structural genes was significantly inhibited, and the intracellular reactive oxygen species (ROS) level was reduced. Additionally, the antimicrobial agents can change membrane permeability. Overall, our results demonstrated that antimicrobial agents, safe to mammalian cells, have an obvious impact on aflatoxin production, which indicated that antimicrobial agents may be adopted as a new generation of potential agents for controlling aflatoxin contamination.

Genetic bioengineering of overexpressed guanylate binding protein family BmAtlastin-n enhances silkworm resistance to Nosema bombycis

Microsporidia are obligate single-celled eukaryote parasites. Microsporidian infection can cause large economic losses to beneficial insects such as silkworms and honey bees. Identification of resistance biomacromolecules and breeding of transgenic lines resistant to the microsporidian Nosema bombycis are important for disease management. We previously used transcriptome analysis to identify a guanylate binding protein family BmAtlastin-n gene that was significantly upregulated after Nosema bombycis infection, and we determined that the molecule was highly expressed in resistance-related tissues such as the midgut, fat body and the epidermis. The transgenic silkworm line overexpressing BmAtlastin-n biomolecules had economic characters similar to those of non-transgenic lines. The transgenic OE-BmAtlastin-n lines had significantly improved survival after microspore infection. We used RT-PCR and H&E staining to show that the number of spores in the transgenic lines was significantly lower than in the control lines. In this study, we identified a BmAtlastin-n macromolecule with resistance to N. bombycis and developed a transgenic line. The results improved understanding of the GBP protein family and provided biomacromolecule material for the treatment and prevention of microsporidia.

Community structure of fungal pathogens causing spikelet rot disease of naked oat from different ecological regions of China

Spikelet rot disease (SRD) is an emerging disease of the grain surface of naked oat in China that affects both grain yield and quality. The typical symptom is discoloration from the black structures of the causal fungi. Here, we investigated the fungal communities on the grain surfaces of cultivar Bayou 13 grown in ten ecological oat-producing regions of China, to identify the main pathogens of naked oat SRD. Our results showed that the growth of Alternaria spp. and Davidiella spp. exhibited a competitive relationship and was mainly affected by the elevations of all 10 ecological regions. The dominant pathogens were Davidiella spp. in Shannan Prefecture in Tibet and Haidong Prefecture in Qinghai Province and Alternaria spp. in the other eight regions. The ratios of black pathogens of interest to all pathogens in Shannan Prefecture and Haidong Prefecture were significantly lower than those of the other eight regions, thus indicating that SRD mainly occurred in regions below 2000 m (elevation). We isolated black fungal pathogens from grain surfaces and deduced that they were Alternaria spp. by sequence comparison. The blackened appearance of the grain surfaces was more evident under spray inoculation with a spore suspension of Alternaria than under the control in greenhouse experiments. The recovered pathogen was the same as the pathogen used for inoculation. We thus concluded that Alternaria alone causes naked oat SRD and mainly infects naked oat in regions below 2000 m, which provides a basis for the recognition and management of SRD of naked oat.

Steccherinum tenuissimum and S. xanthum spp. nov. (Polyporales, Basidiomycota): New species from China

Two new wood-inhabiting fungal species, Steccherinum tenuissimum and S. xanthum spp. nov. are described based on a combination of morphological features and molecular evidence. Steccherinum tenuissimum is characterized by an annual growth habit, resupinate basidiomata with an odontioid hymenial surface, a dimitic hyphal system with clamped generative hyphae, strongly encrusted cystidia and basidiospores measuring 3-5 × 2-3.5 μm. Steccherinum xanthum is characterized by odontioid basidiomata and a monomitic hyphal system with generative hyphae bearing clamp connections and covering by crystals, colourless, thin-walled, smooth, IKI-, CB-and has basidiospores measuring 2.7-5.5 × 1.8-4.0 μm. Sequences of the ITS and nLSU nrRNA gene regions of the studied samples were generated, and phylogenetic analyses were performed with maximum likelihood, maximum parsimony and Bayesian inference methods. The phylogenetic analyses based on molecular data of ITS + nLSU sequences showed that two new Steccherinum species felled into the residual polyporoid clade. Further investigation was obtained for more representative taxa in Steccherinum based on ITS + nLSU sequences, which demonstrated that S. tenuissimum and S. xanthum were sister to S. robustius with high support (100% BP, 100% BS and 1.00 BPP).

Deletion of pksA attenuates the melanogenesis, growth and sporulation ability and causes increased sensitivity to stress response and antifungal drugs in the human pathogenic fungus Fonsecaea monophora

Fonsecaea monophora, which is very similar to Fonsecaea pedrosoi in morphological features, has been commonly misdiagnosed as F. pedrosoi. Like F. pedrosoi, F. monophora has been also identified as a predominant pathogen of Chromoblastomycosis (CBM). Melanin has been recognized as a virulence factor in several fungi, however, it is still largely unknown about the biological role of melanin and how melanin is synthesized in F. monophora. In this study, we identified two putative polyketide synthase genes (pks), AYO21_03016 (pksA) and AYO21_10638, by searching against the genome of F. monophora. AYO21_03016 and AYO21_10638 were further targeted disrupted by Agrobacterium tumefaciens-mediated transformation (ATMT). We discovered that pksA gene was the major polyketide synthase required for melanin synthesis in F. monophora, rather than AYO21_10638. Phenotypic analysis showed that, knocking out of the pksA gene attenuated melanogenesis, growth rate, sporulation ability and virulence of F. monophora, as compared with wild-type and complementation strain (pksA-C). Furthermore, the ΔpksA mutant was confirmed to be more sensitive to the oxidative stress, extreme pH environment, and antifungal drugs including itraconazole (ITC), terbinafine (TER), and amphotericin B (AMB). Taken together, these findings enabled us to comprehend the role of pksA in regulating DHN-melanin pathway and its effect on the biological function of F. monophora.

P-type Na+/K+ ATPases essential and nonessential for cellular homeostasis and insect pathogenicity of Beauveria bassiana

ENA1 and ENA2 are P-type IID/ENA Na+/K+-ATPases required for cellular homeostasis in yeasts but remain poorly understood in filamentous fungal insect pathogens. Here, we characterized seven genes encoding five ENA1/2 homologues (ENA1a-c and ENA2a/b) and two P-type IIC/NK Na+/K+-ATPases (NK1/2) in Beauveria bassiana, an insect-pathogenic fungus serving as a main source of fungal insecticides worldwide. Most of these genes were highly responsive to alkaline pH and Na+/K+ cues at transcription level. Cellular Na+, K+ and H+ homeostasis was disturbed only in the absence of ena1a or ena2b. The disturbed homeostasis featured acceleration of vacuolar acidification, elevation of cytosolic Na+/K+ level at pH 5.0 to 9.0, and stabilization of extracellular H+ level to initial pH 7.5 during a 5-day period of submerged incubation. Despite little defect in hyphal growth and asexual development, the Δena1a and Δena2b mutants were less tolerant to metal cations (Na+, K+, Li+, Zn2+, Mn2+ and Fe3+), cell wall perturbation, oxidation, non-cation hyperosmolarity and UVB irradiation, severely compromised in insect pathogenicity via normal cuticle infection, and attenuated in virulence via hemocoel injection. The deletion mutants of five other ENA and NK genes showed little change in vacuolar pH and all examined phenotypes. Therefore, only ENA1a and ENA2b evidently involved in both transmembrane and vacuolar activities are essential for cellular cation homeostasis, insect pathogenicity and multiple stress tolerance in B. bassiana. These findings provide a novel insight into ENA1a- and ENA2b-dependent vacuolar pH stability, cation-homeostatic process and fungal fitness to host insect and environment.

Suppressors of mRNA Decapping Defects Restore Growth Without Major Effects on mRNA Decay Rates or Abundance

Faithful degradation of mRNAs is a critical step in gene expression, and eukaryotes share a major conserved mRNA decay pathway. In this major pathway, the two rate-determining steps in mRNA degradation are the initial gradual removal of the poly(A) tail, followed by removal of the cap structure. Removal of the cap structure is carried out by the decapping enzyme, containing the Dcp2 catalytic subunit. Although the mechanism and regulation of mRNA decay is well understood, the consequences of defects in mRNA degradation are less clear. Dcp2 has been reported as either essential or nonessential. Here, we clarify that Dcp2 is not absolutely required for spore germination and extremely slow growth, but in practical terms it is impossible to continuously culture dcp2∆ under laboratory conditions without suppressors arising. We show that null mutations in at least three different genes are each sufficient to restore growth to a dcp2∆, of which kap123∆ and tl(gag)g∆ appear the most specific. We show that kap123∆ and tl(gag)g∆ suppress dcp2 by mechanisms that are different from each other and from previously isolated dcp2 suppressors. The suppression mechanism for tL(GAG)G is determined by the unique GAG anticodon of this tRNA, and thus likely by translation of some CUC or CUU codons. Unlike previously reported suppressors of decapping defects, these suppressors do not detectably restore decapping or mRNA decay to normal rates, but instead allow survival while only modestly affecting RNA homeostasis. These results provide important new insight into the importance of decapping, resolve previously conflicting publications about the essentiality of DCP2, provide the first phenotype for a tl(gag)g mutant, and show that multiple distinct mechanisms can bypass Dcp2 requirement.

Pathogenesis-related genes of entomopathogenic fungi

All living things on Earth experience various diseases such as those caused by viruses, bacteria, and fungi. Insects are no exception to this rule, and fungi that cause disease in insects are called entomopathogenic fungi. These fungi have been developed as microbial insecticides and are used to control various pests. Generally, the mode of action of entomopathogenic fungi is divided into the attachment of conidia, germination, penetration, growth, and generation of secondary infectious conidia. In each of these steps, that entomopathogenic fungi use genes in a complex manner (specific or diverse) has been shown by gene knock-out and RNA-sequencing analysis. In this review, the information mechanism of entomopathogenic fungi was divided into six steps: (1) attachment of conidia to host, (2) germination and appressorium, (3) penetration, (4) fungal growth in hemolymph, (5) conidia production on host, and (6) transmission and dispersal. The strategy used by the fungi in each step was described at the genetic level. In addition, an approach for studying the mode of action of the fungi is presented.

Hevein-Like Antimicrobial Peptides Wamps: Structure-Function Relationship in Antifungal Activity and Sensitization of Plant Pathogenic Fungi to Tebuconazole by WAMP-2-Derived Peptides

Keywords: hevein-like antimicrobial peptides; antifungal activity; antifungal determinants; synergy; chemosensitization; tebuconazole; plant pathogenic fungi.

Effect of H2A.Z deletion is rescued by compensatory mutations in Fusarium graminearum

Fusarium head blight is a destructive disease of grains resulting in reduced yields and contamination of grains with mycotoxins worldwide; Fusarium graminearum is its major causal agent. Chromatin structure changes play key roles in regulating mycotoxin biosynthesis in filamentous fungi. Using a split-marker approach in three F. graminearum strains INRA156, INRA349 and INRA812 (PH-1), we knocked out the gene encoding H2A.Z, a ubiquitous histone variant reported to be involved in a diverse range of biological processes in yeast, plants and animals, but rarely studied in filamentous fungi. All ΔH2A.Z mutants exhibit defects in development including radial growth, sporulation, germination and sexual reproduction, but with varying degrees of severity between them. Heterogeneity of osmotic and oxidative stress response as well as mycotoxin production was observed in ΔH2A.Z strains. Adding-back wild-type H2A.Z in INRA349ΔH2A.Z could not rescue the phenotypes. Whole genome sequencing revealed that, although H2A.Z has been removed from the genome and the deletion cassette is inserted at H2A.Z locus only, mutations occur at other loci in each mutant regardless of the genetic background. Genes affected by these mutations encode proteins involved in chromatin remodeling, such as the helicase Swr1p or an essential subunit of the histone deacetylase Rpd3S, and one protein of unknown function. These observations suggest that H2A.Z and the genes affected by such mutations are part or the same genetic interaction network. Our results underline the genetic plasticity of F. graminearum facing detrimental gene perturbation. These findings suggest that intergenic suppressions rescue deleterious phenotypes in ΔH2A.Z strains, and that H2A.Z may be essential in F. graminearum. This assumption is further supported by the fact that H2A.Z deletion failed in another Fusarium spp., i.e., the rice pathogen Fusarium fujikuroi.

The Role of Saccharides in the Mechanisms of Pathogenicity of Fusarium oxysporum f. sp. lupini in Yellow Lupine (Lupinus luteus L.)

The primary aim of this study was to determine the relationship between soluble sugar levels (sucrose, glucose, or fructose) in yellow lupine embryo axes and the pathogenicity of the hemibiotrophic fungus Fusarium oxysporum f. sp. Schlecht lupini. The first step of this study was to determine the effect of exogenous saccharides on the growth and sporulation of F. oxysporum. The second one focused on estimating the levels of ergosterol as a fungal growth indicator in infected embryo axes cultured in vitro on sugar containing-medium or without it. The third aim of this study was to record the levels of the mycotoxin moniliformin as the most characteristic secondary metabolite of F. oxysporum in the infected embryo axes with the high sugar medium and without it. Additionally, morphometric measurements, i.e., the length and fresh weight of embryo axes, were done. The levels of ergosterol were the highest in infected embryo axes with a sugar deficit. At the same time, significant accumulation of the mycotoxin moniliformin was recorded in those tissues. Furthermore, it was found that the presence of sugars in water agar medium inhibited the sporulation of the pathogenic fungus F. oxysporum in relation to the control (sporulation of the pathogen on medium without sugar), the strongest inhibiting effect was observed in the case of glucose. Infection caused by F. oxysporum significantly limited the growth of embryo axes, but this effect was more visible on infected axes cultured under sugar deficiency than on the ones cultured with soluble sugars. The obtained results thus showed that high sugar levels may lead to reduced production of mycotoxins by F. oxysporum, limiting infection development and fusariosis.

Fungicidal Effect of Pyraclostrobin against Botrytis cinerea in Relation to Its Crystal Structure

Pyraclostrobin (PYR) is a commonly used strobilurin fungicide, which inhibits mitochondrial respiration at the ubiquinol oxidation center site of the cytochrome bc1 complex. Little information is available regarding the crystal structure of PYR on its fungicidal effect. In this study, the crystal structures of eight PYRs (PYR-A to H) from different sources are determined by using high-resolution X-ray powder diffraction (XRPD) and model construction with the Pawley refinement module. The effects of PYRs on mycelium growth, the kinetics of mycelial growth, conidial germination, and tube elongation of conidia of Botrytis cinerea from tomato are compared. The level of organic acids in the mitochondrial tricarboxylic acid cycle of PYR-treated B. cinerea is analyzed. The results show that PYR-A to PYR-H have their own unique character of XRPD patterns, but the crystal morphology of eight PYRs presents in the triclinic crystal system and space group P1̅. PYR-D with the eclipsed conformation and rational edge angles α (72.599°) and β (98.612°) in the crystal cell shows the highest inhibitory effect against mycelium growth with EC₅₀ as 3.383 μg mL^-1, the best time-dependent effects on the mycelium growth kinetics, and the strongest inhibition on tube elongation of conidia, whereas PYR-E with anticonformation is the worst. Moreover, a significant accumulation of fumarate, malate, and oxalate in the PYR-D-treated mycelium is observed. These findings reinforce the need for a definite crystal structure of PYR to limit usage and mitigate future selection pressure for gray mold management.

Identification and characterization a novel polar tube protein (NbPTP6) from the microsporidian Nosema bombycis

BACKGROUND

Microsporidians are opportunistic pathogens with a wide range of hosts, including invertebrates, vertebrates and even humans. Microsporidians possess a highly specialized invasion structure, the polar tube. When spores encounter an appropriate environmental stimulation, the polar tube rapidly everts out of the spore, forming a 50-500 µm hollow tube that serves as a conduit for sporoplasm passage into host cells. The polar tube is mainly composed of polar tube proteins (PTPs). So far, five major polar tube proteins have been isolated from microsporidians. Nosema bombycis, the first identified microsporidian, infects the economically important insect silkworm and causes heavy financial loss to the sericulture industry annually.

RESULTS

A novel polar tube protein of N. bombycis (NbPTP6) was identified. NbPTP6 was rich in histidine (H) and serine (S), which contained a signal peptide of 16 amino acids at the N-terminus. NbPTP6 also had 6 potential O-glycosylation sites and 1 potential N-glycosylation site. The sequence alignment analysis revealed that NbPTP6 was homologous with uncharacterized proteins from other microsporidians (Encephalitozoon cuniculi, E. hellem and N. ceranae). Additionally, the NbPTP6 gene was expressed in mature N. bombycis spores. Indirect immunofluorescence analysis (IFA) result showed that NbPTP6 is localized on the whole polar tube of the germinated spores. Moreover, IFA, enzyme-linked immunosorbent (ELISA) and fluorescence-activated cell sorting (FACS) assays results revealed that NbPTP6 had cell-binding ability.

CONCLUSIONS

Based on our results, we have confirmed that NbPTP6 is a novel microsporidian polar tube protein. This protein could adhere with the host cell surface, so we speculated it might play an important role in the process of microsporidian infection.

The histone acetyltransferase GcnE regulates conidiation and biofilm formation in Aspergillus fumigatus

Histone modifications play a crucial role in eukaryotic gene regulation. The Spt-Ada-Gcn5-acetyltransferase (SAGA) complex controls histone acetylation, with Gcn5 (GcnE) acting as the acetyltransferase. In the Aspergillus species, GcnE has been shown to regulate asexual development and secondary metabolism. Apart from this, GcnE is required for pathogenicity in plant fungal pathogen A. flavus; however, the role of GcnE in the pathogenicity of human pathogenic fungus A. fumigatus is unknown. In this study, we uncovered the key roles of GcnE in A. fumigatus conidiation, stress responses, and biofilm formation. We observed that deletion of gcnE resulted in aberrant conidiation in which conidiophores displayed abnormal phialide formation. In addition, the ΔgcnE mutant grew slightly faster under limited nitrogen sources (1 mM of ammonium or nitrate) compared to the wild type. The ΔgcnE mutant exhibited increased susceptibility to cell wall-perturbing agents, H2O2 and menadione but enhanced tolerance to LiCl. Furthermore, we showed that GcnE is involved in biofilm formation, and overexpression of adherence-related genes such as somA or uge3 partially rescued biofilm formation defects in the ΔgcnE mutant background. Interestingly, GcnE was not required for virulence in a neutropenic murine model of invasive aspergillosis. These results suggest that GcnE is critical for conidiation and biofilm formation but not virulence in A. fumigatus.

Optimal timing for Agrobacterium-mediated DNA transformation of Trichoderma reesei conidia revealed by live cell imaging

Trichoderma reesei is the foremost fungal producer of enzymes for industrial processes. Here, we use fluorescent live cell imaging of germinating conidia to improve Agrobacterium tumefaciens-mediated transformation (ATMT) efficiency. We define the timing of (a) morphological changes and (b) nuclear reorganisation during initial conidia germination. This reveals that conidia swell for 7 h, during which nuclei undergo 2 non-synchronised mitotic divisions. Histones are recruited to the nucleus during the first 2 h, suggesting that conidia enter S-phase immediately after activation. This correlates with a significantly increased ATMT efficiency at 2 h after germination initiation. This finding promises to improve genetic manipulation efficiency in T. reesei.

3-Dimensional organization and dynamics of the microsporidian polar tube invasion machinery

Microsporidia, a divergent group of single-celled eukaryotic parasites, harness a specialized harpoon-like invasion apparatus called the polar tube (PT) to gain entry into host cells. The PT is tightly coiled within the transmissible extracellular spore, and is about 20 times the length of the spore. Once triggered, the PT is rapidly ejected and is thought to penetrate the host cell, acting as a conduit for the transfer of infectious cargo into the host. The organization of this specialized infection apparatus in the spore, how it is deployed, and how the nucleus and other large cargo are transported through the narrow PT are not well understood. Here we use serial block-face scanning electron microscopy to reveal the 3-dimensional architecture of the PT and its relative spatial orientation to other organelles within the spore. Using high-speed optical microscopy, we also capture and quantify the entire PT germination process of three human-infecting microsporidian species in vitro: Anncaliia algerae, Encephalitozoon hellem and E. intestinalis. Our results show that the emerging PT experiences very high accelerating forces to reach velocities exceeding 300 μm⋅s-1, and that firing kinetics differ markedly between species. Live-cell imaging reveals that the nucleus, which is at least 7 times larger than the diameter of the PT, undergoes extreme deformation to fit through the narrow tube, and moves at speeds comparable to PT extension. Our study sheds new light on the 3-dimensional organization, dynamics, and mechanism of PT extrusion, and shows how infectious cargo moves through the tube to initiate infection.

Transcription Factor PdeR Is Involved in Fungal Development, Metabolic Change, and Pathogenesis of Gray Mold Botrytis cinerea

The necrotrophic fungus Botrytis cinerea releases extracellular enzymes that facilitate its penetration into a host. This study functionally characterized the gene pdeR of B. cinerea, which is predicted to encode a Zn(II)₂Cys₆ zinc finger transcription factor. To investigate the role of pdeR, deleted and complemented strains of pdeR in B. cinerea were generated, which were designated as ΔpdeR and PdeRc, respectively. The ΔpdeR strain exhibited impaired germination and growth compared to the wild-type and PdeRc strains, particularly when provided with maltose as the sole carbon source. When all of the strains were grown on a minimal medium containing polysaccharide as the sole carbon source, the ΔpdeR exclusively showed defects in polysaccharide hydrolysis with reduced gene expression encoding for amylase and cellulase. As far as the involvement of pdeR in carbon metabolism is concerned, metabolic changes were investigated in the ΔpdeR mutant. Comparisons of relative, normalized concentrations of each metabolite showed that the amounts of six metabolites including glucose and trehalose were significantly changed in the ΔpdeR strain. Based on pleiotropic changes derived from the deletion of pdeR, we hypothesized that pdeR has an important role in pathogenesis. When the ΔpdeR strain was inoculated onto pepper plant, the ΔpdeR strain did not cause expansion of the disease lesions from the infection sites, which grew on the surface without any penetration. Taken together, these results show that the deletion of pdeR affected the extracellular enzymatic activity, leading to changes in fungal development, metabolism, and virulence.

Oligomycins inhibit Magnaporthe oryzae Triticum and suppress wheat blast disease

Oligomycins are macrolide antibiotics, produced by Streptomyces spp. that show antagonistic effects against several microorganisms such as bacteria, fungi, nematodes and the oomycete Plasmopara viticola. Conidiogenesis, germination of conidia and formation of appressoria are determining factors pertaining to pathogenicity and successful diseases cycles of filamentous fungal phytopathogens. The goal of this research was to evaluate the in vitro suppressive effects of two oligomycins, oligomycin B and F along with a commercial fungicide Nativo® 75WG on hyphal growth, conidiogenesis, conidial germination, and appressorial formation of the wheat blast fungus, Magnaporthe oryzae Triticum (MoT) pathotype. We also determined the efficacy of these two oligomycins and the fungicide product in vivo in suppressing wheat blast with a detached leaf assay. Both oligomycins suppressed the growth of MoT mycelium in a dose dependent manner. Between the two natural products, oligomycin F provided higher inhibition of MoT hyphal growth compared to oligomycin B with a minimum inhibitory concentration of 0.005 and 0.05 μg/disk, respectively. The application of the compounds completely halted conidial formation of the MoT mycelium in agar medium. Further bioassays showed that these compounds significantly inhibited MoT conidia germination and induced lysis. The compounds also caused abnormal germ tube formation and suppressed appressorial formation of germinated spores. Interestingly, the application of these macrolides significantly inhibited wheat blast on detached leaves of wheat. This is the first report on the inhibition of mycelial growth, conidiogenesis, germination of conidia, deleterious morphological changes in germinated conidia, and suppression of blast disease of wheat by oligomycins from Streptomyces spp. Further study is needed to unravel the precise mode of action of these natural compounds and consider them as biopesticides for controlling wheat blast.

Lipo-chitooligosaccharides as regulatory signals of fungal growth and development

Lipo-chitooligosaccharides (LCOs) are signaling molecules produced by rhizobial bacteria that trigger the nodulation process in legumes, and by some fungi that also establish symbiotic relationships with plants, notably the arbuscular and ecto mycorrhizal fungi. Here, we show that many other fungi also produce LCOs. We tested 59 species representing most fungal phyla, and found that 53 species produce LCOs that can be detected by functional assays and/or by mass spectroscopy. LCO treatment affects spore germination, branching of hyphae, pseudohyphal growth, and transcription in non-symbiotic fungi from the Ascomycete and Basidiomycete phyla. Our findings suggest that LCO production is common among fungi, and LCOs may function as signals regulating fungal growth and development.

Interruption of Aspergillus niger spore germination by the bacterially produced secondary metabolite collimomycin

Collimonas fungivorans Ter331 (CfTer331) is a soil bacterium that produces collimomycin, a secondary metabolite that inhibits the vegetative growth of fungi. Here we show that CfTer331 can also interfere with fungal spore germination and that collimomycin biosynthesis is required for this activity. More specifically, in co-cultures of Aspergillus niger N402 (AnN402) co-nidiospores with CfTer331, the rate of transition from the isotropic to polarized stage of the germination process was reduced and the relatively few AnN402 conidiospores that completed the germination process were less likely to survive than those that were arrested in the isotropic phase. By contrast, a collimomycin-deficient mutant of CfTer331 had no effect on germination: in its presence, as in the absence or delayed presence of CfTer331, unhindered germination of conidiospores allowed rapid establishment of AnN402 mycelium and the subsequent acidification of the culture medium to the detriment of any bacteria present. However, when challenged early enough with CfTer331, the collimomycin-dependent arrest of the AnN402 germination process enabled CfTer331 to prevent AnN402 from forming mycelia and to gain dominance in the culture. We propose that the collimomycin-dependent arrest of spore germination represents an early intervention strategy used by CfTer331 to mitigate niche construction by fungi in nature.

Growth kinetic and nitrogen source optimization for liquid culture fermentation of Metarhizium robertsii blastospores and bioefficacy against the corn leafhopper Dalbulus maidis

The cosmopolitan entomopathogenic and root endophytic fungus Metarhizium robertsii has a versatile lifestyle and during liquid fermentation undergoes a dimorphic transformation from hyphae to conidia or microsclerotia, or from hyphae to blastospores. In all cases, these processes are mediated by environmental and nutritional cues. Blastospores could be used in spray applications to control arthropod pests above ground and may serve as an attractive alternative to the traditional solid-grown aerial conidial spores of Metarhizium spp. found in commercial products. Nitrogen is a vital nutrient in cell metabolism and growth; however, it is the expensive component in liquid cultures of entomopathogenic fungi. Our goals in this study were to optimize nitrogen sources and titers for maximum production of M. robertsii blastospores cultured in shake flasks at highly aerated conditions and to further determine their virulence against the corn leafhopper Dalbulus maidis, an important vector of serious pathogens in maize crops worldwide. Our fermentation studies revealed that the low-cost corn steep liquor (CSL) was the most suitable nitrogen source to improve blastospore growth in M. robertsii. The growth kinetic assays determined the optimal titer of 80 g L^-1 and a yield up to 4.7 × 10⁸ cells mL^-1 within 5 days of cultivation (3 days preculture and 2 days culture), at a total cost of US$0.30 L^-1. Moreover, the blastospore growth kinetic was strongly dependent on glucose and nitrogen consumptions accompanied by a slight drop in the culture pH. Insect bioassays evidenced a high virulence of these blastospores, either as dried or fresh cells, to D. maidis adults fed on maize plants. Our findings provide insights into the nutritional requirements for optimal and cost-efficient production of M. robertsii blastospores and elucidate the potential of blastospores as an ecofriendly tool against the corn leafhopper.

Culture medium for improved production of conidia for identification and systematic studies of Fusarium pathogens

Fusarium guttiforme and Fusarium ananatum are the etiological agents of fusariosis and fruitlet core rot in pineapple, respectively, producing mycotoxins that are harmful to the health of consumers. These two fungi are morphologically similar and difficulty in obtaining macroconidia of the species limits their identification. Different types of media are available for the culture of these pathogens, but not all of them favor F. ananatum and F. guttiforme macroconidia production. Therefore, the objective of this study was to develop a simple culture medium to improve rapid macro- and microconidia formation in both F. guttiforme and F. ananatum to facilitate taxonomic, pathogenicity and mycotoxin studies. In vitro analysis showed that basal medium with carboxymethyl cellulose (CMC) was better than other media tested with the highest macroconidia production at 7 days of incubation. The highest production of microconidia was with synthetic nutrient medium (SN) at 7 days. F. ananatum produced a relatively high number of microconidia with one septum in comparison to F. guttiforme when cultured in CMC, which suggests an additional character useful for Fusarium taxonomy. CMC medium may serve as an improved alternative to culture media currently used in Fusarium research and contribute to further knowledge of the taxonomy and mycotoxins of Fusarium species.

The high-affinity phosphodiesterase PcPdeH is involved in the polarized growth and pathogenicity of Phytophthora capsici

The cAMP signaling pathway has been shown to be important in controlling morphological changes and pathogenicity in plant pathogens. In the present study, we identified PcPdeH, a gene encoding a high-affinity phosphodiesterase (PDE), which is a key regulator of the cAMP signaling pathway. To elucidate the function of PcPdeH, PcPdeH-knockout mutants were obtained using a type II CRISPR/Cas9 system in Phytophthora capsici. The knockout transformants of PcPdeH showed vegetative growth defects and abnormal cyst germination. Infection assays indicated that compared with the wild type, PcPdeH-knockout mutants showed significantly reduced virulence on pepper and tobacco leaves and exhibited increased (1.5-2-fold) cAMP levels relative to the wild-type and CK strains. Based on these phenotypic features, we propose that PcPdeH is crucial for vegetative growth, cyst germination and pathogenicity in P. capsici.

Development of fungal spore staining methods for flow cytometric quantification and their application in chlorine-based disinfection

Fungal contamination in drinking water has been becoming a hot topic. The routine enumeration method of fungal spores is heterotrophic plate counts (HPC). However, this method is time-consuming and labor-intensive and there is also the difficulty of enumerating viable but non-culturable cells. In this study, a rapid, simple and accurate method for quantifying fungal spores and discriminating their viability in water was established using flow cytometry (FCM) combined with fluorescence dyes. The optimal staining conditions are as follows: spores suspensions are sonicated at 495 W for 5 min as pretreatment, and then 10 μL of SYBR Green I (100×) and 30 mM Ethylene diamine tetraacetic acid are added to a 500 μL water sample, which incubate at 35 °C for 20 min in dark. The concentration of fungal spores measured by FCM was highly correlated with HPC results and microscope observations, with correlation coefficient of 0.996 and 0.988, respectively. This staining method can be widely applied to the enumeration and viability evaluation of fungal spores. In addition, chlorine-based inactivation of three genera of fungal spores was assessed by plating and FCM. The result showed that all three genera of fungal spores lost culturability firstly and then membrane integrity decreased, preliminarily revealing the inactivation mechanism. The inactivation rate constants of membrane damage varied in the following order: chlorine dioxide > chlorine > chloramine. This study concluded that FCM is an appropriate and alternative tool to detect fungal spores' viability and can be used for evaluating the fungal inactivation by disinfectants.

The enhancement of plant secondary metabolites content in Lactuca sativa L. by encapsulated bioactive agents

Encapsulated bioactive agents applied to the Lactuca sativa L. present an innovative approach to stimulate the production of plant secondary metabolites increasing its nutritive value. Calcium and copper ions were encapsulated in biopolymeric microparticles (microspheres and microcapsules) either as single agents or in combination with biocontrol agents, Trichoderma viride spores, a fungal plant growth mediator. Both, calcium and copper ions are directly involved in the synthesis of plant secondary metabolites and alongside, Trichoderma viride can provide indirect stimulation and higher uptake of nutrients. All treatments with microparticles had a positive effect on the enhancement of plant secondary metabolites content in Lactuca sativa L. The highest increase of chlorophylls, antioxidant activity and phenolic was obtained by calcium-based microparticles in both, conventionally and hydroponically grown lettuces. Non-encapsulated fungus Trichoderma viride enhanced the synthesis of plant secondary metabolites only in hydroponics cultivation signifying the importance of its encapsulation. Encapsulation proved to be simple, sustainable and environmentally favorable for the production of lettuce with increased nutritional quality, which is lettuce fortified with important bioactive compounds.

Surface Dielectric Barrier Discharge plasma: a suitable measure against fungal plant pathogens

Fungal diseases seriously affect agricultural production and the food industry. Crop protection is usually achieved by synthetic fungicides, therefore more sustainable and innovative technologies are increasingly required. The atmospheric pressure low-temperature plasma is a novel suitable measure. We report on the effect of plasma treatment on phytopathogenic fungi causing quantitative and qualitative losses of products both in the field and postharvest. We focus our attention on the in vitro direct inhibitory effect of non-contact Surface Dielectric Barrier Discharge on conidia germination of Botrytis cinerea, Monilinia fructicola, Aspergillus carbonarius and Alternaria alternata. A few minutes of treatment was required to completely inactivate the fungi on an artificial medium. Morphological analysis of spores by Scanning Electron Microscopy suggests that the main mechanism is plasma etching due to Reactive Oxygen Species or UV radiation. Spectroscopic analysis of plasma generated in humid air gives the hint that the rotational temperature of gas should not play a relevant role being very close to room temperature. In vivo experiments on artificially inoculated cherry fruits demonstrated that inactivation of fungal spores by the direct inhibitory effect of plasma extend their shelf life. Pre-treatment of fruits before inoculation improve the resistance to infections maybe by activating defense responses in plant tissues.

Quantitative proteomics analysis reveals important roles of N-glycosylation on ER quality control system for development and pathogenesis in Magnaporthe oryzae

Genetic studies have shown essential functions of N-glycosylation during infection of the plant pathogenic fungi, however, systematic roles of N-glycosylation in fungi is still largely unknown. Biological analysis demonstrated N-glycosylated proteins were widely present at different development stages of Magnaporthe oryzae and especially increased in the appressorium and invasive hyphae. A large-scale quantitative proteomics analysis was then performed to explore the roles of N-glycosylation in M. oryzae. A total of 559 N-glycosites from 355 proteins were identified and quantified at different developmental stages. Functional classification to the N-glycosylated proteins revealed N-glycosylation can coordinate different cellular processes for mycelial growth, conidium formation, and appressorium formation. N-glycosylation can also modify key components in N-glycosylation, O-glycosylation and GPI anchor pathways, indicating intimate crosstalk between these pathways. Interestingly, we found nearly all key components of the endoplasmic reticulum quality control (ERQC) system were highly N-glycosylated in conidium and appressorium. Phenotypic analyses to the gene deletion mutants revealed four ERQC components, Gls1, Gls2, GTB1 and Cnx1, are important for mycelial growth, conidiation, and invasive hyphal growth in host cells. Subsequently, we identified the Gls1 N-glycosite N497 was important for invasive hyphal growth and partially required for conidiation, but didn’t affect colony growth. Mutation of N497 resulted in reduction of Gls1 in protein level, and localization from ER into the vacuole, suggesting N497 is important for protein stability of Gls1. Our study showed a snapshot of the N-glycosylation landscape in plant pathogenic fungi, indicating functions of this modification in cellular processes, developments and pathogenesis.

The fungal pathogen Magnaporthe oryzae can cause rice blast and wheat blast diseases, which threatens worldwide food production. During infection, M. oryzae follows a sequence of distinct developmental stages adapted to survival and invasion of the host environment. M. oryzae attaches onto the host by the conidium, and then develops an appressorium to breach the host cuticle. After penetrating, it forms invasive hyphae to quickly spread in the host cells. Numerous genetic studies have focused on the mechanisms underlying each step in the infection process, but systemic approaches are needed for a broader, integrated understanding of regulatory events during M. oryzae pathogenesis. Many infection-related signaling events are regulated through post-translational protein modifications within the pathogen. N-linked glycosylation, in which a glycan moiety is added to the amide group of an asparagine residue, is an abundant modification known to be essential for M. oryzae infection. In this study, we employed a quantitative proteomics analysis to unravel the overall regulatory mechanisms of N-glycosylation at different developmental stages of M. oryzae. We detected changes in N-glycosylation levels at 559 glycosylated residues (N-glycosites) in 355 proteins during different stages, and determined that the ER quality control system is elaborately regulated by N-glycosylation. The insights gained will help us to better understand the regulatory mechanisms of infection in pathogenic fungi. These findings may be also important for developing novel strategies for fungal disease control.

Changes in Cuticle Components and Morphology of 'Satsuma' Mandarin (Citrus unshiu) during Ambient Storage and Their Potential Role on Penicillium digitatum Infection

To elucidate the role of fruit cuticle in fungal infection, changes in cuticle composition and morphology of 'Satsuma' mandarin during ambient (at 25 °C) storage and their role in Penicillium digitatum infection were investigated. Results showed that the epicuticular wax yield increased from 1.11 μg cm-2 to 4.21 μg cm-2 during storage for 20 days and then decreased to 1.35 μg cm-2 as storage time prolonged to 40 days. Intracuticular wax content of fruits stored for 20 days showed a peak value that was 1.7-fold higher than that of fruits stored for 40 days. The contents of cutin monomers of fruits showed a decreased trend during storage, while their proportions in the cutin stayed stable. Acids were identified as the most abundant components in epicuticular wax independently of the storage time, followed by alkanes and terpenoids. Terpenoids were found as the predominant components in intracuticular wax during the whole storage, followed by alkanes and acids. The flattened platelets crystals of fruits at harvest changed into small granule-like wax ones after 10 days of storage then gradually distributed across the surface of the fruits as stored for 40 days. Results of in vitro tests showed that mycelial growth of Penicillium digitatum could be promoted by epicuticular wax and conidial germination could be inhibited by cutin at different storage stages. These results shed new light on the chemical basis for cuticle involvement in fungal infection.

Effects of the antifungal peptide Skh-AMP1 derived from Satureja khuzistanica on cell membrane permeability, ROS production, and cell morphology of conidia and hyphae of Aspergillus fumigatus

Skh-AMP1 (GRTSKQELCTWERGSVRQADKTIAG) is an antifungal peptide isolated from Satureja khuzistanica which has been shown to have strong antifungal activity against Aspergillus and Candida species, but no obvious hemolytic effects or cell cytotoxicity in vitro. In the present study, Skh-AMP1 was synthesized, and its mode of action on the plasma membrane, mitochondria, and morphological and ultrastructural changes against conidia and hyphae of Aspergillus fumigatus were evaluated. The results indicated that Skh-AMP1 had sporicidal activities against the non-germinated conidia of A. fumigatus at concentrations of 40 and 80 μM. Skh-AMP1 induced the release of K⁺ and the uptake of propidium iodide and enhanced reactive oxygen species (ROS) production in the conidia and hyphae of the fungus. Scanning and transmission electron microscopy showed deformation and shrinkage of the hyphae and conidia, cell membrane disruption and detachment from the cell wall, microvesicle formation, vacuolation and depletion of cytoplasm and organelles of the hyphae of A. fumigatus exposed to 40-80 μM of the peptide. The results further demonstrated that the antifungal activity of Skh-AMP1 may be related to its ability to disrupt fungal cell membrane permeabilization and induce enhanced ROS production. Therefore, Skh-AMP1 can be introduced as a novel antifungal candidate for developing new therapeutic agents.

Isolation and Culture of Arbuscular Mycorrhizal Fungi from Field Samples

The isolation of arbuscular mycorrhizal fungi from different land use is the starting point for selecting and producing inoculants. There are different techniques to isolate and produce large-scale arbuscular mycorrhizal fungi-based inoculum, being soil, inert substrate, and in vitro culture techniques among the most used by different biofertilizer producers. This chapter describes an active operating method to isolate and produce large-scale fungal inoculant in substrate-based manufacturing. In addition, critical parameters are presented for the optimal production of arbuscular mycorrhizal fungal inoculum. All the steps of the process are enlisted: from choosing the source of inoculum, its production, scaling, sustaining quality control, to shelf life.

Stimulating Duddingtonia flagrans chlamydospore production through dehydration

Duddingtonia flagrans is a nematode-trapping fungus that has shown promising results as a tool to combat parasitic nematode infections in livestock. The fungus interrupts the parasitic lifecycle by trapping and killing larval stages on pasture to prevent re-infection of animals. One barrier to the fungus' commercial use is scaling up production of the fungus, and specifically of chlamydospores, which survive the digestive tract to grow in fecal pats on pasture, thus have potential as a feed through anthelmintic. The purpose of this study was to evaluate the effect of dehydration on sporulation of the fungus. Disks of Duddingtonia flagrans type strain (ATCC® 13423™) were grown on 17% cornmeal agar for 26 days at 30 °C, then split into three groups; dried quickly at 38 °C and 37% humidity over 48 h ("incubated"), dried more slowly at 24 °C and 55% humidity over 10 days ("air-dried"), or kept at 30 °C and sealed with parafilm to prevent loss of moisture as a control ("wet"). Half of each dried culture was resuspended in water, then heated to liquify and homogenized through vortexing. Spores were then counted in a Neubauer hematocytometer. Both the "air-dried" and "incubated" drying techniques yielded significantly more spores than the "wet" control (Welch's two sample t test p values of .0359 and .0411, respectively). The difference in average chlamydospores per milliliter was insignificant between the two drying techniques, although a visual representation of the data shows less spore count variability in the "air-dried" technique.