Genes, gene clusters, and biosynthesis of trichothecenes and fumonisins inFusarium

Effector Protein Serine Carboxypeptidase FgSCP Is Essential for Full Virulence in Fusarium graminearum and Is Involved in Modulating Plant Immune Responses

Fusarium head blight caused by Fusarium graminearum is a significant pathogen affecting wheat crops. During the infection process, effector proteins are secreted to modulate plant immunity and promote infection. The toxin deoxynivalenol is produced in infected wheat grains, posing a threat to human and animal health. Serine carboxypeptidases (SCPs) belong to the α/β hydrolase family of proteases and are widely distributed in plant and fungal vacuoles, as well as animal lysosomes. Research on SCPs mainly focuses on the isolation, purification, and production of a small number of fungi. The role of SCPs in plant secretion, growth and development, and stress resistance has also been extensively studied. However, their functions in F. graminearum, a fungal pathogen, remain relatively unknown. In this study, the biological functions of the FgSCP gene in F. graminearum were investigated. The study revealed that mutations in FgSCP affected the nutritional growth, sexual reproduction, and stress tolerance of F. graminearum. Furthermore, the deletion of FgSCP resulted in reduced pathogenicity and hindered the biosynthesis of deoxynivalenol. The upregulation of FgSCP expression 3 days after infection indicated its involvement in host invasion, possibly acting as a "smokescreen" to deceive the host and suppress the expression of host defensive genes. Subsequently, we confirmed the secretion ability of FgSCP and its ability to inhibit the cell death induced by INF1 in Nicotiana benthamiana cells, indicating its potential role as an effector protein in suppressing plant immune responses and promoting infection. In summary, we have identified FgSCP as an essential effector protein in F. graminearum, playing critical roles in growth, virulence, secondary metabolism, and host invasion.

Fusarium mycotoxins: The major food contaminants

Mycotoxins, which are secondary metabolites produced by toxicogenic fungi, are natural food toxins that cause acute and chronic adverse reactions in humans and animals. The genus Fusarium is one of three major genera of mycotoxin-producing fungi. Trichothecenes, fumonisins, and zearalenone are the major Fusarium mycotoxins that occur worldwide. Fusarium mycotoxins have the potential to infiltrate the human food chain via contamination during crop production and food processing, eventually threatening human health. The occurrence and development of Fusarium mycotoxin contamination will change with climate change, especially with variations in temperature, precipitation, and carbon dioxide concentration. To address these challenges, researchers have built a series of effective models to forecast the occurrence of Fusarium mycotoxins and provide guidance for crop production. Fusarium mycotoxins frequently exist in food products at extremely low levels, thus necessitating the development of highly sensitive and reliable detection techniques. Numerous successful detection methods have been developed to meet the requirements of various situations, and an increasing number of methods are moving toward high-throughput features. Although Fusarium mycotoxins cannot be completely eliminated, numerous agronomic, chemical, physical, and biological methods can lower Fusarium mycotoxin contamination to safe levels during the preharvest and postharvest stages. These theoretical innovations and technological advances have the potential to facilitate the development of comprehensive strategies for effectively managing Fusarium mycotoxin contamination in the future.

Control of Fusarium Head Blight of Wheat with Bacillus velezensis E2 and Potential Mechanisms of Action

Wheat plants are impacted by Fusarium head blight (FHB) infection, which poses a huge threat to wheat growth, development, storage and food safety. In this study, a fungal strain was isolated from diseased wheat plants and identified as Fusarium asiaticum F1, known to be a member of the Fusarium graminearum species complex, agents causally responsible for FHB. In order to control this disease, new alternatives need to be developed for the use of antagonistic bacteria. Bacillus velezensis E2 (B. velezensis E2), isolated from a previous investigation in our laboratory, showed a notable inhibitory effect on F. asiaticum F1 growth and deoxynivalenol (DON) synthesis in grains. The spore germination of F. asiaticum F1 was significantly reduced and the spores showed vesicular structures when treated with B. velezensis E2. Observations using scanning electron microscopy (SEM) showed that the hyphae of F. asiaticum F1 were shrunken and broken when treated with B. velezensis E2. The RNA-seq results of F1 hyphae treated with B. velezensis E2 showed that differentially expressed genes (DEGs), which were involved in multiple metabolic pathways such as toxin synthesis, autophagy process and glycan synthesis, especially the genes associated with DON synthesis, were significantly downregulated. In summary, those results showed that B. velezensis E2 could inhibit F. asiaticum F1 growth and reduce the gene expression of DON synthesis caused by F1. This study provides new insights and antagonistic mechanisms for the biological control of FHB during wheat growth, development and storage.

Profiling of deubiquitinases that control virulence in the pathogenic plant fungus Fusarium graminearum

Eukaryotes have evolved sophisticated post-translational modifications to regulate protein function and numerous biological processes, including ubiquitination controlled by the coordinated action of ubiquitin-conjugating enzymes and deubiquitinating enzymes (Dubs). However, the function of deubiquitination in pathogenic fungi is largely unknown. Here, the distribution of Dubs in the fungal kingdom was surveyed and their functions were systematically characterized using the phytopathogen Fusarium graminearum as the model species, which causes devastating diseases of all cereal species world-wide. Our findings demonstrate that Dubs are critical for fungal development and virulence, especially the ubiquitin-specific protease 15 (Ubp15). Global ubiquitome analysis and subsequent experiments identified three important substrates of Ubp15, including the autophagy-related protein Atg8, the mitogen-activated protein kinase Gpmk1, and the mycotoxin deoxynivalenol (DON) biosynthetic protein Tri4. Ubp15 regulates the deubiquitination of the Atg8, thereby impacting its subcellular localization and the autophagy process. Moreover, Ubp15 also modulates the deubiquitination of Gpmk1 and Tri4. This modulation subsequently influences their protein stabilities and further affects the formation of penetration structures and the biosynthetic process of DON, respectively. Collectively, our findings reveal a previously unknown regulatory pathway of a deubiquitinating enzyme for fungal virulence and highlight the potential of Ubp15 as a target for combating fungal diseases.

Liquid-liquid phase separation of H3K27me3 reader BP1 regulates transcriptional repression

BACKGROUND

Bromo-adjacent homology-plant homeodomain domain containing protein 1 (BP1) is a reader of histone post-translational modifications in fungi. BP1 recognizes trimethylation of lysine 27 in histone H3 (H3K27me3), an epigenetic hallmark of gene silencing. However, whether and how BP1 participates in transcriptional repression remains poorly understood.

RESULTS

We report that BP1 forms phase-separated liquid condensates to modulate its biological function in Fusarium graminearum. Deletion assays reveal that intrinsically disordered region 2 (IDR2) of BP1 mediates its liquid-liquid phase separation. The phase separation of BP1 is indispensable for its interaction with suppressor of Zeste 12, a component of polycomb repressive complex 2. Furthermore, IDR2 deletion abolishes BP1-H3K27me3 binding and alleviates the transcriptional repression of secondary metabolism-related genes, especially deoxynivalenol mycotoxin biosynthesis genes.

CONCLUSIONS

BP1 maintains transcriptional repression by forming liquid-liquid phase-separated condensates, expanding our understanding of the relationship between post-translational modifications and liquid-liquid phase separation.

Regulation of TRI5 expression and deoxynivalenol biosynthesis by a long non-coding RNA in Fusarium graminearum

Deoxynivalenol (DON) is the most frequently detected mycotoxin in cereal grains and processed food or feed. Two transcription factors, Tri6 and Tri10, are essential for DON biosynthesis in Fusarium graminearum. In this study we conduct stranded RNA-seq analysis with tri6 and tri10 mutants and show that Tri10 acts as a master regulator controlling the expression of sense and antisense transcripts of TRI6 and over 450 genes with diverse functions. TRI6 is more specific for regulating TRI genes although it negatively regulates TRI10. Two other TRI genes, including TRI5 that encodes a key enzyme for DON biosynthesis, also have antisense transcripts. Both Tri6 and Tri10 are essential for TRI5 expression and for suppression of antisense-TRI5. Furthermore, we identify a long non-coding RNA (named RNA5P) that is transcribed from the TRI5 promoter region and is also regulated by Tri6 and Tri10. Deletion of RNA5P by replacing the promoter region of TRI5 with that of TRI12 increases TRI5 expression and DON biosynthesis, indicating that RNA5P suppresses TRI5 expression. However, ectopic constitutive overexpression of RNA5P has no effect on DON biosynthesis and TRI5 expression. Nevertheless, elevated expression of RNA5P in situ reduces TRI5 expression and DON production. Our results indicate that TRI10 and TRI6 regulate each other's expression, and both are important for suppressing the expression of RNA5P, a long non-coding RNA with cis-acting inhibitory effects on TRI5 expression and DON biosynthesis in F. graminearum.

Genome-wide transcriptome analysis of toxigenic Fusarium verticillioides in response to variation of temperature and water activity on maize kernels

Fusarium verticillioides is one of the important mycotoxigenic pathogens of maize since it causes severe yield losses and produces fumonisins (FBs) to threaten human and animal health. Previous studies showed that temperature and water activity (aw) are two pivotal environmental factors affecting F. verticillioides growth and FBs production during maize storage. However, the genome-wide transcriptome analysis of differentially expressed genes (DEGs) in F. verticillioides under the stress combinations of temperature and aw has not been studied in detail. In this study, DEGs of F. verticillioides and their related regulatory pathways were analyzed in response to the stress of temperature and aw combinations using RNA-Seq. The results showed that the optimal growth conditions for F. verticillioides were 0.98 aw and 25 °C, whereas the highest per-unit yield of the fumonisin B1 (FB1) was observed at 0.98 aw and 15 °C. The RNA-seq analysis showed that 9648 DEGs were affected by temperature regardless of aw levels, whereas only 218 DEGs were affected by aw regardless of temperature variations. Gene Ontology (GO) analysis revealed that a decrease in temperature at both aw levels led to a significant upregulation of genes associated with 24 biological processes, while three biological processes were downregulated. Furthermore, when aw was decreased at both temperatures, seven biological processes were significantly upregulated and four were downregulated. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that the genes, whose expression was upregulated when the temperature decreased, were predominantly associated with the proteasome pathway, whereas the genes, whose expression was downregulated when the aw decreased, were mainly linked to amino acid metabolism. For the FB1, except for the FUM15 gene, the other 15 biosynthetic-related genes were highly expressed at 0.98 aw and 15 °C. In addition, the expression pattern analysis of other biosynthetic genes involved in secondary metabolite production and regulation of fumonisins production was conducted to explore how this fungus responds to the stress combinations of temperature and aw. Overall, this study primarily examines the impact of temperature and aw on the growth of F. verticillioides and its production of FB1 using transcriptome data. The findings presented here have the potential to contribute to the development of novel strategies for managing fungal diseases and offer valuable insights for preventing fumonisin contamination in food and feed storage.

Targeting of Specialized Metabolites Biosynthetic Enzymes to Membranes and Vesicles by Posttranslational Palmitoylation: A Mechanism of Non-Conventional Traffic and Secretion of Fungal Metabolites

In nature, the formation of specialized (secondary) metabolites is associated with the late stages of fungal development. Enzymes involved in the biosynthesis of secondary metabolites in fungi are located in distinct subcellular compartments including the cytosol, peroxisomes, endosomes, endoplasmic reticulum, different types of vesicles, the plasma membrane and the cell wall space. The enzymes traffic between these subcellular compartments and the secretion through the plasma membrane are still unclear in the biosynthetic processes of most of these metabolites. Recent reports indicate that some of these enzymes initially located in the cytosol are later modified by posttranslational acylation and these modifications may target them to membrane vesicle systems. Many posttranslational modifications play key roles in the enzymatic function of different proteins in the cell. These modifications are very important in the modulation of regulatory proteins, in targeting of proteins, intracellular traffic and metabolites secretion. Particularly interesting are the protein modifications by palmitoylation, prenylation and miristoylation. Palmitoylation is a thiol group-acylation (S-acylation) of proteins by palmitic acid (C16) that is attached to the SH group of a conserved cysteine in proteins. Palmitoylation serves to target acylated proteins to the cytosolic surface of cell membranes, e.g., to the smooth endoplasmic reticulum, whereas the so-called toxisomes are formed in trichothecene biosynthesis. Palmitoylation of the initial enzymes involved in the biosynthesis of melanin serves to target them to endosomes and later to the conidia, whereas other non-palmitoylated laccases are secreted directly by the conventional secretory pathway to the cell wall space where they perform the last step(s) of melanin biosynthesis. Six other enzymes involved in the biosynthesis of endocrosin, gliotoxin and fumitremorgin believed to be cytosolic are also targeted to vesicles, although it is unclear if they are palmitoylated. Bioinformatic analysis suggests that palmitoylation may be frequent in the modification and targeting of polyketide synthetases and non-ribosomal peptide synthetases. The endosomes may integrate other small vesicles with different cargo proteins, forming multivesicular bodies that finally fuse with the plasma membrane during secretion. Another important effect of palmitoylation is that it regulates calcium metabolism by posttranslational modification of the phosphatase calcineurin. Mutants defective in the Akr1 palmitoyl transferase in several fungi are affected in calcium transport and homeostasis, thus impacting on the biosynthesis of calcium-regulated specialized metabolites. The palmitoylation of secondary metabolites biosynthetic enzymes and their temporal distribution respond to the conidiation signaling mechanism. In summary, this posttranslational modification drives the spatial traffic of the biosynthetic enzymes between the subcellular organelles and the plasma membrane. This article reviews the molecular mechanism of palmitoylation and the known fungal palmitoyl transferases. This novel information opens new ways to improve the biosynthesis of the bioactive metabolites and to increase its secretion in fungi.

Food Safety Aspects of Breeding Maize to Multi-Resistance against the Major (Fusarium graminearum, F. verticillioides, Aspergillus flavus) and Minor Toxigenic Fungi (Fusarium spp.) as Well as to Toxin Accumulation, Trends, and Solutions-A Review

Maize is the crop which is most commonly exposed to toxigenic fungi that produce many toxins that are harmful to humans and animals alike. Preharvest grain yield loss, preharvest toxin contamination (at harvest), and storage loss are estimated to be between 220 and 265 million metric tons. In the past ten years, the preharvest mycotoxin damage was stable or increased mainly in aflatoxin and fumonisins. The presence of multiple toxins is characteristic. The few breeding programs concentrate on one of the three main toxigenic fungi. About 90% of the experiments except AFB1 rarely test toxin contamination. As disease resistance and resistance to toxin contamination often differ in regard to F. graminearum, F. verticillioides, and A. flavus and their toxins, it is not possible to make a food safety evaluation according to symptom severity alone. The inheritance of the resistance is polygenic, often mixed with epistatic and additive effects, but only a minor part of their phenotypic variation can be explained. All tests are made by a single inoculum (pure isolate or mixture). Genotype ranking differs between isolates and according to aggressiveness level; therefore, the reliability of such resistance data is often problematic. Silk channel inoculation often causes lower ear rot severity than we find in kernel resistance tests. These explain the slow progress and raise skepticism towards resistance breeding. On the other hand, during genetic research, several effective putative resistance genes were identified, and some overlapped with known QTLs. QTLs were identified as securing specific or general resistance to different toxicogenic species. Hybrids were identified with good disease and toxin resistance to the three toxigenic species. Resistance and toxin differences were often tenfold or higher, allowing for the introduction of the resistance and resistance to toxin accumulation tests in the variety testing and the evaluation of the food safety risks of the hybrids within 2-3 years. Beyond this, resistance breeding programs and genetic investigations (QTL-analyses, GWAM tests, etc.) can be improved. All other research may use it with success, where artificial inoculation is necessary. The multi-toxin data reveal more toxins than we can treat now. Their control is not solved. As limits for nonregulated toxins can be introduced, or the existing regulations can be made to be stricter, the research should start. We should mention that a higher resistance to F. verticillioides and A. flavus can be very useful to balance the detrimental effect of hotter and dryer seasons on aflatoxin and fumonisin contamination. This is a new aspect to secure food and feed safety under otherwise damaging climatic conditions. The more resistant hybrids are to the three main agents, the more likely we are to reduce the toxin losses mentioned by about 50% or higher.

Overproduction of mycotoxin biosynthetic enzymes triggers Fusarium toxisome-shaped structure formation via endoplasmic reticulum remodeling

Mycotoxin deoxynivalenol (DON) produced by the Fusarium graminearum complex is highly toxic to animal and human health. During DON synthesis, the endoplasmic reticulum (ER) of F. graminearum is intensively reorganized, from thin reticular structure to thickened spherical and crescent structure, which was referred to as "DON toxisome". However, the underlying mechanism of how the ER is reorganized into toxisome remains unknown. In this study, we discovered that overproduction of ER-localized DON biosynthetic enzyme Tri4 or Tri1, or intrinsic ER-resident membrane proteins FgHmr1 and FgCnx was sufficient to induce toxisome-shaped structure (TSS) formation under non-toxin-inducing conditions. Moreover, heterologous overexpression of Tri1 and Tri4 proteins in non-DON-producing fungi F. oxysporum f. sp. lycopersici and F. fujikuroi also led to TSS formation. In addition, we found that the high osmolarity glycerol (HOG), but not the unfolded protein response (UPR) signaling pathway was involved in the assembly of ER into TSS. By using toxisome as a biomarker, we screened and identified a novel chemical which exhibited high inhibitory activity against toxisome formation and DON biosynthesis, and inhibited Fusarium growth species-specifically. Taken together, this study demonstrated that the essence of ER remodeling into toxisome structure is a response to the overproduction of ER-localized DON biosynthetic enzymes, providing a novel pathway for management of mycotoxin contamination.

Phylogenetic Variation of Tri1 Gene and Development of PCR-RFLP Analysis for the Identification of NX Genotypes in Fusarium graminearum Species Complex

NX toxins have been described as a novel group of type A trichothecenes produced by members of the Fusarium graminearum species complex (FGSC). Differences in structure between NX toxins and the common type B trichothecenes arise from functional variation in the trichothecene biosynthetic enzyme Tri1 in the FGSC. The identified highly conserved changes in the Tri1 gene can be used to develop specific PCR-based assays to identify the NX-producing strains. In this study, the sequences of the Tri1 gene from type B trichothecene- and NX-producing strains were analyzed to identify DNA polymorphisms between the two different kinds of trichothecene producers. Four sets of Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods were successfully developed to distinguish the common type B trichothecene producers and NX producers within FGSC. These promising diagnostic methods can be used for high-throughput genotype detection of Fusarium strains as a step forward for crop disease management and mycotoxin control in agriculture. Additionally, it was found that the Tri1 gene phylogeny differs from the species phylogeny, which is consistent with the previous studies.

Virulence factors of the genus Fusarium with targets in plants

Fusarium spp. comprise various species of filamentous fungi that cause severe diseases in plant crops of both agricultural and forestry interest. These plant pathogens produce a wide range of molecules with diverse chemical structures and biological activities. Genetic functional analyses of some of these compounds have shown their role as virulence factors (VF). However, their mode of action and contributions to the infection process for many of these molecules are still unknown. This review aims to analyze the state of the art in Fusarium VF, emphasizing their biological targets on the plant hosts. It also addresses the current experimental approaches to improve our understanding of their role in virulence and suggests relevant research questions that remain to be answered with a greater focus on species of agroeconomic importance. In this review, a total of 37 confirmed VF are described, including 22 proteinaceous and 15 non-proteinaceous molecules, mainly from Fusarium oxysporum and Fusarium graminearum and, to a lesser extent, in Fusarium verticillioides and Fusarium solani.

Characterization of Fusarium verticillioides Med1 LxxLL Motif Involved in Fumonisin Biosynthesis

The Med1 transcriptional coactivator is a crucial component of the Mediator middle complex, which regulates the expression of specific genes involved in cell development, differentiation, reproduction, and homeostasis. The Med1 LxxLL motif, a five-amino-acid peptide sequence, is essential for Med1-mediated gene expression. Our previous study revealed that the disruption of the Med1 subunit leads to a significant increase in fumonisin B1 (FB1) production in the maize pathogen Fusarium verticillioides. However, our understanding of how Med1 regulates FB1 biosynthesis in F. verticillioides, particularly through the Med1 LxxLL motifs, remains limited. To characterize the role of LxxLL motifs, we generated a series of Med1 LxxLL deletion and amino acid substitution mutants. These mutants exhibited impaired mycelial growth and conidia germination while demonstrating enhanced conidia production and virulence. Similar to the Med1 deletion mutant, Med1 LxxLL motif mutants also exhibited increased FB1 biosynthesis in F. verticillioides. Proteomic profiling revealed that the Med1 LxxLL motif regulated the biosynthesis of several key substances that affected FB1 production, including starch and carotenoid. Subsequent studies demonstrated that the production of amylopectin, which is strongly linked to FB1 biosynthesis, was significantly increased in Med1 LxxLL motif mutants. In addition, the disruption of carotenoid metabolic genes decreased carotenoid content, thus stimulating FB1 biosynthesis in F. verticillioides. Taken together, our results provide valuable insights into how the Med1 LxxLL motif regulates FB1 biosynthesis in the mycotoxigenic fungus F. verticillioides.

Exogenous Melatonin Regulates Plant-Disease Interaction by Inducing Maize Resistance and Decreasing the Pathogenicity of Fusarium graminearum

Plants cannot avoid environmental challenges and are constantly threatened by diverse biotic and abiotic stresses. However, plants have developed a unique immune system to defend themselves against the invasion of various pathogens. Melatonin, N-acetyl-5-methoxytryptamine has positive physiological effects in plants that are involved in disease resistance. The processes underlying melatonin-induced pathogen resistance in plants are still unknown. The current study explores how melatonin regulates the plant-disease interaction in maize. The results showed that 400 μM melatonin strongly reduced the disease lesion on maize stalks by 1.5 cm and corn by 4.0 cm caused by Fusarium graminearum PH-1. Furthermore, after treatment with melatonin, the plant defense enzymes like SOD significantly increased, while POD and APX significantly decreased compared to the control. In addition, melatonin can also improve maize's innate immunity, which is mediated by melatonin treatments through the salicylic acid signaling pathway, and up-regulate the defense-associated expression of PR1, LOX1, OXR, serPIN, and WIPI genes in maize. Melatonin not only inhibits the disease in the maize stalks and corn, but also down-regulates the deoxynivalenol (DON) production-related expression of genes Tri1, Tri4, Tri5, and Tri6 in maize. Overall, this study sheds new light on the mechanisms by which melatonin regulates antioxidant enzymes and defense-related genes involved in plant immunity to effectively suppress plant diseases.

Global distribution, toxicity to humans and animals, biodegradation, and nutritional mitigation of deoxynivalenol: A review

Deoxynivalenol (DON) is one of the main types of B trichothecenes, and it causes health-related issues in humans and animals and imposes considerable challenges to food and feed safety globally each year. This review investigates the global hazards of DON, describes the occurrence of DON in food and feed in different countries, and systematically uncovers the mechanisms of the various toxic effects of DON. For DON pollution, many treatments have been reported on the degradation of DON, and each of the treatments has different degradation efficacies and degrades DON by a distinct mechanism. These treatments include physical, chemical, and biological methods and mitigation strategies. Biodegradation methods include microorganisms, enzymes, and biological antifungal agents, which are of great research significance in food processing because of their high efficiency, low environmental hazards, and drug resistance. And we also reviewed the mechanisms of biodegradation methods of DON, the adsorption and antagonism effects of microorganisms, and the different chemical transformation mechanisms of enzymes. Moreover, nutritional mitigation including common nutrients (amino acids, fatty acids, vitamins, and microelements) and plant extracts was discussed in this review, and the mitigation mechanism of DON toxicity was elaborated from the biochemical point of view. These findings help explore various approaches to achieve the best efficiency and applicability, overcome DON pollution worldwide, ensure the sustainability and safety of food processing, and explore potential therapeutic options with the ability to reduce the deleterious effects of DON in humans and animals.

Bioinformatic Analysis of Secondary Metabolite Biosynthetic Potential in Pathogenic Fusarium

Fusarium species are among the filamentous fungi with the most pronounced impact on agricultural production and human health. The mycotoxins produced by pathogenic Fusarium not only attack various plants including crops, causing various plant diseases that lead to reduced yields and even death, but also penetrate into the food chain of humans and animals to cause food poisoning and consequent health hazards. Although sporadic studies have revealed some of the biosynthetic pathways of Fusarium toxins, they are insufficient to satisfy the need for a comprehensive understanding of Fusarium toxin production. In this study, we focused on 35 serious pathogenic Fusarium species with available genomes and systematically analyzed the ubiquity of the distribution of identified Fusarium- and non-Fusarium-derived fungal toxin biosynthesis gene clusters (BGCs) in these species through the mining of core genes and the comparative analysis of corresponding BGCs. Additionally, novel sesterterpene synthases and PKS_NRPS clusters were discovered and analyzed. This work is the first to systematically analyze the distribution of related mycotoxin biosynthesis in pathogenic Fusarium species. These findings enhance the knowledge of mycotoxin production and provide a theoretical grounding for the prevention of fungal toxin production using biotechnological approaches.

Type A Trichothecene Metabolic Profile Differentiation, Mechanisms, Biosynthetic Pathways, and Evolution in Fusarium Species-A Mini Review

Trichothecenes are the most common Fusarium toxins detected in grains and related products. Type A trichothecenes are among the mycotoxins of greatest concern to food and feed safety due to their high toxicity. Recently, two different trichothecene genotypes within Fusarium species were reported. The available information showed that Tri1 and Tri16 genes are the key determinants of the trichothecene profiles of T-2 and DAS genotypes. In this review, polymorphisms in the Tri1 and Tri16 genes in the two genotypes were investigated. Meanwhile, the functions of genes involved in DAS and NEO biosynthesis are discussed. The possible biosynthetic pathways of DAS and NEO are proposed in this review, which will facilitate the understanding of the synthesis process of trichothecenes in Fusarium strains and may also inspire researchers to design and conduct further research. Together, the review provides insight into trichothecene profile differentiation and Tri gene evolutionary processes responsible for the structural diversification of trichothecene produced by Fusarium.

Current Insights in Fungal Importance-A Comprehensive Review

Besides plants and animals, the Fungi kingdom describes several species characterized by various forms and applications. They can be found in all habitats and play an essential role in the excellent functioning of the ecosystem, for example, as decomposers of plant material for the cycling of carbon and nutrients or as symbionts of plants. Furthermore, fungi have been used in many sectors for centuries, from producing food, beverages, and medications. Recently, they have gained significant recognition for protecting the environment, agriculture, and several industrial applications. The current article intends to review the beneficial roles of fungi used for a vast range of applications, such as the production of several enzymes and pigments, applications regarding food and pharmaceutical industries, the environment, and research domains, as well as the negative impacts of fungi (secondary metabolites production, etiological agents of diseases in plants, animals, and humans, as well as deteriogenic agents).

Population structure and genetic diversity of Fusarium graminearum from southwestern Russia and the Russian Far East as compared with northern Europe and North America

Genetic variation at variable number tandem repeat (VNTR) markers was used to assess population structure and diversity among 296 Fusarium graminearum isolates from northern Europe (Finland, northwestern Russia, and Norway), southern Europe (southwestern and western Russia), and Asia (Siberia and the Russian Far East). We identified at least two highly differentiated and geographically structured genetic populations (E1 and E2) in Eurasia (Φ_PT = 0.35). Isolates from northern Europe were almost exclusively from the E1 population (95.6%) and had the 3ADON (3-acetyldeoxynivalenol) trichothecene genotype (97.3%). In contrast, all isolates from southern Europe were from the E2 population and 94.4% had the 15ADON (15-acetyldeoxynivalenol) genotype. The E2 population also predominated in the Asian sampling locations (92.7%) where 3ADON and 15ADON genotypes occurred at nearly equal frequencies. Southern European isolates were more closely related to those from Asia (Φ_PT = 0.06) than to geographically closer populations from northern Europe (Φ_PT ≥ 0.31). Northern European populations also harbored substantially less genetic diversity (Ne ≤ 2.1) than populations in southern Europe or Asia (Ne ≥ 3.4), indicative of a selective sweep or recent introduction and subsequent range expansion in northern Europe. Bayesian analyses incorporating previously described genetic populations from North America (NA1 and NA2) surprisingly identified NA2 and E2 as a single genetic population, consistent with hypotheses of a recent Eurasian origin for NA2. Additionally, more than 10% of the isolates from Asia and southern Europe were assigned to the NA1 population, indicating recent introductions of NA1 into parts of Eurasia. Collectively, these results demonstrate that there are at least three genetic populations of F. graminearum in the Northern Hemisphere and indicate that population-level diversity in Eurasia and North America has been shaped by recent transcontinental introductions.

Effect of Amino Acids on Fusarium oxysporum Growth and Pathogenicity Regulated by TORC1-Tap42 Gene and Related Interaction Protein Analysis

Free amino acids (AAs) formed in fermented meat products are important nitrogen sources for the survival and metabolism of contaminating fungi. These AAs are mainly regulated by the TORC1-Tap42 signaling pathway. Fusarium spp., a common contaminant of fermented products, is a potential threat to food safety. Therefore, there is an urgent need to clarify the effect of different AAs on Fusarium spp. growth and metabolism. This study investigated the effect of 18 AAs on Fusarium oxysporum (Fo17) growth, sporulation, T-2 toxin (T-2) synthesis and Tri5 expression through Tap42 gene regulation. Co-immunoprecipitation and Q Exactive LC-MS/MS methods were used to detect the interacting protein of Tap42 during specific AA treatment. Tap42 positively regulated L-His, L-Ile and L-Tyr absorption for Fo17 colony growth. Acidic (L-Asp, L-Glu) and sulfur-containing (L-Cys, L-Met) AAs significantly inhibited the Fo17 growth which was not regulated by Tap42. The L-Ile and L-Pro addition significantly activated the sporulation of ΔFoTap42. L-His and L-Ser inhibited the sporulation of ΔFoTap42. In T-2 synthesis, ΔFoTap42 was increased in GYM medium, but was markedly inhibited in L-Asp and L-Glu addition groups. Dose-response experiments showed that 10-70 mg/mL of neutral AA (L-Thr) and alkaline AA (L-His) significantly increased the T-2 production and Tri5 expression of Fo17, but Tri5 expression was not activated in ΔFoTap42. Inhibition of T-2 synthesis and Tri5 expression were observed in Fo17 following the addition of 30-70 mg/mL L-Asp. KEGG enrichment pathway analysis demonstrated that interacting proteins of Tap42 were from glycerophospholipid metabolism, pentose phosphate pathway, glyoxylate and dicarboxylate metabolism, glycolysis and gluconeogenesis, and were related to the MAPK and Hippo signaling pathways. This study enhanced our understanding of AA regulation in fermented foods and its effect on Fusarium growth and metabolism, and provided insight into potential ways to control fungal contamination in high-protein fermented foods.

The mitotic exit mediated by small GTPase Tem1 is essential for the pathogenicity of Fusarium graminearum

The mitotic exit is a key step in cell cycle, but the mechanism of mitotic exit network in the wheat head blight fungus Fusarium graminearum remains unclear. F. graminearum infects wheat spikelets and colonizes the entire head by growing through the rachis node at the bottom of each spikelet. In this study, we found that a small GTPase FgTem1 plays an important role in F. graminearum pathogenicity and functions in regulating the formation of infection structures and invasive hyphal growth on wheat spikelets and wheat coleoptiles, but plays only little roles in vegetative growth and conidiation of the phytopathogen. FgTem1 localizes to both the inner nuclear periphery and the spindle pole bodies, and negatively regulates mitotic exit in F. graminearum. Furthermore, the regulatory mechanisms of FgTem1 have been further investigated by high-throughput co-immunoprecipitation and genetic strategies. The septins FgCdc10 and FgCdc11 were demonstrated to interact with the dominant negative form of FgTem1, and FgCdc11 was found to regulate the localization of FgTem1. The cell cycle arrest protein FgBub2-FgBfa1 complex was shown to act as the GTPase-activating protein (GAP) for FgTem1. We further demonstrated that a direct interaction exists between FgBub2 and FgBfa1 which crucially promotes conidiation, pathogenicity and DON production, and negatively regulates septum formation and nuclear division in F. graminearum. Deletions of FgBUB2 and FgBFA1 genes caused fewer perithecia and immature asci formations, and dramatically down-regulated trichothecene biosynthesis (TRI) gene expressions. Double deletion of FgBUB2/FgBFA1 genes showed that FgBUB2 and FgBFA1 have little functional redundancy in F. graminearum. In summary, we systemically demonstrated that FgTem1 and its GAP FgBub2-FgBfa1 complex are required for fungal development and pathogenicity in F. graminearum.

Vacuole Proteins with Optimized Microtubule Assembly Is Required for Fum1 Protein Localization and Fumonisin Biosynthesis in Mycotoxigenic Fungus Fusarium verticillioides

Fumonisin contamination of corn caused by Fusarium verticillioides is a major concern worldwide. While key genes involved in fumonisin biosynthesis are known, the location within the fungal cell where this process occurs has yet to be fully characterized. In this study, three key enzymes, i.e., Fum1, Fum8, and Fum6, associated with early steps of fumonisin biosynthesis pathway, were tagged with GFP, and we examined their cellular localization. Results showed that these three proteins co-localized with the vacuole. To further understand the role of the vacuole in fumonisin B₁ (FB₁) biosynthesis, we disrupted two predicted vacuole associated proteins, FvRab7 and FvVam7, resulting in a significant reduction of FB₁ biosynthesis and a lack of Fum1-GFP fluorescence signal. Furthermore, we used the microtubule-targeting drug carbendazim to show that proper microtubule assembly is critical for proper Fum1 protein localization and FB₁ biosynthesis. Additionally, we found that α1 tubulin is a negative regulator in FB₁ biosynthesis. We concluded that vacuole proteins with optimized microtubule assembly play a crucial role in proper Fum1 protein localization and fumonisin production in F. verticillioides.

Comparative transcriptomics identifies the key in planta-expressed genes of Fusarium graminearum during infection of wheat varieties

Fusarium head blight (FHB), caused mainly by the fungus Fusarium graminearum, is one of the most devastating diseases in wheat, which reduces the yield and quality of grain. Fusarium graminearum infection of wheat cells triggers dynamic changes of gene expression in both F. graminearum and wheat, leading to molecular interactions between pathogen and host. The wheat plant in turn activates immune signaling or host defense pathways against FHB. However, the mechanisms by which F. graminearum infects wheat varieties with different levels of host resistance are largely limited. In this study, we conducted a comparative analysis of the F. graminearum transcriptome in planta during the infection of susceptible and resistant wheat varieties at three timepoints. A total of 6,106 F. graminearum genes including those functioning in cell wall degradation, synthesis of secondary metabolites, virulence, and pathogenicity were identified during the infection of different hosts, which were regulated by hosts with different genetic backgrounds. Genes enriched with metabolism of host cell wall components and defense response processes were specifically dynamic during the infection with different hosts. Our study also identified F. graminearum genes that were specifically suppressed by signals derived from the resistant plant host. These genes may represent direct targets of the plant defense against infection by this fungus. Briefly, we generated databases of in planta-expressed genes of F. graminearum during infection of two different FHB resistance level wheat varieties, highlighted their dynamic expression patterns and functions of virulence, invasion, defense response, metabolism, and effector signaling, providing valuable insight into the interactions between F. graminearum and susceptible/resistant wheat varieties.

The COP9 signalosome complex regulates fungal development and virulence in the wheat scab fungus Fusarium graminearum

The COP9 signalosome (Csn) complex is an evolutionarily conserved complex that regulates various important cellular processes. However, the function of the Csn complex in pathogenic fungi remains elusive. Here, the distribution of Csn subunits in the fungal kingdom was surveyed, and their biological functions were systematically characterized in the fungal pathogen Fusarium graminearum, which is among the top 10 plant fungal pathogens. The results obtained from bioinformatic analyses suggested that the F. graminearum Csn complex consisted of seven subunits (Csn1-Csn7) and that Csn5 was the most conserved subunit across the fungi kingdom. Yeast two-hybrid assays demonstrated that the seven Csn subunits formed a complex in F. graminearum. The Csn complex was localized to both the nucleus and cytoplasm and necessary for hyphal growth, asexual and sexual development and stress response. Transcriptome profiling revealed that the Csn complex regulated the transcription abundance of TRI genes necessary for mycotoxin deoxynivalenol (DON) biosynthesis, subsequently regulating DON production to control fungal virulence. Collectively, the roles of the Csn complex in F. graminearum were comprehensively analyzed, providing new insights into the functions of the Csn complex in fungal virulence and suggesting that the complex may be a potential target for combating fungal diseases.

Transcriptome Profile of Fusarium graminearum Treated by Putrescine

Fusarium graminearum (F. graminearum) is the main pathogen of Fusarium head blight (FHB) in wheat, barley, and corn. Deoxynivalenol (DON), produced by F. graminearum, is the most prevalent toxin associated with FHB. The wheat defense compound putrescine can promote DON production during F. graminearum infection. However, the underlying mechanisms of putrescine-induced DON synthesis are not well-studied. To investigate the effect of putrescine on the global transcriptional regulation of F. graminearum, we treated F. graminearum with putrescine and performed RNA deep sequencing. We found that putrescine can largely affect the transcriptome of F. graminearum. Gene ontology (GO) and KEGG enrichment analysis revealed that having a large amount of DEGs was associated with ribosome biogenesis, carboxylic acid metabolism, glycolysis/gluconeogenesis, and amino acid metabolism pathways. Co-expression analysis showed that 327 genes had similar expression patterns to FgTRI genes and were assigned to the same module. In addition, three transcription factor genes were identified as hub genes in this module, indicating that they may play important roles in DON synthesis. These results provide important clues for further analysis of the molecular mechanisms of putrescine-induced DON synthesis and will facilitate the study of the pathogenic mechanisms of FHB.

A Novel Trichothecene Toxin Phenotype Associated with Horizontal Gene Transfer and a Change in Gene Function in Fusarium

Fusarium trichothecenes are among the mycotoxins of most concern to food and feed safety. Production of these mycotoxins and presence of the trichothecene biosynthetic gene (TRI) cluster have been confirmed in only two multispecies lineages of Fusarium: the Fusarium incarnatum-equiseti (Incarnatum) and F. sambucinum (Sambucinum) species complexes. Here, we identified and characterized a TRI cluster in a species that has not been formally described and is represented by Fusarium sp. NRRL 66739. This fungus is reported to be a member of a third Fusarium lineage: the F. buharicum species complex. Cultures of NRRL 66739 accumulated only two trichothecenes, 7-hydroxyisotrichodermin and 7-hydroxyisotrichodermol. Although these are not novel trichothecenes, the production profile of NRRL 66739 is novel, because in previous reports 7-hydroxyisotrichodermin and 7-hydroxyisotrichodermol were components of mixtures of 6-8 trichothecenes produced by several Fusarium species in Sambucinum. Heterologous expression analysis indicated that the TRI13 gene in NRRL 66739 confers trichothecene 7-hydroxylation. This contrasts the trichothecene 4-hydroxylation function of TRI13 in other Fusarium species. Phylogenetic analyses suggest that NRRL 66739 acquired the TRI cluster via horizontal gene transfer from a close relative of Incarnatum and Sambucinum. These findings provide insights into evolutionary processes that have shaped the distribution of trichothecene production among Fusarium species and the structural diversity of the toxins.

Genetic Regulation of Mycotoxin Biosynthesis

Mycotoxin contamination in food poses health hazards to humans. Current methods of controlling mycotoxins still have limitations and more effective approaches are needed. During the past decades of years, variable environmental factors have been tested for their influence on mycotoxin production leading to elucidation of a complex regulatory network involved in mycotoxin biosynthesis. These regulators are putative targets for screening molecules that could inhibit mycotoxin synthesis. Here, we summarize the regulatory mechanisms of hierarchical regulators, including pathway-specific regulators, global regulators and epigenetic regulators, on the production of the most critical mycotoxins (aflatoxins, patulin, citrinin, trichothecenes and fumonisins). Future studies on regulation of mycotoxins will provide valuable knowledge for exploring novel methods to inhibit mycotoxin biosynthesis in a more efficient way.

How to Completely Squeeze a Fungus-Advanced Genome Mining Tools for Novel Bioactive Substances

Fungal species have the capability of producing an overwhelming diversity of bioactive substances that can have beneficial but also detrimental effects on human health. These so-called secondary metabolites naturally serve as antimicrobial "weapon systems", signaling molecules or developmental effectors for fungi and hence are produced only under very specific environmental conditions or stages in their life cycle. However, as these complex conditions are difficult or even impossible to mimic in laboratory settings, only a small fraction of the true chemical diversity of fungi is known so far. This also implies that a large space for potentially new pharmaceuticals remains unexplored. We here present an overview on current developments in advanced methods that can be used to explore this chemical space. We focus on genetic and genomic methods, how to detect genes that harbor the blueprints for the production of these compounds (i.e., biosynthetic gene clusters, BGCs), and ways to activate these silent chromosomal regions. We provide an in-depth view of the chromatin-level regulation of BGCs and of the potential to use the CRISPR/Cas technology as an activation tool.

Enantioselective effect of chiral fungicide prothioconazole on Fusarium graminearum: Fungicidal activity and DON biosynthesis

Prothioconazole, a chiral triazole fungicide, is widely used to control Fusarium head blight (FHB) of wheat. Fusarium graminearum (F. graminearum), as the main pathogen of FHB, can produce many secondary metabolites including deoxynivalenol (DON), which threatens the health of humans and animals. However, some fungicides may stimulate F. graminearum to synthesize more DON under certain conditions. Until now, the fungicidal activity and enantioselective effect of prothioconazole enantiomers on DON production, transcriptome and metabolome of F. graminearum were unclear. The fungicidal activity of R-(-)-prothioconazole against F. graminearum was 9.12-17.73 times higher than that of S-(+)-prothioconazole under all conditions. Prothioconazole enantiomers can induce F. graminearum to synthesize more DON under 0.99 water activity (a_w) and 30 °C, especially R-(-)-prothioconazole. The expression levels of TRI6, TRI10 and TRI101 under R-(-)-prothioconazole treatment were significantly higher than those under S-(+)-prothioconazole treatment. Most genes in glycolysis, pyruvate metabolism, the target of rapamycin (TOR) signaling transduction pathway and the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling transduction pathway showed higher expression levels under R-(-)-prothioconazole treatment than uner S-(+)-prothioconazole treatment and the control. The peroxisome pathway displayed higher transcriptional activity under S-(+)-prothioconazole treatment compared with R-(-)-prothioconazole and the control. Based on metabolomic data, R-(-)-prothioconazole can significantly influence phenylalanine metabolism, and no significantly enriched pathway was found under S-(+)-prothioconazole treatment. These results are helpful to understand the risk of prothioconazole enantiomers on DON production of F. graminearum and uncover the relevant underlying mechanisms of prothioconazole enantiomers.

Nivalenol Mycotoxin Concerns in Foods: An Overview on Occurrence, Impact on Human and Animal Health and Its Detection and Management Strategies

Mycotoxins are secondary metabolites produced by fungi that infect a wide range of foods worldwide. Nivalenol (NIV), a type B trichothecene produced by numerous Fusarium species, has the ability to infect a variety of foods both in the field and during post-harvest handling and management. NIV is frequently found in cereal and cereal-based goods, and its strong cytotoxicity poses major concerns for both human and animal health. To address these issues, this review briefly overviews the sources, occurrence, chemistry and biosynthesis of NIV. Additionally, a brief overview of several sophisticated detection and management techniques is included, along with the implications of processing and environmental factors on the formation of NIV. This review’s main goal is to offer trustworthy and current information on NIV as a mycotoxin concern in foods, with potential mitigation measures to assure food safety and security.

Effect of Compactin on the Mycotoxin Production and Expression of Related Biosynthetic and Regulatory Genes in Toxigenic Fusarium culmorum

Zearalenone (ZEN) and deoxynivalenol (DON) are mycotoxins produced by various species of Fusarium fungi. They contaminate agricultural products and negatively influence human and animal health, thus representing a serious problem of the agricultural industry. Earlier we showed that compactin, a secondary metabolite of Penicillium citrinum, is able to completely suppress the aflatoxin B1 biosynthesis by Aspergillus flavus. Using the F. culmorum strain FC-19 able to produce DON and ZEN, we demonstrated that compactin also significantly suppressed both DON (99.3%) and ZEN (100%) biosynthesis. The possible mechanisms of this suppression were elucidated by qPCR-based analysis of expression levels of 48 biosynthetic and regulatory genes. Expression of eight of 13 TRI genes, including TRI4, TRI5, and TRI101, was completely suppressed. A significant down-regulation was revealed for the TRI10, TRI9, and TRI14 genes. TRI15 was the only up-regulated gene from the TRI cluster. In the case of the ZEN cluster, almost complete suppression was observed for PKS4, PKS13, and ZEB1 genes, and the balance between two ZEB2 isoforms was altered. Among regulatory genes, an increased expression of GPA1 and GPA2 genes encoding α- and β-subunits of a G-protein was shown, whereas eight genes were down-regulated. The obtained results suggest that the main pathway for a compactin-related inhibition of the DON and ZEN biosynthesis affects the transcription of genes involved in the G-protein-cAMP-PKA signaling pathway. The revealed gene expression data may provide a better understanding of genetic mechanisms underlying mycotoxin production and its regulation.

Fusarium abutilonis and F. guadeloupense, two novel species in the Fusarium buharicum clade supported by multilocus molecular phylogenetic analyses

This study was conducted to elucidate evolutionary relationships and species diversity within the Fusarium buharicum species complex (FBSC). We also evaluate the potential of these species to produce mycotoxins and other bioactive secondary metabolites. Maximum likelihood and maximum parsimony analyses of sequences from portions of four marker loci (ITS rDNA, TEF1, RPB1, and RPB2) and the combined 4495 bp data set support recognition of seven genealogically exclusive species within the FBSC. Two of the three newly discovered species are formally described as F. abutilonis and F. guadeloupense based on concordance of gene genealogies and morphological data. Fusarium abutilonis induces leaf, stem, and root lesions on several weedy Malvaceae (Abution theophrasti, Anoda cristata, Sida spinosa) and a fabaceous host (Senna obtusifolia) in North America and also was recovered from soil in New Caledonia. Fusarium abutilonis, together with its unnamed sister, Fusarium sp. ex common marsh mallow (Hibiscus moscheutos) from Washington state, and F. buharicum pathogenic to cotton and kenaf in Russia and Iran, respectively, were strongly supported as a clade of malvaceous pathogens. The four other species of the FBSC are not known to be phytopathogenic; however, F. guadeloupense was isolated from human blood in Texas and soil in Guadeloupe. The former isolate is unique because it represents the only known case of a fusarial infection disseminated hematogenously by a species lacking microconidia and the only documented fusariosis caused by a member of the FBSC. Whole genome sequence data and extracts of cracked maize kernel cultures were analyzed to assess the potential of FBSC isolates to produce mycotoxins, pigments, and phytohormones.

The autophagy-related proteins FvAtg4 and FvAtg8 are involved in virulence and fumonisin biosynthesis in Fusarium verticillioides

Autophagy is the main intracellular degradation system by which cytoplasmic materials are transported to and degraded in the vacuole/lysosome of eukaryotic cells, and it also controls cellular differentiation and virulence in a variety of filamentous fungi. However, the contribution of the autophagic pathway to fungal development and pathogenicity in the important maize pathogen and mycotoxigenic fungus Fusarium verticillioides is still unknown. In this study, we characterized two autophagy-related proteins, FvAtg4 and FvAtg8. The F. verticillioides deletion mutants ΔFvAtg4 and ΔFvAtg8 were impaired in autophagosome formation, aerial hyphal formation, sexual growth, lipid turnover, pigmentation and fungal virulence. Interestingly, ΔFvAtg4 and ΔFvAtg8 were defective in fumonisin B1 (FB1) synthesis, which may have resulted from decreased intracellular levels of alanine in the mutants. Our results indicate that FvAtg4 and FvAtg8 contribute to F. verticillioides pathogenicity by regulating the autophagic pathway to control lipid turnover, fumonisin biosynthesis, and pigmentation during its infectious cycle.

Biosynthesis of fungal polyketides by collaborating and trans-acting enzymes

Covering: 1999 up to 2021Fungal polyketides encompass a range of structurally diverse molecules with a wide variety of biological activities. The giant multifunctional enzymes that synthesize polyketide backbones remain enigmatic, as do many of the tailoring enzymes involved in functional modifications. Recent advances in elucidating biosynthetic gene clusters (BGCs) have revealed numerous examples of fungal polyketide synthases that require the action of collaborating enzymes to synthesize the carbon backbone. This review will discuss collaborating and trans-acting enzymes involved in loading, extending, and releasing polyketide intermediates from fungal polyketide synthases, and additional modifications introduced by trans-acting enzymes demonstrating the complexity encountered when investigating natural product biosynthesis in fungi.

An Efficient Strategy Combining Immunoassays and Molecular Identification for the Investigation of Fusarium Infections in Ear Rot of Maize in Guizhou Province, China

Fusarium is one of the most important phytopathogenic and mycotoxigenic fungi that caused huge losses worldwide due to the decline of crop yield and quality. To systematically investigate the infections of Fusarium species in ear rot of maize in the Guizhou Province of China and analyze its population structure, 175 samples of rotted maize ears from 76 counties were tested by combining immunoassays and molecular identification. Immunoassay based on single-chain variable fragment (scFv) and alkaline phosphatase (AP) fusion protein was first employed to analyze these samples. Fusarium pathogens were isolated and purified from Fusarium-infected samples. Molecular identification was performed using the partial internal transcribed spacer (ITS) and translation elongation factor 1α (TEF-1α) sequences. Specific primers were used to detect toxigenic chemotypes, and verification was performed by liquid chromatography tandem mass spectrometry (LC-MS/MS). One-hundred and sixty three samples were characterized to be positive, and the infection rate was 93.14%. Sixteen species of Fusarium belonging to six species complexes were detected and Fusarium meridionale belonging to the Fusarium graminearum species complex (FGSC) was the dominant species. Polymerase chain reaction (PCR) identification illustrated that 69 isolates (56.10%) were potential mycotoxin-producing Fusarium pathogens. The key synthetic genes of NIV, NIV + ZEN, DON + ZEN, and FBs were detected in 3, 35, 7, and 24 isolates, respectively. A total of 86.11% of F. meridionale isolates carried both NIV- and ZEN-specific segments, while Fusarium verticillioides isolates mainly represented FBs chemotype. All the isolates carrying DON-producing fragments were FGSC. These results showed that there are different degrees of Fusarium infections in Guizhou Province and their species and toxigenic genotypes display regional distribution patterns. Therefore, scFv-AP fusion-based immunoassays could be conducted to efficiently investigate Fusarium infections and more attention and measures should be taken for mycotoxin contamination in this region.

The plasma membrane H+ -ATPase FgPMA1 regulates the development, pathogenicity, and phenamacril sensitivity of Fusarium graminearum by interacting with FgMyo-5 and FgBmh2

Fusarium graminearum, as the causal agent of Fusarium head blight (FHB), not only causes yield loss, but also contaminates the quality of wheat by producing mycotoxins, such as deoxynivalenol (DON). The plasma membrane H⁺ -ATPases play important roles in many growth stages in plants and yeasts, but their functions and regulation in phytopathogenic fungi remain largely unknown. Here we characterized two plasma membrane H⁺ -ATPases: FgPMA1 and FgPMA2 in F. graminearum. The FgPMA1 deletion mutant (∆FgPMA1), but not FgPMA2 deletion mutant (∆FgPMA2), was impaired in vegetative growth, pathogenicity, and sexual and asexual development. FgPMA1 was localized to the plasma membrane, and ∆FgPMA1 displayed reduced integrity of plasma membrane. ∆FgPMA1 not only impaired the formation of the toxisome, which is a compartment where DON is produced, but also suppressed the expression level of DON biosynthetic enzymes, decreased DON production, and decreased the amount of mycelial invasion, leading to impaired pathogenicity by exclusively developing disease on inoculation sites of wheat ears and coleoptiles. ∆FgPMA1 exhibited decreased sensitivity to some osmotic stresses, a cell wall-damaging agent (Congo red), a cell membrane-damaging agent (sodium dodecyl sulphate), and heat shock stress. FgMyo-5 is the target of phenamacril used for controlling FHB. We found FgPMA1 interacted with FgMyo-5, and ∆FgPMA1 showed an increased expression level of FgMyo-5, resulting in increased sensitivity to phenamacril, but not to other fungicides. Furthermore, co-immunoprecipitation confirmed that FgPMA1, FgMyo-5, and FgBmh2 (a 14-3-3 protein) form a complex to regulate the sensitivity to phenamacril and biological functions. Collectively, this study identified a novel regulating mechanism of FgPMA1 in pathogenicity and phenamacril sensitivity of F. graminearum.

The Evolution of the Satratoxin and Atranone Gene Clusters of Stachybotrys chartarum

Stachybotrys chartarum is frequently isolated from damp building materials or improperly stored animal forage. Human and animal exposure to the secondary metabolites of this mold is linked to severe health effects. The mutually exclusive production of either satratoxins or atranones defines the chemotypes A and S. Based upon the genes (satratoxin cluster, SC1-3, sat or atranone cluster, AC1, atr) that are supposed to be essential for satratoxin and atranone production, S. chartarum can furthermore be divided into three genotypes: the S-type possessing all sat- but no atr-genes, the A-type lacking the sat- but harboring all atr-genes, and the H-type having only certain sat- and all atr-genes. We analyzed the above-mentioned gene clusters and their flanking regions to shed light on the evolutionary relationship. Furthermore, we performed a deep re-sequencing and LC-MS/MS (Liquid chromatography-mass spectrometry) analysis. We propose a first model for the evolution of the S. chartarum genotypes. We assume that genotype H represents the most ancient form. A loss of the AC1 and the concomitant acquisition of the SC2 led to the emergence of the genotype S. According to our model, the genotype H also developed towards genotype A, a process that was accompanied by a loss of SC1 and SC3.

Bacillomycin D-C16 inhibits growth of Fusarium verticillioides and production of fumonisin B1 in maize kernels

Fusarium verticillioides causes ear and kernel rot in maize and produces mycotoxins, like fumonisin B₁ (FB₁). Bacillomycin D-C16 is a natural antimicrobial lipopeptide produced by Bacillus subtilis. In this study, the inhibitory effects of Bacillomycin D-C16 on the growth of F. verticillioides and on the production of FB₁ in maize were investigated. Bacillomycin D-C16 displayed strong fungicidal activity against F. verticillioides, with a minimum inhibitory concentration (MIC) of 32 g/L. Scanning electron microscopy (SEM) showed that Bacillomycin D-C16 altered the morphology of F. verticillioides mycelia. Bacillomycin D-C16 reduced the ergosterol content, increased the release of nucleic acids and proteins, and increased the levels of reactive oxygen species (ROS) in fungal mycelia. Bacillomycin D-C16 also significantly inhibited the production of FB₁ by inhibiting mycelial growth and decreasing the levels of fumonisin biosynthetic genes 1 (fum1), fum6 and fum14. The application of Bacillomycin D-C16 on maize kernels prior to storage inhibited the growth of F. verticillioides and the production of FB₁. Our results suggested that Bacillomycin D-C16 has a significant antifungal activity that could be used as a potential natural antimicrobial agent to control food contamination and to ensure food safety.

Bioprospecting Phenols as Inhibitors of Trichothecene-Producing Fusarium: Sustainable Approaches to the Management of Wheat Pathogens

Fusarium spp. are ubiquitous fungi able to cause Fusarium head blight and Fusarium foot and root rot on wheat. Among relevant pathogenic species, Fusarium graminearum and Fusarium culmorum cause significant yield and quality loss and result in contamination of the grain with mycotoxins, mainly type B trichothecenes, which are a major health concern for humans and animals. Phenolic compounds of natural origin are being increasingly explored as fungicides on those pathogens. This review summarizes recent research activities related to the antifungal and anti-mycotoxigenic activity of natural phenolic compounds against Fusarium, including studies into the mechanisms of action of major exogenous phenolic inhibitors, their structure-activity interaction, and the combined effect of these compounds with other natural products or with conventional fungicides in mycotoxin modulation. The role of high-throughput analysis tools to decipher key signaling molecules able to modulate the production of mycotoxins and the development of sustainable formulations enhancing potential inhibitors' efficacy are also discussed.

Plant defense compound triggers mycotoxin synthesis by regulating H2B ub1 and H3K4 me2/3 deposition

Fusarium graminearum produces the mycotoxin deoxynivalenol (DON) which promotes its expansion during infection on its plant host wheat. Conditional expression of DON production during infection is poorly characterized. Wheat produces the defense compound putrescine, which induces hypertranscription of DON biosynthetic genes (FgTRIs) and subsequently leads to DON accumulation during infection. Further, the regulatory mechanisms of FgTRIs hypertranscription upon putrescine treatment were investigated. The transcription factor FgAreA regulates putrescine-mediated transcription of FgTRIs by facilitating the enrichment of histone H2B monoubiquitination (H2B ub1) and histone 3 lysine 4 di- and trimethylations (H3K4 me2/3) on FgTRIs. Importantly, a DNA-binding domain (bZIP) specifically within the Fusarium H2B ub1 E3 ligase Bre1 othologs is identified, and the binding of this bZIP domain to FgTRIs depends on FgAreA-mediated chromatin rearrangement. Interestingly, H2B ub1 regulates H3K4 me2/3 via the methyltransferase complex COMPASS component FgBre2, which is different from Saccharomyces cerevisiae. Taken together, our findings reveal the molecular mechanisms by which host-generated putrescine induces DON production during F. graminearum infection. Our results also provide a novel insight into the role of putrescine during phytopathogen-host interactions and broaden our knowledge of H2B ub1 biogenesis and crosstalk between H2B ub1 and H3K4 me2/3 in eukaryotes.

Temperature-Responded Biological Fitness of Carbendazim-Resistance Fusarium graminearum Mutants Conferring the F167Y, E198K, and E198L Substitutions

Understanding the effects of temperature on Fusarium graminearum infection can provide theoretical guidance for chemical control of Fusarium head blight (FHB). Here, we evaluated the effects of various temperatures on biological fitness development of wild-type sensitive strain 2021 and carbendazim-resistance mutants conferring β₂-tubulin substitutions F167Y, E198K, and E198L. The results showed that mycelial growth and conidiation of four strains increased with the increase in temperature between 10 and 25°C. Conidia of F167Y displayed strong adaptability to low temperature. The virulence of the four strains was largely similar at the same temperature, showing an upward trend between 10 and 25°C. At 10°C, the hyphal growth of all strains was significantly inhibited, metabolism was slowed down, and the accumulation of secondary metabolites decreased. Subsequently, the production of deoxynivalenol (DON) and its intermediates pyruvate and aurofusarin decreased at low temperature, and the expression of DON biosynthesis-related genes Tri5, FgPK, and AUR decreased accordingly. At the same temperature, the aurofusarin production of the strains F167Y and E198K was higher than that of strains 2021 and E198L. The contents of DON and pyruvic acid in carbendazim-resistance mutants were higher than those in the wild-type strain 2021. The sensitivity of four strains to different fungicides changed at various temperatures. The sensitivity to most fungicides increased with decreasing temperature. The carbendazim-resistance mutants showed positive cross-resistance with other benzimidazoles. However, there was no cross-resistance to pyraclostrobin and azoles. These results would direct us to use fungicides preventing the infection of F. graminearum with changeable atmospheric temperature at the wheat flower stage.

Role of Dicer-Dependent RNA Interference in Regulating Mycoparasitic Interactions

Dicer-like proteins (DCLs) play a vital role in RNA interference (RNAi), by cleaving RNA filament into small RNAs. Although DCL-mediated RNAi can regulate interspecific communication between pathogenic/mutualistic organisms and their hosts, its role in mycoparasitic interactions is yet to be investigated. In this study, we deleted dcl genes in the mycoparasitic fungus Clonostachys rosea and characterize the functions of DCL-dependent RNAi in mycoparasitism. Deletion of dcl2 resulted in a mutant with reduced secondary metabolite production, antagonism toward the plant-pathogenic fungus Botrytis cinerea, and reduced ability to control Fusarium foot rot disease on wheat, caused by Fusarium graminearum. Transcriptome sequencing of the in vitro interaction between the C. rosea Δdcl2 strain and B. cinerea or F. graminearum identified the downregulation of genes coding for transcription factors, membrane transporters, hydrolytic enzymes, and secondary metabolites biosynthesis enzymes putatively involved in antagonistic interactions, in comparison with the C. rosea wild-type interaction. A total of 61 putative novel microRNA-like RNAs (milRNAs) were identified in C. rosea, and 11 were downregulated in the Δdcl2 mutant. In addition to putative endogenous gene targets, these milRNAs were predicted to target B. cinerea and F. graminearum virulence factor genes, which showed an increased expression during interaction with the Δdcl2 mutant incapable of producing the targeting milRNAs. In summary, this study constitutes the first step in elucidating the role of RNAi in mycoparasitic interactions, with important implications for biological control of plant diseases, and poses the base for future studies focusing on the role of cross-species RNAi regulating mycoparasitic interactions. IMPORTANCE Small RNAs mediated RNA interference (RNAi) known to regulate several biological processes. Dicer-like endoribonucleases (DCLs) play a vital role in the RNAi pathway by generating sRNAs. In this study, we investigated a role of DCL-mediated RNAi in interference interactions between mycoparasitic fungus Clonostachys rosea and the two fungal pathogens Botrytis cinerea and Fusarium graminearum (here called mycohosts). We found that the dcl mutants were not able to produce 11 sRNAs predicted to finetune the regulatory network of genes known to be involved in production of hydrolytic enzymes, antifungal compounds, and membrane transporters needed for antagonistic action of C. rosea. We also found C. rosea sRNAs putatively targeting known virulence factors in the mycohosts, indicating RNAi-mediated cross-species communication. Our study expanded the understanding of underlying mechanisms of cross-species communication during interference interactions and poses a base for future works studying the role of DCL-based cross-species RNAi in fungal interactions.

Glycosyltransferase FvCpsA Regulates Fumonisin Biosynthesis and Virulence in Fusarium verticillioides

Fusarium verticillioides is the major maize pathogen associated with ear rot and stalk rot worldwide. Fumonisin B1 (FB1) produced by F. verticillioides, poses a serious threat to human and animal health. However, our understanding of FB1 synthesis and virulence mechanism in this fungus is still very limited. Glycosylation catalyzed by glycosyltransferases (GTs) has been identified as contributing to fungal infection and secondary metabolism synthesis. In this study, a family 2 glycosyltransferase, FvCpsA, was identified and characterized in F. verticillioides. ΔFvcpsA exhibited significant defects in vegetative growth. Moreover, ΔFvcpsA also increased resistance to osmotic and cell wall stress agents. In addition, expression levels of FUM genes involved in FB1 production were greatly up-regulated in ΔFvcpsA. HPLC (high performance liquid chromatography) analysis revealed that ΔFvcpsA significantly increased FB1 production. Interestingly, we found that the deletion of FvCPSA showed penetration defects on cellophane membrane, and thus led to obvious defects in pathogenicity. Characterization of FvCpsA domain experiments showed that conserved DXD and QXXRW domains were vital for the biological functions of FvCpsA. Taken together, our results indicate that FvCpsA is critical for fungal growth, FB1 biosynthesis and virulence in F. verticillioides.

Trehalose-6-phosphate phosphatase inhibitor: N-(phenylthio) phthalimide, which can inhibit the DON biosynthesis of Fusarium graminearum

Fusarium head blight(FHB)caused by Fusarium graminearum species complex (FGSC) is one of the most important diseases around the world. Deoxynivalenol (DON) is a type of mycotoxin produced by FGSC when infecting cereal crops. It is a serious threat to the health of both humans and livestock. Trehalose-6-phosphate phosphatase (TPP), a conserved metabolic enzyme found in many plants and pathogens, catalyzes the formation of trehalose. N-(phenylthio) phthalimide (NPP) has been reported to inhibit the normal growth of nematodes by inhibiting the activity of TPP, but this inhibitor of nematodes has not previously been tested against F. graminearum. In this study, we found that TPP in F. graminearum (FgTPP) had similar secondary structures and conserved cysteine (Cys356) to nematodes by means of bioinformatics. At the same time, the sensitivity of F. graminearum strains to NPP was determined. NPP exhibited a better inhibitory effect on conidia germination than mycelial growth. In addition, the effects of NPP on DON biosynthesis and trehalose biosynthesis pathway in PH-1 were also determined. We found that NPP decreased DON production, trehalose content, glucose content and TPP enzyme activity but increased trehalose-6-phosphate content and trehalose-6-phosphate synthase (TPS) enzyme activity. Moreover, the expression of TRI1, TRI4, TRI5, TRI6, and TPP genes were downregulated, on the contrary, the TPS gene was upregulated. Finally, in order to further determine the control ability of NPP on DON production in the field, we conducted a series of field experiments, and found that NPP could effectively reduce the DON content in wheat grain and had a general control effect on FHB. In conclusion, the research in this study will provide important theoretical basis for controlling FHB caused by F. graminearum and reducing DON production in the field.

Biosynthesis, regulation, and biological significance of fumonisins in fungi: current status and prospects

Fumonisins are one of the most important mycotoxin classes due to their widespread occurrence and potential health threat to humans and animals. Currently, most of the research focuses on the control of fumonisin contamination in the food supply chain. In recent years, significant progress in biochemistry, enzymology, and genetic regulation of fumonisin biosynthesis has been achieved using molecular technology. Furthermore, new insights into the roles of fumonisins in the interaction between fungi and plant hosts have been reported. This review provides an overview of the current understanding of the biosynthesis and regulation of fumonisins. The ecological significance of fumonisins to Fusarium species that produce the toxins is discussed, and the complex regulatory networks of fumonisin synthesis is proposed.

FgSfl1 and Its Conserved PKA Phosphorylation Sites Are Important for Conidiation, Sexual Reproduction, and Pathogenesis in Fusarium graminearum

The fungal plant pathogen, Fusarium graminearum, contains two genes, FgCPK1 and FgCPK2, encoding the catalytic subunits of cAMP-dependent protein kinase A. FgCPK1 and FgCPK2 are responsible for most of the PKA activities and have overlapping functions in various cellular processes in F. graminearum. The cpk1 cpk2 double mutant was significantly reduced in growth, rarely produced conidia, and was non-pathogenic. In this study, we found that the cpk1 cpk2 double mutant was unstable and produced fast-growing spontaneous sectors that were defective in plant infection. All spontaneous suppressor strains had mutations in FgSFL1, a transcription factor gene orthologous to SFL1 in yeast. Thirteen suppressor strains had non-sense mutations at Q501, three suppressor strains had frameshift mutations at W198, and five suppressor strains had mutations in the HSF binding domain of FgSfl1. Only one suppressor strain had both a non-synonymous mutation at H225 and a non-sense mutation at R490. We generated the SFL1 deletion mutant and found that it produced less than 2% of conidia than that of the wild-type strain PH-1. The sfl1 mutant was significantly reduced in the number of perithecia on carrot agar plates at 7 days post-fertilization (dpf). When incubated for more than 12 days, ascospore cirrhi were observed on the sfl1 mutant perithecia. The infection ability of the sfl1 deletion mutant was also obviously defective. Furthermore, we found that in addition to the S223 and S559 phosphorylation sites, FgSFL1 had another predicted phosphorylation site: T452. Interestingly, the S223 phosphorylation site was responsible for sexual reproduction, and the T452 phosphorylation site was responsible for growth and sexual reproduction. Only the S559 phosphorylation site was found to play an important role in conidiation, sexual reproduction, and infection. Overall, our results indicate that FgSFL1 and its conserved PKA phosphorylation sites are important for vegetative growth, conidiation, sexual reproduction, and pathogenesis in F. graminearum.