Evolution of structural diversity of trichothecenes, a family of toxins produced by plant pathogenic and entomopathogenic fungi

Analysis of substrate specificity of cytochrome P450 monooxygenases involved in trichothecene toxin biosynthesis

Trichothecenes are a structurally diverse family of toxic secondary metabolites produced by certain species of multiple fungal genera. All trichothecene analogs share a core 12,13-epoxytrichothec-9-ene (EPT) structure but differ in presence, absence and types of substituents attached to various positions of EPT. Formation of some of the structural diversity begins early in the biosynthetic pathway such that some producing species have few trichothecene biosynthetic intermediates in common. Cytochrome P450 monooxygenases (P450s) play critical roles in formation of trichothecene structural diversity. Within some species, relaxed substrate specificities of P450s allow individual orthologs of the enzymes to modify multiple trichothecene biosynthetic intermediates. It is not clear, however, whether the relaxed specificity extends to biosynthetic intermediates that are not produced by the species in which the orthologs originate. To address this knowledge gap, we used a mutant complementation-heterologous expression analysis to assess whether orthologs of three trichothecene biosynthetic P450s (TRI11, TRI13 and TRI22) from Fusarium sporotrichioides, Trichoderma arundinaceum, and Paramyrothecium roridum can modify trichothecene biosynthetic intermediates that they do not encounter in the organism in which they originated. The results indicate that TRI13 and TRI22 could not modify the intermediates that they do not normally encounter, whereas TRI11 could modify an intermediate that it does not normally encounter. These findings indicate that substrate promiscuity varies among trichothecene biosynthetic P450s. One structural feature that likely impacts the ability of the P450s to use biosynthetic intermediates as substrates is the presence and absence of an oxygen atom attached to carbon atom 3 of EPT.

Role of tri18 gene in Epiroridin E production and toxin resistance mechanisms in Paramyrothecium roridum

Type D trichothecene toxins represent a class of macrocyclic trichothecene toxins with significant cytotoxicities towards human and crops. These toxins can also be used as anti-tumor compounds by the combination of antibody-drug conjugate. Therefore, it is urgent to investigate the biosynthetic routine of type D trichothecene toxins and explore type D trichothecene toxin-resistant genes, in order to ameliorate the hazard of trichothecene toxins and to facilitate the heterologous expression of toxin-biosynthetic cluster. In this study, tri18 gene was firstly knocked out in Paramyrothecium roridum, leading to the complete absence of type D trichothecene toxin epiroridin E, which can be restored by the complement of tri18 gene. Additionally, the knockout of tri18 gene led to a significant reduction in the pathogenicity of P. roridum towards pumpkin. Meanwhile, the enzymatic properties of Tri18 protein towards trichothecene deoxynivalenol (DON) toxin were also characterized. Moreover, tri3 and tri17KR with broad spectrum toxin-resistance function within the tri cluster were initially discovered through heterologous expression in toxin-sensitive Saccharomyces cerevisiae. And this study provides innovative type D trichothecene toxin resistant enzymes, which can provides green platform for the production of type D trichothecene toxins, thus promoting the application of these toxins in biomedical field.

Microbiome changes in Akanthomyces attenuatus JEF-147-infected two-spotted spider mites

The two-spotted spider mite (Tetranychus urticae Koch) is an agriculturally serious polyphagous pest that has acquired strong resistance against acaricides because of its short life cycle and continuous exposure to acaricides. As an alternative, mite-pathogenic fungi with different modes of action could be used to control the mites. The spider mite has symbiotic microorganisms that could be involved in the physiological and ecological adaptations to biotic stresses. In this study, mite-pathogenic fungi were used to control female adults, and the microbiomes changes in the fungus-infected mites were analyzed. The acaricidal activity of 77 fungal isolates was tested, and Akanthomyces attenuatus JEF-147 exhibited the highest acaricidal activity. Subsequently a dose-response assay and morphological characterization was undertaken For microbiome analysis in female adults infected with A. attenuatus JEF-147, 16S rDNA and ITS1 were sequenced using Illumina Miseq. Infected mite showed a higher Shannon index in bacterial diversity but lower index in fungal diversity. In beta diversity using principal component analysis, JEF-147-treated mites were significantly different from non-treated controls in both bacteria and fungi. Particularly in bacterial abundance, arthropod defense-related Rickettsia increased, but arthropod reproduction-associated Wolbachia decreased. The change in major bacterial abundance in the infected mites could be explained by a trade-off between reproduction and immunity against the early stage of fungal attack. In fungal abundance, Akanthomyces showed up as expected. Foremost, this work reports microbiome changes in a fungus-infected mite and suggests a possible trade-off in mites against fungal pathogens. Future studies will focus on gene-based investigations related to this topic.

Genome Mining of Fungal Unique Trichodiene Synthase-like Sesquiterpene Synthases

Sesquiterpenoids served as an important source for natural product drug discovery. Although genome mining approaches have revealed numerous novel sesquiterpenoids and biosynthetic enzymes, the comprehensive landscape of fungal sesquiterpene synthases (STSs) remains elusive. In this study, 123 previously reported fungal STSs were subjected to phylogenetic analysis, resulting in the identification of a fungi-specific STS family known as trichodiene synthase-like sesquiterpene synthases (TDTSs). Subsequently, the application of hidden Markov models allowed the discovery of 517 TDTSs from our in-house fungi genome library of over 400 sequenced genomes, and these TDTSs were defined into 79 families based on a sequence similarity network. Based on the novelty of protein sequences and the completeness of their biosynthetic gene clusters, 23 TDTS genes were selected for heterologous expression in Aspergillus oryzae. In total, 10 TDTSs were active and collectively produced 12 mono- and sesquiterpenes, resulting in the identification of the first chamipinene synthase, as well as the first fungi-derived cedrene, sabinene, and camphene synthases. Additionally, with the guidance of functionally characterized TDTSs, we found that TDTSs in Family 1 could produce bridged-cyclic sesquiterpenes, while those in Family 2 could synthesize spiro- and bridged-cyclic sesquiterpenes. Our research presents a new avenue for the genome mining of fungal sesquiterpenoids.

A Role in 15-Deacetylcalonectrin Acetylation in the Non-Enzymatic Cyclization of an Earlier Bicyclic Intermediate in Fusarium Trichothecene Biosynthesis

The trichothecene biosynthesis in Fusarium begins with the cyclization of farnesyl pyrophosphate to trichodiene, followed by subsequent oxygenation to isotrichotriol. This initial bicyclic intermediate is further cyclized to isotrichodermol (ITDmol), a tricyclic precursor with a toxic trichothecene skeleton. Although the first cyclization and subsequent oxygenation are catalyzed by enzymes encoded by Tri5 and Tri4, the second cyclization occurs non-enzymatically. Following ITDmol formation, the enzymes encoded by Tri101, Tri11, Tri3, and Tri1 catalyze 3-O-acetylation, 15-hydroxylation, 15-O-acetylation, and A-ring oxygenation, respectively. In this study, we extensively analyzed the metabolites of the corresponding pathway-blocked mutants of Fusarium graminearum. The disruption of these Tri genes, except Tri3, led to the accumulation of tricyclic trichothecenes as the main products: ITDmol due to Tri101 disruption; a mixture of isotrichodermin (ITD), 7-hydroxyisotrichodermin (7-HIT), and 8-hydroxyisotrichodermin (8-HIT) due to Tri11 disruption; and a mixture of calonectrin and 3-deacetylcalonectrin due to Tri1 disruption. However, the ΔFgtri3 mutant accumulated substantial amounts of bicyclic metabolites, isotrichotriol and trichotriol, in addition to tricyclic 15-deacetylcalonectrin (15-deCAL). The ΔFgtri5ΔFgtri3 double gene disruptant transformed ITD into 7-HIT, 8-HIT, and 15-deCAL. The deletion of FgTri3 and overexpression of Tri6 and Tri10 trichothecene regulatory genes did not result in the accumulation of 15-deCAL in the transgenic strain. Thus, the absence of Tri3p and/or the presence of a small amount of 15-deCAL adversely affected the non-enzymatic second cyclization and C-15 hydroxylation steps.

In Vitro Antimalarial Activity of Trichothecenes against Liver and Blood Stages of Plasmodium Species

Trichothecenes (TCNs) are a large group of tricyclic sesquiterpenoid mycotoxins that have intriguing structural features and remarkable biological activities. Herein, we focused on three TCNs (anguidine, verrucarin A, and verrucarol) and their ability to target both the blood and liver stages of Plasmodium species, the parasite responsible for malaria. Anguidine and verrucarin A were found to be highly effective against the blood and liver stages of malaria, while verrucarol had no effect at the highest concentration tested. However, these compounds were also found to be cytotoxic and, thus, not selective, making them unsuitable for drug development. Nonetheless, they could be useful as chemical probes for protein synthesis inhibitors due to their direct impact on parasite synthesis processes.

Agrobacterium-mediated transfer of the Fusarium graminearum Tri6 gene into barley using mature seed-derived shoot tips as explants

KEY MESSAGE

We transferred the Tri6 gene into the elite barley GemCraft via new transformation method through shoot organogenesis and identified the rearrangements of transgenes and phenotypic variations in the transgenic plants. Despite its agronomic and economic importance, barley transformation is still very challenging for many elite varieties. In this study, we used direct shoot organogenesis to transform the elite barley cultivar GemCraft with the RNAi constructs containing Tri6 gene of Fusarium graminearum, which causes fusarium head blight (FHB). We isolated 4432 shoot tips and co-cultured these explants with Agrobacterium tumefaciens. A total of 25 independent T0 transgenic plants were generated including 15 events for which transgene-specific PCR amplicons were observed. To further determine the presence of transgenes, the T1 progenies of all 15 T0 plants were analyzed, and the expected PCR products were obtained in 10 T1 lines. Droplet digital (dd) PCR analysis revealed various copy numbers of transgenes in the transgenic plants. We determined the insertion site of transgenes using long-read sequencing data and observed the rearrangements of transgenes. We found phenotypic variations in both T1 and T2 generation plants. FHB disease was evaluated under growth chamber conditions, but no significant differences in disease severity or deoxynivalenol accumulation were observed between two Tri6 transgenic lines and the wildtype. Our results demonstrate the feasibility of the shoot tip transformation and may open the door for applying this system for genetic improvement and gene function research in other barley genotypes.

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.

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.

Endophyte genomes support greater metabolic gene cluster diversity compared with non-endophytes in Trichoderma

Trichoderma is a cosmopolitan genus with diverse lifestyles and nutritional modes, including mycotrophy, saprophytism, and endophytism. Previous research has reported greater metabolic gene repertoires in endophytic fungal species compared to closely-related non-endophytes. However, the extent of this ecological trend and its underlying mechanisms are unclear. Some endophytic fungi may also be mycotrophs and have one or more mycoparasitism mechanisms. Mycotrophic endophytes are prominent in certain genera like Trichoderma, therefore, the mechanisms that enable these fungi to colonize both living plants and fungi may be the result of expanded metabolic gene repertoires. Our objective was to determine what, if any, genomic features are overrepresented in endophytic fungi genomes in order to undercover the genomic underpinning of the fungal endophytic lifestyle. Here we compared metabolic gene cluster and mycoparasitism gene diversity across a dataset of thirty-eight Trichoderma genomes representing the full breadth of environmental Trichoderma's diverse lifestyles and nutritional modes. We generated four new Trichoderma endophyticum genomes to improve the sampling of endophytic isolates from this genus. As predicted, endophytic Trichoderma genomes contained, on average, more total biosynthetic and degradative gene clusters than non-endophytic isolates, suggesting that the ability to create/modify a diversity of metabolites potential is beneficial or necessary to the endophytic fungi. Still, once the phylogenetic signal was taken in consideration, no particular class of metabolic gene cluster was independently associated with the Trichoderma endophytic lifestyle. Several mycoparasitism genes, but no chitinase genes, were associated with endophytic Trichoderma genomes. Most genomic differences between Trichoderma lifestyles and nutritional modes are difficult to disentangle from phylogenetic divergences among species, suggesting that Trichoderma genomes maybe particularly well-equipped for lifestyle plasticity. We also consider the role of endophytism in diversifying secondary metabolism after identifying the horizontal transfer of the ergot alkaloid gene cluster to Trichoderma.

UDP-glucosyltransferase HvUGT13248 confers type II resistance to Fusarium graminearum in barley

Fusarium head blight (FHB) of barley (Hordeum vulgare) causes yield losses and accumulation of trichothecene mycotoxins (e.g. deoxynivalenol [DON]) in grains. Glucosylation of DON to the nontoxic DON-3-O-glucoside (D3G) is catalyzed by UDP-glucosyltransferases (UGTs), such as barley UGT13248. We explored the natural diversity of UGT13248 in 496 barley accessions and showed that all carried potential functional alleles of UGT13248, as no genotypes showed strongly increased seedling sensitivity to DON. From a TILLING population, we identified 2 mutant alleles (T368I and H369Y) that, based on protein modeling, likely affect the UDP-glucose binding of UGT13248. In DON feeding experiments, DON-to-D3G conversion was strongly reduced in spikes of these mutants compared to controls, and plants overexpressing UGT13248 showed increased resistance to DON and increased DON-to-D3G conversion. Moreover, field-grown plants carrying the T368I or H369Y mutations inoculated with Fusarium graminearum showed increased FHB disease severity and reduced D3G production. Barley is generally considered to have type II resistance that limits the spread of F. graminearum from the infected spikelet to adjacent spikelets. Point inoculation experiments with F. graminearum showed increased infection spread in T368I and H369Y across the spike compared to wild type, while overexpression plants showed decreased spread of FHB symptoms. Confocal microscopy revealed that F. graminearum spread to distant rachis nodes in T368I and H369Y mutants but was arrested at the rachis node of the inoculated spikelet in wild-type plants. Taken together, our data reveal that UGT13248 confers type II resistance to FHB in barley via conjugation of DON to D3G.

Dynamic geospatial modeling of mycotoxin contamination of corn in Illinois: unveiling critical factors and predictive insights with machine learning

Mycotoxin contamination of corn is a pervasive problem that negatively impacts human and animal health and causes economic losses to the agricultural industry worldwide. Historical aflatoxin (AFL) and fumonisin (FUM) mycotoxin contamination data of corn, daily weather data, satellite data, dynamic geospatial soil properties, and land usage parameters were modeled to identify factors significantly contributing to the outbreaks of mycotoxin contamination of corn grown in Illinois (IL), AFL >20 ppb, and FUM >5 ppm. Two methods were used: a gradient boosting machine (GBM) and a neural network (NN). Both the GBM and NN models were dynamic at a state-county geospatial level because they used GPS coordinates of the counties linked to soil properties. GBM identified temperature and precipitation prior to sowing as significant influential factors contributing to high AFL and FUM contamination. AFL-GBM showed that a higher aflatoxin risk index (ARI) in January, March, July, and November led to higher AFL contamination in the southern regions of IL. Higher values of corn-specific normalized difference vegetation index (NDVI) in July led to lower AFL contamination in Central and Southern IL, while higher wheat-specific NDVI values in February led to higher AFL. FUM-GBM showed that temperature in July and October, precipitation in February, and NDVI values in March are positively correlated with high contamination throughout IL. Furthermore, the dynamic geospatial models showed that soil characteristics were correlated with AFL and FUM contamination. Greater calcium carbonate content in soil was negatively correlated with AFL contamination, which was noticeable in Southern IL. Greater soil moisture and available water-holding capacity throughout Southern IL were positively correlated with high FUM contamination. The higher clay percentage in the northeastern areas of IL negatively correlated with FUM contamination. NN models showed high class-specific performance for 1-year predictive validation for AFL (73%) and FUM (85%), highlighting their accuracy for annual mycotoxin prediction. Our models revealed that soil, NDVI, year-specific weekly average precipitation, and temperature were the most important factors that correlated with mycotoxin contamination. These findings serve as reliable guidelines for future modeling efforts to identify novel data inputs for the prediction of AFL and FUM outbreaks and potential farm-level management practices.

A Mycovirus VIGS Vector Confers Hypovirulence to a Plant Pathogenic Fungus to Control Wheat FHB

Mycovirus-mediated hypovirulence has the potential to control fungal diseases. However, the availability of hypovirulence-conferring mycoviruses for plant fungal disease control is limited as most fungal viruses are asymptomatic. In this study, the virus-induced gene silencing (VIGS) vector p26-D4 of Fusarium graminearum gemytripvirus 1 (FgGMTV1), a tripartite circular single-stranded DNA mycovirus, is successfully constructed to convert the causal fungus of cereal Fusarium head blight (FHB) into a hypovirulent strain. p26-D4, with an insert of a 75-150 bp fragment of the target reporter transgene transcript in both sense and antisense orientations, efficiently triggered gene silencing in Fusarium graminearum. Notably, the two hypovirulent strains, p26-D4-Tri101, and p26-D4-FgPP1, obtained by silencing the virulence-related genes Tri101 and FgPP1 with p26-D4, can be used as biocontrol agents to protect wheat from a fungal disease FHB and mycotoxin contamination at the field level. This study not only describes the first mycovirus-derived VIGS system but also proves that the VIGS vector can be used to establish multiple hypovirulent strains to control pathogenic fungi.

Genomic Based Analysis of the Biocontrol Species Trichoderma harzianum: A Model Resource of Structurally Diverse Pharmaceuticals and Biopesticides

Fungi represents a rich repository of taxonomically restricted, yet chemically diverse, secondary metabolites that are synthesised via specific metabolic pathways. An enzyme's specificity and biosynthetic gene clustering are the bottleneck of secondary metabolite evolution. Trichoderma harzianum M10 v1.0 produces many pharmaceutically important molecules; however, their specific biosynthetic pathways remain uncharacterised. Our genomic-based analysis of this species reveals the biosynthetic diversity of its specialised secondary metabolites, where over 50 BGCs were predicted, most of which were listed as polyketide-like compounds associated clusters. Gene annotation of the biosynthetic candidate genes predicted the production of many medically/industrially important compounds including enterobactin, gramicidin, lovastatin, HC-toxin, tyrocidine, equisetin, erythronolide, strobilurin, asperfuranone, cirtinine, protoilludene, germacrene, and epi-isozizaene. Revealing the biogenetic background of these natural molecules is a step forward towards the expansion of their chemical diversification via engineering their biosynthetic genes heterologously, and the identification of their role in the interaction between this fungus and its biotic/abiotic conditions as well as its role as bio-fungicide.

Fusarium graminearum Effector FgNls1 Targets Plant Nuclei to Induce Wheat Head Blight

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most devastating diseases of wheat and barley worldwide. Effectors suppress host immunity and promote disease development. The genome of F. graminearum contains hundreds of effectors with unknown function. Therefore, investigations of the functions of these effectors will facilitate developing novel strategies to enhance wheat resistance to FHB. We characterized a F. graminearum effector, FgNls1, containing a signal peptide and multiple eukaryotic nuclear localization signals. A fusion protein of green fluorescent protein and FgNls1 accumulated in plant cell nuclei when transiently expressed in Nicotiana benthamiana. FgNls1 suppressed Bax-induced cell death when co-expressed in N. benthamiana. We revealed that the expression of FgNLS1 was induced in wheat spikes infected with F. graminearum. The Fgnls1 mutants significantly reduced initial infection and FHB spread within a spike. The function of FgNLS1 was restored in the Fgnls1-complemented strains. Wheat histone 2B was identified as an interacting protein by FgNls1-affinity chromatography. Furthermore, transgenic wheat plants that silence FgNLS1 expression had significantly lower FHB severity than control plants. This study demonstrates a critical role of FgNls1 in F. graminearum pathogenesis and indicates that host-induced gene silencing targeting F. graminearum effectors is a promising approach to enhance FHB resistance. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

T-2 and HT-2 Toxins: Toxicity, Occurrence and Analysis: A Review

One of the major classes of mycotoxins posing serious hazards to humans and animals and potentially causing severe economic impact to the cereal industry are the trichothecenes, produced by many fungal genera. As such, indicative limits for the sum of T-2 and HT-2 were introduced in the European Union in 2013 and discussions are ongoing as to the establishment of maximum levels. This review provides a concise assessment of the existing understanding concerning the toxicological effects of T-2 and HT-2 in humans and animals, their biosynthetic pathways, occurrence, impact of climate change on their production and an evaluation of the analytical methods applied to their detection. This study highlights that the ecology of F. sporotrichioides and F. langsethiae as well as the influence of interacting environmental factors on their growth and activation of biosynthetic genes are still not fully understood. Predictive models of Fusarium growth and subsequent mycotoxin production would be beneficial in predicting the risk of contamination and thus aid early mitigation. With the likelihood of regulatory maximum limits being introduced, increased surveillance using rapid, on-site tests in addition to confirmatory methods will be required. allowing the industry to be proactive rather than reactive.

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.

Trichoderma koningiopsis (Hypocreaceae) has the smallest mitogenome of the genus Trichoderma

Introduction

Fungal mitogenomes exhibit remarkable variation in conformation, size, gene content, arrangement and expression, including their intergenic spacers and introns.

Methods

The complete mitochondrial genome sequence of the mycoparasitic fungus Trichoderma koningiopsis was determined using the Illumina next-generation sequencing technology. We used data from our recent Illumina NGS-based project of T. koningiopsis genome sequencing to study its mitochondrial genome. The mitogenome was assembled, annotated, and compared with other fungal mitogenomes.

Results

T. koningiopsis strain POS7 mitogenome is a circular molecule of 27,560 bp long with a GC content of 27.80%. It harbors the whole complement of the 14 conserved mitochondrial protein-coding genes (PCG) such as atp6, atp8, atp9, cox1, cox2, cox3, cob, nad1, nad2, nad3, nad4, nad4L, nad5, and nad6, also found in the same gene order to other Hypocreales. The mitogenome also contains 26 transfer RNA genes (tRNAs), 5 of them with more than one copy. Other genes also present in the assembled mitochondrial genome are a small rRNA subunit and a large rRNA subunit containing ribosomal protein S3 gene. Despite the small genome size, two introns were detected in the T. koningiopsis POS7 mitogenome, one of them in cox3 gene and the other in rnl gene, accounting 7.34% of this mitogenome with a total size of 2,024 bp. A phylogenetic analysis was done using the 14 PCGs genes of T. koningiopsis strain POS7 mitogenome to compare them with those from other fungi of the Subphyla Pezizomycotina and Saccharomycotina. T. koningiopsis strain POS7 was clustered together with other representatives of Trichoderma lineage, within the Hypocreales group, which is also supported by previous phylogenetic studies based on nuclear markers.

Discussion

The mitochondrial genome of T. koningiopsis POS7 will allow further investigations into the taxonomy, phylogenetics, conservation genetics, and evolutionary biology of this important genus as well as other closely related species.

High-Quality Genome and Annotation Resource of Orange Pink Rot Pathogen Trichothecium roseum Strain YXFP-22015 Isolated from Hubei, China

Trichothecium roseum is widely distributed throughout the world and forms pink powdery molds on various fruits and vegetables, lowering their quality and leading to great economic losses. Due to the limited availability of high-quality genomic and annotation resources, little is known about the pathogenesis of T. roseum at the molecular level. In this study, we reported a high-quality genome assembly of strain YXFP-22015 using Oxford Nanopore Technologies (ONT) for long read sequencing and MGISEQ-2000 for short read sequencing. The genome was also well-annotated based on the combination of RNA-seq by MGISEQ-2000 and in silico prediction. Further analysis on this will contribute to a better understanding of T. roseum infection mechanisms.

Molecular interaction between plants and Trichoderma species against soil-borne plant pathogens

Trichoderma spp. (Hypocreales) are used worldwide as a lucrative biocontrol agent. The interactions of Trichoderma spp. with host plants and pathogens at a molecular level are important in understanding the various mechanisms adopted by the fungus to attain a close relationship with their plant host through superior antifungal/antimicrobial activity. When working in synchrony, mycoparasitism, antibiosis, competition, and the induction of a systemic acquired resistance (SAR)-like response are considered key factors in deciding the biocontrol potential of Trichoderma. Sucrose-rich root exudates of the host plant attract Trichoderma. The soluble secretome of Trichoderma plays a significant role in attachment to and penetration and colonization of plant roots, as well as modulating the mycoparasitic and antibiosis activity of Trichoderma. This review aims to gather information on how Trichoderma interacts with host plants and its role as a biocontrol agent of soil-borne phytopathogens, and to give a comprehensive account of the diverse molecular aspects of this interaction.

Pathogenesis and defense mechanism while Beauveria bassiana JEF-410 infects poultry red mite, Dermanyssus gallinae

The poultry red mite, Dermanyssus gallinae (Mesostigmata: Dermanyssidae), is a major pest that causes great damage to chicken egg production. In one of our previous studies, the management of red mites using entomopathogenic fungi was evaluated, and the acaricidal fungus Beauveria bassiana JEF-410 was selected for further research. In this study, we tried to elucidate the pathogenesis of B. bassiana JEF-410 and the defense mechanisms of red mites at a transcriptome level. Red mites collected from a chicken farm were treated with B. bassiana JEF-410. When the mortality of infected red mites reached 50%, transcriptome analyses were performed to determine the interaction between B. bassiana JEF-410 and red mites. Uninfected red mites and non-infecting fungus served as controls. In B. bassiana JEF-410, up-regulated gene expression was observed in tryptophan metabolism and secondary metabolite biosynthesis pathways. Genes related to acetyl-CoA synthesis were up-regulated in tryptophan metabolism, suggesting that energy metabolism and stress management were strongly activated. Secondary metabolites associated with fungal up-regulated DEGs were related to the production of substances toxic to insects such as beauvericin and beauveriolide, efflux pump of metabolites, energy production, and resistance to stress. In red mites, physical and immune responses that strengthen the cuticle against fungal infection were highly up-regulated. From these gene expression analyses, we identified essential factors for fungal infection and subsequent defenses of red mites. These results will serve as a strong platform for explaining the interaction between B. bassiana JEF-410 and red mites in the stage of active infection.

Computer-aided, resistance gene-guided genome mining for proteasome and HMG-CoA reductase inhibitors

Secondary metabolites (SMs) are biologically active small molecules, many of which are medically valuable. Fungal genomes contain vast numbers of SM biosynthetic gene clusters (BGCs) with unknown products, suggesting that huge numbers of valuable SMs remain to be discovered. It is challenging, however, to identify SM BGCs, among the millions present in fungi, that produce useful compounds. One solution is resistance gene-guided genome mining, which takes advantage of the fact that some BGCs contain a gene encoding a resistant version of the protein targeted by the compound produced by the BGC. The bioinformatic signature of such BGCs is that they contain an allele of an essential gene with no SM biosynthetic function, and there is a second allele elsewhere in the genome. We have developed a computer-assisted approach to resistance gene-guided genome mining that allows users to query large databases for BGCs that putatively make compounds that have targets of therapeutic interest. Working with the MycoCosm genome database, we have applied this approach to look for SM BGCs that target the proteasome β6 subunit, the target of the proteasome inhibitor fellutamide B, or HMG-CoA reductase, the target of cholesterol reducing therapeutics such as lovastatin. Our approach proved effective, finding known fellutamide and lovastatin BGCs as well as fellutamide- and lovastatin-related BGCs with variations in the SM genes that suggest they may produce structural variants of fellutamides and lovastatin. Gratifyingly, we also found BGCs that are not closely related to lovastatin BGCs but putatively produce novel HMG-CoA reductase inhibitors.

ONE-SENTENCE SUMMARY

A new computer-assisted approach to resistance gene-directed genome mining is reported along with its use to identify fungal biosynthetic gene clusters that putatively produce proteasome and HMG-CoA reductase inhibitors.

Genomic Comparisons of Two Armillaria Species with Different Ecological Behaviors and Their Associated Soil Microbial Communities

Armillaria species show considerable variation in ecological roles and virulence, from mycorrhizae and saprophytes to important root pathogens of trees and horticultural crops. We studied two Armillaria species that can be found in coniferous forests of northwestern USA and southwestern Canada. Armillaria altimontana not only is considered as a weak, opportunistic pathogen of coniferous trees, but it also appears to exhibit in situ biological control against A. solidipes, formerly North American A. ostoyae, which is considered a virulent pathogen of coniferous trees. Here, we describe their genome assemblies and present a functional annotation of the predicted genes and proteins for the two Armillaria species that exhibit contrasting ecological roles. In addition, the soil microbial communities were examined in association with the two Armillaria species within a 45-year-old plantation of western white pine (Pinus monticola) in northern Idaho, USA, where A. altimontana was associated with improved tree growth and survival, while A. solidipes was associated with reduced growth and survival. The results from this study reveal a high similarity between the genomes of the beneficial/non-pathogenic A. altimontana and pathogenic A. solidipes; however, many relatively small differences in gene content were identified that could contribute to differences in ecological lifestyles and interactions with woody hosts and soil microbial communities.

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.

Spores of Trichoderma Strains over P. vulgaris Beans: Direct Effect on Insect Attacks and Indirect Effect on Agronomic Parameters

Acanthoscelides obtectus is an insect pest that attacks wild and cultivated common beans (Phaseolus vulgaris L). Four Trichoderma strains, the T. arundinaceum IBT 40837 wild-type strain (=Ta37), a producer of trichothecene harzianum A (HA), two transformants of T. arundinaceum strain, Ta37-17.139 (=Δtri17) and Ta37-23.74 (=Δtri23), and the T. brevicompactum IBT 40841 wild-type strain (=Tb41), which produces the trichothecene trichodermin, were assessed to establish their direct effect on insect attacks and their indirect effect on the plants grown from the beans treated with those fungal strains and exposed to insect attacks. Treatments of bean seeds with different Trichoderma strains led to different survival rates in the insects, and the Tb41 strain caused the lowest survival rate of all. An 86.10% of the insect cadavers (in contact with Δtri23) showed growth of this strain. This was the treatment that attracted the greatest number of insects. The daily emergence was reduced in beans treated with the Ta37, Tb41, and Δtri17 strains. The undamaged beans treated with Ta37 and Δtri23 showed a high capacity of germination (80.00% and 75.00%, respectively), whereas the Δtri17 and Tb41 treatments increased the capacity of germination in the damaged beans (66.67%). The undamaged beans treated with Δtri23 had the greatest dry weights for the aerial part (4.22 g) and root system in the plants (0.62 g). More studies on the mechanisms of insect control, plant growth promotion, and trichodermol and trichodermin production by Δtri23 and Tb41, respectively, should be explored in order to commercialize these fungal species on a large scale.

Effects of trichothecene production by Trichoderma arundinaceum isolates from bean-field soils on the defense response, growth and development of bean plants (Phaseolus vulgaris)

The trichothecene toxin-producing fungus Trichoderma arundinaceum has potential as a biological control agent. However, most biocontrol studies have focused only on one strain, IBT 40837. In the current study, three Trichoderma isolates recovered from bean-field soils produced the trichothecene harzianum A (HA) and trichodermol, the latter being an intermediate in the HA biosynthesis. Based on phylogenetic analysis, the three isolates were assigned to the species T. arundinaceum. Their genome sequences had a high degree of similarity to the reference IBT 40837 strain, in terms of total genome size, number of predicted genes, and diversity of putative secondary metabolite biosynthetic gene clusters. HA production by these bean-field isolates conferred significant in vitro antifungal activity against Rhizoctonia solani and Sclerotinia sclerotiorum, which are some of the most important bean pathogens. Furthermore, the bean-field isolates stimulated germination of bean seeds and subsequent growth of above ground parts of the bean plant. Transcriptomic analysis of bean plants inoculated with these T. arundinaceum bean-field soil isolates indicated that HA production significantly affected expression of plant defense-related genes; this effect was particularly significant in the expression of chitinase-encoding genes. Together, these results indicate that Trichoderma species producing non-phytotoxic trichothecenes can induce defenses in plants without negatively affecting germination and development.

Gradient boosting and bayesian network machine learning models predict aflatoxin and fumonisin contamination of maize in Illinois - First USA case study

Mycotoxin contamination of corn results in significant agroeconomic losses and poses serious health issues worldwide. This paper presents the first report utilizing machine learning and historical aflatoxin and fumonisin contamination levels in-order-to develop models that can confidently predict mycotoxin contamination of corn in Illinois, a major corn producing state in the USA. Historical monthly meteorological data from a 14-year period combined with corresponding aflatoxin and fumonisin contamination data from the State of Illinois were used to engineer input features that link weather, fungal growth, and aflatoxin production in combination with gradient boosting (GBM) and bayesian network (BN) modeling. The GBM and BN models developed can predict mycotoxin contamination with overall 94% accuracy. Analyses for aflatoxin and fumonisin with GBM showed that meteorological and satellite-acquired vegetative index data during March significantly influenced grain contamination at the end of the corn growing season. Prediction of high aflatoxin contamination levels was linked to high aflatoxin risk index in March/June/July, high vegetative index in March and low vegetative index in July. Correspondingly, high levels of fumonisin contamination were linked to high precipitation levels in February/March/September and high vegetative index in March. During corn flowering time in June, higher temperatures range increased prediction of high levels of fumonisin contamination, while high aflatoxin contamination levels were linked to high aflatoxin risk index. Meteorological events prior to corn planting in the field have high influence on predicting aflatoxin and fumonisin contamination levels at the end of the year. These early-year events detected by the models can directly assist farmers and stakeholders to make informed decisions to prevent mycotoxin contamination of Illinois grown corn.

Insights on KP4 Killer Toxin-like Proteins of Fusarium Species in Interspecific Interactions

KP4 killer toxins are secreted proteins that inhibit cell growth and induce cell death in target organisms. In Fusarium graminearum, KP4-like (KP4L) proteins contribute to fungal virulence in wheat seedling rot and are expressed during Fusarium head blight development. However, fungal KP4L proteins are also hypothesized to support fungal antagonism by permeabilizing cell walls of competing fungi to enable penetration of toxic compounds. Here, we report the differential expression patterns of F. graminearum KP4L genes (Fgkp4l-1, -2, -3 and -4) in a competitive interaction, using Trichoderma gamsii as the antagonist. The results from dual cultures indicate that Fgkp4l-3 and Fgkp4l-4 could participate in the recognition at the distance of the antagonist, while all Fgkp4l genes were highly activated in the pathogen during the physical interaction of both fungi. Only Fgkp4l-4 was up-regulated during the interaction with T. gamsii in wheat spikes. This suggests the KP4L proteins could participate in supporting F. graminearum interspecific interactions, even in living plant tissues. The distribution of KP4L orthologous within the genus Fusarium revealed they are more represented in species with broad host-plant range than in host-specific species. Phylogeny inferred provides evidence that KP4L genes evolved through gene duplications, gene loss and sequence diversification in the genus Fusarium.

Trichoderma - genomes and genomics as treasure troves for research towards biology, biotechnology and agriculture

The genus Trichoderma is among the best studied groups of filamentous fungi, largely because of its high relevance in applications from agriculture to enzyme biosynthesis to biofuel production. However, the physiological competences of these fungi, that led to these beneficial applications are intriguing also from a scientific and ecological point of view. This review therefore summarizes recent developments in studies of fungal genomes, updates on previously started genome annotation efforts and novel discoveries as well as efforts towards bioprospecting for enzymes and bioactive compounds such as cellulases, enzymes degrading xenobiotics and metabolites with potential pharmaceutical value. Thereby insights are provided into genomes, mitochondrial genomes and genomes of mycoviruses of Trichoderma strains relevant for enzyme production, biocontrol and mycoremediation. In several cases, production of bioactive compounds could be associated with responsible genes or clusters and bioremediation capabilities could be supported or predicted using genome information. Insights into evolution of the genus Trichoderma revealed large scale horizontal gene transfer, predominantly of CAZyme genes, but also secondary metabolite clusters. Investigation of sexual development showed that Trichoderma species are competent of repeat induced point mutation (RIP) and in some cases, segmental aneuploidy was observed. Some random mutants finally gave away their crucial mutations like T. reesei QM9978 and QM9136 and the fertility defect of QM6a was traced back to its gene defect. The Trichoderma core genome was narrowed down to 7000 genes and gene clustering was investigated in the genomes of multiple species. Finally, recent developments in application of CRISPR/Cas9 in Trichoderma, cloning and expression strategies for the workhorse T. reesei as well as the use genome mining tools for bioprospecting Trichoderma are highlighted. The intriguing new findings on evolution, genomics and physiology highlight emerging trends and illustrate worthwhile perspectives in diverse fields of research with Trichoderma.

Searching for the Fusarium spp. Which Are Responsible for Trichothecene Contamination in Oats Using Metataxonomy to Compare the Distribution of Toxigenic Species in Fields from Spain and the UK

The contamination of oats with Fusarium toxins poses a high risk for food safety. Among them, trichothecenes are the most frequently reported in European oats, especially in northern countries. The environmental conditions related to the climate change scenario might favour a distribution shift in Fusarium species and the presence of these toxins in Southern European countries. In this paper, we present an ambitious work to determine the species responsible for trichothecene contamination in Spanish oats and to compare the results in the United Kingdom (UK) using a metataxonomic approach applied to both oat grains and soil samples collected from both countries. Regarding T-2 and HT-2 toxin producers, F. langsethiae was detected in 38% and 25% of the oat samples from the UK and Spain, respectively, and to the best of our knowledge, this is the first report of the detection of this fungus in oats from Spain. The relevant type B trichothecene producer, F. poae, was the most frequently detected Fusarium species in oats from both origins. Other important trichothecene producers, such as the Fusarium tricinctum species complex or Fusarium cerealis, were also frequently detected in oat fields. Many Fusarium toxins, including T-2 and HT-2 toxins, deoxynivalenol, or nivalenol, were detected in oat samples. The results obtained in this work revealed a clear change in the distribution of trichothecene producers and the necessity to establish the potential of these species to colonize oats and their ability to produce mycotoxins.

Genome-Wide Characterization Reveals Variation Potentially Involved in Pathogenicity and Mycotoxins Biosynthesis of Fusarium proliferatum Causing Spikelet Rot Disease in Rice

Fusarium proliferatum is the primary cause of spikelet rot disease in rice (Oryza sativa L.) in China. The pathogen not only infects a wide range of cereals, causing severe yield losses but also contaminates grains by producing various mycotoxins that are hazardous to humans and animals. Here, we firstly reported the whole-genome sequence of F. proliferatum strain Fp9 isolated from the rice spikelet. The genome was approximately 43.9 Mb with an average GC content of 48.28%, and it was assembled into 12 scaffolds with an N₅₀ length of 4,402,342 bp. There is a close phylogenetic relationship between F. proliferatum and Fusarium fujikuroi, the causal agent of the bakanae disease of rice. The expansion of genes encoding cell wall-degrading enzymes and major facilitator superfamily (MFS) transporters was observed in F. proliferatum relative to other fungi with different nutritional lifestyles. Species-specific genes responsible for mycotoxins biosynthesis were identified among F. proliferatum and other Fusarium species. The expanded and unique genes were supposed to promote F. proliferatum adaptation and the rapid response to the host's infection. The high-quality genome of F. proliferatum strain Fp9 provides a valuable resource for deciphering the mechanisms of pathogenicity and secondary metabolism, and therefore shed light on development of the disease management strategies and detoxification of mycotoxins contamination for spikelet rot disease in rice.

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.

Fusarium culmorum Produces NX-2 Toxin Simultaneously with Deoxynivalenol and 3-Acetyl-Deoxynivalenol or Nivalenol

Fusarium culmorum is a major pathogen of grain crops. Infected plants accumulate deoxynivalenol (DON), 3-acetyl-deoxynivalenol (3-ADON), or nivalenol (NIV), which are mycotoxins of the trichothecene B group. These toxins are also produced by F. graminearum species complex. New trichothecenes structurally similar to trichothecenes B but lacking the carbonyl group on C-8, designated NX toxins, were recently discovered in atypical isolates of F. graminearum from North America. Only these isolates and a few strains of a yet to be characterized Fusarium species from South Africa are known to produce NX-2 and other NX toxins. Here, we report that among 20 F. culmorum strains isolated from maize, wheat, and oat in Europe and Asia over a period of 70 years, 18 strains produced NX-2 simultaneously with 3-ADON and DON or NIV. Rice cultures of strains producing 3-ADON accumulated NX-2 in amounts corresponding to 2−8% of 3-ADON (1.2−36 mg/kg). A strain producing NIV accumulated NX-2 and NIV at comparable amounts (13.6 and 10.3 mg/kg, respectively). In F. graminearum, producers of NX-2 possess a special variant of cytochrome P450 monooxygenase encoded by TRI1 that is unable to oxidize C-8. In F. culmorum, producers and nonproducers of NX-2 possess identical TRI1; the reason for the production of NX-2 is unknown. Our results indicate that the production of NX-2 simultaneously with trichothecenes B is a common feature of F. culmorum.

Rapid and mass production of biopesticide Trichoderma Brev T069 from cassava peels using newly established solid-state fermentation bioreactor system

Converting agricultural waste into value-added biopesticides to replace chemical pesticides for plant protection is a good alternative for environmental sustainability and resource recycling. In this study, five tropical wastes (cassava peels, banana pseudostem, coconut shell, sugarcane bagasse, and pineapple peels) were screened as substrates for the rapid production of biopesticide Trichoderma Brev T069. Five single tests and a Box-Behnken design (BBD) with response surface methodology were used to optimize the culture conditions to improve the spore yield. The results showed that cassava peel was the optimal solid fermentation substrate, and the optimization enabled a spore yield of 9.31 × 10⁹ spores/g at 3rd day, which was equal to 93.19% of spore yield obtained at 5th day (9.99 × 10⁹ spores/g). A newly packed-bed bioreactor with agitation and ventilation system was developed and used to expand the production that 250 kg of biopesticide (2.89 × 10⁹ spores/g) could be available on the 3rd day. A pot experiment indicated that the biopesticide T. Brev T069 obtained under this production system, when applied at 1 × 10⁷ spores/g of soil had a 64.65% biocontrol efficiency on banana fusarium wilt. This study provides a practical solution for turning a tropical waste into an effective biopesticide which can prevent banana wilt disease, thereby helping to reduce disease management cost and overcome environmental hazards caused by synthetic pesticides.

DNA Sequence-Based Identification of Fusarium: A Work in Progress

Accurate species-level identification of an etiological agent is crucial for disease diagnosis and management because knowing the agent's identity connects it with what is known about its host range, geographic distribution, and toxin production potential. This is particularly true in publishing peer-reviewed disease reports, where imprecise and/or incorrect identifications weaken the public knowledge base. This can be a daunting task for phytopathologists and other applied biologists that need to identify Fusarium in particular, because published and ongoing multilocus molecular systematic studies have highlighted several confounding issues. Paramount among these are: (i) this agriculturally and clinically important genus is currently estimated to comprise more than 400 phylogenetically distinct species (i.e., phylospecies), with more than 80% of these discovered within the past 25 years; (ii) approximately one-third of the phylospecies have not been formally described; (iii) morphology alone is inadequate to distinguish most of these species from one another; and (iv) the current rapid discovery of novel fusaria from pathogen surveys and accompanying impact on the taxonomic landscape is expected to continue well into the foreseeable future. To address the critical need for accurate pathogen identification, our research groups are focused on populating two web-accessible databases (FUSARIUM-ID v.3.0 and the nonredundant National Center for Biotechnology Information nucleotide collection that includes GenBank) with portions of three phylogenetically informative genes (i.e., TEF1, RPB1, and RPB2) that resolve at or near the species level in every Fusarium species. The objectives of this Special Report, and its companion in this issue (Torres-Cruz et al. 2022), are to provide a progress report on our efforts to populate these databases and to outline a set of best practices for DNA sequence-based identification of fusaria.

Subcellular localization of fungal specialized metabolites

Fungal specialized metabolites play an important role in the environment and have impacted human health and survival significantly. These specialized metabolites are often the end product of a series of sequential and collaborating biosynthetic enzymes that reside within different subcellular compartments. A wide variety of methods have been developed to understand fungal specialized metabolite biosynthesis in terms of the chemical conversions and the biosynthetic enzymes required, however there are far fewer studies elucidating the compartmentalization of the same enzymes. This review illustrates the biosynthesis of specialized metabolites where the localization of all, or some, of the biosynthetic enzymes have been determined and describes the methods used to identify the sub-cellular localization.

Diversity of Fusarium spp. Associated with Wheat Node and Grain in Representative Sites Across the Western Canadian Prairies

Fusarium head blight (FHB) and Fusarium crown and root rot (FCRR) are major wheat diseases. Populations of FHB and FCRR pathogens are highly dynamic, and shifts in these populations in different regions is reported. Analyzing fungal populations associated with wheat node and grain tissues collected from different regions can provide useful information and predict diseases that might affect subsequent crops and effective disease management practices. In this study, wheat node and grain samples were collected from four representative sites across the western Canadian prairies in the 2018 growing season to characterize the major Fusarium spp. and other mycobiota associated with wheat in these regions. In total, 994 fungal isolates were recovered, and based on culture and molecular diagnostic methods, three genera constituted over 90% of all fungal isolates, namely Alternaria (39.6%), Fusarium (27.8%), and Parastagonospora (23.9%). A quantitative PCR (qPCR) diagnostic toolkit was developed to quantify the most frequently isolated Fusarium spp. in infected wheat tissues: Fusarium avenaceum, F. culmorum, F. graminearum, and F. poae. This qPCR specificity was validated in silico, in vitro, and in planta and proved specific to the target species. The qPCR results showed that F. graminearum was not detected frequently from wheat node and grain samples collected from four locations in this study. F. poae was the most abundant Fusarium species in grain samples in all tested locations. However, in node samples, F. culmorum (Beaverlodge and Scott) and F. avenaceum (Lacombe and Lethbridge) were the most abundant species. Trichothecene genotyping showed that the 3ADON is the most dominant trichothecene genotype (68%), followed by type-A trichothecenes (29.5%), whereas the 15ADON trichothecene genotype was least dominant (2.5%) and the NIV genotype was not detected. Moreover, a total of 129 translation elongation factor 1-alpha (TEF1α) sequences from nine Fusarium spp. were compared at the haplotype level to evaluate genetic variability and distribution. F. avenaceum and F. poae exhibited higher diversity as reflected by higher number of haplotypes present in these two species compared with the rest.

Diversity of biologically active secondary metabolites in the ascomycete order Sordariales

Ascomycetes belonging to the order Sordariales are a well-known reservoir of secondary metabolites with potential beneficial applications. Species of the Sordariales are ubiquitous, and they are commonly found in soils and in lignicolous, herbicolous, and coprophilous habitats. Some of their species have been used as model organisms in modern fungal biology or were found to be prolific producers of potentially useful secondary metabolites. However, the majority of sordarialean species are poorly studied. Traditionally, the classification of the Sordariales has been mainly based on morphology of the ascomata, ascospores, and asexual states, characters that have been demonstrated to be homoplastic by modern taxonomic studies based on multi-locus phylogeny. Herein, we summarize for the first time relevant information about the available knowledge on the secondary metabolites and the biological activities exerted by representatives of this fungal order, as well as a current outlook of the potential opportunities that the recent advances in omic tools could bring for the discovery of secondary metabolites in this order.

Incidence of toxigenic Aspergillus and Fusarium species occurring in maize kernels from Kenyan households

Aspergillus and Fusarium are fungal genera that include toxigenic and pathogenic species, able to suffuse farmers’ crops and secrete an array of small molecular weight secondary metabolites which can cause health complications to humans and animals when ingested. In sub-Sahara Africa, contamination and persistence of these fungi is increased by the tropical climatic conditions which are ideal for the fungi to thrive. This study evaluated the incidence, regional distribution and toxigenic potential of Aspergillus and Fusarium species occurring in maize kernels from Eastern, Western, Coastal and the Lake Victoria agro-ecological zones of Kenya. Maize kernels were collected from 16 households in each agro-ecological zone. Single spore technique was used to isolate pure cultures of Aspergillus and Fusarium which were identified morphologically. Further, molecular analysis was done using the internal transcribed spacer 1 (ITS 1) region of the ribosomal DNA for Aspergillus and the translation elongation factor-1 alpha (TEF-1α) for Fusarium. The potential of the isolated fungi to produce mycotoxins was probed by polymerase chain reaction (PCR) based on the aflatoxin regulatory aflaR gene in Aspergillus, and the fumonisin backbone structure gene FUM1 in Fusarium. Among the potentially aflatoxigenic A. flavus species isolated, 55% were from Eastern, 27% from the Coastal zone, 13% from Lake Victoria zone and 5% from Western Kenya. Among the potentially fumonisin producing F. verticillioides isolated, 45% were from the Lake Victoria agro-ecological zone, 30% were from Western, 15% from Eastern Kenya and 10% from the Coastal agro-ecological zone. This study adds data on potential mycotoxin hotspots in Kenya useful in employing targeted and regional mycotoxin mitigation strategies in efforts to avert future mycotoxicoses outbreaks in Kenya.

Comprehensive Review of Fungi on Coffee

Coffee is grown in more than 80 countries as a cash crop and consumed worldwide as a beverage and food additive. It is susceptible to fungal infection during growth, processing and storage. Fungal infections, in particular, can seriously affect the quality of coffee and threaten human health. The data for this comprehensive review were collected from the United States Department of Agriculture, Agricultural Research Service (USDA ARS) website and published papers. This review lists the fungal species reported on coffee based on taxonomy, life mode, host, affected plant part and region. Five major fungal diseases and mycotoxin-producing species (post-harvest diseases of coffee) are also discussed. Furthermore, we address why coffee yield and quality are affected by fungi and propose methods to control fungal infections to increase coffee yield and improve quality. Endophytic fungi and their potential as biological control agents of coffee disease are also discussed.

Lactic Acid Bacteria from African Fermented Cereal-Based Products: Potential Biological Control Agents for Mycotoxins in Kenya

Cereals play an important role in global food security. Data from the UN Food and Agriculture Organization projects increased consumption of cereals from 2.6 billion tonnes in 2017 to approximately 2.9 billion tonnes by 2027. However, cereals are prone to contamination by toxigenic fungi, which lead to mycotoxicosis. The current methods for mycotoxin control involve the use of chemical preservatives. However, there are concerns about the use of chemicals in food preservation due to their effects on the health, nutritional quality, and organoleptic properties of food. Therefore, alternative methods are needed that are affordable and simple to use. The fermentation technique is based on the use of microorganisms mainly to impart desirable sensory properties and shelf-life extension. The lactic acid bacteria (LAB) are generally regarded as safe (GRAS) due to their long history of application in food fermentation systems and ability to produce antimicrobial compounds (hydroxyl fatty acids, organic acids, phenyllactic acid, hydrogen peroxide, bacteriocins, and carbon dioxide) with a broad range of antifungal activity. Hence, LAB can inhibit the growth of mycotoxin-producing fungi, thereby preventing the production of mycotoxins. Fermentation is also an efficient technique for improving nutrient bioavailability and other functional properties of cereal-based products. This review seeks to provide evidence of the potential of LAB from African fermented cereal-based products as potential biological agents against mycotoxin-producing fungi.

Assessment of Two Novel Host-Derived Beauveria bassiana (Hypocreales: Cordycipitaceae) Isolates Against the Citrus Pest, Diaphorina citri (Hemiptera: Liviidae)

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), vectors 'Candidatus Liberibacter spp.', the causative agent of Citrus Greening Disease (CGD) or Huanglongbing (HLB). Managing populations of psyllids in the Lower Rio Grande Valley (LRGV), TX, United States is imperative given a continuous increase in HLB-positive trees. A component of integrated pest management (IPM) program is the use of strains of entomopathogenic fungi for the biological control of D. citri. In an attempt to find endemic strains of entomopathogenic fungi that grow favorably under LRGV environmental conditions and naturally infect D. citri, psyllids were collected from local residential areas, surface sterilized, and plated on a semi-selective agar medium. Collection of over 9,300 samples from 278 sites throughout the LRGV led to the positive identification of two Beauveria bassiana (Balsamo-Crivellii) Vuillemin (Hypocreales: Cordycipitaceae) isolates, ACP18001 and ACP18002. Chi-square analysis of primary and secondary acquisition bioassays revealed that both field isolated strains outperformed Cordyceps (Isaria) fumosorosea (Wize) (Hypocreales: Cordycipitaceae) Apopka97 under both primary (direct spray) and secondary acquisition (adult exposure to sprayed foliage) bioassays with ACP18002 marginally outperforming ACP18001 under secondary acquisition. Slopes of the dose response regression lines for the three fungi were not significantly different. In addition, the thermal profiles for vegetative growth of each isolate indicated that the field isolates grew at higher rates than the standard at higher temperatures. The new isolates may prove to be good candidates for the management of D. citri populations in the LRGV.

Use of the volatile trichodiene to reduce Fusarium head blight and trichothecene contamination in wheat

Fusarium graminearum is the primary cause of Fusarium head blight (FHB), one of the most economically important diseases of wheat worldwide. FHB reduces yield and contaminates grain with the trichothecene mycotoxin deoxynivalenol (DON), which poses a risk to plant, human and animal health. The first committed step in trichothecene biosynthesis is formation of trichodiene (TD). The volatile nature of TD suggests that it could be a useful intra or interspecies signalling molecule, but little is known about the potential signalling role of TD during F. graminearum-wheat interactions. Previous work using a transgenic Trichoderma harzianum strain engineered to emit TD (Th + TRI5) indicated that TD can function as a signal that can modulate pathogen virulence and host plant resistance. Herein, we demonstrate that Th + TRI5 has enhanced biocontrol activity against F. graminearum and reduced DON contamination by 66% and 70% in a moderately resistant and a susceptible cultivar, respectively. While Th + TRI5 volatiles significantly influenced the expression of the pathogenesis-related 1 (PR1) gene, the effect was dependent on cultivar. Th + TRI5 volatiles strongly reduced DON production in F. graminearum plate cultures and downregulated the expression of TRI genes. Finally, we confirm that TD fumigation reduced DON accumulation in a detached wheat head assay.

New Trichothecenes Isolated from the Marine Algicolous Fungus Trichoderma brevicompactum

Eight trichothecenes, including four new compounds 1–4 and four known entities 5–8, together with one known cyclonerane (9) were isolated from the solid-state fermentation of Trichoderma brevicompactum NTU439 isolated from the marine alga Mastophora rosea. The structures of 1–9 were determined by 1D/2D NMR (nuclear magnetic resonance), MS (mass spectrometry), and IR (infrared spectroscopy) spectroscopic data. All of the compounds were evaluated for cytotoxic activity against HCT-116, PC-3, and SK-Hep-1 cancer cells by the SRB assay, and compound 8 showed promising cytotoxic activity against all three cancer cell lines with the IC₅₀ values of 3.3 ± 0.3, 5.3 ± 0.3, and 1.8 ± 0.8 μM, respectively. Compounds 1–2, 4–6, and 7–8 potently inhibited LPS-induced NO production, and compounds 5 and 8 showed markedly inhibited gelatinolysis of MMP-9 in S1 protein-stimulated THP-1 monocytes.