Fungal Pathogen Fusarium Graminearum Research Articles

Hordedane diterpenoid phytoalexins restrict Fusarium graminearum infection but enhance Bipolaris sorokiniana colonization of barley roots

Plant immunity is a multilayered process that includes recognition of patterns or effectors from pathogens to elicit defense responses. These include the induction of a cocktail of defense metabolites that typically restrict pathogen virulence. Here, we investigate the interaction between barley roots and the fungal pathogens Bipolaris sorokiniana (Bs) and Fusarium graminearum (Fg) at the metabolite level. We identify hordedanes, a previously undescribed set of labdane-related diterpenoids with antimicrobial properties, as critical players in these interactions. Infection of barley roots by Bs and Fg elicits hordedane synthesis from a 600-kb gene cluster. Heterologous reconstruction of the biosynthesis pathway in yeast and Nicotiana benthamiana produced several hordedanes, including one of the most functionally decorated products 19-β-hydroxy-hordetrienoic acid (19-OH-HTA). Barley mutants in the diterpene synthase genes of this cluster are unable to produce hordedanes but, unexpectedly, show reduced Bs colonization. By contrast, colonization by Fusarium graminearum, another fungal pathogen of barley and wheat, is 4-fold higher in the mutants completely lacking hordedanes. Accordingly, 19-OH-HTA enhances both germination and growth of Bs, whereas it inhibits other pathogenic fungi, including Fg. Analysis of microscopy and transcriptomics data suggest that hordedanes delay the necrotrophic phase of Bs. Taken together, these results show that adapted pathogens such as Bs can subvert plant metabolic defenses to facilitate root colonization.

Manure amendments and fungistasis, and relation with protection of wheat from Fusarium graminearum

Certain soils promote crop health because they are pathogen-suppressive (i.e., fungistatic) or disease-suppressive, but the effect of soil management on these properties is not fully understood. Here, we tested the hypothesis that manure could favor fungistasis by screening 26 manured or non-manured wheat fields from Serbia for their ability to control survival/growth of the fungal plant pathogen Fusarium graminearum Fg1. Quantitative PCR showed that the pathogen grew after inoculation in all 26 autoclaved soils. In absence of autoclaving, the pathogen was stable or grew in 16 soils (37 % manured) but declined in the 10 others (70 % manured). For most soils, there was no significant link between soil chemistry and fungistasis, except with Mionica in western/central Serbia. Mionica soils MI2 and MI3, which had received manure, exhibited higher levels of organic matter and potassium compared with soils MI4 and MI5, which had not received manure and were non-fungistatic. Using Mionica soils, we then tested the hypothesis that fungistatic (manured) soils rather than non-fungistatic (non-manured) soils would protect wheat from F. graminearum disease. Indeed, fungistatic soils were suppressive to wheat damping-off. Non-fungistatic soil MI4 was conducive, as expected, but non-fungistatic soil MI5 turned out to be suppressive. Metabarcoding showed that the structure of prokaryotic and fungal rhizosphere communities depended mostly on field location, with a significant effect of F. graminearum inoculation. In conclusion, our findings show that certain farming practices (here, manure amendments) may promote soil fungistasis towards F. graminearum. However, both fungistatic and non-fungistatic soils can be suppressive to F. graminearum disease in wheat, and their differences in rhizosphere microbiota suggest different phytoprotection mechanisms.

Inhibition of fusarium graminearum growth and spore germination by a streptomyces amritsarensis strain capable of killing and growing on microcystis scum.

Developing energy-saving and ecofriendly strategies for treating harvested Microcystis biomass. Streptomyces amritsarensis HG-16 was first reported to effectively kill various morphotypes of natural Microcystis colonies at very high cell densities. Concurrently, HG-16 grown on lysed Microcystis maintained its antagonistic activity against plant pathogenic fungus Fusarium graminearum. It could completely inhibit spore germination and destroy mycelial structure of F. graminearum. Transcriptomic analysis revealed that HG-16 attacked F. graminearum in a comprehensive way: interfering with replication, transcription, and translation processes, inhibiting primary metabolisms, hindering energy production and simultaneously destroying stress-resistant systems of F. graminearum. The findings of this study provide a sustainable and economical option for resource reclamation from Microcystis biomass: utilizing Microcystis slurry to propagate HG-16, which can subsequently be employed as a biocontrol agent for managing F. graminearum.

Edeine B1 produced by Brevibacillus brevis reduces the virulence of a plant pathogenic fungus by inhibiting mitochondrial respiration.

Plant pathogenic fungi cause serious diseases, which result in the loss of crop yields and reduce the quality of crops worldwide. To counteract the escalating risks of chemical fungicides, interest in biological control agents to manage plant diseases has significantly increased. In this study, we comprehensively screened microbial culture filtrates using a yeast screening system to find microbes exhibiting respiratory inhibition activity. Consequently, we found a soil-borne microbe Brevibacillus brevis HK544 strain exhibiting a respiration inhibitory activity and identified edeine B1 (EB1) from the culture filtrate of HK544 as the active compound of the respiration inhibition activity. Furthermore, against a plant pathogenic fungus Fusarium graminearum, our results showed that EB1 has effects on multiple aspects of respiration with the downregulation of most of the mitochondrial-related genes based on transcriptome analysis, differential EB1-sensitivity from targeted mutagenesis, and the synergistic effects of EB1 with electron transport chain complex inhibitors. With the promising plant disease control efficacy of B. brevis HK544 producing EB1, our results suggest that B. brevis HK544 has potential as a biocontrol agent for Fusarium head blight.IMPORTANCEAs a necrotrophic fungus, Fusarium graminearum is a highly destructive pathogen causing severe diseases in cereal crops and mycotoxin contamination in grains. Although chemical control is considered the primary approach to control plant disease caused by F. graminearum, fungicide-resistant strains have been detected in the field after long-term continuous application of fungicides. Moreover, applying chemical fungicides that trigger mycotoxin biosynthesis is a great concern for many researchers. Biocontrol of Fusarium head blight (FHB) by biological control agents (BCAs) represents an alternative approach and could be used as part of the integrated management of FHB and mycotoxin production. The most extensive studies on bacterial BCAs-fungal communications in agroecosystems have focused on antibiosis. Although many BCAs in agricultural ecology have already been used for fungal disease control, the molecular mechanisms of antibiotics produced by BCAs remain to be elucidated. Here, we found a potential BCA (Brevibacillus brevis HK544) with a strong antifungal activity based on the respiration inhibition activity with its active compound edeine B1 (EB1). Furthermore, our results showed that EB1 secreted by HK544 suppresses the expression of the mitochondria-related genes of F. graminearum, subsequently suppressing fungal development and the virulence of F. graminearum. In addition, EB1 exhibited a synergism with complex I inhibitors such as rotenone and fenazaquin. Our work extends our understanding of how B. brevis HK544 exhibits antifungal activity and suggests that the B. brevis HK544 strain could be a valuable source for developing new crop protectants to control F. graminearum.

The trichothecene mycotoxin deoxynivalenol facilitates cell-to-cell invasion during wheat-tissue colonization by Fusarium graminearum.

Fusarium head blight disease on small-grain cereals is primarily caused by the ascomycete fungal pathogen Fusarium graminearum. Infection of floral spike tissues is characterized by the biosynthesis and secretion of potent trichothecene mycotoxins, of which deoxynivalenol (DON) is widely reported due to its negative impacts on grain quality and consumer safety. The TRI5 gene encodes an essential enzyme in the DON biosynthesis pathway and the single gene deletion mutant, ΔTri5, is widely reported to restrict disease progression to the inoculated spikelet. In this study, we present novel bioimaging evidence revealing that DON facilitates the traversal of the cell wall through plasmodesmata, a process essential for successful colonization of host tissue. Chemical complementation of ΔTri5 did not restore macro- or microscopic phenotypes, indicating that DON secretion is tightly regulated both spatially and temporally. A comparative qualitative and quantitative morphological cellular analysis revealed infections had no impact on plant cell wall thickness. Immunolabelling of callose at plasmodesmata during infection indicates that DON can increase deposits when applied exogenously but is reduced when F. graminearum hyphae are present. This study highlights the complexity of the interconnected roles of mycotoxin production, cell wall architecture and plasmodesmata in this highly specialized interaction.

Con7 is a key transcription regulator for conidiogenesis in the plant pathogenic fungus Fusarium graminearum.

The ascomycete fungus Fusarium graminearum is the primary cause of head blight disease in wheat and barley, as well as ear and stalk rot in maize. Given the importance of conidia and ascospores in the disease cycle of F. graminearum, precise spatiotemporal regulation of these biological processes is crucial. In this study, we characterized the Magnaporthe oryzae Con7p ortholog and discovered that FgCon7 significantly influences various crucial aspects of fungal development and pathogenicity. Notably, overexpression of FgABAA partially restored developmental defects in the FgCON7 deletion mutant. ChIP-qPCR analysis confirmed a direct genetic link between FgABAA and FgCON7. Furthermore, our research revealed a clear correlation between FgCon7 and chitin accumulation and the expression of chitin synthase genes. These findings offer valuable insights into the genetic mechanisms regulating conidiation and the significance of mycelial differentiation in this plant pathogenic fungus.

Microbiome dynamics during malting of barley grains infested by Fusarium graminearum strains

AbstractBarley grain harvested for malting poses an interesting case study for the impacts of plant‐associated microbiomes because the conditions created during malting favour continued vigorous microbial activity after grain harvest. Suppression of pathogens is among the key functions performed by microbiomes, and it would be beneficial if we could harness this function. Over a 3‐year field trial, we micro‐malted barley that had been experimentally infested with each of seven different strains of the fungal pathogen Fusarium graminearum, and profiled bacterial microbiomes at key stages in the malting process (grain, post‐steeping, post‐germination and final dried malt). The greatest impacts on bacterial microbiomes were observed to be from the year and stage of malting, with comparatively fewer impacts of barley cultivar or pathogen strain. Relatively limited impacts of the presence and strain identity of fungal pathogen on the bacterial microbiome of malting barley probably reflects the colonization by other fungi, as our inoculation took place under field conditions with supplemental irrigation. Both community level shifts and significant responses by individual taxa were evident. Microbiome characteristics or the relative abundances of specific bacterial taxa helped to explain pathogen biomass, mycotoxin production and beer gushing. Manipulative experiments will be required to test hypotheses suggested by these microbiome profiles.

Estimating Fusarium head blight severity in winter wheat using deep learning and a spectral index

AbstractFusarium head blight (FHB) of wheat (Triticum aestivum L.), caused by the fungal pathogen Fusarium graminearum (Fg), reduces grain yield and quality due to the production of the mycotoxin deoxynivalenol. Manual rating for incidence (percent of infected wheat heads/spikes) and severity (percent of spikelets infected) to estimate FHB resistance is time‐consuming and subject to human error. This study uses a deep learning model, combined with a spectral index, to provide rapid phenotyping of FHB severity. An object detection model was used to localize wheat heads within boundary boxes. Corresponding boxes were used to prompt Meta's Segment Anything Model to segment wheat heads. Using 2576 images of wheat heads point inoculated with Fg in a controlled environment, a spectral index was developed using the red and green bands to differentiate healthy from infected tissue and estimate disease severity. Stratified random sampling was applied to pixels within the segmentation mask, and the model classified pixels as healthy or infected with an accuracy of 87.8%. Linear regression determined the relationship between the index and visual severity scores. The severity estimated by the index was able to predict visual scores (R2 = 0.83, p = < 2e‐16). This workflow was also applied to plot size images of infected wheat heads from an outside dataset with varying cultivars and lighting to assess model transferability. It correctly classified pixels as healthy or infected with a prediction accuracy of 85.8%. These methods may provide rapid estimation of FHB severity to improve selection efficiency for resistance or estimate disease pressure for effective management.

Proteomic Analysis of Cell Wall Proteins with Various Linkages in Fusarium graminearum.

The fungal cell wall, primarily comprising a glucan-chitin matrix and cell wall proteins (CWPs), serves as a key mediator for fungal interactions with the environment and plays a pivotal role in virulence. In this study, we employed a comprehensive proteomics approach to analyze the CWPs in the plant pathogenic fungus Fusarium graminearum. Our methodology successfully extracted and identified 1373 CWPs, highlighting their complex linkages, including noncovalent bonds, disulfide bridges, alkali-sensitive linkages, and glycosylphosphatidylinositol (GPI) anchors. A significant subset of these proteins, enriched in Gene Ontology terms, suggest multifunctional roles of CWPs. Through the integration of transcriptomic and proteomic data, we observed differential expression patterns of CWPs across developmental stages. Specifically, we focused on two genes, Fca7 and Cpd1, which were upregulated in planta, and confirmed their localization predominantly outside the plasma membrane, primarily in the cell wall and periplasmic space. The disruption of FCA7 reduced virulence on wheat, aligning with previous findings and underscoring its significance. Overall, our findings offer a comprehensive proteomic profile of CWPs in F. graminearum, laying the groundwork for a deeper understanding of their roles in the development and interactions with host plants.

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.

Sulfur metabolism-mediated fungal glutathione biosynthesis is essential for oxidative stress resistance and pathogenicity in the plant pathogenic fungus Fusarium graminearum.

Fusarium graminearum is a destructive fungal pathogen that causes Fusarium head blight (FHB) on a wide range of cereal crops. To control fungal diseases, it is essential to comprehend the pathogenic mechanisms that enable fungi to overcome host defenses during infection. Pathogens require an oxidative stress response to overcome host-derived oxidative stress. Here, we identify the underlying mechanisms of the Fgbzip007-mediated oxidative stress response in F. graminearum. ChIP-seq and subsequent genetic analyses revealed that the role of glutathione in pathogenesis is not dependent on antioxidant functions in F. graminearum. Altogether, this study establishes a comprehensive framework for the Fgbzip007 regulon on pathogenicity and oxidative stress responses, offering a new perspective on the role of glutathione in pathogenicity.

Bacteria existing in pre-pollinated styles (silks) can defend the exposed male gamete fertilization channel of maize against an environmental Fusarium pathogen.

In flowering plants, fertilization requires exposing maternal style channels to the external environment to capture pollen and transmit its resident sperm nuclei to eggs. This results in progeny seed. However, environmental fungal pathogens invade developing seeds through the style. We hypothesized that prior to environmental exposure, style tissue already possesses bacteria that can protect styles and seed from such pathogens. We further hypothesized that farmers have been inadvertently selecting immature styles over many generations to have such bacteria. We tested these hypotheses in maize, a wind-pollinated crop, which has unusually long styles (silks) that are invaded by the economically-important fungal pathogen Fusarium graminearum (Fg). Here, unpollinated silk-associated bacteria were cultured from a wild teosinte ancestor of maize and diverse maize landraces selected by indigenous farmers across the Americas, grown in a common Canadian field for one season. The bacteria were taxonomically classified using 16S rRNA sequencing. In total, 201 bacteria were cultured, spanning 29 genera, 63 species, and 62 unique OTUs, dominated by Pseudomonas, Pantoea and Microbacterium. These bacteria were tested for their ability to suppress Fg in vitro which identified 10 strains belonging to 6 species: Rouxiella badensis, Pantoea ananatis, Pantoea dispersa, Pseudomonas koreensis, Rahnella aquatilis, and Ewingella americana. Two anti-Fg strains were sprayed onto silks before/after Fg inoculation, resulting in ≤90% reductions in disease (Gibberella ear rot) and 70-100% reductions in associated mycotoxins (deoxynivalenol and zearalenone) in progeny seeds. These strains also protected progeny seeds post-harvest. Confocal fluorescent imaging showed that one silk bacterium (Rouxiella AS112) colonized susceptible entry points of Fg on living silks including stigmatic trichomes, wounds, and epidermal surfaces where they formed thick biofilms. Post-infection, AS112 was associated with masses of dead Fg hyphae. These results suggest that the maize style (silk) is endowed with potent bacteria from the mother plant to protect itself and progeny from Fusarium. The evidence suggests this trait may have been selected by specific indigenous peoples, though this interpretation requires further study.

The Fusarium graminearum Transporters Abc1 and Abc6 Are Important for Xenobiotic Resistance, Trichothecene Accumulation, and Virulence to Wheat.

The plant pathogenic fungus Fusarium graminearum is the causal agent of Fusarium head blight (FHB) disease on small-grain cereals. F. graminearum produces trichothecene mycotoxins such as deoxynivalenol (DON) that are required for full virulence. DON must be exported outside the cell to cause FHB disease, a process that may require the involvement of membrane-bound transporters. In this study, we show that the deletion of membrane-bound transporters results in reduced DON accumulation as well as reduced FHB symptoms on wheat. Deletion of the ATP-binding cassette (ABC) transporter gene Abc1 results in the greatest reduction in DON accumulation and virulence. Deletion of another ABC transporter gene, Abc6, also reduces FHB symptoms to a lesser degree. Combining deletions fails to reduce DON accumulation or virulence in an additive fashion, even when a ∆abc1 deletion is included. Heterologous expression of F. graminearum transporters in a DON-sensitive strain of yeast confirms Abc1 as a major DON resistance mechanism; furthermore, it suggests that Abc1 is directly participating in DON transport rather than facilitating DON transport though other means. Yeast expression further indicates that multiple transporters, including Abc1, play an important role in resistance to the wheat phytoalexin 2-benzoxazolinone (BOA) and other xenobiotics. Thus, Abc1 may contribute to virulence on wheat both by facilitating export of DON and by providing resistance to the wheat phytoalexin BOA. This research provides useful information that may aid in designing novel management techniques of FHB or other destructive plant diseases.

Protein Disulfide Isomerase FgEps1 Is a Secreted Virulence Factor in Fusarium graminearum.

Protein disulfide isomerase (PDI) is a member of the thioredoxin (Trx) superfamily with important functions in cellular stability, ion uptake, and cellular differentiation. While PDI has been extensively studied in humans and animals, its role in fungi remains relatively unknown. In this study, the biological functions of FgEps1, a disulfide bond isomerase in the fungal pathogen Fusarium graminearum, were investigated. It was found that FgEps1 mutation affected nutritional growth, asexual and sexual reproduction, and stress tolerance. Additionally, its deletion resulted in reduced pathogenicity and impaired DON toxin biosynthesis. The involvement of FgEps1 in host infection was also confirmed, as its expression was detected during the infection period. Further investigation using a yeast signal peptide secretion system and transient expression in Nicotiana benthamiana showed that FgEps1 suppressed the immune response of plants and promoted infection. These findings suggest that virulence factor FgEps1 plays a crucial role in growth, development, virulence, secondary metabolism, and host infection in F. graminearum.

A combined transcriptomic and physiological approach to understanding the adaptive mechanisms to cope with oxidative stress in Fusarium graminearum.

In plant-pathogen interactions, oxidative bursts are crucial for plants to defend themselves against pathogen infections. Rapid production and accumulation of reactive oxygen species kill pathogens directly and cause local cell death, preventing pathogens from spreading to adjacent cells. Meanwhile, the pathogens have developed several mechanisms to tolerate oxidative stress and successfully colonize plant tissues. In this study, we investigated the mechanisms responsible for resistance to oxidative stress by analyzing the transcriptomes of six oxidative stress-sensitive strains of the plant pathogenic fungus Fusarium graminearum. Weighted gene co-expression network analysis identified several pathways related to oxidative stress responses, including the DNA repair system, autophagy, and ubiquitin-mediated proteolysis. We also identified hub genes with high intramodular connectivity in key modules and generated deletion or conditional suppression mutants. Phenotypic characterization of those mutants showed that the deletion of FgHGG4, FgHGG10, and FgHGG13 caused sensitivity to oxidative stress, and further investigation on those genes revealed that transcriptional elongation and DNA damage responses play roles in oxidative stress response and pathogenicity. The suppression of FgHGL7 also led to hypersensitivity to oxidative stress, and we demonstrated that FgHGL7 plays a crucial role in heme biosynthesis and is essential for peroxidase activity. This study increases the understanding of the adaptive mechanisms to cope with oxidative stress in plant pathogenic fungi. IMPORTANCE Fungal pathogens have evolved various mechanisms to overcome host-derived stresses for successful infection. Oxidative stress is a representative defense system induced by the host plant, and fungi have complex response systems to cope with it. Fusarium graminearum is one of the devastating plant pathogenic fungi, and understanding its pathosystem is crucial for disease control. In this study, we investigated adaptive mechanisms for coping with oxidative stress at the transcriptome level using oxidative stress-sensitive strains. In addition, by introducing genetic modification technique such as CRISPR-Cas9 and the conditional gene expression system, we identified pathways/genes required for resistance to oxidative stress and also for virulence. Overall, this study advances the understanding of the oxidative stress response and related mechanisms in plant pathogenic fungi.

Structural diversification of natural substrates modified by the O-methyltransferase AurJ from Fusarium Graminearum

Aromatic polyketide and phenylpropanoid derivatives are a large class of natural products produced by bacteria, fungi, and plants. The O-methylation is a unique decoration that can increase structural diversity of aromatic compounds and improve their pharmacological properties, but the substrate specificity of O-methyltransferase hinders the discovery of more natural products with O-methylation through biosynthesis. Here, we reported that the O-methyltransferase AurJ from plant pathogenic fungus Fusarium graminearum could methylate a broad range of natural substrates of monocyclic, bicyclic, and tricyclic aromatic precursors, exhibiting excellent substrate tolerance. This finding will partly change our stereotype about the specificity of traditional methyltransferases, and urge us to mine more O-methyltransferases with good substrate tolerance and discover more methylated natural products for drug discovery and development through directed evolution and combinatorial biosynthesis.

Ubiquitination of acetyltransferase Gcn5 contributes to fungal virulence in Fusarium graminearum.

The histone acetyltransferase general control non-depressible 5 (Gcn5) plays a critical role in the epigenetic landscape and chromatin modification for regulating a wide variety of biological events. However, the post-translational regulation of Gcn5 itself is poorly understood. Here, we found that Gcn5 was ubiquitinated and deubiquitinated by E3 ligase Tom1 and deubiquitinating enzyme Ubp14, respectively, in the important plant pathogenic fungus Fusarium graminearum. Tom1 interacted with Gcn5 in the nucleus and subsequently ubiquitinated Gcn5 mainly at K252 to accelerate protein degradation. Conversely, Ubp14 deubiquitinated Gcn5 and enhanced its stability. In the deletion mutant Δubp14, protein level of Gcn5 was significantly reduced and resulted in attenuated virulence in the fungus by affecting the mycotoxin production, autophagy process, and the penetration ability. Our findings indicate that Tom1 and Ubp14 show antagonistic functions in the control of the protein stability of Gcn5 via post-translational modification and highlight the importance of Tom1-Gcn5-Ubp14 circuit in the fungal virulence. IMPORTANCE Post-translational modification (PTM) enzymes have been reported to be involved in regulating numerous cellular processes. However, the modification of these PTM enzymes themselves is largely unknown. In this study, we found that the E3 ligase Tom1 and deubiquitinating enzyme Ubp14 contributed to the regulation of ubiquitination and deubiquitination of acetyltransferase Gcn5, respectively, in Fusarium graminearum, the causal agent of Fusarium head blight of cereals. Our findings provide deep insights into the modification of acetyltransferase Gcn5 and its dynamic regulation via ubiquitination and deubiquitination. To our knowledge, this work is the most comprehensive analysis of a regulatory network of ubiquitination that impinges on acetyltransferase in filamentous pathogens. Moreover, our findings are important because we present the novel roles of the Tom1-Gcn5-Ubp14 circuit in fungal virulence, providing novel possibilities and targets to control fungal diseases.

Basal defense is enhanced in a wheat cultivar resistant to Fusarium head blight

Fusarium head blight (FHB), mainly caused by the fungal pathogen Fusarium graminearum, is one of the most destructive wheat diseases. Besides directly affecting the yield, the mycotoxin residing in the kernel greatly threatens the health of humans and livestock. Xinong 979 (XN979) is a widely cultivated wheat elite with high yield and FHB resistance. However, its resistance mechanism remains unclear. In this study, we studied the expression of genes involved in plant defense in XN979 by comparative transcriptomics. We found that the FHB resistance in XN979 consists of two lines of defense. The first line of defense, which is constitutive, is knitted via the enhanced basal expression of lignin and jasmonic acid (JA) biosynthesis genes. The second line of defense, which is induced upon F. graminearum infection, is contributed by the limited suppression of photosynthesis and the struggle of biotic stress-responding genes. Meanwhile, the effective defense in XN979 leads to an inhibition of fungal gene expression, especially in the early infection stage. The formation of the FHB resistance in XN979 may coincide with the breeding strategies, such as selecting high grain yield and lodging resistance traits. This study will facilitate our understanding of wheat–F. graminearum interaction and is insightful for breeding FHB-resistant wheat.

Analysis of the Biological Activity and Whole Genome Sequencing of Bacillus cereus CDHWZ7 Isolated from the Rhizosphere of Lycium ruthenicum on the Tibetan Plateau

This study examined the biological activity and genome of Bacillus cereus CDHWZ7 isolated from the root of Lycium ruthenicum in the Dachaidan saline area, Haixi Prefecture, Qinghai Province, China. The results revealed that B. cereus CDHWZ7 exhibited strong inhibition activity against the pathogenic fungi Fusarium graminearum, F. acuminatum, and F. oxysporum. CDHWZ7 also demonstrated cellulose-degrading activity, nitrogen-fixing activity, and the ability to secrete indole-3-acetic acid (IAA) at 55.00 mg∙L−1. The strain CDHWZ7 can grow at a salt concentration of 3–11%, a pH range of 5–11, and a temperature of 4 °C–18 °C, and shows good salt tolerance, acid and alkaline tolerance, and low-temperature fitness. The genome of strain CDHWZ7 was sequenced using Illumina HiSeq + PacBio, revealing a circular structure of 5,648,783 bp in length, containing two intact plasmids with an average GC content of 35.2%, and a total number of 5672 encoded genes. It contained 106 tRNA genes, 42 rRNA genes, and 134 sRNA genes. A total of 137 genes were annotated as carbohydrases, with a total base length of 3,968,396,297 bp. The numbers of coding sequences assigned to the Kyoto Encyclopedia of Genes and Genomes, Clusters of Orthologous Groups of Proteins, and Gene Ontology Databases were 4038, 4133, and 2160, respectively. Further analysis of the genome identified genes encoding chitinase activity, cellulases, secondary metabolites, phytohormone production, volatile compounds, nitrogen and phosphate metabolism, and resistance responses to biotic stresses (glycine betaine transporter protein, catalase, superoxide dismutase, low-affinity potassium transporter protein, cold-shock protein, heat-shock protein), as well as genes related to proliferation, stress response, and resistance to pathogenic fungi. Therefore, this study determined that strain CDHWZ7 has several excellent biological traits, such as antagonism to pathogenic fungi, nitrogen-fixation ability, cellulose-degradation ability, and IAA-production ability. The genome sequence of strain CDHWZ7 and several biodefense functional genes were also analyzed, revealing the potential use of strain CDHWZ7 in the development of biological agents.

Genome-Wide Characterization of the RNA Exosome Complex in Relation to Growth, Development, and Pathogenicity of Fusarium graminearum.

The RNA exosome complex is a conserved, multisubunit RNase complex that contributes to the processing and degradation of RNAs in mammalian cells. However, the roles of the RNA exosome in phytopathogenic fungi and how it relates to fungal development and pathogenicity remain unclear. Herein, we identified 12 components of the RNA exosome in the wheat fungal pathogen Fusarium graminearum. Live-cell imaging showed that all the components of the RNA exosome complex are localized in the nucleus. FgEXOSC1 and FgEXOSCA were successfully knocked out; they are both involved in the vegetative growth, sexual reproduction, and pathogenicity of F. graminearum. Moreover, deletion of FgEXOSC1 resulted in abnormal toxisomes, decreased deoxynivalenol (DON) production, and downregulation of the expression levels of DON biosynthesis genes. The RNA-binding domain and N-terminal region of FgExosc1 are required for its normal localization and functions. Transcriptome sequencing (RNA-seq) showed that the disruption of FgEXOSC1 resulted in differential expression of 3,439 genes. Genes involved in processing of noncoding RNA (ncRNA), rRNA and ncRNA metabolism, ribosome biogenesis, and ribonucleoprotein complex biogenesis were significantly upregulated. Furthermore, subcellular localization, green fluorescent protein (GFP) pulldown, and coimmunoprecipitation (co-IP) assays demonstrated that FgExosc1 associates with the other components of the RNA exosome to form the RNA exosome complex in F. graminearum. Deletion of FgEXOSC1 and FgEXOSCA reduced the relative expression of some of the other subunits of the RNA exosome. Deletion of FgEXOSC1 affected the localization of FgExosc4, FgExosc6, and FgExosc7. In summary, our study reveals that the RNA exosome is involved in vegetative growth, sexual reproduction, DON production, and pathogenicity of F. graminearum. IMPORTANCE The RNA exosome complex is the most versatile RNA degradation machinery in eukaryotes. However, little is known about how this complex regulates the development and pathogenicity of plant-pathogenic fungi. In this study, we systematically identified 12 components of the RNA exosome complex in Fusarium head blight fungus Fusarium graminearum and first unveiled their subcellular localizations and established their biological functions in relation to the fungal development and pathogenesis. All the RNA exosome components are localized in the nucleus. FgExosc1 and FgExoscA are both required for the vegetative growth, sexual reproduction, DON production and pathogenicity in F. graminearum. FgExosc1 is involved in ncRNA processing, rRNA and ncRNA metabolism process, ribosome biogenesis and ribonucleoprotein complex biogenesis. FgExosc1 associates with the other components of RNA exosome complex and form the exosome complex in F. graminearum. Our study provides new insights into the role of the RNA exosome in regulating RNA metabolism, which is associated with fungal development and pathogenicity.