Fusarium oxysporum: exploring the molecular arsenal of a vascular wilt fungus

Advancing forest pathology: the need for community-driven molecular experimental model systems

Forests world-wide are under escalating threat from emerging and invasive fungal and oomycete pathogens, driven by globalization and shifting climate dynamics. Effective strategies to manage the current scale and rate of changes in forest health remain hindered by our limited ability to study the underlying mechanisms of pathogen-host and pathogen-microbiome interactions, especially at a molecular and cellular level, compared to general plant pathology, where experimental and model systems exist. Such models facilitate the integration of diverse methodologies from a broader base of the research community, allowing for a more holistic and deeper examination of complex research questions. Here, we propose a framework for the development of such model systems also for forest pathology. This goal is more feasible than ever, thanks to rapid technological advancements, increasing open data availability and a globally interconnected research community. These factors create a unique opportunity to integrate ecosystem-focused research in forest pathology with a unified model organism strategy. Achieving this goal will require a dedicated community effort in the coming years, as such model systems are not discovered but built.

Fusaric acid-mediated S-glutathionylation of MaAKT1 channel confers the virulence of Foc TR4 to banana

Our previous studies have demonstrated that the phytotoxin fusaric acid (FSA), secreted by several Fusarium species, acts as a key factor in the development of plant diseases; however, the underlying mechanism remains unknown. In this study, we showed that the symptoms of Fusarium wilt in banana seedlings closely resembled those observed in plants grown under potassium (K+) deficiency conditions. Mechanistically, we found that FSA induces the accumulation of intracellular reactive oxygen species (ROS), which in turn inhibits banana K+ in banana roots. This inhibition occurs via S-glutathionylation of the banana AKT1 (MaAKT1) channel, leading to reduced K+ influx and reduced K+ content in banana roots. Through mutagenesis, electrophysiological studies, immunofluorescence staining, and co-immunoprecipitation experiment, we demonstrated that mutation of Cys202, a highly conserved site in the transmembrane segment 5 of MaAKT1, diminished the biochemical interaction of glutathione (GSH) and the channel induced by FSA, and alleviated Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) and FSA-induced yellowing symptom. The evolutionarily conserved function of this site for S-glutathionylation was also observed in Arabidopsis AKT1 (AtAKT1) channel, as mutation of its homologue site in AtAKT1 similarly reduced the GSH-AtAKT1 interaction under FSA stress. Collectively, our results suggest that FSA contributes to disease progression by decreasing K+ absorption through S-glutathionylation of MaAKT1 channel at the conserved Cys202 residue. These findings uncover a previously unrecognized role of FSA in regulating K+ homeostasis in bananas, and provide a foundation for future strategies to treat Fusarium wilt and increase banana production by targeting the conserved S-glutathionylation site in MaAKT1 channel.

Spermidine treatment limits the development of the fungus in flax shoots by suppressing polyamine metabolism and balanced defence reactions, thus increasing flax resistance to fusariosis

Introduction

Flax (Linum usitatissimum) is an important industrial crop in temperate regions, but fungal diseases, especially those caused by Fusarium oxysporum sp. lini, pose a serious risk. These infections can lead to major crop losses, reducing interest in flax cultivation.

Methods

This study investigated the effects of exogenous spermidine (Spd) on the interactions between flax and Fusarium oxysporum sp. lini. Flax plants treated with either 10 mM or 100 mM Spd were monitored for changes in polyamine levels, gene expression, and hydrogen peroxide (H2O2) content following infection.

Results and discussion

Notably, plants treated with 10 mM Spd showed enhanced resistance, exhibiting better phenotypic health and lower fungal murein levels, especially in shoots. Chitinase expression in these plants remained similar to or lower than control levels, suggesting minimal additional defence activation was required. Additionally, a marked ROS burst occurred two days post-infection, followed by redox balance restoration, indicating a controlled defence response. These results suggest that moderate Spd treatment improves flax resilience against fusarium wilt while avoiding excessive defence activation, highlighting Spd's potential for sustainable crop protection strategies.

Molecular Tracking of Emerging Fusarium Species in Keratitis: F. veterinarium, F. contaminatum, and F. curvatum

Fungal keratitis, which is caused primarily by Neocosmospora and Fusarium species, is a significant global health issue that affects more than a million people annually in tropical and subtropical regions. Neocosmospora solani (formerly Fusarium solani) is a leading cause of corneal infections, along with members of the Fusarium oxysporum species complex (FOSC). This study provides new insights by reporting a series of ocular fusariosis cases caused by FOSC members and presenting molecular evidence linking specific haplotypes within FOSC to human infections. We describe three cases of Fusarium keratitis selected from a comprehensive review of clinicopathological data in our institution's archives. These cases were chosen for their distinctive clinical presentations and the involvement of less common Fusarium species. Two of these patients were diagnosed with keratitis and anterior endophthalmitis, and the third patient had a corneal ulcer previously treated with topical antivirals and antibiotics. All patients were successfully treated with topical amphotericin B. The Fusarium isolates from these patients were subjected to detailed molecular characterization, including DNA sequencing (tef1α, rpb2, CaM, tub2, and LSU), amplified fragment length polymorphism (AFLP) marker analysis, and MALDI-TOF MS analysis. Remarkably, our study reports the first case of human infection by F. veterinarium, alongside cases involving F. contaminatum and F. curvatum. Furthermore, a molecular survey using haplotypic networks based on tef1α sequences identified genotypes associated with human infections and revealed the emergence of F. veterinarium clade VII. Our findings emphasize the need for vigilance regarding emerging species within the FOSC, particularly F. veterinarium. This highlights the need for improved diagnostic tools and targeted research to combat fusarioid-related infections effectively.

The MdERF61-mdm-miR397b-MdLAC7b module regulates apple resistance to Fusarium solani via lignin biosynthesis

Apple replant disease (ARD) is a worldwide problem that threatens the industry. However, the genetic mechanism underlying plant disease resistance against ARD remains unclear. In this study, a negative regulatory microRNA in Malus domestica, mdm-miR397b, and its direct target MdLAC7b (Laccase) was selected for examination based on our previous small RNA and degradome sequencing results. Overexpressing the mdm-miR397b-MdLAC7b module altered the lignin deposition and jasmonic acid contents in apple roots, which also led to increased resistance to Fusarium solani. Additionally, Y1H library screening using mdm-miR397b promoter recombinants identified a transcription factor, MdERF61, that represses mdm-miR397b transcriptional activity by directly binding to 2 GCC-boxes in the mdm-miR397b promoter. In summary, our results suggest that the MdERF61-mdm-miR397b-MdLAC7b module plays a crucial role in apple resistance to F. solani and offers insights for enhancing plant resistance to soil-borne diseases in apples.

The Good, the Bad, and the Fungus: Insights into the Relationship Between Plants, Fungi, and Oomycetes in Hydroponics

Hydroponic systems are examples of controlled environment agriculture (CEA) and present a promising alternative to traditional farming methods by increasing productivity, profitability, and sustainability. In hydroponic systems, crops are grown in the absence of soil and thus lack the native soil microbial community. This review focuses on fungi and oomycetes, both beneficial and pathogenic, that can colonize crops and persist in hydroponic systems. The symptomatology and mechanisms of pathogenesis for Botrytis, Colletotrichum, Fulvia, Fusarium, Phytophthora, Pythium, and Sclerotinia are explored for phytopathogenic fungi that target floral organs, leaves, roots, and vasculature of economically important hydroponic crops. Additionally, this review thoroughly explores the use of plant growth-promoting fungi (PGPF) to combat phytopathogens and increase hydroponic crop productivity; details of PGP strategies and mechanisms are discussed. The benefits of Aspergillus, Penicillium, Taloromyces, and Trichoderma to hydroponics systems are explored in detail. The culmination of these areas of research serves to improve the current understanding of the role of beneficial and pathogenic fungi, specifically in the hydroponic microbiome.

Synergistic growth suppression of Fusarium oxysporum MLY127 through Dimethachlon Nanoencapsulation and co-application with Bacillus velezensis MLY71

Fusarium oxysporum is a destructive plant pathogen with robust survival mechanisms, complicating control efforts. This study aimed to develop nanoformulated fungicides, screen antagonistic bacteria, and evaluate their combined efficacy. A novel self-emulsifying nanoemulsion (DZW) was formulated using zein and benzaldehyde-modified wheat gluten (BgWG) as carriers for dimethachlon (DTN). The preparation process optimized material ratios and emulsification techniques. Concurrently, antagonistic bacterial strains against F. oxysporum were screened via the plate standoff method, identifying Bacillus velezensis MLY71 as both antagonistic and compatible with DTN. The DZW nanoemulsion achieved a particle size of 93.22 nm, an encapsulation efficiency (EE) of 90.57%, and a DTN loading capacity (LC) of 67.09%, with sustained release over 96 h. The combination of DTN (0.04 mg·mL⁻¹) and B. velezensis MLY71 (1 × 10⁴ CFU·mL⁻¹) achieved a 76.66% inhibition rate against F. oxysporum MLY127, 1.71 times greater than DTN alone, indicating significant synergy. At a DTN concentration of 0.20 mg·mL⁻¹, the combination of DZW and MLY71 showed a synergy coefficient of 1.33. This synergy was also observed in soil environments, indicating its adaptability for controlling soil-borne pathogens. As sustainable management continues to gain attention in agricultural disease control, this study offers a promising strategy for achieving higher efficacy with the same fungicide dose or satisfactory control with reduced fungicide application. The excellent drug-loading performance of BgWG also expanded the applications of the wheat by-product gluten.

Genome-Wide Association Study and Marker Development for Fusarium Oxysporum Root Rot Resistance in Soybean

Fusarium oxysporum root rot (FORR) is an important disease threatening soybean production. The development of marker-assisted selection (MAS) molecular markers will help accelerate the disease resistance breeding process and achieve the breeding goal of improving soybean disease resistance. This study evaluated the FORR disease resistance of 356 soybean germplasm accessions (SGAs) and screened resistance-related loci using genome-wide association analysis (GWAS) to develop molecular markers for MAS. A total of 1,355,930 high-quality SNPs were analyzed, 150 SNP sites significantly associated with FORR resistance were identified, and these sites were distributed within 41 QTLs. Additionally, 240 candidate genes were screened near these QTL regions, involving multiple functions such as hormone metabolism, signal transduction, stress defense, and growth regulation. Cleaved amplified polymorphic sequence (CAPS) and Kompetitive Allele-Specific PCR (KASP) molecular markers were developed based on candidate genes with significant SNP loci and beneficial haplotypes. The CAPS markers, S15_50486939-CAPS1 and S15_50452626-CAPS2, can effectively distinguish resistant and sensitive genotypes through enzyme digestion. The KASP marker is based on S07_19078765-G/T and exhibits a genotype clustering pattern consistent with disease resistance, demonstrating its application value in breeding. The CAPS and KASP markers developed in this study can provide reliable tools for MAS in FORR disease-resistant varieties. The research results will help reveal the genetic structure of FORR disease resistance and provide support for efficient breeding.

Mechanism of a novel Bacillus subtilis JNF2 in suppressing Fusarium oxysporum f. sp. cucumerium and enhancing cucumber growth

Cucumber Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerium (FOC), is a prevalent soil-borne disease. In this study, Bacillus subtilis JNF2, isolated from the high incidence area of cucumber Fusarium wilt in Luoyang, demonstrated significant inhibitory effects on FOC and promoted cucumber seedling growth. The biocontrol mechanism of strain JNF2 were elucidated through morphological observation, physiological and biochemical experiments, and whole genome sequence analysis. Pot experiments revealed an 81.33 ± 0.21% control efficacy against Fusarium wilt, surpassing the 64.10 ± 0.06% efficacy of hymexazol. Seedlings inoculated with JNF2 exhibited enhanced stem thickness and leaf area compared to control and hymexazol-treated plants. Physiological tests confirmed JNF2's production of indole-3-acetic acid (IAA), siderophores, and hydrolytic enzymes, such as β-1,3-glucanase, amylase, and protease, which inhibited FOC growth and promoted plant development. Genome analysis identified genes encoding antimicrobial peptides and hydrolases, as well as a novel glycocin synthetic gene cluster. These findings underscore B. subtilis JNF2's potential as a biocontrol agent for sustainable cucumber cultivation.

Identification of hub genes and potential networks by centrality network analysis of PCR amplified Fusarium oxysporum f. sp. lycopersici EF1α gene

BACKGROUND

Fusarium wilt is a devastating soil-borne fungal disease of tomato across the world. Conventional method of disease prevention including usage of common pesticides and methods like soil solarisation are usually ineffective in the treatment of this disease. Therefore, there is an urgent need to identify virulence related genes in the pathogen which can be targeted for fungicide development.

RESULTS

Pathogenicity testing and phylogenetic classification of the pathogen used in this study confirmed it as Fusarium oxysporum f. sp. lycopersici (Fol) strain. A recent discovery indicates that EF1α, a protein with conserved structural similarity across several fungal genera, has a role in the pathogenicity of Magnaporthe oryzae, the rice blast fungus. Therefore, in this study we have done structural and functional classification of EF1α to understand its role in pathogenicity of Fol. The protein model of Fol EF1α was created using the template crystal structure of the yeast elongation factor complex EEF1A:EEF1BA which showed maximum similarity with the target protein. Using the STRING online database, the interactive information among the hub genes of EF1α was identified and the protein-protein interaction network was recognized using the Cytoscape software. On combining the results of functional analysis, MCODE, CytoNCA and CytoHubba 4 hub genes including Fol EF1α were selected for further investigation. The three interactors of Fol EF1α showed maximum similarity with homologous proteins found in Neurospora crassa complexed with the known fungicide, cycloheximide. Through the sequence similarity and PDB database analysis, homologs of Fol EF1α were found: EEF1A:EEF1BA in complex with GDPNP in yeast and EF1α in complex with GDP in Sulfolobus solfataricus. The STITCH database analysis suggested that EF1α and its other interacting partners interact with guanosine diphosphate (GDPNP) and guanosine triphosphate (GTP).

CONCLUSIONS

Our study offers a framework for recognition of several hub genes network in Fusarium wilt that can be used as novel targets for fungicide development. The involvement of EF1α in nucleocytoplasmic transport pathway suggests that it plays role in GTP binding and thus apart from its use as a biomarker, it may be further exploited as an effective target for fungicide development. Since, the three other proteins that were found to be tightly associated Fol EF1α have shown maximum similarity with homologous proteins of Neurospora crassa that form complex with fungicide- Cycloheximide. Therefore, we suggest that cycloheximide can also be used against Fusarium wilt disease in tomato. The active site cavity of Fol EF1α can also be determined for computational screening of fungicides using the homologous proteins observed in yeast and Sulfolobus solfataricus. On this basis, we also suggest that the other closely associated genes that have been identified through STITCH analysis, they can also be targeted for fungicide development.

Oxaloacetate anaplerosis differently contributes to pathogenicity in plant pathogenic fungi Fusarium graminearum and F. oxysporum

Anaplerosis refers to enzymatic reactions or pathways replenishing metabolic intermediates in the tricarboxylic acid (TCA) cycle. Pyruvate carboxylase (PYC) plays an important anaplerotic role by catalyzing pyruvate carboxylation, forming oxaloacetate. Although PYC orthologs are well conserved in prokaryotes and eukaryotes, their pathobiological functions in filamentous pathogenic fungi have yet to be fully understood. Here, we delve into the molecular functions of the ortholog gene PYC1 in Fusarium graminearum and F. oxysporum, prominent fungal plant pathogens with distinct pathosystems, demonstrating variations in carbon metabolism for pathogenesis. Surprisingly, the PYC1 deletion mutant of F. oxysporum exhibited pleiotropic defects in hyphal growth, conidiation, and virulence, unlike F. graminearum, where PYC1 deletion did not significantly impact virulence. To further explore the species-specific effects of PYC1 deletion on pathogenicity, we conducted comprehensive metabolic profiling. Despite shared metabolic changes, distinct reprogramming in central carbon and nitrogen metabolism was identified. Specifically, alpha-ketoglutarate, a key link between the TCA cycle and amino acid metabolism, showed significant down-regulation exclusively in the PYC1 deletion mutant of F. oxysporum. The metabolic response associated with pathogenicity was notably characterized by S-methyl-5-thioadenosine and S-adenosyl-L-methionine. This research sheds light on how PYC1-mediated anaplerosis affects fungal metabolism and reveals species-specific variations, exemplified in F. graminearum and F. oxysporum.

The Ser/Thr protein kinase FonKin4-poly(ADP-ribose) polymerase FonPARP1 phosphorylation cascade is required for the pathogenicity of watermelon fusarium wilt fungus Fusarium oxysporum f. sp. niveum

Poly(ADP-ribosyl)ation (PARylation), catalyzed by poly(ADP-ribose) polymerases (PARPs) and hydrolyzed by poly(ADP-ribose) glycohydrolase (PARG), is a kind of post-translational protein modification that is involved in various cellular processes in fungi, plants, and mammals. However, the function of PARPs in plant pathogenic fungi remains unknown. The present study investigated the roles and mechanisms of FonPARP1 in watermelon Fusarium wilt fungus Fusarium oxysporum f. sp. niveum (Fon). Fon has a single PARP FonPARP1 and one PARG FonPARG1. FonPARP1 is an active PARP and contributes to Fon pathogenicity through regulating its invasive growth within watermelon plants, while FonPARG1 is not required for Fon pathogenicity. A serine/threonine protein kinase, FonKin4, was identified as a FonPARP1-interacting partner by LC-MS/MS. FonKin4 is required for vegetative growth, conidiation, macroconidia morphology, abiotic stress response and pathogenicity of Fon. The S_TKc domain is sufficient for both enzyme activity and pathogenicity function of FonKin4 in Fon. FonKin4 phosphorylates FonPARP1 in vitro to enhance its poly(ADP-ribose) polymerase activity; however, FonPARP1 does not PARylate FonKin4. These results establish the FonKin4-FonPARP1 phosphorylation cascade that positively contributes to Fon pathogenicity. The present study highlights the importance of PARP-catalyzed protein PARylation in regulating the pathogenicity of Fon and other plant pathogenic fungi.

Characterization of the Fusarium circinatum biofilm environmental response role

The capacity to form biofilms is a common trait among many microorganisms present on Earth. In this study, we demonstrate for the first time that the fatal pine pitch canker agent, Fusarium circinatum, can lead a biofilm-like lifestyle with aggregated hyphal bundles wrapped in extracellular matrix (ECM). Our research shows F. circinatum's ability to adapt to environmental changes by assuming a biofilm-like lifestyle. This was demonstrated by varying metabolic activities exhibited by the biofilms in response to factors like temperature and pH. Further analysis revealed that while planktonic cells produced small amounts of ECM per unit of the biomass, heat- and azole-exposed biofilms produced significantly more ECM than nonexposed biofilms, further demonstrating the adaptability of F. circinatum to changing environments. The increased synthesis of ECM triggered by these abiotic factors highlights the link between ECM production in biofilm and resistance to abiotic stress. This suggests that ECM-mediated response may be one of the key survival strategies of F. circinatum biofilms in response to changing environments. Interestingly, azole exposure also led to biofilms that were resistant to DNase, which typically uncouples biofilms by penetrating the biofilm and degrading its extracellular DNA; we propose that DNases were likely hindered from reaching target cells by the ECM barricade. The interplay between antifungal treatment and DNase enzyme suggests a complex relationship between eDNA, ECM, and antifungal agents in F. circinatum biofilms. Therefore, our results show how a phytopathogen's sessile (biofilm) lifestyle could influence its response to the surrounding environment.

The SUMOylation pathway regulates the pathogenicity of Fusarium oxysporum f. sp. niveum in watermelon through stabilizing the pH regulator FonPalC via SUMOylation

SUMOylation is a key post-translational modification, where small ubiquitin-related modifier (SUMO) proteins regulate crucial biological processes, including pathogenesis, in phytopathogenic fungi. Here, we investigated the function and mechanism of the SUMOylation pathway in the pathogenicity of Fusarium oxysporum f. sp. niveum (Fon), the fungal pathogen that causes watermelon Fusarium wilt. Disruption of key SUMOylation pathway genes, FonSMT3, FonAOS1, FonUBC9, and FonMMS21, significantly reduced pathogenicity, impaired penetration ability, and attenuated invasive growth capacity of Fon. Transcription and proteomic analyses identified a diverse set of SUMOylation-regulated differentially expressed genes and putative FonSMT3-targeted proteins, which are predicted to be involved in infection, DNA damage repair, programmed cell death, reproduction, growth, and development. Among 155 putative FonSMT3-targeted proteins, FonPalC, a Pal/Rim-pH signaling regulator, was confirmed to be SUMOylated. The FonPalC protein accumulation was significantly decreased in SUMOylation-deficient mutant ∆Fonsmt3. Deletion of FonPalC resulted in impaired mycelial growth, decreased pathogenicity, enhanced osmosensitivity, and increased intracellular vacuolation in Fon. Importantly, mutations in conserved SUMOylation sites of FonPalC failed to restore the defects in ∆Fonpalc mutant, indicating the critical function of the SUMOylation in FonPalC stability and Fon pathogenicity. Identifying key SUMOylation-regulated pathogenicity-related proteins provides novel insights into the molecular mechanisms underlying Fon pathogenesis regulated by SUMOylation.

Corrigendum: Active substances of myxobacteria against plant diseases and their action mechanisms

[This corrects the article DOI: 10.3389/fmicb.2023.1294854.].

Sir2-mediated cytoplasmic deacetylation facilitates pathogenic fungi infection in host plants

Lysine acetylation is an evolutionarily conserved and widespread post-translational modification implicated in the regulation of multiple metabolic processes, but its function remains largely unknown in plant pathogenic fungi. A comprehensive analysis combined with proteomic, molecular and cellular approaches was presented to explore the roles of cytoplasmic acetylation in Fusarium oxsysporum f.sp. lycopersici (Fol). The divergent cytoplasmic deacetylase FolSir2 was biochemically characterized, which is contributing to fungal virulence. Based on this, a total of 1752 acetylated sites in 897 proteins were identified in Fol via LC-MS/MS analysis. Further analyses of the quantitative acetylome revealed that 115 proteins representing two major pathways, translational and ribosome biogenesis, were hyperacetylated in the ∆Folsir2 strain. We experimentally examined the regulatory roles of FolSir2 on K271 deacetylation of FolGsk3, a serine/tyrosine kinase implicated in a variety of cellular functions, which was found to be crucial for the activation of FolGsk3 and thus modulated Fol pathogenicity. Cytoplasmic deacetylation by FolSir2 homologues has a similar function in Botrytis cinerea and likely other fungal pathogens. These findings reveal a conserved mechanism of silent information regulator 2-mediated cytoplasmic deacetylation that is involved in plant-fungal pathogenicity, providing a candidate target for designing broad-spectrum fungicides to control plant diseases.

Efficacy of rhizobacteria Paenibacillus polymyxa SY42 for the biological control of Atractylodes chinensis root rot

Atractylodes chinensis is one of the most commonly used bulk herbs in East Asia; however, root rot can seriously affect its quality and yields. In contrast to chemical pesticides, biological control strategies are environmentally compatible and safe. For this study, 68 antagonistic bacterial strains were isolated from the rhizospheres of healthy Atractylodes chinensis. Strain SY42 exhibited the most potent fungicidal activities, with inhibition rates against F. oxysporum, F. solani, and F. redolens of 67.07 %, 63.40 % and 68.45 %, respectively. Through morphological observation and molecular characterization, strain SY42 was identified as Paenibacillus polymyxa. The volatile organic components (VOCs) produced by SY42 effectively inhibited the mycelial growth of pathogenic fungi through diffusion. SY42 significantly inhibited the germination of pathogenic fungal spores. Following co-culturing with SY42, the mycelium of the pathogenic fungus was deformed, folded, and even ruptured. SY42 could produce cellulases and proteases to degrade fungal cell walls. Pot experiments demonstrated the excellent biocontrol efficacy of SY42. This study revealed that P. polymyxa SY42 inhibited pathogenic fungi through multiple mechanisms, which verified its utility as a biocontrol agent for the control of A. chinensis root rot.

The melon Fom-1-Prv resistance gene pair: Correlated spatial expression and interaction with a viral protein

The head-to-head oriented pair of melon resistance genes, Fom-1 and Prv, control resistance to Fusarium oxysporum races 0 and 2 and papaya ringspot virus (PRSV), respectively. They encode, via several RNA splice variants, TIR-NBS-LRR proteins, and Prv has a C-terminal extra domain with a second NBS homologous sequence. In other systems, paired R-proteins were shown to operate by "labor division," with one protein having an extra integrated domain that directly binds the pathogen's Avr factor, and the second protein executing the defense response. We report that the expression of the two genes in two pairs of near-isogenic lines was higher in the resistant isoline and inducible by F. oxysporum race 2 but not by PRSV. The intergenic DNA region separating the coding sequences of the two genes acted as a bi-directional promoter and drove GUS expression in transgenic melon roots and transgenic tobacco plants. Expression of both genes was strong in melon root tips, around the root vascular cylinder, and the phloem and xylem parenchyma of tobacco stems and petioles. The pattern of GUS expression suggests coordinated expression of the two genes. In agreement with the above model, Prv's extra domain was shown to interact with the cylindrical inclusion protein of PRSV both in yeast cells and in planta.

Active substances of myxobacteria against plant diseases and their action mechanisms

Myxobacteria have a complex life cycle and unique social behavior, and obtain nutrients by preying on bacteria and fungi in soil. Chitinase, β-1,3 glucanase and β-1,6 glucanase produced by myxobacteria can degrade the glycosidic bond of cell wall of some plant pathogenic fungi, resulting in a perforated structure in the cell wall. In addition, isooctanol produced by myxobacteria can lead to the accumulation of intracellular reactive oxygen species in some pathogenic fungi and induce cell apoptosis. Myxobacteria can also perforate the cell wall of some plant pathogenic oomycetes by β-1,3 glucanase, reduce the content of intracellular soluble protein and protective enzyme activity, affect the permeability of oomycete cell membrane, and aggravate the oxidative damage of pathogen cells. Small molecule compounds such as diisobutyl phthalate and myxovirescin produced by myxobacteria can inhibit the formation of biofilm and lipoprotein of bacteria, and cystobactamids can inhibit the activity of DNA gyrase, thus changing the permeability of bacterial cell membrane. Myxobacteria, as a new natural compound resource bank, can control plant pathogenic fungi, oomycetes and bacteria by producing carbohydrate active enzymes and small molecular compounds, so it has great potential in plant disease control.

Controlling Tomato Fusarium Wilt Disease through Bacillus thuringiensis-Mediated Defense Primining

Background

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. lycopersici (Fol) (Sacc.) W.C. Snyder and H.N. Hans is one of the most prevalent and devastating diseases of tomato plants (Solanum lycoprsicum L.) that leads to a severe reduction in crop yield almost worldwide.

Objective

Evaluation of biocontrol potential of Bacillus thuringiensis (Bt) isolate IBRC-M11096, against Fol in tomato through primin.

Materials and Methods

qRT-PCR technique was applied to analyze the effect of the strain on the hormonal defensive pathways; transcriptional responses of jasmonic acid (COI1, Pin2) and salicylic acid (NRP1 and PR1) pathway genes in Bt-treated plants following inoculation of Fol as compared to the plants only challenged with Fol. Also, the potential of the bacterial strain as a biocontrol agent was studied by evaluating growth indices and area under disease progress curve (AUDPC).

Results

The transcription of both defensive hormonal pathway genes (COI1, Pin2, NPR1, PR1) increased due to bacterial priming. The bacterial priming reduced the AUDPC compared to the inoculation with only Fol. The strain reduced the disease symptoms, and compared to the plants only challenged with the fungus, the bacterial strain significantly raised shoot dry and fresh weights and root dry weight.

Conclusion

Priming with the Bt strain led to improved shoot and root growth indices, reduced AUDPC, and fortified responses of both JA and SA hormonal pathways. However, further full-span studies are required to judge the efficacy of the bacterial strain in the biological control of tomato fusarium wilt under field conditions.

Combined analysis of microRNA and mRNA profiles provides insights into the pathogenic resistant mechanisms of the lotus rhizome rot

Lotus rhizome rot caused by Fusarium oxysporum is a common vascular fungal disease in plants that significantly impacts the yield. However, only a few studies have studied the mechanism of Nelumbo nucifera responding to lotus rhizome rot. Here, we investigated the pathogenic genes and miRNAs in lotus rhizome rot to uncover the pathogenic resistant mechanisms by transcriptome and small RNA sequencing of lotus roots after inoculation with Fusarium oxysporum. GO and KEGG functional enrichment analysis showed that differential miRNAs were mostly enriched in starch and sucrose metabolism, biosynthesis of secondary metabolites, glutathione metabolism, brassinosteroid biosynthesis and flavonoid biosynthesis pathways. Twenty-seven upregulated miRNAs, 19 downregulated miRNAs and their target genes were identified. Correlation analysis found that miRNAs negatively regulate target genes, which were also enriched in starch and sucrose metabolism and glutathione metabolism pathways. Their expression was measured by reverse transcription quantitative PCR (qRT-PCR), and the results were consistent with the transcriptome analysis, thus verifying the reliability of transcriptome data. We selected three miRNAs (miRNA858-y, miRNA171-z and a novel miRNA novel-m0005-5p) to test the relationship between miRNAs and their target genes. The activity of the GUS testing assay indicated that miRNA could decrease the GUS activity by inhibiting the expression of their target genes. Collectively, this study provides a comprehensive analysis of transcriptome and small RNA sequencing of lotus root after inoculation with Fusarium oxysporum, and we identified candidate miRNAs and their target genes for breeding strategies of Nelumbo nucifera.

Degradation of α-Subunits, Doa1 and Doa4, are Critical for Growth, Development, Programmed Cell Death Events, Stress Responses, and Pathogenicity in the Watermelon Fusarium Wilt Fungus Fusarium oxysporum f. sp. niveum

The ubiquitin-proteasome system (UPS) regulates protein quality or control and plays essential roles in several biological and biochemical processes in fungi. Here, we present the characterization of two UPS components, FonDoa1 and FonDoa4, in watermelon Fusarium wilt fungus, Fusarium oxysporum f. sp. niveum (Fon), and their biological functions. FonDoa1 localizes in both the nucleus and cytoplasm, while FonDoa4 is predominantly present in the cytoplasm. Both genes show higher expression in germinating macroconidia at 12 h. Deletion of FonDoa1 or FonDoa4 affects vegetative growth, conidiation, conidial germination/morphology, apoptosis, and responses to environmental stressors. FonDoa1, but not FonDoa4, positively regulates autophagy. The targeted disruption mutants exhibit significantly attenuated pathogenicity on watermelon due to defects in the infection process and invasive fungal growth. Further results indicate that the WD40, PFU, and PUL domains are essential for the function of FonDoa1 in Fon pathogenicity and environmental stress responses. These findings demonstrate the previously uncharacterized biological functions of FonDoa1 and FonDoa4 in phytopathogenic fungi, providing potential targets for developing strategies to control watermelon Fusarium wilt.

Genetic diversity of the breeding collection of tomato varieties in Kazakhstan assessed using SSR, SCAR and CAPS markers

Tomato is one of the most prominent crops in global horticulture and an important vegetable crop in Kazakhstan. The lack of data on the genetic background of local varieties limits the development of tomato breeding in the country. This study aimed to perform an initial evaluation of the breeding collection of tomato varieties from the point of view of their genetic structure and pathogen resistance using a set of PCR based molecular markers, including 13 SSR markers for genetic structure analysis, and 14 SCAR and CAPS markers associated with resistance to five pathogens: three viruses, fungus Fusarium oxysporum, and oomycete P hytophthora infestans. Nine SSR markers were with a PIC value varying from 0.0562 (low information content) to 0.629 (high information content). A weak genetic structure was revealed in the samples of varieties including local cultivars and, predominantly, varieties from Russia and other ex-USSR countries. The local varieties were closely related to several groups of cultivars of Russian origin. Screening for a set of resistance markers revealed the common occurrence of the resistance locus I against Fusarium oxysporum and only the occasional presence of resistance alleles of other markers. No markers of resistance to the three considered viruses were revealed in local tomato varieties. Only two local cultivars had markers of resistance to P. infestans, and only the 'Meruert' cultivar had a combination of resistance markers against P. infestans and F. oxysporum. The obtained results have demonstrated the need for further studies of local tomato varieties with a wider range of molecular markers and source germplasm to lay a foundation for the development of tomato breeding in Kazakhstan.

Artificial trans-kingdom RNAi of FolRDR1 is a potential strategy to control tomato wilt disease

Tomato is cultivated worldwide as a nutrient-rich vegetable crop. Tomato wilt disease caused by Fusarium oxysporum f.sp. Lycopersici (Fol) is one of the most serious fungal diseases posing threats to tomato production. Recently, the development of Spray-Induced Gene Silencing (SIGS) directs a novel plant disease management by generating an efficient and environmental friendly biocontrol agent. Here, we characterized that FolRDR1 (RNA-dependent RNA polymerase 1) mediated the pathogen invasion to the host plant tomato, and played as an essential regulator in pathogen development and pathogenicity. Our fluorescence tracing data further presented that effective uptakes of FolRDR1-dsRNAs were observed in both Fol and tomato tissues. Subsequently, exogenous application of FolRDR1-dsRNAs on pre-Fol-infected tomato leaves resulted in significant alleviation of tomato wilt disease symptoms. Particularly, FolRDR1-RNAi was highly specific without sequence off-target in related plants. Our results of pathogen gene-targeting RNAi have provided a new strategy for tomato wilt disease management by developing an environmentally-friendly biocontrol agent.

FonTup1 functions in growth, conidiogenesis and pathogenicity of Fusarium oxysporum f. sp. niveum through modulating the expression of the tricarboxylic acid cycle genes

The Tup1-Cyc8 complex is a highly conserved transcriptional corepressor that regulates intricate genetic network associated with various biological processes in fungi. Here, we report the role and mechanism of FonTup1 in regulating physiological processes and pathogenicity in watermelon Fusarium wilt fungus, Fusarium oxysporum f. sp. niveum (Fon). FonTup1 deletion impairs mycelial growth, asexual reproduction, and macroconidia morphology, but not macroconidial germination in Fon. The ΔFontup1 mutant exhibits altered tolerance to cell wall perturbing agent (congo red) and osmotic stressors (sorbitol or NaCl), but unchanged sensitivity to paraquat. The deletion of FonTup1 significantly decreases the pathogenicity of Fon toward watermelon plants through attenuating the ability to colonize and grow within the host. Transcriptome analysis revealed that FonTup1 regulates primary metabolic pathways, including the tricarboxylic acid (TCA) cycle, via altering the expression of corresponding genes. Downregulation of three malate dehydrogenase genes, FonMDH1-3, occurs in ΔFontup1, and disruption of FonMDH2 causes significant abnormalities in mycelial growth, conidiation, and virulence of Fon. These findings demonstrate that FonTup1, as a global transcriptional corepressor, plays crucial roles in different biological processes and pathogenicity of Fon through regulating various primary metabolic processes, including the TCA cycle. This study highlights the importance and molecular mechanism of the Tup1-Cyc8 complex in multiple basic biological processes and pathogenicity of phytopathogenic fungi.

Monitoring for a new I3 resistance gene-breaking race of F. oxysporum f. sp. lycopersici (Fusarium wilt) in California processing tomatoes following recent widespread adoption of resistant (F3) cultivars: Challenges with race 3 and 4 differentiation methods

Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (Fol), causes losses in tomato production worldwide, with major impacts on Californian tomato processing. Single-gene resistance is the primary management tool, but its efficacy has been compromised following the emergence of two successive resistance-breaking races, which, in California, emerged within 12 years of resistance deployment. Fol race 3-resistant (F3) processing tomato cultivars (containing the I3 resistance gene) were deployed in the state starting in approximately 2009. The emergence of a new resistance-breaking race (which would be called race 4) is imminent, and early detection will be critical to delay the spread while new resistance is sought. The detection of Fol race 4 is challenged by the lack of validated, rapid, and accurate diagnostic tools. In evaluating in planta phenotyping methods, this study found that rapid seedling phenotyping is not reliable and generates false positives for nonpathogens. Longer (10 weeks) mature plant assays are the most reliable, but may not be sufficiently timely. As an additional challenge, based on field and greenhouse studies, Fol race 3 can cause symptoms in resistant F3 cultivars at frequencies greater (30%) than expected for off-types (<2%). We developed a three-F3 cultivar in planta assay to overcome the challenges this posed to differentiating Fol race 3 and Fol race 4. Using the assay, we determined that all putative resistance-breaking cases were Fol race 3; Fol race 4 was not detected in these early survey efforts. These results highlight the need for developing rapid Fol race 4 detection tools and a better understanding of the factors underlying inconsistent I3 gene expression in Fol race 3.

Fusarium oxysporum f. sp. niveum Pumilio 1 Regulates Virulence on Watermelon through Interacting with the ARP2/3 Complex and Binding to an A-Rich Motif in the 3' UTR of Diverse Transcripts

Fusarium oxysporum f. sp. niveum (Fon), a soilborne phytopathogenic fungus, causes watermelon Fusarium wilt, resulting in serious yield losses worldwide. However, the underlying molecular mechanism of Fon virulence is largely unknown. The present study investigated the biological functions of six FonPUFs, encoding RNA binding Pumilio proteins, and especially explored the molecular mechanism of FonPUF1 in Fon virulence. A series of phenotypic analyses indicated that FonPUFs have distinct but diverse functions in vegetative growth, asexual reproduction, macroconidia morphology, spore germination, cell wall, or abiotic stress response of Fon. Notably, the deletion of FonPUF1 attenuates Fon virulence by impairing the invasive growth and colonization ability inside the watermelon plants. FonPUF1 possesses RNA binding activity, and its biochemical activity and virulence function depend on the RNA recognition motif or Pumilio domains. FonPUF1 associates with the actin-related protein 2/3 (ARP2/3) complex by interacting with FonARC18, which is also required for Fon virulence and plays an important role in regulating mitochondrial functions, such as ATP generation and reactive oxygen species production. Transcriptomic profiling of ΔFonPUF1 identified a set of putative FonPUF1-dependent virulence-related genes in Fon, possessing a novel A-rich binding motif in the 3' untranslated region (UTR), indicating that FonPUF1 participates in additional mechanisms critical for Fon virulence. These findings highlight the functions and molecular mechanism of FonPUFs in Fon virulence. IMPORTANCE Fusarium oxysporum is a devastating plant-pathogenic fungus that causes vascular wilt disease in many economically important crops, including watermelon, worldwide. F. oxysporum f. sp. nievum (Fon) causes serious yield loss in watermelon production. However, the molecular mechanism of Fusarium wilt development by Fon remains largely unknown. Here, we demonstrate that six putative Pumilio proteins-encoding genes (FonPUFs) differentially operate diverse basic biological processes, including stress response, and that FonPUF1 is required for Fon virulence. Notably, FonPUF1 possesses RNA binding activity and associates with the actin-related protein 2/3 complex to control mitochondrial functions. Furthermore, FonPUF1 coordinates the expression of a set of putative virulence-related genes in Fon by binding to a novel A-rich motif present in the 3' UTR of a diverse set of target mRNAs. Our study disentangles the previously unexplored molecular mechanism involved in regulating Fon virulence, providing a possibility for the development of novel strategies for disease management.

Palmitoyl Transferase FonPAT2-Catalyzed Palmitoylation of the FonAP-2 Complex Is Essential for Growth, Development, Stress Response, and Virulence in Fusarium oxysporum f. sp. niveum

Protein palmitoylation, one of posttranslational modifications, is catalyzed by a group of palmitoyl transferases (PATs) and plays critical roles in the regulation of protein functions. However, little is known about the function and mechanism of PATs in plant pathogenic fungi. The present study reports the function and molecular mechanism of FonPATs in Fusarium oxysporum f. sp. niveum (Fon), the causal agent of watermelon Fusarium wilt. The Fon genome contains six FonPAT genes with distinct functions in vegetative growth, conidiation and conidial morphology, and stress response. FonPAT1, FonPAT2, and FonPAT4 have PAT activity and are required for Fon virulence on watermelon mainly through regulating in planta fungal growth within host plants. Comparative proteomics analysis identified a set of proteins that were palmitoylated by FonPAT2, and some of them are previously reported pathogenicity-related proteins in fungi. The FonAP-2 complex core subunits FonAP-2α, FonAP-2β, and FonAP-2μ were palmitoylated by FonPAT2 in vivo. FonPAT2-catalyzed palmitoylation contributed to the stability and interaction ability of the core subunits to ensure the formation of the FonAP-2 complex, which is essential for vegetative growth, asexual reproduction, cell wall integrity, and virulence in Fon. These findings demonstrate that FonPAT1, FonPAT2, and FonPAT4 play important roles in Fon virulence and that FonPAT2-catalyzed palmitoylation of the FonAP-2 complex is critical to Fon virulence, providing novel insights into the importance of protein palmitoylation in the virulence of plant fungal pathogens. IMPORTANCE Fusarium oxysporum f. sp. niveum (Fon), the causal agent of watermelon Fusarium wilt, is one of the most serious threats for the sustainable development of the watermelon industry worldwide. However, little is known about the underlying molecular mechanism of pathogenicity in Fon. Here, we found that the palmitoyl transferase (FonPAT) genes play distinct and diverse roles in basic biological processes and stress response and demonstrated that FonPAT1, FonPAT2, and FonPAT4 have PAT activity and are required for virulence in Fon. We also found that FonPAT2 palmitoylates the core subunits of the FonAP-2 complex to maintain the stability and the formation of the FonAP-2 complex, which is essential for basic biological processes, stress response, and virulence in Fon. Our study provides new insights into the understanding of the molecular mechanism involved in Fon virulence and will be helpful in the development of novel strategies for disease management.

Molecular Analysis of MgO Nanoparticle-Induced Immunity against Fusarium Wilt in Tomato

Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (FOL), is a devastating soilborne disease in tomatoes. Magnesium oxide nanoparticles (MgO NPs) induce strong immunity against Fusarium wilt in tomatoes. However, the mechanisms underlying this immunity remain poorly understood. Comparative transcriptome analysis and microscopy of tomato roots were performed to determine the mechanism of MgO NP-induced immunity against FOL. Eight transcriptomes were prepared from tomato roots treated under eight different conditions. Differentially expressed genes were compared among the transcriptomes. The Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that in tomato roots pretreated with MgO NPs, Rcr3 encoding apoplastic protease and RbohD encoding NADPH oxidase were upregulated when challenge-inoculated with FOL. The gene encoding glycine-rich protein 4 (SlGRP4) was chosen for further analysis. SlGRP4 was rapidly transcribed in roots pretreated with MgO NPs and inoculated with FOL. Immunomicroscopy analysis showed that SlGRP4 accumulated in the cell walls of epidermal and vascular vessel cells of roots pretreated with MgO NPs, but upon FOL inoculation, SlGRP4 further accumulated in the cell walls of cortical tissues within 48 h. The results provide new insights into the probable mechanisms of MgO NP-induced tomato immunity against Fusarium wilt.

Myxobacterial Outer Membrane β-1,6-Glucanase Induced the Cell Death of Fusarium oxysporum by Destroying the Cell Wall Integrity

The β-1,6-glucan is the key linker between mannoproteins in the outermost part of the cell wall and β-1,3-glucan/chitin polysaccharide to maintain the rigid structure of the cell wall. The β-1,6-glucanase GluM, which was purified from the fermentation supernatant of Corallococcus sp. EGB, was able to inhibit the germination of Fusarium oxysporum f. sp. cucumerinum conidia at a minimum concentration of 2.0 U/mL (0.08 μg/mL). The survival rates of GluM-treated conidia and monohyphae were 10.4% and 30.7%, respectively, which were significantly lower than that of β-1,3-glucanase treatment (Zymolyase, 20.0 U/mL; equate to 1.0 mg/mL) (72.9% and 73.9%). In contrast to β-1,3-glucanase treatment, the high-osmolarity glycerol (HOG) pathway of F. oxysporum f. sp. cucumerinum cells was activated after GluM treatment, and the intracellular glycerol content was increased by 2.6-fold. Moreover, the accumulation of reactive oxygen species (ROS) in F. oxysporum f. sp. cucumerinum cells after GluM treatment induced apoptosis, but it was not associated with the increased intracellular glycerol content. Together, the results indicate that β-1,6-glucan is a promising target for the development of novel broad-spectrum antifungal agents. IMPORTANCE Phytopathogenic fungi are the most devastating plant pathogens in agriculture, causing enormous economic losses to global crop production. Biocontrol agents have been promoted as replacements to synthetic chemical pesticides for sustainable agriculture development. Cell wall-degrading enzymes (CWDEs), including chitinases and β-1,3-glucanases, have been considered as important armaments to damage the cell wall. Here, we found that F. oxysporum f. sp. cucumerinum is more sensitive to β-1,6-glucanase GluM treatment (0.08 μg/mL) than β-1,3-glucanase Zymolyase (1.0 mg/mL). The HOG pathway was activated in F. oxysporum f. sp. cucumerinum cells after GluM treatment, and the intracellular glycerol content was significantly increased. Moreover, the decomposition of F. oxysporum f. sp. cucumerinum cell wall by GluM induced the burst of intracellular ROS and apoptosis, which eventually leads to cell death. Therefore, we suggest that the β-1,6-glucan of the fungal cell wall may be a better antifungal target compared to the β-1,3-glucan.

Bacillus cereus EC9 protects tomato against Fusarium wilt through JA/ET-activated immunity

The mechanisms of action and the limitations of effectiveness of natural biocontrol agents should be determined in order to convert them into end products that can be used in practice. Rhizosphere Bacillus spp. protect plants from various pathogens by displaying several modes of action. However, the ability of Bacillus spp. to control plant diseases depends on the interaction between the bacteria, host, and pathogen, and the environmental conditions. We found that soil drenching of tomato plants with the non-antifungal Bacillus cereus strain EC9 (EC9) enhances plant defense against Fusarium oxysporum f. sp. lycopersici (Fol). To study the involvement of plant defense-related phytohormones in the regulation of EC9-activated protection against Fol, we conducted plant bioassays in tomato genotypes impaired in salicylic acid (SA) accumulation, jasmonic acid (JA) biosynthesis, and ethylene (ET) production, and analyzed the transcript levels of pathways-related marker genes. Our results indicate that JA/ET-dependent signaling is required for EC9-mediated protection against Fol in tomato. We provide evidence that EC9 primes tomato plants for enhanced expression of proteinase inhibitor I (PI-I) and ethylene receptor4 (ETR4). Moreover, we demonstrated that EC9 induces callose deposition in tomato roots. Understanding the involvement of defense-related phytohormones in EC9-mediated defense against Fusarium wilt has increased our knowledge of interactions between non-antifungal plant defense-inducing rhizobacteria and plants.

Bacillus subtilis strain F62 against Fusarium oxysporum and promoting plant growth in the grapevine rootstock SO4

Fusarium wilt is a fungal disease that causes economic losses to viticulture, whose causal agent Fusarium sp. has been associated with the decline and death of young vines. This work had the objective of evaluating the antagonistic potential of Bacillus subtilis F62 against F. oxysporum in vitro and in vivo, as well as the growth promotion in the grapevine rootstock SO4. In the in vitro assay, the antagonism by diffusible and volatile compounds of B. subtilis F62 and the inhibition of conidial germination of four Fusarium sp. isolates were evaluated. In the in vivo assay, cuttings and micropropagated plants of SO4 were submitted to four treatments: control, Bac (B. subtilis F62 inoculation), Fus (F. oxysporum inoculation) and Bac + Fus. We observed that inhibition of mycelial growth occurred mainly by diffusible compounds. B. subtilis F62 had a positive effect on the growth promotion and in the biocontrol of F. oxysporum, reducing the frequency of pathogen re-isolation in cuttings (18.1%) and in micropropagated plants (52.4%). These results demonstrate the ability of B. subtilis F62 to upgrade plant development and assist in controlling of the Fusarium wilt in the grapevine rootstock SO4.

The Arabidopsis thaliana-Fusarium oxysporum strain 5176 pathosystem: an overview

Fusarium oxysporum is a soil-borne fungal pathogen of several major food crops. Research on understanding the molecular details of fungal infection and the plant's defense mechanisms against this pathogen has long focused mainly on the tomato-infecting F. oxysporum strains and their specific host plant. However, in recent years, the Arabidopsis thaliana-Fusarium oxysporum strain 5176 (Fo5176) pathosystem has additionally been established to study this plant-pathogen interaction with all the molecular biology, genetic, and genomic tools available for the A. thaliana model system. Work on this system has since produced several new insights, especially with regards to the role of phytohormones involved in the plant's defense response, and the receptor proteins and peptide ligands involved in pathogen detection. Furthermore, work with the pathogenic strain Fo5176 and the related endophytic strain Fo47 has demonstrated the suitability of this system for comparative studies of the plant's specific responses to general microbe- or pathogen-associated molecular patterns. In this review, we highlight the advantages of this specific pathosystem, summarize the advances made in studying the molecular details of this plant-fungus interaction, and point out open questions that remain to be answered.

Combined analysis of the transcriptome and proteome of Eucommia ulmoides Oliv. (Duzhong) in response to Fusarium oxysporum

Eucommia ulmoides Oliv. (Duzhong), a valued traditional herbal medicine in China, is rich in antibacterial proteins and is effective against a variety of plant pathogens. Fusarium oxysporum is a pathogenic fungus that infects plant roots, resulting in the death of the plant. In this study, transcriptomic and proteomic analyses were used to explore the molecular mechanism of E. ulmoides counteracts F. oxysporum infection. Transcriptomic analysis at 24, 48, 72, and 96 h after inoculation identified 17, 591, 1,205, and 625 differentially expressed genes (DEGs), while proteomics identified were 66, 138, 148, 234 differentially expressed proteins (DEPs). Meanwhile, GO and KEGG enrichment analyses of the DEGs and DEPs showed that they were mainly associated with endoplasmic reticulum (ER), fructose and mannose metabolism, protein processing in the ER, type II diabetes mellitus, the ribosome, antigen processing and presentation, and the phagosome. In addition, proteome and transcriptome association analysis and RT-qPCR showed that the response of E. ulmoides to F. oxysporum was likely related to the unfolded protein response (UPR) of the ER pathway. In conclusion, our study provided a theoretical basis for the control of F. oxysporum.

Pea Breeding for Resistance to Rhizospheric Pathogens

Pea (Pisum sativum L.) is a grain legume widely cultivated in temperate climates. It is important in the race for food security owing to its multipurpose low-input requirement and environmental promoting traits. Pea is key in nitrogen fixation, biodiversity preservation, and nutritional functions as food and feed. Unfortunately, like most crops, pea production is constrained by several pests and diseases, of which rhizosphere disease dwellers are the most critical due to their long-term persistence in the soil and difficulty to manage. Understanding the rhizosphere environment can improve host plant root microbial association to increase yield stability and facilitate improved crop performance through breeding. Thus, the use of various germplasm and genomic resources combined with scientific collaborative efforts has contributed to improving pea resistance/cultivation against rhizospheric diseases. This improvement has been achieved through robust phenotyping, genotyping, agronomic practices, and resistance breeding. Nonetheless, resistance to rhizospheric diseases is still limited, while biological and chemical-based control strategies are unrealistic and unfavourable to the environment, respectively. Hence, there is a need to consistently scout for host plant resistance to resolve these bottlenecks. Herein, in view of these challenges, we reflect on pea breeding for resistance to diseases caused by rhizospheric pathogens, including fusarium wilt, root rots, nematode complex, and parasitic broomrape. Here, we will attempt to appraise and harmonise historical and contemporary knowledge that contributes to pea resistance breeding for soilborne disease management and discuss the way forward.

Determining why continuous cropping reduces the production of the morel Morchella sextelata

Artificial cultivation of Morchella sextelata and other morels is expanding in China, but continuous cropping reduces Morchella for unknown reasons. Here, we investigated soil that had been used or not used for M. sextelata cultivation for 0, 1, and 2 years. We found that the continuous cropping of M. sextelata substantially reduced the pH and the nutrient content of the hyphosphere soil and increased sclerotia formation by M. sextelata. Changes in the structure of bacterial and fungal communities were associated with levels of available nitrogen (N) and phosphorus in the soil. With continuous cropping, the richness and diversity of fungal and bacterial communities increased, but the abundance of Bacillus and Lactobacillus decreased and the abundance of pathogenic fungi increased. FAPROTAX analysis indicated that N cycle functions were enriched more with than without continuous cultivation, and that enrichment of N cycle and sulfate respiration functions was higher in the second than in the first year of cultivation. FunGuild analysis indicated that the functions related to pathotrophs and wood saprotrophs were enriched by M. sextelata cultivation. Overall, the results suggest that continuous cropping may reduce M. sextelata production by acidifying the soil and increasing the abundance of pathogenic fungi. Additional research is needed to determine whether increases in the abundance of pathogenic fungi and changes in soil chemistry result in the declines in production that occur with continuous M. sextelata cultivation.

Generation of Fusarium oxysporum-suppressive soil with non-soil carriers using a multiple-parallel-mineralization technique

Disease-suppressive soils exist worldwide. However, the disease-suppression mechanism is unknown, and it’s unclear how to produce such soils. The microbiota that develop in a multiple-parallel-mineralization system (MPM) can increase nutrient production efficiency and decrease root disease in hydroponic systems. Artificial media inoculated with MPM microorganisms can degrade organic matter to produce inorganic nutrients similarly to natural soil, but it’s unknown whether they can also suppress pathogen growth. Here, we produced an artificial medium that inhibited root disease similarly to disease-suppressive soils. Microbial MPM culture solution was inoculated into non-soil carriers (rockwool, rice husk charcoal, and vermiculite) to test whether it could suppress growth of Fusarium oxysporum f. sp. lactucae J. C. Hubb. & Gerik. We inoculated F. oxysporum f. sp. conglutinans (Wollenweber) Snyder et Hansen strain Cong:11 and F. oxysporum f. sp. lactucae J. C. Hubb. & Gerik into artificial media sown each with Arabidopsis thaliana (L.) Heynh. and Lactuca sativa L. var. capitata supplemented with MPM culture microbes. The MPM microorganisms suppressed F. oxysporum f. sp. lactucae J. C. Hubb. & Gerik growth and prevented plant disease. Thus, MPM-inoculated non-soil carriers that can generate inorganic nutrients from organic matter may also suppress disease in the absence of natural soil. Our study shows novel creation of a disease-suppressive effect in non-soil media using the microbial community from MPM culture solution.

Impairment of the cellulose degradation machinery enhances Fusarium oxysporum virulence but limits its reproductive fitness

Fungal pathogens grow in the apoplastic space, in constant contact with the plant cell wall (CW) that hinders microbe progression while representing a source of nutrients. Although numerous fungal CW modifying proteins have been identified, their role during host colonization remains underexplored. Here, we show that the root-infecting plant pathogen Fusarium oxysporum (Fo) does not require its complete arsenal of cellulases to infect the host plant. Quite the opposite: Fo mutants impaired in cellulose degradation become hypervirulent by enhancing the secretion of virulence factors. On the other hand, the reduction in cellulase activity had a severe negative effect on saprophytic growth and microconidia production during the final stages of the Fo infection cycle. These findings enhance our understanding of the function of plant CW degradation on the outcome of host-microbe interactions and reveal an unexpected role of cellulose degradation in a pathogen's reproductive success.

Molecular and Biological Characterization of the First Mymonavirus Identified in Fusarium oxysporum

We characterized a negative sense single-stranded RNA mycovirus, Fusarium oxysporum mymonavirus 1 (FoMyV1), isolated from the phytopathogenic fungus Fusarium oxysporum. The genome of FoMyV1 is 10,114 nt, including five open reading frames (ORFs1–5) that are non-overlapping and linearly arranged. The largest, ORF5, encodes a large polypeptide L containing a conserved regions corresponding to Mononegavirales RNA-dependent RNA polymerase and mRNA-capping enzyme region V; the putative functions of the remaining four ORFs are unknown. The L protein encoded by ORF5 shared a high amino acid identity of 65% with that of Hubei rhabdo-like virus 4, a mymonavirus that associated with arthropods. However, the L protein of FoMyV1 also showed amino acid similarity (27–36%) with proteins of mynonaviruses that infect the phytopathogenic fungi Sclerotinia sclerotiorum and Botrytis cineaea. Phylogenetic analysis based on L protein showed that FoMyV1 is clustered with the members of the genus Hubramonavirus in the family Mymonaviridae. Moreover, we found that FoMyV1 could successfully transfer by hyphal anastomosis to a virus-free strain. FoMyV1 reduced the vegetative growth and conidium production of its fungal host but did not alter its virulence. To the best of our knowledge, this is not only the first mymonavirus described in the species F. oxysporum, but also the first Hubramonavirus species found to infect a fungus. However, the incidence of FoMyV1 infections in the tested F. oxysporum strains was only 1%.

Localisation of phosphoinositides in the grass endophyte Epichloë festucae and genetic and functional analysis of key components of their biosynthetic pathway in E. festucae symbiosis and Fusarium oxysporum pathogenesis

Phosphoinositides (PI) are essential components of eukaryotic membranes and function in a large number of signaling processes. While lipid second messengers are well studied in mammals and yeast, their role in filamentous fungi is poorly understood. We used fluorescent PI-binding molecular probes to localize the phosphorylated phosphatidylinositol species PI[3]P, PI[3,5]P₂, PI[4]P and PI[4,5]P₂ in hyphae of the endophyte Epichloë festucae in axenic culture and during interaction with its grass host Lolium perenne. We also analysed the roles of the phosphatidylinositol-4-phosphate 5-kinase MssD and the predicted phosphatidylinositol-3,4,5-triphosphate 3-phosphatase TepA, a homolog of the mammalian tumour suppressor protein PTEN. Deletion of tepA in E. festucae and in the root-infecting tomato pathogen Fusarium oxysporum had no impact on growth in culture or the host interaction phenotype. However, this mutation did enable the detection of PI[3,4,5]P₃ in septa and mycelium of E. festucae and showed that TepA is required for chemotropism in F. oxysporum. The identification of PI[3,4,5]P₃ in ΔtepA strains suggests that filamentous fungi are able to generate PI[3,4,5]P₃ and that fungal PTEN homologs are functional lipid phosphatases. The F. oxysporum chemotropism defect suggests a conserved role of PTEN homologs in chemotaxis across protists, fungi and mammals.

Grass pea natural variation reveals oligogenic resistance to Fusarium oxysporum f. sp. pisi

Grass pea (Lathyrus sativus L.) is an annual legume species, phylogenetically close to pea (Pisum sativum L.), that may be infected by Fusarium oxysporum f. sp. pisi (Fop), the causal agent of fusarium wilt in peas with vast worldwide yield losses. A range of responses varying from high resistance to susceptibility to this pathogen has been reported in grass pea germplasm. Nevertheless, the genetic basis of that diversity of responses is still unknown, hampering its breeding exploitation. To identify genomic regions controlling grass pea resistance to fusarium wilt, a genome-wide association study approach was applied on a grass pea worldwide collection of accessions inoculated with Fop race 2. Disease responses were scored in this collection that was also subjected to high-throughput based single nucleotide polymorphisms (SNP) screening through genotyping-by-sequencing. A total of 5,651 high-quality SNPs were considered for association mapping analysis, performed using mixed linear models accounting for population structure. Because of the absence of a fully assembled grass pea reference genome, SNP markers' genomic positions were retrieved from the pea's reference genome v1a. In total, 17 genomic regions were associated with three fusarium wilt response traits in grass pea, anticipating an oligogenic control. Seven of these regions were located on pea chromosomes 1, 6, and 7. The candidate genes underlying these regions were putatively involved in secondary and amino acid metabolism, RNA (regulation of transcription), transport, and development. This study revealed important fusarium wilt resistance favorable grass pea SNP alleles, allowing the development of molecular tools for precision disease resistance breeding.

Detection and Characterization of Fusarium Wilt (Fusarium oxysporum f. sp. vasinfectum) Race 4 Causing Fusarium Wilt of Cotton Seedlings in New Mexico

Fusarium wilt (FW), caused by Fusarium oxysporum f. sp. vasinfectum (Atk.) W.C. Snyder & H.N. Hans (FOV), is one of the most destructive diseases of cotton (Gossypium spp.) worldwide. FOV race 4 (FOV4) is a highly virulent nominal race of this pathogen and a significant threat to cotton production in the western and southwestern USA and, potentially, the entire Cotton Belt. A field survey to identify FOV4 was performed in three southern counties of New Mexico in 619 cotton fields from 2018 to 2020. From 132 samples of cotton plants that exhibited wilt symptoms, Fusarium spp. were the most frequently isolated group of fungal species, with an isolation frequency of 57.4%. Eighty-four Fusarium spp. isolates were subsequently characterized by a DNA sequence analysis of three genes, EF-1α, PHO, and BT, encoding for translation elongation factor, phosphate permease, and β-tubulin, respectively. Forty-two isolates from 10 cotton fields were identified as FOV4 and confirmed with a positive 500-bp fragment diagnostic for FOV4. Twenty-six (62%) of the 42 FOV4 isolates were T type and the remainder (38%) were null type with and without a Tfo1 insertion in PHO, respectively. Each FOV4-infested field contained the same FOV4 genotype. Ten representative FOV4 isolates (one each from the 10 FOV4-infested fields) were evaluated for their pathogenicity on resistant Pima PHY 841 RF and susceptible Upland PHY 725 RF at 7, 14, 21, and 28 days after inoculation under temperature-controlled conditions at 21 to 22°C. Based on the disease severity rating, mortality rate, and area under the disease progress curve value, all 10 isolates were pathogenic to both cotton cultivars and differed in virulence; four isolates of the T genotype as a whole were more virulent than the six isolates of the N genotype. PHY 841 RF had significantly higher levels of resistance than PHY 725 RF to all FOV4 isolates. The results provide the first comprehensive account of the occurrence, distribution, and virulence of FOV4 in cotton production in New Mexico and will be useful for developing an effective strategy to manage FW in the state of New Mexico and the entire western and southwestern Cotton Belt.

Target of rapamycin controls hyphal growth and pathogenicity through FoTIP4 in Fusarium oxysporum

Fusarium oxysporum is the causal agent of the devastating Fusarium wilt by invading and colonizing the vascular system in various plants, resulting in substantial economic losses worldwide. Target of rapamycin (TOR) is a central regulator that controls intracellular metabolism, cell growth, and stress responses in eukaryotes, but little is known about TOR signalling in F. oxysporum. In this study, we identified conserved FoTOR signalling pathway components including FoTORC1 and FoTORC2. Pharmacological assays showed that F. oxysporum is hypersensitive to rapamycin in the presence of FoFKBP12 while the deletion mutant strain ΔFofkbp12 is insensitive to rapamycin. Transcriptomic data indicated that FoTOR signalling controls multiple metabolic processes including ribosome biogenesis and cell wall-degrading enzymes (CWDEs). Genetic analysis revealed that FoTOR1 interacting protein 4 (FoTIP4) acts as a new component of FoTOR signalling to regulate hyphal growth and pathogenicity of F. oxysporum. Importantly, transcript levels of genes associated with ribosome biogenesis and CWDEs were dramatically downregulated in the ΔFotip4 mutant strain. Electrophoretic mobility shift assays showed that FoTIP4 can bind to the promoters of ribosome biogenesis- and CWDE-related genes to positively regulate the expression of these genes. These results suggest that FoTOR signalling plays central roles in regulating hyphal growth and pathogenicity of F. oxysporum and provide new insights into FoTOR1 as a target for controlling and preventing Fusarium wilt in plants.

Fol-milR1, a pathogenicity factor of Fusarium oxysporum, confers tomato wilt disease resistance by impairing host immune responses

Although it is well known that miRNAs play crucial roles in multiple biological processes, there is currently no evidence indicating that milRNAs from Fusarium oxysporum f. sp. lycopersici (Fol) interfere with tomato resistance during infection. Here, using sRNA-seq, we demonstrate that Fol-milR1, a trans-kingdom small RNA, is exported into tomato cells after infection. The knockout strain ∆Fol-milR1 displays attenuated pathogenicity to the susceptible tomato cultivar 'Moneymaker'. On the other hand, Fol-milR1 overexpression strains exhibit enhanced virulence against the resistant cultivar 'Motelle'. Several tomato mRNAs are predicted targets of Fol-milR1. Among these genes, Solyc06g007430 (encoding the CBL-interacting protein kinase, SlyFRG4) is regulated at the posttranscriptional level by Fol-milR1. Furthermore, SlyFRG4 loss-of-function alleles created using CRISPR/Cas9 in tomato ('Motelle') exhibit enhanced disease susceptibility to Fol, further supporting the idea that SlyFRG4 is essential for tomato wilt disease resistance. Notably, our results using immunoprecipitation with specific antiserum suggest that Fol-milR1 interferes with the host immunity machinery by binding to tomato ARGONAUTE 4a (SlyAGO4a). Furthermore, virus-induced gene silenced (VIGS) knock-down SlyAGO4a plants exhibit reduced susceptibility to Fol. Together, our findings support a model in which Fol-milR1 is an sRNA fungal effector that suppresses host immunity by silencing a disease resistance gene, thus providing a novel virulence strategy to achieve infection.

Ero1-Pdi1 module-catalysed dimerization of a nucleotide sugar transporter, FonNst2, regulates virulence of Fusarium oxysporum on watermelon

Fusarium oxysporum f. sp. niveum (Fon) is a soil-borne fungus causing vascular Fusarium wilt on watermelon; however, the molecular network regulating Fon virulence remains to be elucidated. Here, we report the function and mechanism of nucleotide sugar transporters (Nsts) in Fon. Fon genome harbours nine FonNst genes with distinct functions in vegetative growth, asexual production, cell wall stress response and virulence. FonNst2 and FonNst3 are required for full virulence of Fon on watermelon and FonNst2 is mainly involved in fungal colonization of the plant tissues. FonNst2 and FonNst3 form homo- or hetero-dimers but function independently in Fon virulence. FonNst2, which has UDP-galactose transporter activity in yeast, interacts with FonEro1 and FonPdi1, both of which are required for full virulence of Fon. FonNst2, FonPdi1 and FonEro1 target to endoplasmic reticulum (ER) and are essential for ER homeostasis and function. FonEro1-FonPdi1 module catalyses the dimerization of FonNst2, which is critical for Fon virulence. Undimerized FonNst2 is unstable and degraded via ER-associated protein degradation in vivo. These data demonstrate that FonEro1-FonPdi1 module-catalysed dimerization of FonNst2 is critical for Fon virulence on watermelon and provide new insights into the regulation of virulence in plant fungal pathogens via disulfide bond formation of key pathogenicity factors.

Complete genome sequence of a novel mitovirus from the phytopathogenic fungus Fusarium oxysporum

Fusarium oxysporum is a cosmopolitan plant pathogen that causes fusarium wilt and fusarium root rot in many economically important crops. There is still limited information about mycoviruses that infect F. oxysporum. Here, a novel mitovirus tentatively named "Fusarium oxysporum mitovirus 1" (FoMV1) was identified in F. oxysporum strain B2-10. The genome of FoMV1 is 2,453 nt in length with a predicted AU content of 71.6% and contains one large open reading frame (ORF) using the fungal mitochondrial genetic code. The ORF putatively encodes an RNA-dependent RNA polymerase (RdRp) of 723 aa with a molecular mass of 84.98 kDa. The RdRp domain of FoMV1 shares 29.01% to 68.43% sequence identity with the members of the family Mitoviridae. Phylogenetic analysis further suggested that FoMV1 is a new member of a distinct species in the genus Mitovirus.

Discovery and modulation of diterpenoid metabolism improves glandular trichome formation, artemisinin production and stress resilience in Artemisia annua

Plants synthesize diverse diterpenoids with numerous functions in organ development and stress resistance. However, the role of diterpenoids in glandular trichome (GT) development and GT-localized biosynthesis in plants remains unknown. Here, the identification of 10 diterpene synthases (diTPSs) revealed the diversity of diterpenoid biosynthesis in Artemisia annua. Protein-protein interactions (PPIs) between AaKSL1 and AaCPS2 in the plastids highlighted their potential functions in modulating metabolic flux to gibberellins (GAs) or ent-isopimara-7,15-diene-derived metabolites (IDMs) through metabolic engineering. A phenotypic analysis of transgenic plants suggested a complex repertoire of diterpenoids in Artemisia annua with important roles in GT formation, artemisinin accumulation and stress resilience. Metabolic engineering of diterpenoids simultaneously increased the artemisinin yield and stress resistance. Transcriptome and metabolic profiling suggested that bioactive GA₄ /GA₁ promote GT formation. Collectively, these results expand our knowledge of diterpenoids and show the potential of diterpenoids to simultaneously improve both the GT-localized metabolite yield and stress resistance, in planta.

FoEG1, a secreted glycoside hydrolase family 12 protein from Fusarium oxysporum, triggers cell death and modulates plant immunity

Fusarium oxysporum is an important soilborne fungal pathogen with many different formae speciales that can colonize the plant vascular system and cause serious crop wilt disease worldwide. We found a glycoside hydrolase family 12 protein FoEG1, secreted by F. oxysporum, that acted as a pathogen-associated molecular pattern (PAMP) targeting the apoplast of plants to induce cell death. Purified FoEG1 protein triggered cell death in different plants and induced the plant defence response to enhance the disease resistance of plants. The ability of FoEG1 to induce cell death was mediated by leucine-rich repeat (LRR) receptor-like kinases BAK1 and SOBIR1, and this ability was independent of its hydrolase activity. The mutants of cysteine residues did not affect the ability of FoEG1 to induce cell death, and an 86 amino acid fragment from amino acid positions 144 to 229 of FoEG1 was sufficient to induce cell death in Nicotiana benthamiana. In addition, the expression of FoEG1 was strongly induced in the early stage of F. oxysporum infection of host plants, and FoEG1 deletion or loss of enzyme activity reduced the virulence of F. oxysporum. Therefore, our results suggest that FoEG1 can contribute to the virulence of F. oxysporum depending on its enzyme activity and can also act as a PAMP to induce plant defence responses.

Secreted in Xylem Genes: Drivers of Host Adaptation in Fusarium oxysporum

Fusarium oxysporum (Fo) is a notorious pathogen that significantly contributes to yield losses in crops of high economic status. It is responsible for vascular wilt characterized by the browning of conductive tissue, wilting, and plant death. Individual strains of Fo are host specific (formae speciales), and approximately, 150 forms have been documented so far. The pathogen secretes small effector proteins in the xylem, termed as Secreted in Xylem (Six), that contribute to its virulence. Most of these proteins contain cysteine residues in even numbers. These proteins are encoded by SIX genes that reside on mobile pathogenicity chromosomes. So far, 14 proteins have been reported. However, formae speciales vary in SIX protein profile and their respective gene sequence. Thus, SIX genes have been employed as ideal markers for pathogen identification. Acquisition of SIX-encoding mobile pathogenicity chromosomes by non-pathogenic lines, through horizontal transfer, results in the evolution of new virulent lines. Recently, some SIX genes present on these pathogenicity chromosomes have been shown to be involved in defining variation in host specificity among formae speciales. Along these lines, the review entails the variability (formae speciales, races, and vegetative compatibility groups) and evolutionary relationships among members of F. oxysporum species complex (FOSC). It provides updated information on the diversity, structure, regulation, and (a)virulence functions of SIX genes. The improved understanding of roles of SIX in variability and virulence of Fo has significant implication in establishment of molecular framework and techniques for disease management. Finally, the review identifies the gaps in current knowledge and provides insights into potential research landscapes that can be explored to strengthen the understanding of functions of SIX genes.