Whole-genome sequencing reveals that mutations in myosin-5 confer resistance to the fungicide phenamacril in Fusarium graminearum

Characterization of Candida albicans myosin-1 motor function and its regulation by phosphorylation at TEDS site

Class I myosin is a single-headed myosin, distributed from fungi to mammals. The pathogenic yeast Candida albicans expresses a solo class I myosin gene (CaMyo1). The yeast-to-hyphae transition of Candida albicans depends on CaMyo1 and phosphorylation at its TEDS site (S366). In this study, we characterized the motor activity of CaMyo1 using purified CaMyo1IQ2 (a truncated CaMyo1 containing the motor domain and two IQ motifs) recombinantly expressed in insect Sf9 cells. We found that S366 phosphorylation activated the actin-activated ATPase activity of CaMyo1IQ2 from ∼4 s-1 in the dephosphorylated state to ∼10 s-1 in the phosphorylated state. The ADP release rate of acto-CaMyo1IQ2 is >150 s-1 regardless of S366 phosphorylation, which is at least 10 times faster than the actin-activated ATPase rate (4-10 s-1), suggesting that CaMyo1 is a low-duty ratio motor. Interestingly, in the absence of actin, CaMyo1IQ2 has relatively high ATPase activity (∼ 0.7 s-1) with the ADP release (∼ 1 s-1) as the rate-limiting step, suggesting a substantial portion of cycling through futile actin-detached path. Both S366D and S366E mutants exhibit intermediate actin-activated ATPase activity between unphosphorylated and phosphorylated wild-type, demonstrating partial phosphomimetic functionality at residue S366.

Comprehensive analysis of the mechanisms conferring resistance to phenamacril in the Fusarium species

The filamentous fungal genus Fusarium contains many species that cause catastrophic diseases in fruits, cereal, and vegetables. These diseases cause substantial losses in yield and contaminate affected crops with toxins. This causes huge losses in the agricultural sector and threatens human and animal health. The most efficient approach to control the Fusarium spp. is fungicide application. Phenamacril is a site-specific fungicide that exerts its antifungal effect on sensitive Fusarium spp. It is a new fungicide developed that targets Fusarium graminearum by inhibiting myosin-5, an important protein in fungal growth and disease development. Because of its remarkable specificity, the new fungicide phenamacril is regarded as environmentally benign. However, many research findings have reported the emergence of the resistance of Fusarium spp. to phenamacril in both the field and laboratory. This article comprehensively analyzes the mechanisms underlying Fusarium spp. resistance to phenamacril. We examine the molecular, genetic, and environmental factors contributing to this resistance. We emphasize the importance of continued research and integrating different approaches to monitoring and managing drug-resistant Fusarium spp. populations. Integrating current inventions to inform strategies for sustainable disease control practices, and increase plant health, and yield will contribute to ongoing global efforts to achieve food and nutritional sustainability for the world's rapidly growing population while ensuring the effectiveness of the fungicidal product.

Design, synthesis and antifungal activity of novel pyrazole-amide-isothiazole derivatives as succinate dehydrogenase inhibitors

To discover new fungicides to protect food safety and quality, thirty-four novel pyrazole-amide-isothiazole compounds were designed, synthesised by using scaffold hopping theory for the first time. The bioactivity of all the target compounds against five plant pathogens (Including Penicillium digitatum, Physalospora piricola, Helminthosporium maydis, Sclerotinia sclerotiorum and Botrytis cinerea) were determined, the results showed that most of the compounds exhibited certain biological activities against B. cinerea in vitro. Compounds 7-XHU-6 had better antifungal activities than fluopyram with the EC50 values were 1.02, 1.78 mg/L, respectively. Moreover, the SDH inhibiting activities results indicated that 7-XHU-6 possessed outstanding activities with an IC50 value of 0.47 mg/L which better than fluopyram (IC50 = 0.88 mg/L). Besides, the in vivo experiments indicated that compound 7-XHU-6 had excellent protection efficiency and therapeutic efficiency. In addition, molecular docking studies demonstrated that compound 7-XHU-6 (-10 kcal/mol) has superior binding energy compared to fluopyram (-8.6 kcal/mol).

Design, synthesis and systemic acquired resistance of 2-benzothiadiazolylquinoline-4-carboxamides by COI1 based virtual screening

Coronatine-insensitive 1 (COI1) has been identified as a target receptor of plant elicitor coronatine (COR). To discover novel plant elicitor leads, most of the potential molecules among 129 compounds discovered from the ZINC database by docking based virtual screening targeting COI1 were quinoline amides. On this lead basis, 2-benzothiadiazolylquinoline-4-carboxamides were rationally designed and synthesized for bioassay. All target compounds did not show significantly in vitro antifungal activity, compounds 4d, 4e and 4o displayed good in vivo systemic acquired resistance activity for Arabidopsis thaliana against Hyaloperonospora arabidopsidis isolate Noco2 with over 80% of inhibitory rate at the concentration of 50 μM. These results indicate that 2-benzothiadiazolylquinoline-4-carboxamides are promising plant elicitor leads for further study.

Pyruvate Kinase-Based Novel 2-Thiazol-2-yl-1,3,4-oxadiazoles Discovery as Fungicidal Highly Active Leads

To discover novel inhibitors of pyruvate kinase (PK) as fungicidal candidates, a series of 2-thiazol-2-yl-1,3,4-oxadiazole derivatives were designed by a prediction model with Rhizoctonia solani PK (RsPK) as a protein target and YZK-C22 as a ligand. Fungicidal screening indicated that 5b, 5g, 5h, 5j, 5l, 5p, 5q, and 5s exhibited equal or higher activity compared to YZK-C22 against Botrytis cinerea, Cercospora arachidicola, or R. solani. To our surprise, 5s showed comparable activity to flutriafol with an EC50 of 0.21 μg/mL vs 0.20 μg/mL, but over 14 times more active than the lead compound YZK-C22 against R. solani with its EC50 of 0.21 μg/mL vs 3.14 μg/mL (mole ratio over 17-fold). Compound 5s also displayed 2.30-fold better inhibition potency against RsPK compared with YZK-C22. Moreover, this higher potency of 5s against RsPK was also reflected in a steeper dose-response tendency in the fluorescence quenching assay and a lower dissociation constant in the microscale thermophoresis (MST) assay when compared with YZK-C22. The results in this study not only broadened the structural diversity of PK inhibitors but also supported 5s as a promising PK-based highly active fungicide lead compound, with stronger binding ability to RsPK than YZK-C22.

Uncovering the Differed Susceptibility of Fusarium oxysporum (Fo32931 and FocII5) to Fungicide Phenamacril: From Computational and Experimental Perspectives

Fo32931 and FoCII5 are two subtypes of Fusarium oxysporum (Fo), a pathogenic filamentous fungus. Phenamacril (PHA), a Fusarium-specific fungicide that targets myosin I, exhibits significant hyphal growth inhibition in Fo32931 but shows weak resistance in FocII5, despite only two amino acid differences in the PHA-binding pocket of myosin I. In this study, we aim to elucidate the molecular basis for the differential sensitivity ofF. oxysporum myosin I variants (FoMyoI32931 and FoMyoIcII5) to phenamacril through computational methods and biochemical validation. The results suggest that phenamacril functions as an allosteric inhibitor for FoMyoI32931, inhibiting the large oscillation of the converter lever domain (CLD) upon ATP binding and promoting the opening of the outer cleft, further impairing protein function. PHA significantly reduced the coupling between the CLD, especially the converter, and the catalytic center, diminishing the response of the CLD to the motor domain in FoMyoI32931. From the residue mutation experiment, we found that the S418T substitution in FoMyoIcII5 is the key to the reduced phenamacril sensitivity of FocII5. According to the microscale thermophoresis (MST) assay and pocket conformation analysis, the S418T mutation disturbs the orientation of pocket residues, especially Lys537, leading to a looser pocket and reduced interaction between Lys537 and phenamacril, which lowers the binding affinity of FoMyoIcII5 for phenamacril. These findings provide deeper insights into the reasons for the lower sensitivity of FoCII5 to phenamacril from both molecular and structural perspectives and will also guide the design of novel inhibitors against resistant Fusarium spp., like FoCII5.

From Natural Hosts to Agricultural Threats: The Evolutionary Journey of Phytopathogenic Fungi

Since the domestication of plants, pathogenic fungi have consistently threatened crop production, evolving genetically to develop increased virulence under various selection pressures. Understanding their evolutionary trends is crucial for predicting and designing control measures against future disease outbreaks. This paper reviews the evolution of fungal pathogens from natural habitats to agricultural settings, focusing on eight significant phytopathogens: Pyricularia oryzae, Botrytis cinerea, Puccinia spp., Fusarium graminearum, F. oxysporum, Blumeria graminis, Zymoseptoria tritici, and Colletotrichum spp. Also, we explore the mechanism used to understand evolutionary trends in these fungi. The studied pathogens have evolved in agroecosystems through either (1) introduction from elsewhere; or (2) local origins involving co-evolution with host plants, host shifts, or genetic variations within existing strains. Genetic variation, generated via sexual recombination and various asexual mechanisms, often drives pathogen evolution. While sexual recombination is rare and mainly occurs at the center of origin of the pathogen, asexual mechanisms such as mutations, parasexual recombination, horizontal gene or chromosome transfer, and chromosomal structural variations are predominant. Farming practices like mono-cropping resistant cultivars and prolonged use of fungicides with the same mode of action can drive the emergence of new pathotypes. Furthermore, host range does not necessarily impact pathogen adaptation and evolution. Although halting pathogen evolution is impractical, its pace can be slowed by managing selective pressures, optimizing farming practices, and enforcing quarantine regulations. The study of pathogen evolution has been transformed by advancements in molecular biology, genomics, and bioinformatics, utilizing methods like next-generation sequencing, comparative genomics, transcriptomics and population genomics. However, continuous research remains essential to monitor how pathogens evolve over time and to develop proactive strategies that mitigate their impact on agriculture.

The Mechanisms of Developing Fungicide Resistance in Fusarium graminearum Causing Fusarium Head Blight and Fungicide Resistance Management

Fusarium head blight (FHB), primarily caused by Fusarium graminearum, is one of the economically significant diseases in small grains. FHB causes severe damage to wheat production and grain quality. Several management strategies have been developed to control FHB, and chemical control through fungicides plays a significant role. Although fungicides have effectively controlled F. graminearum in the field, the continuous exposure causes a selection pressure in the pathogen population towards fungicide resistance. Several studies have identified fungicide-resistant F. graminearum isolates and fungicide-resistance mechanisms. Although new fungicides with a new mode of action can be introduced into the market, developing a new fungicide is time-consuming, and extra efforts are needed for testing, approvals, and registrations. Therefore, it is essential to strategize the methods to delay the fungicide resistance. This review focuses on the impact of several fungicide applications currently used on FHB, focusing on Fusarium graminearum, the status of the fungicide sensitivity for fungicide classes, the resistance mechanisms against fungicides, and the mitigation strategies to delay the development of fungicide resistance in the pathogen population. Studying the fungicide resistance mechanisms and the mitigation strategies will be helpful in the future to use the available fungicides against F. graminearum without losing its effectiveness.

Biological and molecular characterization of pydiflumetofen and phenamacril dual-resistant Fusarium graminearum strains

BACKGROUND

Fusarium head blight (FHB) caused by Fusarium graminearum species complex (FGSG) remains a major challenge to cereal crops and resistance to key fungicides by the pathogen threatens control efficacy. Pydiflumetofen, a succinate dehydrogenase inhibitor, and phenamacril, a cyanoacrylate fungicide targeting myosin I, have been applied to combat this disease. Nonetheless, emergence of pydiflumetofen resistance in a subset of field isolates alongside laboratory-induced facile generation of phenamacril-resistant isolates signals a critical danger of resistance proliferation.

RESULTS

Our study investigates the development of dual resistance to these fungicides in F. graminearum. Utilizing pydiflumetofen-resistant (PyR) and -sensitive (PyS) isolates, we obtained dual-resistant (PyRPhR) and phenamacril-resistant (PySPhR) mutants on potato sucrose agar containing phenamacril. Mutation rates for phenamacril resistance were comparable between pydiflumetofen-resistant and -sensitive isolates, implying independent pathways for resistance development. The mutants compromised in fungal growth, competitive viability and deoxynivalenol production, suggesting fitness penalties for the dual-resistant mutants. However, no cross-resistance was found with tebuconazole or fludioxonil. In addition, we characterized four critical amino acid changes (S217L, C423R, K537T, E420G) in the Myo1 that were verified to confer phenamacril resistance in F. graminearum.

CONCLUSION

This research indicates the possibility of resistance development for both pydiflumetofen and phenamacril in F. graminearum and emphasizes the need for fungicide resistance management for FHB. © 2024 Society of Chemical Industry.

Harnessing RNA interference for the control of Fusarium species: A critical review

Fusarium fungi are a pervasive threat to global agricultural productivity. They cause a spectrum of plant diseases that result in significant yield losses and threaten food safety by producing mycotoxins that are harmful to human and animal health. In recent years, the exploitation of the RNA interference (RNAi) mechanism has emerged as a promising avenue for the control of Fusarium-induced diseases, providing both a mechanistic understanding of Fusarium gene function and a potential strategy for environmentally sustainable disease management. However, despite significant progress in elucidating the presence and function of the RNAi pathway in different Fusarium species, a comprehensive understanding of its individual protein components and underlying silencing mechanisms remains elusive. Accordingly, while a considerable number of RNAi-based approaches to Fusarium control have been developed and many reports of RNAi applications in Fusarium control under laboratory conditions have been published, the applicability of this knowledge in agronomic settings remains an open question, and few convincing data on RNAi-based disease control under field conditions have been published. This review aims to consolidate the current knowledge on the role of RNAi in Fusarium disease control by evaluating current research and highlighting important avenues for future investigation.

New insights into mycotoxin risk management through fungal population genetics and genomics

Mycotoxin contamination of food and feed is a major global concern. Chronic or acute dietary exposure to contaminated food and feed can negatively affect both human and animal health. Contamination occurs through plant infection by toxigenic fungi, primarily Aspergillus and Fusarium spp., either before or after harvest. Despite the application of various management strategies, controlling these pathogens remains a major challenge primarily because of their ability to adapt to environmental changes and selection pressures. Understanding the genetic structure of plant pathogen populations is pivotal for gaining new insights into their biology and epidemiology, as well as for understanding the mechanisms behind their adaptability. Such deeper understanding is crucial for developing effective and preemptive management strategies tailored to the evolving nature of pathogenic populations. This review focuses on the population-level variations within the two most economically significant toxigenic fungal genera according to space, host, and pathogenicity. Outcomes in terms of migration patterns, gene flow within populations, mating abilities, and the potential for host jumps are examined. We also discuss effective yet often underutilized applications of population genetics and genomics to address practical challenges in the epidemiology and disease control of toxigenic fungi.

Unveiling the Mechanism of Phenamacril Resistance in F. graminearum: Computational and Experimental Insights into the C423A Mutation in FgMyoI

Phenamacril (PHA) is a highly selective fungicide for controlling fusarium head blight (FHB) mainly caused by F. graminearum and F. asiaticum. However, the C423A mutation in myosin I of F. graminearum (FgMyoI) leads to natural resistance to PHA. Here, based on the computational approaches and biochemical validation, we elucidate the atomic-level mechanism behind the natural resistance of F. graminearum to the fungicide PHA due to the C423A mutation in FgMyoI. The mutation leads to a rearrangement of pocket residues, resulting in increased size and flexibility of the binding pocket, which impairs the stable binding of PHA. MST experiments confirm that the mutant protein FgMyoIC423A exhibits significantly reduced affinity for PHA compared to wild-type FgMyoI and the nonresistant C423K mutant. This decreased binding affinity likely underlies the development of PHA resistance in F. graminearum. Conversely, the nonresistant C423K mutant retains sensitivity to PHA due to the introduction of a strong hydrogen bond donor, which facilitates stable binding of PHA in the pocket. These findings shed light on the molecular basis of PHA resistance and provide new directions for the creation of new myosin inhibitors.

FgPfn participates in vegetative growth, sexual reproduction, pathogenicity, and fungicides sensitivity via affecting both microtubules and actin in the filamentous fungus Fusarium graminearum

Fusarium head blight (FHB), caused by Fusarium graminearum species complexes (FGSG), is an epidemic disease in wheat and poses a serious threat to wheat production and security worldwide. Profilins are a class of actin-binding proteins that participate in actin depolymerization. However, the roles of profilins in plant fungal pathogens remain largely unexplored. Here, we identified FgPfn, a homolog to profilins in F. graminearum, and the deletion of FgPfn resulted in severe defects in mycelial growth, conidia production, and pathogenicity, accompanied by marked disruptions in toxisomes formation and deoxynivalenol (DON) transport, while sexual development was aborted. Additionally, FgPfn interacted with Fgα1 and Fgβ2, the significant components of microtubules. The organization of microtubules in the ΔFgPfn was strongly inhibited under the treatment of 0.4 μg/mL carbendazim, a well-known group of tubulin interferers, resulting in increased sensitivity to carbendazim. Moreover, FgPfn interacted with both myosin-5 (FgMyo5) and actin (FgAct), the targets of the fungicide phenamacril, and these interactions were reduced after phenamacril treatment. The deletion of FgPfn disrupted the normal organization of FgMyo5 and FgAct cytoskeleton, weakened the interaction between FgMyo5 and FgAct, and resulting in increased sensitivity to phenamacril. The core region of the interaction between FgPfn and FgAct was investigated, revealing that the integrity of both proteins was necessary for their interaction. Furthermore, mutations in R72, R77, R86, G91, I101, A112, G113, and D124 caused the non-interaction between FgPfn and FgAct. The R86K, I101E, and D124E mutants in FgPfn resulted in severe defects in actin organization, development, and pathogenicity. Taken together, this study revealed the role of FgPfn-dependent cytoskeleton in development, DON production and transport, fungicides sensitivity in F. graminearum.

Comparative transcriptome analysis provides insights into the resistance regulation mechanism and inhibitory effect of fungicide phenamacril in Fusarium asiaticum

Fusarium asiaticum is a destructive phytopathogenic fungus that causes Fusarium head blight of wheat (FHB), leading to serious yield and economic losses to cereal crops worldwide. Our previous studies indicated that target-site mutations (K216R/E, S217P/L, or E420K/G/D) of Type I myosin FaMyo5 conferred high resistance to phenamacril. Here, we first constructed one sensitive strain H1S and three point mutation resistant strains HA, HC and H1R. Then we conducted comparative transcriptome analysis of these F. asiaticum strains after 1 and 10 μg·mL-1 phenamacril treatment. Results indicated that 2135 genes were differentially expressed (DEGs) among the sensitive and resistant strains. The DEGs encoding ammonium transporter MEP1/MEP2, nitrate reductase, copper amine oxidase 1, 4-aminobutyrate aminotransferase, amino-acid permease inda1, succinate-semialdehyde dehydrogenase, 2, 3-dihydroxybenzoic acid decarboxylase, etc., were significantly up-regulated in all the phenamacril-resistant strains. Compared to the control group, a total of 1778 and 2097 DEGs were identified in these strains after 1 and 10 μg·mL-1 phenamacril treatment, respectively. These DEGs involved in 4-aminobutyrate aminotransferase, chitin synthase 1, multiprotein-bridging factor 1, transcriptional regulatory protein pro-1, amino-acid permease inda1, ATP-dependent RNA helicase DED1, acetyl-coenzyme A synthetase, sarcoplasmic/endoplasmic reticulum calcium ATPase 2, etc., showed significantly down-regulated expression in phenamacril-sensitive strain but not in resistant strains after phenamacril treatment. In addition, cyanide hydratase, mating-type protein MAT-1, putative purine nucleoside permease, plasma membrane protein yro2, etc., showed significantly co-down-regulated expression in all the strains after phenamacril treatment. Taken together, This study provides deep insights into the resistance regulation mechanism and the inhibitory effect of fungicide phenamacril and these new annotated proteins or enzymes are worth for the discovery of new fungicide targets.

Design, Synthesis, Antifungal Activity, and Molecular Docking Studies of Novel Chiral Isoxazoline-Benzofuran-Sulfonamide Derivatives

Succinate dehydrogenase (SDH) is one of the most important molecular targets for the development of novel fungicides. With the emerging problem of resistance in plant fungal pathogens, novel compounds with high fungicidal activity need to be developed, but the study of chiral pesticides for the inhibition of highly destructive plant pathogens has been rarely reported in recent years. Therefore, a series of novel chiral isoxazoline-benzofuran-sulfonamide derivatives were designed to investigate potential novel antifungal molecules. The chiral target compound 3a was cultured as a single crystal and confirmed using X-ray diffraction. All the target compounds were tested for antifungal activity, and compounds 3c, 3i, 3s, and 3r were found to have significant antifungal effects against S. sclerotiorum with EC50 values of 0.42 mg/L, 0.33 mg/L, 0.37 mg/L, and 0.40 mg/L, respectively, which were superior to the commercial fungicide fluopyram (EC50 = 0.47 mg/L). The IC50 value of compound 3i against the SDH of S. sclerotiorum was 0.63 mg/mL, which was further demonstrated by enzyme activity assays. Scanning electron microscopy showed that 3i had a significant inhibitory effect on S. sclerotiorum. In addition, the fluorescence quenching analysis assay indicated that compound 3i had a similar effect with the positive control fluopyram. Molecular docking exhibited that target compounds with chiral configuration had better affinity than racemic configuration, and 3i possessed stronger action than fluopyram, which was in keeping with the in vitro test results. These results would provide a basis and reference for the development of novel chiral fungicides.

Resistance of the Ginseng Gray Mold Pathogen, Botrytis cinerea, to Boscalid and Pyraclostrobin Fungicides in China

Gray mold caused by Botrytis cinerea severely threatens the yield of ginseng (Panax ginseng). Various categories of fungicides have been utilized to control gray mold on this crop. In this study, the resistance of 102 isolates of B. cinerea from 11 commercial ginseng-growing regions in China to fungicides was examined. A total of 32.4% were resistant to boscalid, with EC50 values that ranged from 12.26 to 235.87 μg/ml, and 94.1% were resistant to pyraclostrobin, with EC50 values that ranged from 5.88 to 487.72 μg/ml. Except for sdhA and sdhD, the amino acid substitutions of P225F, P225L, N230I, H272Y, and H272R in the sdhB subunit from 24 (4 sensitive [S] and 20 resistant [R]), 5 (1 S and 4 R), 1 (S), 1 (R), and 8 (4 S and 4 R) strains, respectively, and the concurrent amino acid substitutions of G85A + I93V + M158V + V168I in the sdhC subunit from 5 (4 S and 1 R) strains were identified. A G143A substitution in cytochrome b was identified in 96 isolates that were resistant to pyraclostrobin and three that were sensitive to it. The Bcbi-143/144 intron was identified in the other three isolates sensitive to pyraclostrobin, but it was absent in the isolates that harbored the G143A mutation. The results showed that the populations of B. cinerea on ginseng have developed strong resistance to pyraclostrobin. Therefore, it is not recommended to continue using this fungicide to control gray mold on P. ginseng. Boscalid is still effective against most isolates. However, to prevent fungicide resistance, it is recommended to use a mixture of boscalid with other categories of fungicides.

Characterization of the fludioxonil and phenamacril dual resistant mutants of Fusarium graminearum

Fusarium graminearum is an important fungal pathogen causing Fusarium head blight (FHB) in wheat and other cereal crops worldwide. Due to lack of resistant wheat cultivars, FHB control mainly relies on application of chemical fungicides. Both fludioxonil (a phenylpyrrole compound) and phenamacril (a cyanoacrylate fungicide) have been registered for controlling FHB in China, however, fludioxonil-resistant isolates of F. graminearum have been detected in field. To evaluate the potential risk of dual resistance of F. graminearum to both compounds, fludioxonil and phenamacril dual resistant (DR) mutants of F. graminearum were obtained via fungicide domestication in laboratory. Result showed that resistance of the DR mutants to both fludioxonil and phenamacril were genetically stable after sub-cultured for ten generations or stored at 4 °C for 30 days on fungicide-free PDA. Cross-resistance assay showed that the DR mutants remain sensitive to other groups of fungicides, including carbendazim, tebuconazole, pydiflumetofen, and fluazinam. In addition, the DR mutants exhibited defects in mycelia growth, conidiation, mycotoxin deoxynivalenol (DON) production, and virulence Moreover, the DR mutants displayed increased sensitivity to osmotic stress. Sequencing results showed that amino acid point mutations S217L/T in the myosin I protein is responsible for phenamacril resistance in the DR mutants. Our results indicate that mutations leading to fludioxonil and phenamacril dual resistance could result in fitness cost for F. graminearum. Our results also suggest that the potential risk of F. graminearum developing resistance to both fludioxonil and phenamacril in field could be rather low, which provides scientific guidance in controlling FHB with fludioxonil and phenamacril.

Determining the biocontrol capacities of Trichoderma spp. originating from Turkey on Fusarium culmorum by transcriptional and antagonistic analyses

In this study aiming to investigate potential fungal biocontrol agents for Fusarium culmorum, several isolates of Trichoderma spp. were evaluated for their antagonistic effects by means of transcriptional analyses. At first, 21 monosporic Trichoderma spp. isolates were obtained from natural wood debris and wood area soils in Manisa, Turkey. Trichoderma spp. Isolates were identified as belonging to four different species (T. atroviride, T. harzianum, T. koningii, and T. brevicompactum) by tef1-α sequencing. Then, the linear growth rate (LGR) of each species was calculated and determined to be in a range between 13.22 ± 0.71 mm/day (T. atroviride TR2) and 25.06 ± 1.45 mm/day (T. harzianum K30). Inter-simple sequence repeat (ISSR) genotyping validated the tef1-α sequencing results by presenting two sub-clusters in the dendrogram. We determined the genetically most similar (TR1 & TR2; 97.77%) and dissimilar (K9 & K17; 40.40%) individuals belonging to the same and different species, respectively. Dual sandwich culture tests (which are useful for antagonism studies) revealed that T. harzianum K21 (the least suppressive) and T. brevicompactum K26 (the most suppressive) isolates suppressed F. culmorum with growth rates of 3% and 46%, respectively. Expressions of genes previously associated with mycoparasitism-plant protection-secondary metabolism (nag1, tgf-1, and tmk-1) were tested by quantitative real-time polymerase chain reaction (qRT-PCR) in both those isolates. While there were no significant differences (p>0.05) in expression that were present in the K21 isolate, those three genes were upregulated with fold change values of 2.69 ± 0.26 (p<0.001), 2.23 ± 0.16 (p<0.001), and 5.38 ± 2.01 (p<0.05) in K26, meaning that the presence of significant alteration in the physiological processes of the fungus. Also, its mycoparasitism potential was tested on Triticum aestivum L. cv Basribey in planta, which was infected with the F. culmorum FcUK99 strain. Results of the trials, including specific plant growth parameters (weight or length of plantlets), confirmed the mycoparasitic potential of the isolate. It can be concluded that (i) nag1, tgf-1, and tmk-1 genes could be approved as reliable markers for evaluation of BCA capacities of Trichoderma spp. and (ii) the T. brevicompactum K26 strain can be suggested as a promising candidate for combating in F. culmorum diseases following the necessary procedures to ensure it is non-hazardous and safe.

The intrinsic resistance of Fusarium solani to the Fusarium-specific fungicide phenamacril is attributed to the natural variation of both T218S and K376M in myosin5

Fusarium solani is responsible for causing root rot in various crops, resulting in wilting and eventual demise. Phenamacril, a specific inhibitor of myosin5 protein, has gained recognition as an effective fungicide against a broad spectrum of Fusarium species. It has been officially registered for controlling Fusarium diseases through spray application, root irrigation, and seed dipping. In this study, phenamacril was observed to exhibit negligible inhibitory effects on F. solani causing crop root rot, despite the absence of prior exposure to phenamacril. Considering the high selectivity of phenamacril, this phenomenon was attributed to intrinsic resistance and further investigated for its underlying mechanism. Sequence alignment analysis of myosin5 proteins across different Fusarium species revealed significant differences at positions 218 and 376. Subsequent homology modeling and molecular docking results indicated that substitutions T218S, K376M, and T218S&K376M impaired the binding affinity between phenamacril and myosin5 in F. solani. Mutants carrying these substitutions were generated via site-directed mutagenesis. A phenamacril-sensitivity test showed that the EC50 values of mutants carrying T218S, K376M, and T218S&K376M were reduced by at least 6.13-fold, 9.66-fold, and 761.90-fold respectively compared to the wild-type strain. Fitness testing indicated that mutants carrying K376M or T218S&K376M had reduced sporulation compared to the wild-type strain. Additionally, mutants carrying T218S exhibited an enhanced virulence compared to the wild-type strain. However, there were no significant differences observed in mycelial growth rates between the mutants and the wild-type strain. Thus, the intrinsic differences observed at positions 218 and 376 in myosin5 between F. solani and other Fusarium species are specifically associated with phenamacril resistance. The identification of these resistance-associated positions in myosin5 of F. solani has significantly contributed to the understanding of phenamacril resistance mechanisms, thereby discouraging the use of phenamacril for controlling F. solani.

Antifungal Compound from the Predatory Bacterium Lysobacter enzymogenes Inhibits a Plant Pathogenic Fungus by Targeting the AAA ATPase VpVeb1

Heat-stable antifungal factor (HSAF) isolated from Lysobacter enzymogenes is considered a potential biocontrol agent. However, the target of HSAF in phytopathogenic fungi remains unclear. In this study, we investigated the target of HSAF in Valsa pyri that causes fatal pear Valsa canker. Thirty-one HSAF-binding proteins were captured and identified by surface plasmon resonance (SPR) and high-performance liquid chromatography-mass spectrometry (LC-MS/MS), and 11 deletion mutants were obtained. Among these mutants, only ΔVpVEB1 showed decreased sensitivity to HSAF. Additionally, ΔVpVEB1 exhibited significantly reduced virulence in V. pyri. Molecular docking and SPR results revealed that HSAF bound to threonine 569 and glycine 570 of VpVeb1, which are crucial for AAA ATPase activity. Another study showed that HSAF could decrease the ATPase activity of VpVeb1, leading to the reduced virulence of V. pyri. Taken together, this study first identified the potential target of HSAF in fungi. These findings will help us better understand the model of action of HSAF to fungi.

CoMFA Directed Molecular Design for Significantly Improving Fungicidal Activity of Novel [1,2,4]-Triazolo-[3,4-b][1,3,4]-thiadizoles

Target based molecular design via the aid of computation is one of the most efficient methods in the discovery of novel pesticides. Here, a combination of the comparative molecular field analysis (CoMFA) and molecular docking was applied for discovery of potent fungicidal [1,2,4]-triazolo-[3,4-b][1,3,4]-thiadiazoles. Bioassay results indicated that the synthesized target compounds 3a, 3b, and 3c exhibited good activity against Alternaria solani, Botrytis cinerea, Cercospora arachidicola, Fusarium graminearum, Physalospora piricola, Rhizoctonia solani, and Sclerotinia sclerotiorum with an EC50 value falling between 0.64 and 16.10 μg/mL. Specially, 3c displayed excellent fungicidal activity against C. arachidicola and R. solani, which was 5 times more potent than the lead YZK-C22. The enzymatic inhibition assay and fluorescence quenching analysis with R. solani pyruvate kinase (RsPK) showed a weaker binding affinity between RsPK and 3a, 3b, or 3c. Transcriptomic analyses showed that 3c exerted its fungicidal activity by disrupting steroid biosynthesis and ribosome biogenesis in eukaryotes. These findings support that 3c is a promising fungicide candidate, and a fine modification from a lead may lead to a totally different mode of action.

Transcriptomic Profiling of Fusarium pseudograminearum in Response to Carbendazim, Pyraclostrobin, Tebuconazole, and Phenamacril

Fusarium pseudograminearum has been identified as a significant pathogen. It causes Fusarium crown rot (FCR), which occurs in several major wheat-producing areas in China. Chemical control is the primary measure with which to control this disease. In this study, transcriptome sequencing (RNA-Seq) was used to determine the different mechanisms of action of four frequently used fungicides including carbendazim, pyraclostrobin, tebuconazole, and phenamacril on F. pseudograminearum. In brief, 381, 1896, 842, and 814 differentially expressed genes (DEGs) were identified under the carbendazim, pyraclostrobin, tebuconazole, and phenamacril treatments, respectively. After the joint analysis, 67 common DEGs were obtained, and further functional analysis showed that the ABC transported pathway was significantly enriched. Moreover, FPSE_04130 (FER6) and FPSE_11895 (MDR1), two important ABC multidrug transporter genes whose expression levels simultaneously increased, were mined under the different treatments, which unambiguously demonstrated the common effects. In addition, Mfuzz clustering analysis and WGCNA analysis revealed that the core DEGs are involved in several critical pathways in each of the four treatment groups. Taken together, these genes may play a crucial function in the mechanisms of F. pseudograminearum's response to the fungicides stress.

Exploration of Fungicidal Activity and Mode of Action of Ferimzone Analogs

Lead discovery and molecular target identification are important for developing novel pesticides. Scaffold hopping, an effective approach of modern medicinal and agrochemical chemistry for a rational design of target molecules, is aiming to design novel molecules with similar structures and similar/better biological performance. Herein, 24 new ferimzone derivatives were designed and synthesized by a scaffold-hopping strategy. In vitro bioassays indicated that compound 5o showed similar potency to ferimzone against Cercospora arachidicola and 2-fold higher potency than ferimzone against Alternaria solani. Compounds 5q, 6a, and 6d displayed fungicidal activity with EC₅₀ values ranging from 1.17 to 3.84 μg/mL against Rhizoctonia solani, and compounds 5q and 6a displayed 1.6-1.8-fold higher activity than ferimzone against Fusarium graminearum. The in vivo bioassays at 200 μg/mL indicated that compound 5q was more potent than ferimzone against Pyricularia oryzae (90% vs 70% efficacy, respectively). Density functional theory (DFT) calculations elucidated the structure-energy relationship. Although the mode of action of ferimzone is still unclear, studies suggested that compound 5q significantly inhibited the growth and reproduction of R. solani, and its energy metabolism pathways (e.g., starch, sucrose, lipids, and glutathione) were seriously downregulated after a 5q treatment.

Diversity and Exploration of Endophytic Bacilli for the Management of Head Scab (Fusarium graminearum) of Wheat

Fusarium graminearum causing head scab (HS) or head blight (HB) disease in wheat is one of the nasty fungi reported to cause significant grain quality and yield loss. Biological control using endophytic bacteria has emerged as a prospective option for containing fungal diseases in an environmentally benevolent, durable, and sustainable manner. In this regard, 112 endophytic bacilli were isolated from the anthesis stage (Zadok’s growth stage 65) from five different wheat genotypes with an aim to identify prospective antagonistic strains against F. graminearum. The molecular identity of the strains was confirmed by matching 16S rRNA sequences of bacterial strains with the gene sequences of type strains available in the National Center for Biotechnology Information database and reported 38 different species of Bacillus in all the five wheat cultivars. Further, it has been observed that only fourteen strains (B. clarus NOK09, B. mojavensis NOK16, B. subtilis NOK33, B. rugosus NOK47, B. mojavensis NOK52, B. clarus NOK59, B. coahuilensis NOK72, B. cabrialesii NOK78, B. cabrialesii NOK82, B. rugosus NOK85, B. amyloliquefaciens NOK89, B. australimaris NOK95, B. pumilus NOK103, and B. amyloliquefaciens NOK109) displayed in-vitro antagonistic effect against Fusarium graminearum fungus. Furthermore, the three endophytic Bacillus strains showing the strongest antagonistic effect (>70% of growth inhibition of fungal mycelium) under in-vitro antagonistic assay were selected for field experiments. In a two-year consecutive field study, a combination of three strains (B. clarus NOK09 + B. subtilis NOK33 + B. amyloliquefaciens NOK109) displayed a remarkable reduction in HS disease index by 81.47% and 77.85%, respectively. Polymerase chain reaction assay detected three genes (ituD, bmyC, and srfA) involved in antibiotic biosynthesis pathways. Additional attributes such as potassium solubilization, siderophore release, and hydrolytic enzyme (protease, lipase, amylase, chitinase, and pectinase) synthesis have been observed in these strains. Overall, the present study was successful in profiling endophytic bacilli and selecting the combination of effective antagonistic endophytic Bacillus strains that could be the best alternative for the sustainable and ecological sound management of HS disease in wheat under field conditions.

Host induced gene silencing of the Sclerotinia sclerotiorum ABHYDROLASE-3 gene reduces disease severity in Brassica napus

Sclerotinia sclerotiorum is a pathogenic fungus that infects hundreds of crop species, causing extensive yield loss every year. Chemical fungicides are used to control this phytopathogen, but with concerns about increasing resistance and impacts on non-target species, there is a need to develop alternative control measures. In the present study, we engineered Brassica napus to constitutively express a hairpin (hp)RNA molecule to silence ABHYRDOLASE-3 in S. sclerotiorum. We demonstrate the potential for Host Induced Gene Silencing (HIGS) to protect B. napus from S. sclerotiorum using leaf, stem and whole plant infection assays. The interaction between the transgenic host plant and invading pathogen was further characterized at the molecular level using dual-RNA sequencing and at the anatomical level through microscopy to understand the processes and possible mechanisms leading to increased tolerance to this damaging necrotroph. We observed significant shifts in the expression of genes relating to plant defense as well as cellular differences in the form of structural barriers around the site of infection in the HIGS-protected plants. Our results provide proof-of-concept that HIGS is an effective means of limiting damage caused by S. sclerotiorum to the plant and demonstrates the utility of this biotechnology in the development of resistance against fungal pathogens.

Novel [1,2,4]-Triazolo[3,4-b]-[1,3,4]thiadizoles as Potent Pyruvate Kinase Inhibitors for Fungal Control

To discover novel target-based fungicidal candidates, a molecular design model was established with a three-dimensional (3D) structure of Rhizoctonia solani pyruvate kinase (RsPK) simulated with the AlphaFold 2 and YZK-C22 as a fungicidal lead. A series of novel [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole derivatives were rationally designed, synthesized, evaluated for their fungicidal performance, and validated for their mode of action. The in vitro bioassays with R. solani indicated that compounds 5g, 5o, and 5z with an EC₅₀ value ranging from 1.01 to 1.54 μg/mL displayed higher fungicidal activity than the positive control YZK-C22 with its EC₅₀ of 3.14 μg/mL. Especially, 5o exhibited high potency and a broad spectrum against Alternaria solani, Botrytis cinerea, Cercospora arachidicola, Physalospora piricola, R. solani, and Sclerotinia sclerotiorum with its EC₅₀ value falling between 1.54 and 13.10 μg/mL. Like all positive controls, 5g, 5o, and 5z showed excellent in vivo growth inhibition against Pseudoperonospora cubensis at 200 μg/mL. Even though the PK enzymatic inhibition assay showed that 5o was approximately 2.6 times less active than YZK-C22 (IC₅₀: 29.14 vs 11.15 μg/mL, respectively), the similar fluorescence quenching patterns of RsPK by 5o and YZK-C22, and the docking results of interactions between RsPK and 5o or YZK-C22 implied that they might share the similar binding site in the RsPK active pocket. Our studies suggested that 5o could be used as a potent fungicidal lead for further optimization. The results of comparative molecular field analysis (CoMFA) provided a direction for further molecular design.

Comparative transcriptome analysis reveals the resistance regulation mechanism and fungicidal activity of the fungicide phenamacril in Fusarium oxysporum

Fusarium oxysporum (Fo) is an important species complex of soil-borne pathogenic fungi that cause vascular wilt diseases of agricultural crops and some opportunistic diseases of humans. The fungicide phenamacril has been extensively reported to have antifungal activity against Fusarium graminearum and Fusarium fujikuroi. In this study, we found that the amino acid substitutions (V151A and S418T) in Type I myosin FoMyo5 cause natural low resistance to phenamacril in the plant pathogenic Fo isolates. Therefore, we compared the transcriptomes of two phenamacril-resistant Fo isolates FoII5, Fo1st and one phenamacril-sensitive isolate Fo3_a after 1 μg/mL phenamacril treatment. Among the 2728 differentially expressed genes (DEGs), 14 DEGs involved in oxidation–reduction processes and MFS transporters, were significantly up-regulated in phenamacril-resistant isolates. On the other hand, 14 DEGs involved in ATP-dependent RNA helicase and ribosomal biogenesis related proteins, showed significantly down-regulated expression in both phenamacril-resistant and -sensitive isolates. These results indicated that phenamacril not only seriously affected the cytoskeletal protein binding and ATPase activity of sensitive isolate, but also suppressed ribosome biogenesis in all the isolates. Hence, this study helps us better understand resistance regulation mechanism and fungicidal activity of phenamacril and provide reference for the development of new fungicides to control Fo.

Comparative Transcriptome Analyses Reveal Conserved and Distinct Mechanisms of the SDHI Fungicide Benzovindiflupyr Inhibiting Colletotrichum

Colletotrichum leaf disease (CLD) is an annual production concern for commercial growers worldwide. The succinate dehydrogenase inhibitor (SDHI) fungicide benzovindiflupyr shows higher bioactivity against CLD than other SDHIs. However, the mechanism underlying such difference remains unclear. In this study, benzovindiflupyr exhibits good inhibitory activity against Colletotrichum siamense and C. nymphaeae in vitro and in vivo. To reveal its mechanism for inhibiting Colletotrichum, we compared transcriptomes of C. siamense and C. nymphaeae under treatment with benzovindiflupyr and boscalid. Benzovindiflupyr exhibited higher inhibitory activity against SDH enzyme than boscalid, resulting in a greater reduction in the ATP content of Colletotrichum isolates. Most of the metabolic pathways induced in these fungicide-treated isolates were similar, indicating that benzovindiflupyr exhibited a conserved mechanism of SDHIs inhibiting Colletotrichum. At the same level of suppressive SDH activity, benzovindiflupyr activated more than three times greater gene numbers of Colletotrichum than boscalid, suggesting that benzovindiflupyr could activate distinct mechanisms against Colletotrichum. Membrane-related gene ontology terms, mainly including intrinsic components of membrane, were highly abundant for the benzovindiflupyr-treated isolates rather than boscalid-treated isolates. Only benzovindiflupyr increased the relative conductivities of hyphae, indicating that it could damage the cell membrane and increase mycelial electrolyte leakage. Thus, we proposed that the high bioactivity of benzovindiflupyr against Colletotrichum occurred by inhibiting SDH activity and damaging the cell membrane at the same time. The research improves our understanding the mode of action of SDHI fungicides against Colletotrichum.

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

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

Recent Advances in the Pesticide Activities of 2-Cyanoacrylate Derivatives

2-Cyanoacrylates are a unique class of compounds with high photosystem II electron transport inhibitory activity. Through the in-depth study of molecular design, synthesis, biological activity, structure-activity relationship, and action mechanism, a large number of 2-cyanoacrylate derivatives with excellent herbicidal activity were found. In addition, 2-cyanoacrylate derivatives with different substituents have also been found to have good fungicidal or anti-plant virus activities. To further guide the design and development of new pesticide candidates, the representative research work of 2-cyanoacrylate derivatives with herbicidal, fungicidal, and anti-plant virus activities was reviewed.

PCR-RFLP for Detection of Fusarium graminearum Genotypes with Resistance to Phenamacril

Phenamacril is a cyanoacrylate fungicide that provides excellent control of Fusarium head blight (FHB) or wheat scab, which is caused predominantly by Fusarium graminearum and F. asiaticum. Previous studies revealed that codon mutations of the myosin-5 gene of Fusarium spp. conferred resistance to phenamacril in in vitro lab experiments. In this study, PCR restriction fragment length polymorphism (RFLP) was developed to detect three common mutations (A135T, GCC to ACC at codon 135; S217L, TCA to TTA at codon 217; and E420K, GAA to AAA at codon 420) in F. graminearum induced by fungicide domestication in vitro. PCR products of 841 bp (for mutation of A135T), 802 bp (for mutation of S217L), or 1,649 bp (for mutation of E420K) in the myosin-5 gene were amplified by appropriate primer pairs. Restriction enzyme KpnI, TasI, or DraI was used to distinguish phenamacril-sensitive and -resistant strains with mutation genotypes of A135T, S217L, and E420K, respectively. KpnI digested the 841-bp PCR products of phenamacril-resistant strains with codon mutation A135T into two fragments of 256 and 585 bp. In contrast, KpnI did not digest the PCR products of sensitive strains. TasI digested the 802-bp PCR products of phenamacril-resistant strains with codon mutation S217L into three fragments of 461, 287, and 54 bp. In contrast, TasI digestion of the 802-bp PCR products of phenamacril-sensitive strains resulted in only two fragments of 515 and 287 bp. DraI digested the 1,649-bp PCR products of phenamacril-resistant strains with codon mutation E420K into two fragments of 932 and 717 bp, while the PCR products of phenamacril-sensitive strains was not digested. The three genotypes of resistance mutations were determined by analyzing electrophoresis patterns of the digestion fragments of PCR products. The PCR-RFLP method was evaluated on 48 phenamacril-resistant strains induced by fungicide domestication in vitro and compared with the conventional method (mycelial growth on fungicide-amended agar). The accuracy of the PCR-RFLP method for detecting the three mutation genotypes of F. graminearum resistant to phenamacril was 95.12% compared with conventional method. Bioinformatics analysis revealed that the PCR-RFLP method could also be used to detect the codon mutations of A135T and E420K in F. asiaticum.

Discovery of a species-specific novel antifungal compound against Fusarium graminearum through an integrated molecular modeling strategy

BACKGROUND

The cyanoacrylate fungicide phenamacril targeting fungal myosin I has been widely used for controlling Fusarium head blight (FHB) of wheat caused by the pathogenic fungus Fusarium graminearum worldwide. Therefore, there is great interest in the discovery and development of novel FgMyo1 inhibitors through structure-based drug design for the treatment of FHB.

RESULTS

In this study, the binding mechanism of phenamacril with FgMyo1 was predicted by an integrated molecular modeling strategy. The predicted key phenamacril-binding residues of FgMyo1 were further experimentally validated by point mutagenesis and phenamacril sensitivity assessment. Four novel key residues responsible for phenamacril binding were identified, highlighting the reliability of the theoretical predictions. The subsequent optimization of phenamacril derivatives led to the discovery of a novel compound (10) which shows better activity than phenamacril against conidial germination of F. graminearum, but not against other fungal species. Moreover, 10 also inhibits conidial germination of phenamacril-resistant strains effectively. Further experiments illustrated that application of 10 could dramatically inhibit deoxynivalenol biosynthesis.

CONCLUSION

Overall, our results further optimize and develop the binding model of phenamacril-myosin I. Furthermore, 10 was found and has the potential to be developed as a species-specific fungicide for management of FHB. © 2020 Society of Chemical Industry.

Overexpression of three P450 genes is responsible for resistance to novel pyrimidine amines in Magnaporthe oryzae

BACKGROUND

A series of pyrimidine amine derivatives has been synthesized by modifying the pyrimidine ring group of diflumetorim-a mitochondrial complex I inhibiting fungicide. One derivative, code number SYP-34773, is investigated in this study involving Magnaporthe oryzae, the causal agent of rice blast, which is the most devastating disease in rice. The response, resistance profile and mechanism of M. oryzae to SYP-34773 were investigated, which provides or provide?? important data for the registration and rational use of pyrimidine amines.

RESULTS

SYP-34773 showed greater control efficacy than fungicide isoprothiolane in the field. The baseline sensitivity was established at a mean 50% effective concentration (EC₅₀ ) of 0.08 μg ml^-1 . Four stable SYP-34773-resistant isolates with reduced sensitivity were generated from one (S118) of ten sensitive isolates with a resistance factor of EC₅₀ ranging from 7.00 to 15.00. Conidia production and pathogenicity were similar to that of S118, although there was a significant decrease in mycelial growth and conidial germination in resistant isolates. Positive cross-resistance was observed between SYP-34773 and diflumetorim; and the SYP-34773-resistant isolates were still sensitive to isoprothiolane, carbendazim, fluazinam, azoxystrobin, or prochloraz. RNA-Seq analyses revealed three cytochrome P450 genes were upregulated in the resistant isolate under the treatment with SYP-34773, as confirmed by quantitative real-time PCR. The SYP-34773 content was significantly reduced in the resistant isolate when compared with the parental isolate.

CONCLUSION

The study demonstrated that SYP-34773 exhibits high activity against M. oryzae. Overexpression of three cytochrome P450 genes has an important role in the resistance of M. oryzae to novel pyrimidine amines. © 2020 Society of Chemical Industry.

Comparative Genome Sequence Analyses of Geographic Samples of Aspergillus fumigatus-Relevance for Amphotericin B Resistance

Amphotericin B (AMB) is a major fungicidal polyene agent that has a broad spectrum of action against invasive fungal infections. AMB is typically used as the last-line drug against serious and life-threatening infections when other drugs have failed to eliminate the fungal pathogens. Recently, AMB resistance in Aspergillus fumigatus has become more evident. For example, a high rate of AMB resistance (96%) was noted in the A. fumigatus population in Hamilton, Ontario, Canada. AMB-resistant strains have also been found in other countries. However, the mechanism of AMB resistance remains largely unknown. Here, we investigated the potential genes and mutations associated with AMB resistance using whole-genome sequences and examined AMB resistance distribution among genetic populations. A total of 196 whole-genome sequences representing strains from 11 countries were examined. Analyses of single nucleotide polymorphisms (SNPs) at the whole-genome level revealed that these strains belonged to three divergent genetic clusters, with the majority (90%) of AMB resistant strains located in one of the three clusters, Cluster 2. Our analyses identified over 60 SNPs significantly associated with AMB resistance. Together, these SNPs represent promising candidates from which to investigate the putative molecular mechanisms of AMB resistance and for their potential use in developing rapid diagnostic markers for clinical screening of AMB resistance in A. fumigatus.

Trifluoromethyloxadiazoles: inhibitors of histone deacetylases for control of Asian soybean rust

BACKGROUND

Trifluoromethyloxadiazoles (TFMOs) are selective inhibitors of class II histone deacetylases (HDACs). To date, class II HDACs have not been addressed as target enzymes by commercial fungicides.

RESULTS

Antifungal testing of a broad variety of TFMOs against several important plant pathogens showed activity against only rusts, and especially Phakopsora pachyrhizi, the cause of Asian soybean rust. A structure-activity relationship was established, leading to highly active fungicides that inhibit fungal class II and HOS3-type HDACs of Aspergillus nidulans. Studies of the enzyme-inhibitor binding mode using protein structural information based on the crystal structure of human HDAC4 argue that TFMOs inhibit these enzymes only after undergoing hydration.

CONCLUSION

Fungal class II HDACs are potential target enzymes for the control of at least some biotrophic crop diseases, in particular Asian soybean rust. As with any novel mode-of-action, class II HDAC fungicides would offer the potential to control fungal isolates that show reduced sensitivity toward existing commercial fungicides.

Review on Structures of Pesticide Targets

Molecular targets play important roles in agrochemical discovery. Numerous pesticides target the key proteins in pathogens, insect, or plants. Investigating ligand-binding pockets and/or active sites in the proteins' structures is usually the first step in designing new green pesticides. Thus, molecular target structures are extremely important for the discovery and development of such pesticides. In this manuscript, we present a review of the molecular target structures, including those of antiviral, fungicidal, bactericidal, insecticidal, herbicidal, and plant growth-regulator targets, currently used in agrochemical research. The data will be helpful in pesticide design and the discovery of new green pesticides.

Effects of Mutations in the Phenamacril-Binding Site of Fusarium Myosin-1 on Its Motor Function and Phenamacril Sensitivity

Phenamacril is a Fusarium-specific fungicide used for Fusarium head blight management. The target of phenamacril is FgMyo1, the sole class I myosin in Fusarium graminearum. The point mutation S217L in FgMyo1 is responsible for the high resistance of F. graminearum to phenamacril. Recent structural studies have shown that phenamacril binds to the 50 kDa cleft of the FgMyo1 motor domain, forming extensive interactions, including a hydrogen bond between the cyano group of phenamacril and the hydroxyl group of S217. Here, we produced FgMyo1_IQ2, a truncated FgMyo1 composed of the motor domain and two IQ motifs complexed with the F. graminearum calmodulin in insect Sf9 cells. Phenamacril potently inhibited both the basal and the actin-activated ATPase activities of FgMyo1_IQ2, with an IC₅₀ in a micromolar range. S217 mutations of FgMyo1_IQ2 substantially increased the IC₅₀ of phenamacril. S217T or S217L each increased the IC₅₀ of phenamacril for ∼60-fold, while S217A only increased the IC₅₀ for ∼4-fold. These results indicate that the hydroxyl group of S217 plays an important, but nonessential role in phenamacril binding and that the bulky side chain at the position 217 sterically hinders phenamacril binding. On the other hand, S217P, which might alter the local conformation of the phenamacril-binding site, completely abolished the phenamacril inhibition. Because the cyano group of phenamacril does not form discernible interactions with FgMyo1 other than the nonessential hydrogen bond with the S217 hydroxyl group, we propose the cyano group of phenamacril as a key modification site for the development of novel fungicides.

SYAUP-CN-26 applies its antifungal activity against Botrytis cinerea by disrupting mitochondrial structure and function

This study investigated the effect of SYAUP-CN-26 on mitochondrial structure and function of Botrytis cinerea. The mitochondria, with the addition of SYAUP-CN-26 (EC₅₀ [1.823 mg/L], EC₉₀ [19.263 mg/L], and minimum inhibitory concentration [MIC] [79.754 mg/L]), emerged malformed shape, rough surface and unordered structure. As the concentration of SYAUP-CN-26 increases, the decrease in ATP content and the enhancement in the inhibition of mitochondrial respiratory chain complexes function confirmed that mitochondrial function was disrupted. And the respiratory superposing inhibition showed that SYAUP-CN-26 inhibited the tricarboxylic acid cycle (TCA) pathway of B. cinerea cells. Overall, these results indicated that SYAUP-CN-26 could inhibit mitochondrial structure and function to effect the growth of B. cinerea cells, and inhibition of mitochondrial respiratory chain complexes was a key factor for disruption of B. cinerea mitochondrial function and antifungal activity.

Undefeated-Changing the phenamacril scaffold is not enough to beat resistant Fusarium

Filamentous fungi belonging to the genus Fusarium are notorious plant-pathogens that infect, damage and contaminate a wide variety of important crops. Phenamacril is the first member of a novel class of single-site acting cyanoacrylate fungicides which has proven highly effective against important members of the genus Fusarium. However, the recent emergence of field-resistant strains exhibiting qualitative resistance poses a major obstacle for the continued use of phenamacril. In this study, we synthesized novel cyanoacrylate compounds based on the phenamacril-scaffold to test their growth-inhibitory potential against wild-type Fusarium and phenamacril-resistant strains. Our findings show that most chemical modifications to the phenamacril-scaffold are associated with almost complete loss of fungicidal activity and in vitro inhibition of myosin motor domain ATPase activity.

Pathogenomics and Management of Fusarium Diseases in Plants

There is an urgency to supplant the heavy reliance on chemical control of Fusarium diseases in different economically important, staple food crops due to development of resistance in the pathogen population, the high cost of production to the risk-averse grower, and the concomitant environmental impacts. Pathogenomics has enabled (i) the creation of genetic inventories which identify those putative genes, regulators, and effectors that are associated with virulence, pathogenicity, and primary and secondary metabolism; (ii) comparison of such genes among related pathogens; (iii) identification of potential genetic targets for chemical control; and (iv) better characterization of the complex dynamics of host–microbe interactions that lead to disease. This type of genomic data serves to inform host-induced gene silencing (HIGS) technology for targeted disruption of transcription of select genes for the control of Fusarium diseases. This review discusses the various repositories and browser access points for comparison of genomic data, the strategies for identification and selection of pathogenicity- and virulence-associated genes and effectors in different Fusarium species, HIGS and successful Fusarium disease control trials with a consideration of loss of RNAi, off-target effects, and future challenges in applying HIGS for management of Fusarium diseases.

Characterization of the Resistance Mechanism and Risk of Fusarium verticillioides to the Myosin Inhibitor Phenamacril

Fusarium verticillioides is a major pathogen of maize that causes ear rot and produces mycotoxins. Phenamacril is a novel cyanoacrylate fungicide that exhibits favorable activity against Fusarium species. In this study, the phenamacril-resistant mutants of F. verticillioides were obtained by ultraviolet mutagenesis. Single point mutations of S73L or E276K in the myosin-1 FvMyo1 were proven to be responsible for the high-level resistance of F. verticillioides to phenamacril. Phenamacril had a significant impact on the localization of the wild-type FvMyo1 (FvMyo1^WT-green fluorescent protein [GFP]), but not on the mutated FvMyo1 (FvMyo1^S73L-GFP and FvMyo1^E276K-GFP) at the hyphal tips. Molecular docking analysis suggested that mutation (S73L or E276K) in FvMyo1 altered the binding mode and decreased the binding affinity between phenamacril and myosin-1. There was no significant fitness penalty in mycelial growth, conidiation, and virulence of F. verticillioides associated with resistance to phenamacril. The results will enhance our understanding of the resistance mechanism of F. verticillioides to phenamacril and provide new reference data for the management of maize ear rot.

Resistance risk assessment for Fusarium graminearum to pydiflumetofen, a new succinate dehydrogenase inhibitor

BACKGROUND

Pydiflumetofen is a new generation succinate dehydrogenase inhibitor currently undergoing the process of registration in China for the control of Fusarium head blight in wheat. A resistance risk assessment of Fusarium graminearum to pydiflumetofen was undertaken in this study.

RESULTS

A total of 75 pydiflumetofen-resistant mutants were generated through spontaneous selection and displayed high resistance with an average resistance factor (RF) value of 78. Four mutants were generated through UV mutagenesis and displayed very high resistance with an RF value >1000. The sequence analysis results for Sdh genes and fitness studies revealed the existence of four types of mutations. In particular, 32 spontaneous selection mutants (SP mutants) had an arginine (R) to histidine (H) transition at position 86 in FGSdhC, resulting in seriously reduced fitness. Seven SP mutants had an R to cysteine (C) transition at position 86 in FGSdhC, resulting in reduced fitness. Thirty-six SP mutants had an alanine (A) to valine (V) transition at position 83 in FGSdhC and had no fitness penalties. The efficacy of pydiflumetofen towards a mutant carrying A83V in FGSdhC in vivo was significantly decreased at 42.7%. Four UV mutants had no mutations on all Sdh genes and no fitness penalties. Cross-resistance among boscalid, fluopyram and pydiflumetofen was observed.

CONCLUSION

Sdhc mutations were found and other target site resistance may be present in laboratory PR mutants of F. graminearum. An overall moderate risk of resistance development in F. graminearum was recommended for pydiflumetofen. © 2019 Society of Chemical Industry.

A New Mutation Genotype of K218T in Myosin-5 Confers Resistance to Phenamacril in Rice Bakanae Disease in the Field

In 2017 and 2018, a total of 294 Fusarium fujikuroi isolates were collected from bakanae-diseased rice plants in Jinhua, Shaoxing, and Jiaxing in Zhejiang Province, China. Phenamacril sensitivity of these isolates was determined by the 50% effective concentration value or minimum inhibitory concentration methods. Our results indicated that the phenamacril resistance frequency of F. fujikuroi increased from 18% in 2017 to 47% in 2018, and rice plants infected with F. fujikuroi-resistant isolates could not be protected effectively with 50 mg/liter of phenamacril. Phenamacril-resistant F. fujikuroi isolates obtained from rice fields showed stable resistance, because their fitness levels (i.e., mycelial growth, sporulation, and pathogenicity) were similar to the phenamacril-sensitive isolates. In addition to the point mutation at codon 219 in the myosin-5 gene that conferred resistance to phenamacril, our results also showed another point mutation at codon 218 (AAG→ACG) in myosin-5 that also conferred resistance to phenamacril. In this study, we found rapid development and persistence of diversified genotypes of phenamacril resistance, highlighting the importance of proper use of phenamacril in rice fields. Our results may also help researchers develop new fungicides or new control strategies using combinations of different fungicides in the control of phenamacril-resistant F. fujikuroi isolates.

Structural basis of Fusarium myosin I inhibition by phenamacril

Fusarium is a genus of filamentous fungi that includes species that cause devastating diseases in major staple crops, such as wheat, maize, rice, and barley, resulting in severe yield losses and mycotoxin contamination of infected grains. Phenamacril is a novel fungicide that is considered environmentally benign due to its exceptional specificity; it inhibits the ATPase activity of the sole class I myosin of only a subset of Fusarium species including the major plant pathogens F. graminearum, F. asiaticum and F. fujikuroi. To understand the underlying mechanisms of inhibition, species specificity, and resistance mutations, we have determined the crystal structure of phenamacril-bound F. graminearum myosin I. Phenamacril binds in the actin-binding cleft in a new allosteric pocket that contains the central residue of the regulatory Switch 2 loop and that is collapsed in the structure of a myosin with closed actin-binding cleft, suggesting that pocket occupancy blocks cleft closure. We have further identified a single, transferable phenamacril-binding residue found exclusively in phenamacril-sensitive myosins to confer phenamacril selectivity.

Phenamacril is a recently identified myosin I inhibitor that is a potent and highly species-specific and myosin subtype-selective fungicide. We report the high-resolution structure of the phenamacril-bound myosin I motor domain of the major crop pathogen Fusarium graminearum, providing insight into the molecular mechanism of phenamacril action and resistance. These results are of broad significance for understanding the mode of actions of myosin-based fungicides and for designing novel myosin I inhibitors for crop protection and for treatment of human myosin dysfunction diseases.

Capping proteins regulate fungal development, DON-toxisome formation and virulence in Fusarium graminearum

Deoxynivalenol (DON) is an important trichothecene mycotoxin produced by the cereal pathogen Fusarium graminearum. DON is synthesized in organized endoplasmic reticulum structures called toxisomes. However, the mechanism for toxisome formation and the components of toxisomes are not yet fully understood. In a previous study, we found that myosin I (FgMyo1)-actin cytoskeleton participated in toxisome formation. In the current study, we identified two new components of toxisomes, the actin capping proteins (CAPs) FgCapA and FgCapB. These two CAPs form a heterodimer in F. graminearum, and physically interact with FgMyo1 and Tri1. The deletion mutants ΔFgcapA and ΔFgcapB and the double deletion mutant ΔΔFgcapA/B dramatically reduced hyphal growth, asexual and sexual reproduction and endocytosis. More importantly, the deletion mutants markedly disrupted toxisome formation and DON production, and attenuated virulence in planta. Collectively, these results suggest that the actin CAPs are associated with toxisome formation and contribute to the virulence and development of F. graminearum.

The b-ZIP transcription factor FgTfmI is required for the fungicide phenamacril tolerance and pathogenecity in Fusarium graminearum

BACKGROUND

Fusarium head blight (FHB) is a devastating disease of cereal crops worldwide mainly caused by Fusarium graminearum. Due to the unavailability of FHB-resistant wheat cultivars, chemical fungicide application is currently the most effective approach for controlling FHB now. In the last few years, a novel cyanoacrylate fungicide, phenamacril, has been widely used in China for FHB disease management. In previous studies, we identified that myosin I (FgMyo1) is the target of phenamacril and is essential for mycotoxin deoxynivalenol (DON) biosynthesis and fungal growth. However, the regulation of FgMYO1 gene expression is still largely unknown.

RESULTS

In this study, we identified a b-ZIP transcription factor, FgTfmI, which regulates the mRNA expression of FgMYO1 upon phenamacril treatment. The FgTfmI directly binds to the promoter region of FgMYO1, and is required for the upregulation of FgMYO1 in response to phenamacril treatment. The deletion mutant of FgTFMI (ΔFgTfmI) displayed a slight growth defect, while it showed hypersensitivity to phenamacril, but not to other tested fungicides. FgTfmI also contributed to DON biosynthesis and the infection process in planta.

CONCLUSIONS

The transcription factor FgTfmI plays an important role in regulating transcription of the genes involved in phenamacril tolerance, DON biosynthesis and virulence in F. graminearum. © 2019 Society of Chemical Industry.

PcMuORP1, an Oxathiapiprolin-Resistance Gene, Functions as a Novel Selection Marker for Phytophthora Transformation and CRISPR/Cas9 Mediated Genome Editing

Phytophthora, a genus of oomycetes, contains many devastating plant pathogens, which cause substantial economic losses worldwide. Recently, CRISPR/Cas9-based genome editing tool was introduced into Phytophthora to delineate the functionality of individual genes. The available selection markers for Phytophthora transformation, however, are limited, which can restrain transgenic manipulation in some cases. We hypothesized that PcMuORP1, an endogenous fungicide resistance gene from P. capsici that confers resistance to the fungicide oxathiapiprolin via an altered target site in the ORP1 protein, could be used as an alternative marker. To test this hypothesis, the gene PcMuORP1 was introduced into the CRISPR/Cas9 system and complementation of a deleted gene in P. capsici was achieved using it as a selection marker. All of the oxathiapiprolin-resistant transformants were confirmed to contain the marker gene, indicating that the positive screening rate was 100%. The novel selection marker could also be used in other representative Phytophthora species including P. sojae and P. litchii, also with 100% positive screening rate. Furthermore, comparative studies indicated that use of PcMuORP1 resulted in a much higher efficiency of screening compared to the conventional selection marker NPT II, especially in P. capsici. Successive subculture and asexual reproduction in the absence of selective pressure were found to result in the loss of the selection marker from the transformants, which indicates that the PcMuORP1 gene would have little long term influence on the fitness of transformants and could be reused as the selection marker in subsequent projects. Thus, we have created an alternative selection marker for Phytophthora transformation by using a fungicide resistance gene, which would accelerate functional studies of genes in these species.

Use of GC-MS based metabolic fingerprinting for fast exploration of fungicide modes of action

BACKGROUND

The widespread occurrence of fungicide resistance in fungal plant pathogens requires the development of new compounds with different mode(s) of action (MOA) to avoid cross resistance. This will require a rapid method to identify MOAs.

RESULTS

Here, gas chromatography-mass spectrometry (GC-MS) based metabolic fingerprinting was used to elucidate the MOAs of fungicides. Botrytis cinerea, an important pathogen of vegetables and flowers, can be inhibited by a wide range of chemical fungicides with different MOAs. A sensitive strain of B. cinerea was exposed to EC₅₀ concentrations of 13 fungicides with different known MOAs and one with unknown MOA. The mycelial extracts were analyzed for their "metabolic fingerprint" using GC-MS. A comparison among the GC-MS vector' profiles of cultures treated with fungicides were performeded. A model based on hierarchical clustering was established which allowed these antifungal compounds to be distinguished and classified coinciding with their MOAs. Thus, metabolic fingerprinting represents a rapid, convenient, and information-rich method for classifying the MOAs of antifungal substances. The biomarkers of fungicide MOAs were also established by an analysis of variance and included succinate for succinate dehydrogenase inhibitors and cystathionine for methionine synthesis inhibitors. Using the metabolic model and the common perturbation of metabolites, the new fungicide SYP-14288 was identified as having the same MOA as fluazinam.

CONCLUSION

This study provides a comprehensive database of the metabolic perturbations of B. cinerea induced by diverse MOA inhibitors and highlights the utility of metabolic fingerprinting for defining MOAs, which will assist in the development and optimization of new fungicides.

Molecular characterization of carbendazim resistance of Fusarium species complex that causes sugarcane pokkah boeng disease

BACKGROUND

Pokkah boeng is one of the most serious and devastating diseases of sugarcane and causes significant loss in cane yield and sugar content. Although carbendazim is widely used to prevent fungal diseases, the molecular basis of Fusarium species complex (FSC) resistance to carbendazim remains unknown.

RESULTS

The EC50 (fungicide concentration that inhibits 50% of mycelial growth) values of carbendazim for 35 FSC isolates collected in cane growing regions of China were ranged from 0.5097 to 0.6941 μg mL- 1 of active ingredient (a.i.), in an average of 0.5957 μg a.i. mL- 1. Among carbendazim-induced mutant strains, SJ51M (F. verticillioides) had a CTG rather than CAG codon (Q134L) at position 134 of the FVER_09254 gene, whereas in the mutant strain HC30M (F. proliferatum) codon ACA at position 351 of the FPRO_07779 gene was replaced by ATA (T351I). Gene expression profiling analysis was performed for SJ51M and its corresponding wild type strain SJ51, with and without carbendazim treatment. The gene expression patterns in SJ51 and SJ51M changed greatly as evidenced by the detection of 850 differentially expressed genes (DEGs). Functional categorization indicated that genes associated with oxidation-reduction process, ATP binding, integral component of membrane, transmembrane transport and response to stress showed the largest expression changes between SJ51M and SJ51. The expression levels of many genes involved in fungicide resistance, such as detoxification enzymes, drug efflux transporters and response to stress, were up-regulated in SJ51M compared to SJ51 with and without carbendazim treatment.

CONCLUSION

FSC was sensitive to carbendazim and had the potential for rapid development of carbendazim resistance. The transcriptome data provided insight into the molecular pathways involved in FSC carbendazim resistance.

Phenamacril is a reversible and noncompetitive inhibitor of Fusarium class I myosin

The cyanoacrylate compound phenamacril (also known as JS399-19) is a recently identified fungicide that exerts its antifungal effect on susceptible Fusarium species by inhibiting the ATPase activity of their myosin class I motor domains. Although much is known about the antifungal spectrum of phenamacril, the exact mechanism behind the phenamacril-mediated inhibition remains to be resolved. Here, we describe the characterization of the effect of phenamacril on purified myosin motor constructs from the model plant pathogen and phenamacril-susceptible species Fusarium graminearum, phenamacril-resistant Fusarium species, and the mycetozoan model organism Dictyostelium discoideum Our results show that phenamacril potently (IC50 ∼360 nm), reversibly, and noncompetitively inhibits ATP turnover, actin binding during ATP turnover, and motor activity of F. graminearum myosin-1. Phenamacril also inhibits the ATPase activity of Fusarium avenaceum myosin-1 but has little or no inhibitory effect on the motor activity of Fusarium solani myosin-1, human myosin-1c, and D. discoideum myosin isoforms 1B, 1E, and 2. Our findings indicate that phenamacril is a species-specific, noncompetitive inhibitor of class I myosin in susceptible Fusarium sp.