Chromones from the endophytic fungus Bipolaris eleusines

Eight previously undescribed chromones eleusineketones A-H (1-8), as well as eight known compounds (9-16), were isolated from the endophytic fungus Bipolaris eleusines. These planar structures were created using an in-depth analysis of their spectral data, which included 1D, 2D, and HRESIMS data. Furthermore, the absolute configurations of compounds 1, 2, and 6 were determined by spectroscopic analysis and quantum chemical computational approaches, and compound 5 was determined by single-crystal X-ray diffraction analysis. The cytotoxic activity assay revealed that compounds 1 and 5 both inhibited MDA-MB-231 cells with IC50 values of 14.48 μM and 17.99 μM, respectively.

Identification of biochemical indices for brown spot (Bipolaris oryzae) disease resistance in rice mutants and hybrids

Brown spot caused by Bipolaris oryzae is a major damaging fungal disease of rice which can decrease the yield and value of produce due to grain discoloration. The objectives of the current study were to investigate and understand the biochemical indices of brown spot disease resistance in rice. A total of 108 genotypes (mutant and hybrid) along with Super Basmati and parent RICF-160 were evaluated against brown spot disease. The genotypes exhibiting resistant and susceptible responses to brown spot disease according to the IRRI standard disease rating scale were screened and selected. To study the biochemical response mechanism, forty five selected genotypes along with Super Basmati and RICF-160 were analyzed using the biochemical markers. The physiological and biochemical analysis provided valuable insights and confirmed the resistance of rice hybrids and mutants against brown spot disease. Positive correlations were observed among stress bio-markers and disease response. Rice genotypes i.e. Mu-AS-8, Mu-AS-19, Mu-AS-20 and Mu-AS-35 exhibited moderate resistant response while Hy-AS-92, Hy-AS-98, Hy-AS-99, Hy-AS-101, Hy-AS-102 and Hy-AS-107 showed resistant response to brown spot disease. Brown spot resistant rice genotypes had lesser values of malondialdehyde and total oxidant status and higher antioxidant activities i.e. superoxide dismutase, peroxidase, total phenolic content and lycopene. The selected resistant rice genotypes had resistance capacity against Bipolaris oryzae stress. In conclusion, identified resistant mutants i.e. Mu-AS-8, Mu-AS-19, Mu-AS-20 and Mu-AS-35 and hybrids i.e. Hy-AS-92, Hy-AS-98, Hy-AS-99, Hy-AS-101, Hy-AS-102 and Hy-AS-107 could be used in rice breeding program to achieve sustainable rice production by coping the emerging challenge of brown spot disease under variable climate conditions.

Biological activities and mass fragmentation pathways of meroterpenoid cochlioquinones from plant pathogenic fungus Bipolaris sorokiniana

Cochlioquinones are a member of meroterpenoids that partially possessed phenolic hydroxyls with potential antioxidant activities. This study investigated the mass fragmentation pathways, antioxidant, cytotoxic, and phytotoxic activities of cochlioquinone analogs. The mass fragmentation pathways of cochlioquinones (1-7) were firstly analyzed using UPLC-Q-TOF-MS/MS, in which Retro Diels-Alder reaction, neutral loss, and McLafferty rearrangement were the main cleavage patterns. Compound 8 and 9 (a unique new analog) were then isolated in target. Cochlioquinones (4-6, 9) displayed strong antioxidant activities for DPPH radical scavenging assay as the first antioxidant effects report. In addition, 1-9 exhibited cytotoxic activities against B16 cells (IC50 from 1.91 to 12.33 μM) and Hep G2 cells (IC50 from 3.21 to 77.15 μM), and 5, 7, and 8 showed phytotoxic activities against foxtail leaves. These biological activities imply that cochlioquinones can be as antioxidant agents for food additives or bioactive molecules for cancer drugs and pesticides.

Genome-wide association mapping for field spot blotch resistance in South Asian spring wheat genotypes

Spot blotch caused by Bipolaris sorokiniana ((Sacc.) Shoemaker) (teleomorph: Cochliobolus sativus [Ito and Kuribayashi] Drechsler ex Dastur) is an economically important disease of warm and humid regions. The present study focused on identifying resistant genotypes and single-nucleotide polymorphism (SNP) markers associated with spot blotch resistance in a panel of 174 bread spring wheat lines using field screening and genome-wide association mapping strategies. Field experiments were conducted in Agua Fria, Mexico, during the 2019-2020 and 2020-2021 cropping seasons. A wide range of phenotypic variation was observed among genotypes tested during both years. Twenty SNP markers showed significant association with spot blotch resistance on 15 chromosomes, namely, 1A, 1B, 2A, 2B, 2D, 3A, 3B, 4B, 4D, 5A, 5B, 6A, 6B, 7A, and 7B. Of these, two consistently significant SNPs on 5A, TA003225-0566 and TA003225-1427, may represent a new resistance quantitative trait loci. Further, in the proximity of Tsn1 on 5B, AX-94435238 was the most stable and consistent in both years. The identified genomic regions could be deployed to develop spot blotch-resistant genotypes, particularly in the spot blotch-vulnerable wheat growing areas.

Molecular Mechanism Underlying Pathogenicity Inhibition by Chitosan in Cochliobolus heterostrophus

Chitosan, as a natural nontoxic biomaterial, has been demonstrated to inhibit fungal growth and enhance plant defense against pathogen infection. However, the antifungal pattern and mechanism of how chitosan application evokes plant defense are poorly elucidated. Herein, we provide evidence that chitosan exposure is fungicidal to C. heterostrophus. Chitosan application impairs conidia germination and appressorium formation of C. heterostrophus and has a pronounced effect on reactive oxygen species production, thereby preventing infection in maize. In addition, the toxicity of chitosan to C. heterostrophus requires Mkk1 and Mps1, two key components in the cell wall integrity pathway. The Δmkk1 and Δmps1 mutants were more tolerant to chitosan than the wild-type. To dissect chitosan-mediated plant defense response to C. heterostrophus, we conducted a metabolomic analysis, and several antifungal compounds were upregulated in maize upon chitosan treatment. Taken together, our findings provide a comprehensive understanding of the mechanism of chitosan-alleviated infection of C. heterostrophus, which would promote the application of chitosan in plant protection in agriculture.

Bipoladien A, a Sesterterpenoid Containing an Undescribed 5/8/5/7 Carbon Skeleton from Bipolaris maydis

Bipoladiens A-E (1-5), five new ophiobolin-derived sesterterpenoids, and a known compound 6 (bipolaricin R) were isolated from the cultures of the phytopathogenic fungus Bipolaris maydis. Their structures and absolute configurations were elucidated based on comprehensive spectroscopic analyses, HRESIMS, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analyses. Notably, compound 1 has an undescribed tetracyclic 5/8/5/7 fused carbon skeleton, and compound 2 possesses a rare multicyclic caged ring system. The biosynthetic pathway of 1 was proposed starting from 6 via a series of oxidation and cyclization reactions. Compound 6 showed excellent antiproliferation and apoptosis induction effects against A549 cell line. Additionally, compounds 5 and 6 exhibited noticeable antimicrobial ability against Bacillus cereus, Staphylococcus aureus, and Staphylococcus epidermidis. These findings not only developed the chemical and bioactivities diversities of ophiobolin-sesterterpenoid but also provided an idea to boost the application of natural products in the control of food pathogens.

against Bipolaris sorokiniana

BACKGROUND

Spot blotch is a serious foliar disease of barley (Hordeum vulgare L.) plants caused by Bipolaris sorokiniana, which is a hemibiotrophic ascomycete that has a global impact on productivity. Some Trichoderma spp. is a promising candidate as a biocontrol agent as well as a plant growth stimulant. Also, the application of nanomaterials in agriculture limits the use of harmful agrochemicals and helps improve the yield of different crops. The current study was carried out to evaluate the effectiveness of Trichoderma. cf. asperellum and the biosynthesized titanium dioxide nanoparticles (TiO2 NPs) to manage the spot blotch disease of barley caused by B. sorokiniana and to assess the plant's innate defense response.

RESULTS

Aloe vera L. aqueous leaf extract was used to biosynthesize TiO2 NPs by reducing TiCl4 salt into TiO2 NPs and the biosynthesized NPs were detected using SEM and TEM. It was confirmed that the NPs are anatase-crystalline phases and exist in sizes ranging from 10 to 25 nm. The T. cf. asperellum fungus was detected using morphological traits and rDNA ITS analysis. This fungus showed strong antagonistic activity against B. sorokiniana (57.07%). Additionally, T. cf. asperellum cultures that were 5 days old demonstrated the best antagonistic activity against the pathogen in cell-free culture filtrate. Also, B. sorokiniana was unable to grow on PDA supplemented with 25 and 50 mg/L of TiO2 NPs, and the diameter of the inhibitory zone increased with increasing TiO2 NPs concentration. In an in vivo assay, barley plants treated with T. cf. asperellum or TiO2 NPs were used to evaluate their biocontrol efficiency against B. sorokiniana, in which T. cf. asperellum and TiO2 NPs enhanced the growth of the plant without displaying disease symptoms. Furthermore, the physiological and biochemical parameters of barley plants treated with T. cf. asperellum or TiO2 NPs in response to B. sorokiniana treatment were quantitively estimated. Hence, T. cf. asperellum and TiO2 NPs improve the plant's tolerance and reduce the growth inhibitory effect of B. sorokiniana.

CONCLUSION

Subsequently, T. cf. asperellum and TiO2 NPs were able to protect barley plants against B. sorokiniana via enhancement of chlorophyll content, improvement of plant health, and induction of the barley innate defense system. The present work emphasizes the major contribution of T. cf. asperellum and the biosynthesized TiO2 NPs to the management of spot blotch disease in barley plants, and ultimately to the enhancement of barley plant quality and productivity.

Sativene Sesquiterpenoids from the Plant Endophytic Fungus Bipolaris victoriae S27 and Their Potential as Plant-Growth Regulators

Thirteen new sativene sesquiterpenoids (1 and 3-14), one new natural product (2), and 16 known compounds (15-30) were isolated from the endophytic fungus Bipolaris victoriae S27. Their structures were elucidated by extensive spectroscopic analysis, NMR and ECD calculations, and X-ray crystal diffractions. Compound 1 represented the first example of sativene sesquiterpenoids with a 6/5/3/5-caged tetracyclic ring system. All obtained compounds were evaluated for their plant-growth regulatory activity. The results showed that 1, 3, 4, 6, 8, 11, 12, 17, 19, 26, and 27 could suppress the growth of Arabidopsis thaliana, while 2, 5, 13, 15, 18, and 25 showed promoting effects. Among them, compound 3 showed the most potent plant-growth inhibitory activity, which is obviously superior to that of the marked herbicide glyphosate.

The histidine kinases regulate allyl-isothiocyanate sensitivity in Cochliobolus heterostrophus

BACKGROUD

Two-component histidine kinase (HK) phosphorelay signaling systems play important roles in differentiation, virulence, secondary metabolite production and response to environmental signals. Allyl isothiocyanate (A-ITC) is a hydrolysis product of glucosinolates with excellent antifungal activity. Our previous study indicated that the mycelial growth of Cochliobolus heterostrophus was significantly hindered by A-ITC. However, the function of HK in regulating A-ITC sensitivity was not clear in C. heterostrophus, the causal agent of Southern corn leaf blight.

RESULTS

In this study, the role of HKs was investigated in C. heterostrophus. Deletion of the HK coding gene ChNIK1 resulted in dramatically increased sensitivity of C. heterostrophus to A-ITC. In addition, ΔChnik1 mutant exhibited significantly decreased conidiation and increased sensitivity to NaCl, KCl, tebuconazole and azoxystrobin, but deletion of the other five HK genes did not affect the A-ITC sensitivity of C. heterostrophus. ChSLN1, ChNIK4, ChNIK8 and ChMAK2 are essential for conidiation and response to H2 O2 and sodium dodecyl sulfate. However, deletion of NIKs had on effect on significant virulence.

CONCLUSION

Our findings demonstrate that the HKs play different roles in A-ITC sensitivity in C. heterostrophus. © 2023 Society of Chemical Industry.

Enhanced use of chemical fertilizers and mitigation of heavy metal toxicity using biochar and the soil fungus Bipolaris maydis AF7 in rice: Genomic and metabolomic perspectives

Chemical fertilizers are the primary source of crop nutrition; however, their increasing rate of application has created environmental hazards, such as heavy metal toxicity and eutrophication. The synchronized use of chemical fertilizers and eco-friendly biological tools, such as microorganisms and biochar, may provide an efficient foundation to promote sustainable agriculture. Therefore, the current study aimed to optimize the nutrient uptake using an inorganic fertilizer, sulfate of potash (SOP) from the plant growth-promoting fungus Bipolaris maydis AF7, and biochar under heavy metal toxicity conditions in rice. Bioassay analysis showed that AF7 has high resistance to heavy metals and a tendency to produce gibberellin, colonize the fertilizer, and increase the intake of free amino acids. In the plant experiment, the co-application of AF7 +Biochar+MNF+SOP significantly lowered the heavy metal toxicity, enhanced the nutrient uptake in the rice shoots, and improved the morphological attributes (total biomass). Moreover, the co-application augmented the glucose and sucrose levels, whereas it significantly lowered the endogenous phytohormone levels (salicylic acid and jasmonic acid) in the rice shoots. The increase in nutrient content aligns with the higher expression of the OsLSi6, PHT1, and OsHKT1 genes. The plant growth traits and heavy metal tolerance of AF7 were validated by whole-genome sequencing that showed the presence of the heavy metal tolerance and detoxification protein, siderophore iron transporter, Gibberellin cluster GA4 desaturase, and DES_1 genes, as well as others that regulate glucose, antioxidants, and amino acids. Because the AF7 +biochar+inorganic fertilizer works synergistically, nutrient availability to the crops could be improved, and heavy metal toxicity and environmental hazards could be minimized.

Maydistacins A-G, Terpestacin-type Sesterterpenoids with Anti-inflammatory Activity from the Phytopathogenic Fungus Bipolaris maydis

Seven undescribed terpestacin-type sesterterpenoids, maydistacins A-G (1-7), along with two known congeners (8 and 9), were isolated from the phytopathogenic fungus Bipolaris maydis collected from the leaves of Hypericum longistylum. The structures of 1-7 were elucidated based on extensive spectroscopic analysis, chemical methods, NMR calculations with DP4+ probability analysis, and comparison of experimental and calculated electronic circular dichroism (ECD) calculations. In vitro anti-inflammatory effects of these compounds were tested in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Compound 1 exhibited inhibition of the production of nitric oxide in LPS-induced macrophages, with an IC50 value of 19 ± 2 μM. A dexamethasone control displayed an IC50 value of 6.7 ± 0.6 μM. Compound 1 is the first terpestacin-type sesterterpenoid reported to display anti-inflammatory activity and may provide a novel chemical scaffold for the discovery of new anti-inflammatory drugs.

Infection-specific transcriptional patterns of the maize pathogen Cochliobolus heterostrophus unravel genes involved in asexual development and virulence

Southern corn leaf blight (SCLB) caused by Cochliobolus heterostrophus is a destructive disease that threatens global maize (Zea mays) production. Despite many studies being conducted, very little is known about molecular processes employed by the pathogen during infection. There is a need to understand the fungal arms strategy and identify novel functional genes as targets for fungicide development. Transcriptome analysis based on RNA sequencing was carried out across conidia germination and host infection by C. heterostrophus. The present study revealed major changes in C. heterostrophus gene expression during host infection. Several differentially expressed genes (DEGs) induced during C. heterostrophus infection could be involved in the biosynthesis of secondary metabolites, peroxisome, energy metabolism, amino acid degradation and oxidative phosphorylation. In addition, histone acetyltransferase, secreted proteins, peroxisomal proteins, NADPH oxidase and transcription factors were selected for further functional validation. Here, we demonstrated that histone acetyltransferases (Hat2 and Rtt109), secreted proteins (Cel61A and Mep1), peroxisomal proteins (Pex11A and Pex14), NADPH oxidases (NoxA, NoxD and NoxR) and transcription factors (Crz1 and MtfA) play essential roles in C. heterostrophus conidiation, stress adaption and virulence. Taken together, our study revealed major changes in gene expression associated with C. heterostrophus infection and identified a diverse repertoire of genes critical for successful infection.

Rare Bipolaris Species Fungal Periprosthetic Hip Infection in an Immunocompetent Host: A Case Report

CASE

We present a case report of a 64-year-old man who developed a rare Bipolaris species fungal periprosthetic joint infection (PJI) after revision arthroplasty for complications associated with a metal-on-metal total hip arthroplasty. The patient underwent a 2-stage debridement with antibiotic bead placement and implant retention, along with chronic antifungal suppression. At the 2-year follow-up, the patient remained asymptomatic.

CONCLUSION

Fungal PJI with filamentous fungi such as Bipolaris species is a rare clinical entity. This case report highlights the clinical presentation and management of this rare condition.

The morphoanatomy of Serjania erecta Radlk (Sapindaceae) provides evidence of biotrophic interactions by endophytic fungi within leaves

Background

The leaves of Serjania erecta Radlk (Sapindaceae) are renowned in ethnobotany for their medicinal properties and are significant as a medicinal resource for traditional Brazilian communities. As necrotic spots are common on these leaves, indicating interaction with phytopathogenic fungi, it was hypothesized that biotrophic fungal species colonize the leaf tissues of S. erecta.

Methods

To test this hypothesis, we employed standard techniques in plant anatomy, which enabled us to investigate the interaction of fungal structures with plant tissues and describe the morphoanatomical and histochemical characteristics of the epidermis and limbus of S. erecta.

Results

The anatomical analysis showed the existence of leaf teeth on the leaf tips. Additionally, hyphae, conidiospores, and spores of Bipolaris/Curvularia species were detected on the adaxial epidermis. Moreover, melanized microsclerotia were found in glandular areas of the leaf teeth and the phloem, providing evidence of biotrophic behavior. The hypothesis that biotrophic phytopathogenic fungi interact with S. erecta leaf tissues was confirmed, despite the presence of many bioactive compounds (such as flavonoids, alkaloids, and essential oils), as evidenced by histochemical analyses. The presence of tector, glandular, and scabiform trichomes on the leaf teeth and epidermis was also revealed. This study presents, for the first time, the synthesis of essential oils and alkaloids in the leaves of S. erecta. Additionally, it investigates previously unexplained aspects of the anatomy and histochemistry of the species, as well as its interaction with resident microorganisms. Therefore, it is recommended that future research focus on extracting and characterizing the oils and alkaloids of S. erecta, as well as exploring other aspects related to its microbiome and its relationship.

Comparative genomic and phenotypic analyses of pathogenic fungi Neoscytalidium dimidiatum and Bipolaris papendorfii isolated from human skin scraping

Neoscytalidium dimidiatum and Bipolaris species are fungal plant pathogens that have been reported to cause human diseases. Recently, we have isolated numerous N. dimidiatum and Bipolaris species from the skin scrapings and nails of different patients. In this work, we have sequenced the genome of one strain of N. dimidiatum. The sequenced genome was compared to that of a previously reported Bipolaris papendorfii genome for a better understanding of their complex lifestyle and broad host-range pathogenicity. Both N. dimidiatum UM 880 (~ 43 Mb) and B. papendorfii UM 226 (~ 33 Mb) genomes include 11,015-12,320 putative coding DNA sequences, of which 0.51-2.49% are predicted transposable elements. Analysis of secondary metabolism gene clusters revealed several genes involved in melanin biosynthesis and iron uptake. The arsenal of CAZymes related to plants pathogenicity is comparable between the species, including genes involved in hemicellulose and pectin decomposition. Several important gene encoding keratinolytic peptidases were identified in N. dimidiatum and B. papendorfii, reflecting their potential pathogenic role in causing skin and nail infections. In this study, additional information on the metabolic features of these two species, such as nutritional profiling, pH tolerance, and osmotolerant, are revealed. The genomic characterization of N. dimidiatum and B. papendorfii provides the basis for the future functional studies to gain further insights as to what makes these fungi persist in plants and why they are pathogenic to humans.

Endophytic Metarhizium robertsii suppresses the phytopathogen, Cochliobolus heterostrophus and modulates maize defenses

Fungi in the genus Metarhizium (Hypocreales: Clavicipitaceae) are insect-pathogens and endophytes that can benefit their host plant through growth promotion and protection against stresses. Cochliobolus heterostrophus (Drechsler) Drechsler (Pleosporales: Pleosporaceae) is an economically-significant phytopathogenic fungus that causes Southern Corn Leaf Blight (SCLB) in maize. We conducted greenhouse and lab-based experiments to determine the effects of endophytic M. robertsii J.F. Bisch., Rehner & Humber on growth and defense in maize (Zea mays L.) infected with C. heterostrophus. We inoculated maize seeds with spores of M. robertsii and, at the 3 to 4-leaf stage, the youngest true leaf of M. robertsii-treated and untreated control plants with spores of C. heterostrophus. After 96 h, we measured maize height, above-ground biomass, endophytic colonization by M. robertsii, severity of SCLB, and expression of plant defense genes and phytohormone content. We recovered M. robertsii from 74% of plants grown from treated seed. The severity of SCLB in M. robertsii-treated maize plants was lower than in plants inoculated only with C. heterostrophus. M. robertsii-treated maize inoculated or not inoculated with C. heterostrophus showed greater height and above-ground biomass compared with untreated control plants. Height and above-ground biomass of maize co-inoculated with M. robertsii and C. heterostrophus were not different from M. robertsii-treated maize. M. robertsii modulated the expression of defense genes and the phytohormone content in maize inoculated with C. heterostrophus compared with plants not inoculated with C. heterostrophus and control plants. These results suggest that endophytic M. robertsii can promote maize growth and reduce development of SCLB, possibly by induced systemic resistance mediated by modulation of phytohormones and expression of defense and growth-related genes in maize.

Chemical Investigations of Differentially Oxidized Polycylic Pyrroles from Bipolaris Fungi: Synthetic Entry Into the Bipolamine Alkaloids

indolizidine alkaloids of unusual biosynthetic origin have recently been characterized from several species of fungi within the Pleosporaceae family. Possessing distinct polycyclic architectures with two embedded electron-rich pyrroles as well as reported antibacterial activity against gram positive and negative pathogens, these natural products represent attractive targets for total synthesis. Herein we survey the differential functionalization of a chemically sensitive bispyrrole framework resulting in the preparation of multiple bipolamine alkaloids, work which sheds light on their innate chemical reactivity and potential biosynthetic relationships.

Enzyme activity and population genetic structure analysis in wheat associated with resistance to Bipolaris sorokiniana-common root rot diseases

Common root rot disease (CRR) caused by Bipolaris sorokiniana (Sacc.) (Pleosporaceae), is an important fungal disease of wheat, Triticum aestivum (Poaceae), causing considerable yield losses globally. Incorporating genetic resistance in cultivated crops is considered the most efficient and sustainable solution to counter root rot diseases. Moreover, resistance to CCR is quantitative in nature, and thus the mechanism is poorly understood. To this aim, we analyzed the activities of defense-related enzymes; peroxidase (POX), superoxide dismutase (SOD), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL), β-1,3-glucanase (GLU) and chitinase (CHI), as well as total phenol content (TPC) to CRR on the three known resistant wheat 'Alvand' and 'Bam', 'Mehregan' at different time points (wpi) following CRR pathogen, B. sorokiniana inoculation. Of which, were selected out of 33 wheat cultivars previously screened for resistance to CRR. We also analyzed the genetic variability of the entire germplasm, 33 wheat cultivars using seven simple sequence repeat (SSR) primer pairs. The activity of antioxidant enzymes was increased in the related resistant genotypes. Of which, 'Bam' had the highest increase in PPO, and GLU activities, followed by 'Alvand' in SOD, PAL, and CHI significantly. Whereas, 'Mehregan' showed the highest level of TPC, POX, and CAT activities. In addition, five out of seven used SSR primers produced a total of 20 polymorphic bands, of which the number of alleles in each gene locus varied within 3-7 bands. The polymorphism information content (PIC) value also ranged from 0.44 to 0.81, with the mean of 0.65, Shannon Information Index (I) between 0.29 and 0.63 with an average of 0.47 per locus, and Nei's gene diversity (h) value varied from 0.16 to 0.44 with an average of 0.32. The average number of effective alleles was 1.52, ranging between 1.21 and 1.8. The gene locus Xgwm 140 showed the highest diversity in the population genetic structure, which explains the ability of the primers to resolve the assayed germplasm. Thus, resistance to CRR in wheat was mainly related to the enhancement of antioxidant enzymes, although the specific metabolic pathways require further study. This study presents new insights for understanding resistance mechanisms of the selected wheat cultivars to CRR, thus improving wheat yield in the future.

Identification of meroterpenoids from Bipolaris victoriae S27 and their potential activity against tumor metastasis and inhibition of the NF-κB signaling pathway

Three undescribed meroterpenoids, named bipolacochlioquinones A-C, together with seven known compounds, were isolated from the plant endophytic fungus Bipolaris victoriae S27 derived from the fresh stems of Rubia podantha Diels. Their structures were mainly determined by extensive spectroscopic analysis. The relative configurations of bipolacochlioquinones A-C were assigned using the ROESY spectrum, comparison of their spectral data with that reported in the literatures, and NMR calculations. Moreover, their complete absolute configurations were further established by electronic circular dichroism calculations using density functional theory. Among them, bipolacochlioquinone A is found to represent the first example of previously undescribed 6/6/6/6/6 pentacyclic dioxane-containing cochlioquinones, and bipolacochlioquinone B possesses a rare 6/6/6/6/5 pentacyclic system bearing a tetrahydrofuran ring fused to a polyketide and a sesquiterpenoid subunit. All compounds were evaluated for their inhibitory effects on tumor growth, metastasis, and the NF-κB signaling pathway. Among them, bipolacochlioquinone C and cochlioquinone A show the most potent cytotoxicities and NF-κB inhibitory activities. The effects of bipolacochlioquinone C and cochlioquinone A on the expression of NF-κB-associated proteins were also evaluated using western blotting. These results indicate that bipolacochlioquinone C and cochlioquinone A can inhibit the growth and metastasis of HCT116 and MDA-MB-231 cells by suppressing the NF-κB signaling pathway.

The Autophagy Genes ChATG4 and ChATG8 Are Required for Reproductive Development, Virulence, and Septin Assembly in Cochliobolus heterostrophus

Autophagy is a highly conserved degrading process that is crucial for cell growth and development in eukaryotes, especially when they face starvation and stressful conditions. To evaluate the functions of Atg4 and Atg8 in mycelial growth, asexual and sexual development, and virulence in Cochliobolus heterostrophus, ΔChatg4 and ΔChatg8 mutants were generated by gene replacement. Strains deleted for ChATG4 and ChATG8 genes showed significant changes in vegetative growth and development of conidia and ascospores compared with the wild-type strain. The autophagy process was blocked and virulence was reduced dramatically in ΔChatg4 and ΔChatg8 mutants. In addition, deletion of ChATG4 and ChATG8 disordered Cdc10 subcellular localization and formation of septin rings. The direct physical interaction between ChAtg4 and ChAtg8 was detected by yeast two-hybrid assay, and ChAtg4-GFP was dispersed throughout the cytoplasm, although GFP-ChAtg8 appeared as punctate structures. All phenotypes were restored in complemented strains. Taken together, these findings indicate that ChATG4 and ChATG8 are crucial for autophagy to regulate fungal growth, development, virulence, and localization of septin in C. heterostrophus.

A fungal Bipolaris bicolor strain as a potential bioherbicide for goosegrass (Eleusine indica) control

BACKGROUND

Tea, one of the most important commercial crops on earth, is strongly affected by weeds on productivity and quality. Bioherbicides are shedding new light on weed control in tea gardens in an economical and safe manner.

RESULTS

A pathogenic strain SYNJC-2-2 was isolated from diseased leaves of a noxious weed, goosegrass (Eleusine indica), from a tea garden in Zhejiang Province, China. It was identified as the fungal species Bipolaris bicolor based on the morphological characteristics and phylogenetic analysis. The potential of the B. bicolor strain SYNJC-2-2 as a bioherbicide was assessed by determining its efficacy to control weeds and selectivity to crops, its infection process and the influence of environmental conditions on conidial production and germination. The ED₉₀ (effective dose of conidia resulting in 90 disease index) of SYNJC-2-2 on goosegrass was 2 × 10⁴ conidia mL^-1 . Additionally, three Poaceae weeds, Setaria viridis, Microstegium vimineum and Pennisetum alopecuroides, were also extremely susceptible to SYNJC-2-2. SYNJC-2-2 was safe to 14 out of 17 crop species in nine families, especially tea plants. Conidial germination, hyphal growth and appressorial formation occurred within 3 to 6 h on goosegrass leaves. Hyphae invaded leaf tissues mainly through epidermal cell junctions and cracks, causing cell death and necrotic lesions within 2 days on inoculated leaves and killing goosegrass plants within 7 days. Furthermore, SYNJC-2-2 has a strong adaptability to environmental variables and high conidial production capacity on goosegrass juice agar media.

CONCLUSION

Bipolaris bicolor strain SYNJC-2-2 has the potential to be developed as a bioherbicide for controlling goosegrass, especially in tea gardens.

A novel effector, CsSp1, from Bipolaris sorokiniana, is essential for colonization in wheat and is also involved in triggering host immunity

The hemibiotrophic pathogen Bipolaris sorokiniana causes root rot, leaf blotching, and black embryos in wheat and barley worldwide, resulting in significant yield and quality reductions. However, the mechanism underlying the host-pathogen interactions between B. sorokiniana and wheat or barley remains unknown. The B. sorokiniana genome encodes a large number of uncharacterized putative effector proteins. In this study, we identified a putative secreted protein, CsSp1, with a classic N-terminal signal peptide, that is induced during early infection. A split-marker approach was used to knock out CsSP1 in the Lankao 9-3 strain. Compared with the wild type, the deletion mutant ∆Cssp1 displayed less radial growth on potato dextrose agar plates and produced fewer spores, and complementary transformation completely restored the phenotype of the deletion mutant to that of the wild type. The pathogenicity of the deletion mutant in wheat was attenuated even though appressoria still penetrated the host. Additionally, the infectious hyphae in the deletion mutant became swollen and exhibited reduced growth in plant cells. The signal peptide of CsSp1 was functionally verified through a yeast YTK12 secretion system. Transient expression of CsSp1 in Nicotiana benthamiana inhibited lesion formation caused by Phytophthora capsici. Moreover, CsSp1 localized in the nucleus and cytoplasm of plant cells. In B. sorokiniana-infected wheat leaves, the salicylic acid-regulated genes TaPAL, TaPR1, and TaPR2 were down-regulated in the ∆Cssp1 strain compared with the wild-type strain under the same conditions. Therefore, CsSp1 is a virulence effector and is involved in triggering host immunity.

A maize leucine-rich repeat receptor-like protein kinase mediates responses to fungal attack

A maize receptor kinase controls defense response to fungal pathogens by regulating jasmonic acid and antimicrobial phytoalexin production. Plants use a range of pattern recognition receptors to detect and respond to biotic threats. Some of these receptors contain leucine-rich repeat (LRR) domains that recognize microbial proteins or peptides. Maize (Zea mays) has 226 LRR-receptor like kinases, making it challenging to identify those important for pathogen recognition. In this study, co-expression analysis with genes for jasmonic acid and phytoalexin biosynthesis was used to identify a fungal induced-receptor like protein kinase (FI-RLPK) likely involved in the response to fungal pathogens. Loss-of-function mutants in fi-rlpk displayed enhanced susceptibility to the necrotrophic fungal pathogen Cochliobolus heterostrophus and reduced accumulation of jasmonic acid and the anti-microbial phytoalexins -kauralexins and zealexins- in infected tissues. In contrast, fi-rlpk mutants displayed increased resistance to stem inoculation with the hemibiotrophic fungal pathogen Fusarium graminearum. These data indicate that FI-RLPK is important for fungal recognition and activation of defenses, and that F. graminearum may be able to exploit FI-RLPK function to increase its virulence.

Synergistic Action of Commercially Available Fungicides for Protecting Wheat from Common Root Rot Caused by Bipolaris sorokiniana in China

Wheat (Triticum aestivum) common root rot (CRR) caused by predominant fungal pathogen Bipolaris sorokiniana occurs in all wheat-growing regions worldwide and is difficult to control. In this study, the efficacy of eight fungicides against Bipolaris sorokiniana was examined in in vitro assays, and we determined that the combined application of two fungicides significantly inhibits the growth of fungal mycelium. Half of the maximal effective concentration of a mixture containing fludioxonil and difenoconazole in the ratio 1:4 was 0.0372 mg/liter, and the cotoxicity coefficient was 160.14. Under an environmentally controlled pot assay, seed treatment with the mixture of fludioxonil and difenoconazole in the 1:4 ratio demonstrated the best control efficiency at seedling and adult stages, respectively. The best synergistic mixture on seed treatment was assessed in a 2-year field experiment at Hebei, China. The best control efficacy achieved at the seedling and adult stages was 82.65% and 68.48%, respectively. Overall, the in vitro mycelial growth inhibition assay and controlled-environment and field studies indicated that the synergistic action of a mixture of fludioxonil and difenoconazole provides effective control against wheat CRR. These findings highlight the potential application of the fungicide combination for controlling CRR and reducing the selection pressure on fungal pathogens by lessening the use of various fungicides in the field.

Green silver nano-particles: synthesis using rice leaf extract, characterization, efficacy, and non-target effects

Green synthesis of silver nano-particles (AgNPs) from silver nitrate was carried out using purple-colored rice leaves' extracts containing higher phenols, anthocyanins, and flavonoids. The efficacy of synthesized AgNPs was tested against rice diseases and investigation was carried out to check negative effect of AgNPs on soil microbes. Substantial reduction of total anthocyanins, total phenols, and total flavonoids was observed in reaction mixture during AgNP formation indicating the role of secondary metabolites on AgNP formation and stabilization. Scanning electron microscopy coupled with energy-dispersive spectroscopic images and FTIR spectral analysis of AgNPs confirmed the presence of elemental silver encapped by biomolecules. The optimized reaction parameters for synthesis of AgNPs from silver nitrate were (a) 48 h of incubation, (b) 9:1 (v/v) 1 mM AgNO3:plant extract, and (c) room temperature at 20-30 °C. Zeta potential and hydrodynamic particle sizes of synthesized AgNPs were ranged between - 16.61 to - 29.45 mV and 36-107 nm, respectively, at different time of incubation. AgNPs could control effectively Rhizoctonia solani and Xanthomonas oryzae pv. Oryzae and Helminthosporium oryzae. AgNPs at higher concentration could cause negative effect on microbial biomass carbon and soil enzymes for distant future. But the negative effects of AgNP solution (10% of 1 mM AgNPs) were comparable to commercial fungicide, carbendazim. The synthesized AgNPs with desirable characters were effective against a number of disease-causing pathogens in rice, and it can be recommended as broad-spectrum pesticide.