Isobenzofuranones and isocoumarins from kiwi endophytic fungus Paraphaeosphaeria sporulosa and their antibacterial activity against Pseudomonas syringae pv. actinidiae

Discovery of a Biocontrol Strain Trichaptum laricinum: Its Metabolites and Antifungal Activity against Pathogenic Fungus Colletotrichum anthrisci

Finding safe and environmentally friendly fungicides is one of the important strategies in modern pesticide research and development. In this work, the antipathogenic effects of the fungus Trichaptum laricinum against the anthracnose pathogen Colletotrichum anthrisci were studied. The EtOAc extract of T. laricinum showed remarkable antifungal activity against C. anthrisci with an inhibition rate of 50% at 256 μg/mL. Bioguided isolation of the cultural broth of T. laricinum produced four new drimane sesquiterpenes, trichalarins A-D (1-4), and six other metabolites (5-10). Their structures were established by extensive spectroscopic methods, quantum chemical calculations, and single-crystal X-ray diffraction. All compounds exhibited antifungal activity against C. anthrisci with minimum inhibitory concentrations (MICs) of 8-64 μg/mL in vitro. Further in vivo assay suggested that compounds 2, 6, and 9 could significantly inhibit C. anthrisci growth in avocado fruit with inhibition rates close to 80% at the concentration of 256 μg/mL, while compounds 2 and 6 had an inhibition rate over 90% at the concentration of 512 μg/mL. The EtOAc extract of T. laricinum had no inhibitory effect on Pinus massoniana seed germination and growth at the concentration of 2 mg/mL, showing good environmental friendliness. Thus, the fungus T. laricinum could be considered as an ideal biocontrol strain, and its metabolites provided a diverse material basis for the antibiotic agents.

New meroterpenoids and polyketides from the endophytic fungus Paraphaeosphaeria sp. C-XB-J-1 and their anti-inflammatory and SARS-CoV-2 Mpro inhibitory activities

Seven new meroterpenoids, paraphaeones A-G (1-7), and two new polyketides, paraphaeones H-I (8-9), along with eight known compounds (10-17), were isolated from the endophytic fungus Paraphaeosphaeria sp. C-XB-J-1. The structures of 1-9 were identified through the analysis of 1H, 13C, and 2D NMR spectra, assisted by HR-ESI-MS data. Compounds 1 and 7 exhibited a dose-dependent decrease in lactate dehydrogenase levels, with IC50 values of 1.78 μM and 1.54 μM, respectively. Moreover, they inhibited the secretion of IL-1β and CASP-1, resulting in a reduction in the activity levels of NLRP3 inflammasomes. Fluorescence microscopy results indicated that compound 7 concentration-dependently attenuated cell pyroptosis. Additionally, compounds 4 and 7 showed potential inhibitory effects on the severe acute respiratory syndrome coronavirus-2 main protease (SARS-CoV-2 Mpro), with IC50 values of 10.8 ± 0.9 μM and 12.9 ± 0.7 μM, respectively.

Challenging Aromaticity: Revealing a Thioesterase Domain in a Fungal Nonreducing Polyketide Synthase Governing the Production of 3-Methylene Isochromanone

Thioesterase (TE) domain exerts a great influence over the structure of the final product and TE-released nonreduced polyketides (nrPKs) retain aromaticity. 3-Methylene isochromanones are lactones with a unique olefin at C3 that disrupts the aromaticity, whose biosynthetic details are speculative. Our study unveils the complete biosynthesis of ascochin, in which the construction of the 3-methylene isochromanone backbone is achieved by a nonreducing polyketide synthase (nrPKS) alone and two subsequent oxidations are involved. Intriguingly, the TEAscD serves as a gatekeeper to direct the product release toward formation of nonaromatic 3-methylene isochromanone, rather than the typical aromatic product.

Identification and Characterization of a Plant Endophytic Fungus Paraphaosphaeria sp. JRF11 and Its Growth-Promoting Effects

Endophytic fungi establish mutualistic relationships with host plants and can promote the growth and development of plants. In this study, the endophytic fungus JRF11 was isolated from Carya illinoinensis. Sequence analysis of the internal transcribed spacer (ITS) region and 18S rRNA gene combined with colonial and conidial morphology identified JRF11 as a Paraphaosphaeria strain. Plant-fungus interaction assays revealed that JRF11 showed significant growth-promoting effects on plants. In particular, JRF11 significantly increased the root biomass and soluble sugar content of plants. Furthermore, transcriptome analysis demonstrated that JRF11 treatment reprogrammed a variety of genes involved in plant mitogen-activated protein kinase (MAPK) signaling and starch and sucrose metabolism pathways through Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. Our research indicates that beneficial endophytic fungi are able to interact with plants and exhibit outstanding plant growth-promoting activities.

Scientific and technological advances in the development of sustainable disease management tools: a case study on kiwifruit bacterial canker

Plant disease outbreaks are increasing in a world facing climate change and globalized markets, representing a serious threat to food security. Kiwifruit Bacterial Canker (KBC), caused by the bacterium Pseudomonas syringae pv. actinidiae (Psa), was selected as a case study for being an example of a pandemic disease that severely impacted crop production, leading to huge economic losses, and for the effort that has been made to control this disease. This review provides an in-depth and critical analysis on the scientific progress made for developing alternative tools for sustainable KBC management. Their status in terms of technological maturity is discussed and a set of opportunities and threats are also presented. The gradual replacement of susceptible kiwifruit cultivars, with more tolerant ones, significantly reduced KBC incidence and was a major milestone for Psa containment - which highlights the importance of plant breeding. Nonetheless, this is a very laborious process. Moreover, the potential threat of Psa evolving to more virulent biovars, or resistant lineages to existing control methods, strengthens the need of keep on exploring effective and more environmentally friendly tools for KBC management. Currently, plant elicitors and beneficial fungi and bacteria are already being used in the field with some degree of success. Precision agriculture technologies, for improving early disease detection and preventing pathogen dispersal, are also being developed and optimized. These include hyperspectral technologies and forecast models for Psa risk assessment, with the latter being slightly more advanced in terms of technological maturity. Additionally, plant protection products based on innovative formulations with molecules with antibacterial activity against Psa (e.g., essential oils, phages and antimicrobial peptides) have been validated primarily in laboratory trials and with few compounds already reaching field application. The lessons learned with this pandemic disease, and the acquired scientific and technological knowledge, can be of importance for sustainably managing other plant diseases and handling future pandemic outbreaks.

Effects of Bacillus velezensis GUAL210 control on edible rose black spot disease and soil fungal community structure

Introduction

Rose black spot is an economically important disease that significantly decreases flower yield. Fungicide and biological control are effective approaches for controlling rose black spot. The objective of this study was to evaluate the effect of application of biological and chemical control agents, including Bacillus velezensis (GUAL210), Bacillus sp. (LKW) and fungicide (CP) on the black spot disease and rhizosphere fungal community structure of edible rose.

Methods

In this study, the R. chinensis 'Crimson Glory' was taken as the research object, and the field experiment was designed by randomized block design. The experiment contained 3 treatments (CP, GUAL210, LKW) and 1 control. The control effect and growth promoting effect of fungicide and biological control on rose black spot were compared. The composition and diversity of rhizosphere soil fungal community of different treatments of rose were studied by high-throughput sequencing method. The fungal community composition, correlation of environmental factors and differences in metabolic pathways related to rose disease were analyzed, and the correlation between rhizosphere soil fungal community of rose and biological control of disease was explored.

Results and discussion

Both disease incidence and disease index differed significantly among groups (LKW < GUAL210 < CP < CK), and disease control effect exhibited no significant difference between GUAL210 and LKW (60.96% and 63.86%, respectively). Biological control was superior to chemical control in terms of disease prevention effects and duration, and it significantly increased the number of branches and flowers of rose plants. Ascomycota and Basidiomycota accounted for more than 74% of the total fungal abundance, and the abundance of Ascomycota was highest in CK, followed by GUAL210, CP and LKW, which was consistent with the disease occurrence in each group. The analysis of metabolic pathways showed that the HSERMETANA-PWY in each experimental group was significantly lower than that in control group. The Shannon index in each experimental group was significantly lower than that in control group. PCoA analysis showed that the rhizosphere fungal community structure in each experimental group was significantly different from that in control group. Trichoderma, Paraphaeosphaeria, Suillus, Umbelopsis in GUAL210, and Galerina in LKW replaced Mortierella, Pestalotiopsis, Ustilaginoidea, Paraconiothyrium, Fusarium, and Alternaria as dominant flora, and played a nonneglectable role in reducing disease occurrence. The difference in rhizosphere fungal community structure had an important impact on the incidence of rose black spot disease. Biological control is crucial for establishing environment-friendly ecological agriculture. GUAL210 has promising prospects for application and development, and may be a good substitute for chemical control agents.

Polyketide- and Terpenoid-Derived Metabolites Produced by a Marine-Derived Fungus, Peroneutypa sp

Bioassay-guided investigation of the EtOAc-soluble extract of a culture of the marine-derived fungus Peroneutypa sp. M16 led to the isolation of seven new polyketide- and terpenoid-derived metabolites (1, 2, 4-8), along with known polyketides (3, 9-13). Structures of compounds 1, 2, and 4-8 were established by analysis of spectroscopic data. Absolute configurations of compounds 1, 2, 4, 6, 7, and 8 were determined by the comparison of experimental ECD spectra with calculated CD data. Compound 5 exhibited moderate antiplasmodial activity against both chloroquine-sensitive and -resistant strains of Plasmodium falciparum.

DPPH Radical Scavenging Activity of New Phenolics from the Fermentation Broth of Mushroom Morehella importuna

In recent years, wild morel mushroom species have begun to be widely cultivated in China due to their high edible and medicinal values. To parse the medicinal ingredients, we employed the technique of liquid-submerged fermentation to investigate the secondary metabolites of Morehella importuna. Two new natural isobenzofuranone derivatives (1-2) and one new orsellinaldehyde derivative (3), together with seven known compounds, including one o-orsellinaldehyde (4), phenylacetic acid (5), benzoic acid (6), 4-hydroxy-phenylacetic acid (7), 3,5-dihydroxybenzoic acid (8), N,N'-pentane-1,5-diyldiacetamide (9), and 1H-pyrrole-2-carboxylic acid (10), were obtained from the fermented broth of M. importuna. Their structures were determined according to the data of NMR, HR Q-TOF MS, IR, UV, optical activity, and single-crystal X-ray crystallography. TLC-bioautography displayed that these compounds possess significant antioxidant activity with the half DPPH free radical scavenging concentration of 1.79 (1), 4.10 (2), 4.28 (4), 2.45 (5), 4.40 (7), 1.73 (8), and 6.00 (10) mM. The experimental results would shed light on the medicinal value of M. importuna for its abundant antioxidants.

Endophytes in Agriculture: Potential to Improve Yields and Tolerances of Agricultural Crops

Endophytic fungi and bacteria live asymptomatically within plant tissues. In recent decades, research on endophytes has revealed that their significant role in promoting plants as endophytes has been shown to enhance nutrient uptake, stress tolerance, and disease resistance in the host plants, resulting in improved crop yields. Evidence shows that endophytes can provide improved tolerances to salinity, moisture, and drought conditions, highlighting the capacity to farm them in marginal land with the use of endophyte-based strategies. Furthermore, endophytes offer a sustainable alternative to traditional agricultural practices, reducing the need for synthetic fertilizers and pesticides, and in turn reducing the risks associated with chemical treatments. In this review, we summarise the current knowledge on endophytes in agriculture, highlighting their potential as a sustainable solution for improving crop productivity and general plant health. This review outlines key nutrient, environmental, and biotic stressors, providing examples of endophytes mitigating the effects of stress. We also discuss the challenges associated with the use of endophytes in agriculture and the need for further research to fully realise their potential.

Antibacterial Metabolites from Kiwi Endophytic Fungus Fusarium tricinctum, a Potential Biocontrol Strain for Kiwi Canker Disease

Pseudomonas syringae pv. actinidiae (Psa) is a Gram-negative bacterium causing the kiwifruit canker disease, resulting in serious economic losses to the kiwifruit industry. This study investigated the use of an endophytic fungus, Fusarium tricinctum, obtained from the kiwi plant (Actinidia chinesis) as a potential biocontrol strain against the Psa. F. tricinctum showed an inhibition rate of 59.5% in vitro against Psa. Bioassay-guided isolation was conducted on the cultural broth of F. tricinctum and seven new imidazole alkaloids, (±)-fusaritricine J ((±)-1) and fusaritricines K-P (2-7), and four enniatins (8-11) were identified. Their absolute configurations were established through extensive spectroscopic methods, quantum chemical calculations, and X-ray single crystal diffraction. Compounds 1, 4, 5, and 8-11 showed comparable anti-bacterial activities against Psa as positive control, with MIC values of 25-50 μg/mL. Further cell membrane permeability assay suggested that the most active compound 4 could destroy the bacterial cell wall structure. Hence, F. tricinctum metabolites could be applied as potential anti-Psa agents, and F. tricinctum could be considered a biocontrol strain for the control of the kiwifruit canker disease.

Recent advances in the discovery, biosynthesis, and therapeutic potential of isocoumarins derived from fungi: a comprehensive update

Microorganisms still remain the main hotspots in the global drug discovery avenue. In particular, fungi are highly prolific producers of vast structurally diverse specialized secondary metabolites, which have displayed a myriad of biomedical potentials. Intriguingly, isocoumarins is one distinctive class of fungal natural products polyketides, which demonstrated numerous remarkable biological and pharmacological activities. This review article provides a comprehensive state-of-the-art over the period 2000-2022 about the discovery, isolation, classifications, and therapeutic potentials of isocoumarins exclusively reported from fungi. Indeed, a comprehensive list of 351 structurally diverse isocoumarins were documented and classified according to their fungal sources [16 order/28 family/55 genera] where they have been originally discovered along with their reported pharmacological activities wherever applicable. Also, recent insights around their proposed and experimentally proven biosynthetic pathways are also briefly discussed.

Unexpected Formation of 4-[(1-Carbamoyl-3-oxo-1,3-dihydro-2-benzofuran-1-yl)amino]benzoic Acid from 4-[(3-Amino-1-oxo-1H-2-benzopyran-4-yl)amino]benzoic Acid

With the aim of obtaining derivatives belonging to 2′,3′-diphenyl-3H-spiro[[2]benzofuran-1,4′-imidazole]-3,5′(3′H)-dione nucleus, we synthesized 4-[(3-amino-1-oxo-1H-2-benzopyran-4-yl)amino]benzoic acid (a 3,4-diaminoisocoumarine derivative), a known precursor of 4-[(1-carbamoyl-3-oxo-1,3-dihydro-2-benzofuran-1-yl)amino]benzoic acid (a phthalide–carboxamide-bearing system) by a novel methodology that we report here. The reaction conditions were optimized to afford the latter in 62% yield.

Recent advances in natural phthalides: Distribution, chemistry, and biological activities

Phthalides, an important class of bioactive natural products, are widely distributed in plants, fungi, lichens, and liverworts. Amon them, n-butylphthalide, a phthalide monomer, has been approved to cure ischemic stroke. Owing to their good bioactivities in anti-microbial, anti-inflammatory, anti-tumor, anti-diabetic, and other aspects, a large number of researches have been conducted on phthalides from nature materials. In recent years, hundreds of novel natural phthalides were obtained. This review provides profiles of the advances in the distribution, chemistry, and biological activities of natural phthalides in 2016-2022.

Endophytic community of Chaenomeles speciosa fruits: Screening for biodiversity and antifungal activity

Fruit crops of the genus Chaenomeles Lindl are considered today as a superfood due to accumulation of biologically active compounds with antioxidant ability and known health-promoting properties. Successful introduction of this non-traditional culture in the steppe zone of Ukraine characterised by an unfavourable climate suggests the functioning of effective protective mechanisms in plants, including those that can be provided by the influence of endophytic microorganisms. However, there is little information about the endophytic community of Chaenomeles plants. Herein, the current study was aimed to isolate the endophytic fungi from the Ch. speciosa fruits and evaluate their biological activities against the phytopathogens. The study was carried out based on the collection of the Botanical Garden of Oles Honchar Dnipro National University (Dnipro city, Ukraine). Three media, namely PDA, MPA, and Gause’s medium were used for isolation of endophytic fungi. Colonies of isolates for identification were grown on PDA, Czapek's agar, and Czapek’s yeast autolysate media. Six fungal endophytic isolates derived from both peel and pulp of Ch. speciosa fruits have been morphologically identified using macroscopic and microscopic techniques, and assigned to the genus Penicillium (sections Chrysogena, Penicillium, Viridicata), and genus Talaromyces (section Talaromyces). Species P. expansum, P. viridicatum, and P. hirsutum were identified among the peel isolates, while P. chrysogenum, P. cyclopium, and P. purpurogenum were among the pulp isolates. Antagonistic ability of the endophytic isolates against phytopathogenic fungi was evaluated using the dual culture method. The results showed moderate to high antifungal capacity of the endophytic isolates against the phytopathogenic strains of the Fusarium genus. The growth inhibition of F. culmorum mycelium due to the influence of endophytic isolates was 51.5–81.3%, and the inhibition of the growth of F. oxysporum colonies was in the range of 68.4–86.6% as compared with control. There were no significant differences in the antagonistic ability between endophytic isolates derived from the peel and pulp of the fruit. Taken together, our findings indicated the great potential of the endophytic fungi from Ch. speciosa fruits as a source for the development of biocontrol agents and discovery of new bioactive compounds.

Synthesis, structural characterization, antioxidant and antidiabetic activities, DFT calculation, and molecular docking of novel substituted phenolic and heterocyclic compounds

The current work describes the preparation of three unexpected compounds: a tetrasubstituted phenolic compound, an isocoumarin, and a pyranopyridine, bearing various substituent groups obtained through the condensation of 6-methyl-4-hydroxypyran-2-one 1 with 2-aminopyridine 2 under mild conditions. Plausible mechanisms explaining the formation of these compounds have been presented. Their structures have been elucidated using spectral data and confirmed by crystallographic studies. Furthermore, optimized geometries of and electronic distribution of FMOs orbitals are investigated in the PCM solvent model at the B3LYP/6-311++G(d,p) level of theory. The compounds were tested for their antioxidant and antidiabetic activities. Moreover, the binding interactions between the compounds and α-glucosidase and α-amylase were determined through their docking into the binding sites of the target enzymes using the Autodock package.Communicated by Ramaswamy H. Sarma.