Global diversity and biogeography of potential phytopathogenic fungi in a changing world

Discovery of a polyketide carboxylate phytotoxin from a polyketide glycoside hybrid by β-glucosidase mediated ester bond hydrolysis

Fungal phytotoxins cause significant harm to agricultural production or lead to plant diseases. Discovering new phytotoxins, dissecting their formation mechanism and understanding their action mode are important for controlling the harmful effects of fungal phytopathogens. In this study, a long-term unsolved cluster (polyketide synthase 16, PKS16 cluster) from Fusarium species was thoroughly investigated and a series of new metabolites including both complex α-pyrone-polyketide glycosides and simple polyketide carboxylates were identified from F. proliferatum. The whole pathway reveals an unusual assembly and inactivation process for phytotoxin biosynthesis, with key points as follows: (1) a flavin dependent monooxygenase catalyzes Baeyer-Villiger oxidation on the linear polyketide side chain of α-pyrone-polyketide glycoside 8 to form ester bond compound 1; (2) a β-glucosidase unexpectedly mediates the ester bond hydrolysis of 1 to generate polyketide carboxylate phytotoxin 2; (3) oxidation occurring on the terminal inert carbons of 2 by intracellular oxidase(s) eliminates its phytotoxicity. Our work identifies the chemical basis of the PKS16 cluster in phytotoxicity, shows that polyketide carboxylate is a new structural type of phytotoxin in Fusarium and importantly uncovers a rare ester bond hydrolysis function of β-glucosidase family enzymes.

Unraveling the distribution pattern and driving forces of soil microorganisms under geographic barriers

The Altai Mountains (ALE) and the Greater Khingan Mountains (GKM) in northern China are forest regions dominated by coniferous trees. These geographically isolated regions provide an ideal setting for studying microbial biogeographic patterns. In this study, we employed high-throughput techniques to obtain DNA sequences of soil myxomycetes, bacteria, and fungi and explored the mechanisms underlying the assembly of both local and cross-regional microbial communities in relation to environmental factors. Our investigation revealed that the environmental heterogeneity in ALE and GKM significantly affected the succession and assembly of soil bacterial communities at cross-regional scales. Specifically, the optimal environmental factors affecting bacterial Bray-Curtis similarity were elevation and temperature seasonality. The spatial factors and climate change impact on bacterial communities under the geographical barriers surpassed that of local soil microenvironments. The assembly pattern of bacterial communities transitions from local drift to cross-regional heterogeneous selection. Environmental factors had a relatively weak influence on myxomycetes and fungi. Both soil myxomycetes and fungi faced considerable dispersal limitation at local and cross-regional scales, ultimately leading to weak geographical distribution patterns.IMPORTANCEThe impact of environmental selection and dispersal on the soil microbial spatial distribution is a key concern in microbial biogeography, particularly in large-scale geographical patterns. However, our current understanding remains limited. Our study found that soil bacteria displayed a distinct cross-regional geographical distribution pattern, primarily influenced by environmental selection. Conversely, the cross-regional geographical distribution patterns of soil myxomycetes and fungi were relatively weak. Their composition exhibited a weak association with the environment at local and cross-regional scales, with assembly primarily driven by dispersal limitation.

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.

National-scale investigation reveals the dominant role of phyllosphere fungal pathogens in sorghum yield loss

Fungal plant pathogens threaten crop production and sustainable agricultural development. However, the environmental factors driving their diversity and nationwide biogeographic model remain elusive, impacting our capacity to predict their changes under future climate scenarios. Here, we analyzed potential fungal plant pathogens from 563 samples collected from 57 agricultural fields across China. Over 28.0% of fungal taxa in the phyllosphere were identified as potential plant pathogens, compared to 22.3% in the rhizosphere. Dominant fungal plant pathogen groups were Cladosporium (in the phyllosphere) and Fusarium (in the rhizosphere), with higher diversity observed in the phyllosphere than in rhizosphere soil. Deterministic processes played an important role in shaping the potential fungal plant pathogen community assembly in both habitats. Mean annual precipitation and temperature were the most important factor influencing phyllosphere fungal plant pathogen richness. Significantly negative relationships were found between fungal pathogen diversity and sorghum yield. Notably, compared to the rhizosphere, the phyllosphere fungal plant pathogen diversity played a more crucial role in sorghum yield. Together, our work provides novel insights into the factors governing the spatial patterns of fungal plant pathogens in the crop microbiome, and highlights the potential significance of aboveground phyllosphere fungal plant pathogens in crop productivity.