Arrestin-Coding Genes Regulate Endocytosis, Sporulation, Pathogenicity, and Stress Resistance in Arthrobotrys oligospora

Electron-Transferring Flavoprotein and Its Dehydrogenase Required for Fungal Pathogenicity in Arthrobotrys oligospora

Electron transfer flavoprotein (ETF) plays an important function in fatty acid beta oxidation and the amino acid metabolic pathway. It can provide pathogenicity to some opportunistic fungi via modulating cellular metabolite composition. Arthrobotrys oligospora is a typical invasion fungus to nematodes. Its ETF characterization is still unknown. Here, we showed that the mutations of A. oligospora ETF (Aoetfα and Aoetfβ) and its dehydrogenase (Aoetfdh) led to severe defects in mitochondrial integrity and blocked fatty acid metabolism. The pathogenicity-associated trap structures were completely suppressed when exposed to nematode-derived ascarosides and nutrition signals, including ammonia and urea. Compared to the wild-type strain, the nematode predatory activity was significantly reduced and delayed. But surprisingly, the rich nutrition could restore the massive trap and robust predatory activity in the mutant Aoetfβ beyond all induction cues. Moreover, the deletion of Aoetfβ has led to the accumulation of butyrate-like smell, which has a strong attraction to Caenorhabditis elegans nematodes. Ultimately, ETF and its dehydrogenase play a crucial role in nematode-trapping fungi, highlighting mitochondrial metabolite fluctuations that are connected to pathogenesis and further regulating the interactions between fungi and nematodes.

Foliar mycobiome remains unaltered under urban air-pollution but differentially express stress-related genes

Air pollution caused by tropospheric ozone contributes to the decline of forest ecosystems; for instance, sacred fir, Abies religiosa (Kunth) Schltdl. & Cham. forests in the peri-urban region of Mexico City. Individual trees within these forests exhibit variation in their response to ozone exposure, including the severity of visible symptoms in needles. Using RNA-Seq metatranscriptomic data and ITS2 metabarcoding, we investigated whether symptom variation correlates with the taxonomic and functional composition of fungal mycobiomes from needles collected in this highly polluted area in the surroundings of Mexico City. Our findings indicate that ozone-related symptoms do not significantly correlate with changes in the taxonomic composition of fungal mycobiomes. However, genes coding for 30 putative proteins were differentially expressed in the mycobiome of asymptomatic needles, including eight genes previously associated with resistance to oxidative stress. These results suggest that fungal communities likely play a role in mitigating the oxidative burst caused by tropospheric ozone in sacred fir. Our study illustrates the feasibility of using RNA-Seq data, accessible from global sequence repositories, for the characterization of fungal communities associated with plant tissues, including their gene expression.

Analysis of Nuclear Dynamics in Nematode-Trapping Fungi Based on Fluorescent Protein Labeling

Nematophagous fungi constitute a category of fungi that exhibit parasitic behavior by capturing, colonizing, and poisoning nematodes, which are critical factors in controlling nematode populations in nature, and provide important research materials for biological control. Arthrobotrys oligospora serves as a model strain among nematophagous fungi, which begins its life as conidia, and then its hyphae produce traps to capture nematodes, completing its lifestyle switch from saprophytic to parasitic. There have been many descriptions of the morphological characteristics of A. oligospora lifestyle changes, but there have been no reports on the nuclear dynamics in this species. In this work, we constructed A. oligospora strains labeled with histone H2B-EGFP and observed the nuclear dynamics from conidia germination and hyphal extension to trap formation. We conducted real-time imaging observations on live cells of germinating and extending hyphae and found that the nucleus was located near the tip. It is interesting that the migration rate of this type of cell nucleus is very fast, and we speculate that this may be related to the morphological changes involved in the transformation to a predatory lifestyle. We suggest that alterations in nuclear shape and fixation imply the immediate disruption of the interaction with cytoskeletal mechanisms during nuclear migration. In conclusion, these findings suggest that the signal initiating nuclear migration into fungal traps is generated at the onset of nucleus entry into a trap cell. Our work provides a reference for analysis of the dynamics of nucleus distribution and a means to visualize protein localization and interactions in A. oligospora.

Ammonia and Nematode Ascaroside Are Synergistic in Trap Formation in Arthrobotrys oligospora

Nematode-trapping (NT) fungi are natural predators of the soil living nematodes. Diverse external signals mediate the generation of predatory devices of NT fungi. Among these, broad ascarosides and nitrogenous ammonia are highly efficient inducers for trap structure initiation. However, the overlay effect of ammonia and ascaroside on the trap morphogenesis remains unclear. This study demonstrated that the combination of nitrogenous substances with nematode-derived ascarosides led to higher trap production compared to the single inducing cues; notably, ammonia and Ascr#18 had the most synergistic effect on the trap in A. oligospora. Further, the deletion of ammonia transceptor Amt43 blocked trap formation against ammonia addition in A. oligospora but not for the ascaroside Ascr#18 induction. Moreover, ammonia addition could promote plasma endocytosis in the process of trap formation. In contrast, ascaroside addition would facilitate the stability of intracellular organization away from endocytosis. Therefore, there is a synergistic effect on trap induction from different nitrogenous and ascaroside signals.

Recent Advances in Life History Transition with Nematode-Trapping Fungus Arthrobotrys oligospora and Its Application in Sustainable Agriculture

Parasitic nematodes cause great annual loss in the agricultural industry globally. Arthrobotrys oligospora is the most prevalent and common nematode-trapping fungus (NTF) in the environment and the candidate for the control of plant- and animal-parasitic nematodes. A. oligospora is also the first recognized and intensively studied NTF species. This review highlights the recent research advances of A. oligospora as a model to study the biological signals of the switch from saprophytism to predation and their sophisticated mechanisms for interacting with their invertebrate hosts, which is of vital importance for improving the engineering of this species as an effective biocontrol fungus. The application of A. oligospora in industry and agriculture, especially as biological control agents for sustainable purposes, was summarized, and we discussed the increasing role of A. oligospora in studying its sexual morph and genetic transformation in complementing biological control research.

Amphiphysin AoRvs167-Mediated Membrane Curvature Facilitates Trap Formation, Endocytosis, and Stress Resistance in Arthrobotrysoligospora

Bin1/Amphiphysin/Rvs (BAR) domain-containing proteins mediate fundamental cellular processes, including membrane remodeling and endocytosis. Nematode-trapping (NT) fungi can differentiate to form trapping structures through highly reorganized cell membranes and walls. In this study, we identified the NT fungus Arthrobotrys oligospora ortholog of yeast Rvs167 and documented its involvement in membrane bending and endocytosis. We further confirmed that the deletion of AoRvs167 makes the fungus more hypersensitive to osmotic salt (Nacl), higher temperatures (28 to 30 °C), and the cell wall perturbation agent Congo red. In addition, the disruption of AoRvs167 reduced the trap formation capacity. Hence, AoRvs167 may regulate fungal pathogenicity through the integrity of plasma membranes and cell walls.

Regulatory Mechanism of Trap Formation in the Nematode-Trapping Fungi

Nematode-trapping (NT) fungi play a significant role in the biological control of plant- parasitic nematodes. NT fungi, as a predator, can differentiate into specialized structures called “traps” to capture, kill, and consume nematodes at a nutrient-deprived condition. Therefore, trap formation is also an important indicator that NT fungi transition from a saprophytic to a predacious lifestyle. With the development of gene knockout and multiple omics such as genomics, transcriptomics, and metabolomics, increasing studies have tried to investigate the regulation mechanism of trap formation in NT fungi. This review summarizes the potential regulatory mechanism of trap formation in NT fungi based on the latest findings in this field. Signaling pathways have been confirmed to play an especially vital role in trap formation based on phenotypes of various mutants and multi-omics analysis, and the involvement of small molecule compounds, woronin body, peroxisome, autophagy, and pH-sensing receptors in the formation of traps are also discussed. In addition, we also highlight the research focus for elucidating the mechanism underlying trap formation of NT fungi in the future.