Molecular analysis of arthrosporol, ascaroside and nutritional signaling during the interaction of the nematode-trapping fungus Duddingtonia flagrans with Caenorhabditis elegans

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Organismic interactions are crucial for live on earth. Such interactions are often very sophisticated and have been shaped during evolution. In the case of fungal interactions, they can range from symbiotic to pathogenic to predatory. We are studying nematode-trapping, predatory fungi, which produce different trapping devices, lure nematodes into the traps, invade the nematodes with penetrating hyphae and subsequently colonize the entire worm body. Our model is Duddintonia flagrans, which grows well in the lab and produces adhesive trap networks. D. flagrans is also used as a biocontrol agent in livestock farming, and may be further developed against plant pathogenic nematodes in the future. As a difference to other nematode-trapping fungi, it produces resistant chlamydospores, which may be used for its application in soil. One of the first steps of the fungal-nematode interaction is the fungal sensing of the nematodes and the initiation of trap formation. Because trap formation only makes sense, if a certain number of nematodes is present and other nutrients are not available, an interesting interorganismic communication system based on low-molecular weight compounds evolved. Trap formation is inhibited by secondary metabolites, different arthrosporols and 6-methyl salicylic acid. The fungi are able to sense ascarosides – important nematode molecules – and thereby the presence of nematodes. Ascarosides inhibit the production of the fungal-derived, negative signaling molecules, which leads to trap induction. The system resembles a quorum sensing mechanism, enabling the sensing of the nematode density.In the current research proposal, the signaling cascades underlying trap induction and morphogenesis will be analyzed. Preliminary data suggest the involvement of G-proteins and G-protein coupled membrane receptors (GPCRs) in the integration of the nutritional status and the presence of nematodes. The signaling cascades will be resolved by gene deletion and overexpression experiments. We will test the hypothesis if some fungal ascaroside-sensing GPCRs were acquired by horizontal gene transfer (HGT) from nematodes during evolution.Besides the elucidation of the components of the signaling cascades by gene deletion, gene overexpression and the use of constitutive-active G-alpha alleles, the interaction of the G-proteins with their GPCRs will be studied in time and space by bimolecular fluorescence complementation (BiFC), yeast-two-hybrid and FRET analyses.To further elucidate the process of trap induction and trap morphogenesis, target genes of the signaling cascades will be isolated and characterized after genome-wide transcription analyses.