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Abstract:
Nutritional deprivation triggers a saprotrophic to predatory lifestyle switch in soil dwelling nematode-trapping fungi (NTF). In particular, Arthrobotrys oligospora has evolved to secrete food and sex cues to lure their prey – Nematoda animals – into an adhesive network of traps, specialized structures that originate from the vegetative mycelium. Upon capture, the nematodes are invaded and digested by the fungus, thus serving as a food source. Since many nematodes are pathogens of socially and economically relevant food crops and livestock, understanding the nematode-fungal interaction can pave the way for the application of NTF as biological control agents. We employed RNA-sequencing to examine the response of a highly competent strain of A. oligospora upon exposure to the model nematode Caenorhabditis elegans. A dynamic transcriptomic reaction that indicated a strong reliance on protein secretion was observed. A comprehensive prediction of the secretome of A. oligospora resulted in 1084 transcripts, 64% of which are upregulated in the presence of C. elegans at all tested time points. Transcripts encoding specific conserved domains were over-represented in the upregulated sets, including virulence-associated and carbohydrate-binding domains. A number of secondary metabolism-associated gene clusters showed a strong induction in the presence of C. elegans, suggestive of novel organic compounds that may be relevant for predation. We subsequently predicted the putative effectors of A. oligospora and found that they represent approximately 19% of the secretome and that their expression peaked after 10 hours of introduction of nematodes. In summary, our reverse genetics approach has exposed a number of candidate pathways involved in a soil predator-prey interaction model. Follow-up experiments are currently underway to elucidate molecular mechanisms and gene-to-phenotype relationships at the same time as novel genetic tools to manipulate A. oligospora are being created.
