Autophagy is required for trap formation in the nematode‐trapping fungus <i> <scp>A</scp> rthrobotrys oligospora </i>

<jats:title>Summary</jats:title> <jats:p> Nematode‐trapping fungi live mainly as saprobes in soil environments. When encountering nematodes, these fungi become ‘carnivorous’ and develop specialized trapping devices to attack their hosts for extracting nutrients, especially nitrogen source. Thus, nematode‐trapping fungi are model organisms for understanding the molecular mechanism of the switch between saprobic and parasitic phases of pathogen life cycles. <jats:italic> <jats:styled-content style="fixed-case">A</jats:styled-content> rthrobotrys oligospora </jats:italic> , one of the best‐studied nematode‐trapping fungi, mainly lives as a saprobe. In the presence of nematodes, <jats:italic> <jats:styled-content style="fixed-case">A</jats:styled-content> . oligospora </jats:italic> enters the parasitic stage by forming adhesive reticulate traps to capture nematodes. In filamentous fungi, autophagy has been shown to be involved in morphogenesis and morphology. In this study, we demonstrate that autophagy is induced by nematodes during the early stage of trap formation in <jats:italic> <jats:styled-content style="fixed-case">A</jats:styled-content> . oligospora </jats:italic> . Disruption of <jats:styled-content style="fixed-case"> <jats:italic>atg8</jats:italic> </jats:styled-content> gene not only abolishes the nematode‐induced autophagy, but also suppresses trap formation and reduces pathogenicity for nematodes. During the early stage of trap formation, the expression of genes involved in amino acid biosynthesis is upregulated and the transcriptional activity of <jats:styled-content style="fixed-case">GCN</jats:styled-content> 4 is induced in <jats:italic> <jats:styled-content style="fixed-case">A</jats:styled-content> . oligospora </jats:italic> , suggesting that nematodes induce autophagy probably by triggering intracellular amino acid starvation. Autophagy is thus crucial for trap formation in <jats:italic> <jats:styled-content style="fixed-case">A</jats:styled-content> . oligospora </jats:italic> during infection of nematodes. </jats:p>