ESCRT pathway-dependent MVBs contribute to the morphogenesis of the fungus Arthrobotrys oligospora

Ammonia opens trap formation in the nematode-trapping (NT) fungus Arthrobotrys oligospora, an intriguing morphological switch in NT fungi, where saprophytic mycelia are converted to pathogenic organs. Endocytosis plays a prominent role in nutrient uptake, signaling cascades, and maintenance of cellular homeostasis in higher eukaryotes. Here, we demonstrate that ammonia efficiently promotes endocytosis via the formation of 3D-adhesive mycelial nets in A. oligospora. Trap production is followed by the presence of massive multivesicular bodies (MVBs) and membrane rupture and repair. Additionally, both the ubiquitin-proteasome system and the endosomal sorting complex for transport (ESCRT) pathway are immediately linked to endocytosis regulation and MVB formation in ammonia-induced trap formation. Moreover, disruption of the ESCRT-1 complex subunit proteins AoHse and AoVps27 led to the complete loss of membrane endocytosis and trap formation. Finally, the deletion of the deubiquitinase AoSst2 caused a significant reduction in the number of trap structures produced in response to exposure to ammonia or nematodes. Overall, our results increase our knowledge of the molecular mechanisms underlying the phenotypic changes in the NT fungal group, demonstrating that the endocytosis-ESCRT-MVB pathway participates in the regulation of trapping organs. Author Summary The lifestyle switch of nematode-trapping (NT) fungi is a significant event that increases their pathogenicity to nematode prey, which has resulted in large losses to agricultural crops worldwide. Here, we describe the molecular mechanism underlying how this fungal group forms a NT structure in response to ammonia, a widely preferred nitrogen source in soil niches. Ammonia enhances the endocytosis process, ubiquitin-proteasome system, and endosomal sorting complex for transport (ESCRT) pathway of the model NT fungus A. oligospora, thereby generating enriched multivesicular bodies (MVBs) during trap formation. In this process, the cell membrane morphology is remarkably damaged and then repaired. We further found that disruption of the ESCRT-0 subcomplex or ubiquitinase severely blocked trap production and membrane reorganization. Our study provides a new understanding of endocytosis-ESCRT-MVB flux in the transition of fungal NT organs.