Two Rab GTPases play different roles in conidiation, trap formation, stress resistance, and virulence in the nematode-trapping fungus <italic>Arthrobotrys oligospora</italic>.

Rab GTPases are the largest group of the small GTPases family, which play a pivotal role in the secretion of proteins. <italic>Arthrobotrys oligospora</italic> is a representative nematode-trapping fungus that can produce adhesive networks to capture nematodes. In this study, the roles of two Rab GTPases AoRab-7A and AoRab-2 were characterized by gene knockout in the fungus <italic>A. oligospora.</italic> The disruption of <italic>AoRab-7A</italic> hindered the mycelial growth in different media, the conidiation of Δ<italic>AoRab-7A</italic> transformants was almost abolished, and the transcription of four sporulation-related genes (<italic>AbaA</italic>, <italic>FluG</italic>, <italic>Hyp1</italic>, and <italic>VosA</italic>) was downregulated compared to the wild-type strain (WT). Furthermore, the tolerance of the Δ<italic>AoRab-7A</italic> mutants to sodium dodecyl sulfate (SDS) and H₂O₂ was also significantly reduced compared to the WT, and the transcription of several genes related to environmental resistance, such as genes for catalase and trehalose synthase, was downregulated. Similarly, the extracellular proteolytic activity was decreased. Importantly, the Δ<italic>AoRab-7A</italic> mutants were unable to produce traps and capture nematodes. However, the disruption of gene <italic>AoRab-2</italic> only affected the conidiation slightly but non-significantly, while other phenotypic traits were unaffected. Moreover, the gene <italic>AoRab-7A</italic> was also involved in the autophagy induced by nitrogen deprivation in <italic>A. oligospora</italic>. Our results revealed for the first time that the Rab GTPases are involved in the regulation of mycelial growth, conidiation, trap formation, stress resistance, and pathogenicity in the nematode-trapping fungus <italic>A. oligospora</italic>. [ABSTRACT FROM AUTHOR]