The fungal virulence factor PefD activates sleep neurons of <i>Caenorhabditis elegans</i>

Nematode-trapping fungi (NTF) such as Arthrobotrys flagrans employ sophisticated strategies to immobilize and digest their prey. A critical, yet poorly understood, step in this interaction is the induction of prey paralysis following capture. Here, we characterize PefD (Putative Effector D), a small-secreted protein (SSP) from A. flagrans. We demonstrate that pefD is specifically upregulated during the early and middle stages of infection (12-24 hpi) and localizes to the infection bulb within the nematode. Deletion of pefD significantly delayed the paralysis of Caenorhabditis elegans, while its overexpression accelerated the process. Through heterologous pan-neuronal expression in C. elegans, we show that PefD directly attenuates host locomotion and significantly enhances the activity of the sleep-promoting RIS interneuron. Unlike other effectors such as NipA or CyrA, PefD specifically modulates neuronal activity patterns without inducing general neurodegeneration. Our results identify PefD as a key virulence factor that hijacks the host's endogenous sleep-induction circuitry to facilitate rapid prey immobilization.