CRISPR screens in Drosophilacells identify Vsg as a Tc toxin receptor

Entomopathogenic nematodes are widely used as biopesticides1,2. Their insecticidal activity depends on symbiotic bacteria such as Photorhabdus luminescens, which produces toxin complex (Tc) toxins as major virulence factors3–6. No protein receptors are known for any Tc toxins, which limits our understanding of their specificity and pathogenesis. Here we use genome-wide CRISPR–Cas9-mediated knockout screening in Drosophila melanogasterS2R+ cells and identify Visgun (Vsg) as a receptor for an archetypal P.luminescensTc toxin (pTc). The toxin recognizes the extracellular O-glycosylated mucin-like domain of Vsg that contains high-density repeats of proline, threonine and serine (HD-PTS). Vsg orthologues in mosquitoes and beetles contain HD-PTS and can function as pTc receptors, whereas orthologues without HD-PTS, such as moth and human versions, are not pTc receptors. Vsg is expressed in immune cells, including haemocytes and fat body cells. Haemocytes from Vsg knockout Drosophilaare resistant to pTc and maintain phagocytosis in the presence of pTc, and their sensitivity to pTc is restored through the transgenic expression of mosquito Vsg. Last, Vsg knockout Drosophilashow reduced bacterial loads and lethality from P.luminescensinfection. Our findings identify a proteinaceous Tc toxin receptor, reveal how Tc toxins contribute to P.luminescenspathogenesis, and establish a genome-wide CRISPR screening approach for investigating insecticidal toxins and pathogens.