EpOME functionally antagonises prostaglandin signalling in Spodoptera exigua via a specific GPCR conserved across metazoans.

The eicosanoid PGE2 upregulates intracellular Ca²⁺/cAMP levels and induces a cellular immune response, whereas EpOME inhibits PGE2 activity in insects. However, the molecular interactions between the two antagonistic ligands remain largely unexplored. Here we identify nine homologs of vertebrate C18-oxylipin-associating GPCRs among the GPCRs of Spodoptera exigua (SeGPCRs). Functional homology is validated through RNA interference screening, followed by heterologous expressions in both directions between insect and human cell lines. A deletion mutant of SeGPCR48, generated via CRISPR/Cas9, loses responsiveness to EpOME, which is confirmed functionally and by differential gene expression analysis following RNA-seq. In silico binding assay indicate high binding affinity of EpOME to SeGPCR48, which is supported by experimental follow-up, involving ligand-binding functional assays and point mutagenesis of two residues in the binding pocket. In congruence with the in vitro experiments, the EpOME-SeGPCR48 ligand-receptor pair showed marked inhibitory activity against PGE2-mediated immunity. Collectively, this study identifies an insect EpOME receptor within an orphan GPCR subfamily that is phylogenetically conserved across metazoans.