Ribosome inactivating proteins in insects: HGT, gene expression, and functional implications

Abstract

Ribosome-inactivating proteins (RIPs) are RNA N-glycosidases that depurinate an adenine residue in the conserved alpha-sarcin/ricin loop (SRL) of rRNA, inhibiting protein synthesis. Previously, we reported the existence of these toxins in insects, whose presence is restricted to mosquitoes from the Culicinae subfamily (e.g., Aedes aegypti) and whiteflies from the Aleyrodidae family (e.g., Bemisia tabaci). Both groups of genes are derived from two independent horizontal gene transfer (HGT) events and are evolving under purifying selection. Here, we report and characterize the occurrence of a third HGT event in the Sciaroidea superfamily, which supports the recurrent acquisition of RIP genes by insects. Transcriptomic experiments, available in databases, allowed us to describe the temporal and spatial expression profiles for these foreign genes in these organisms. Furthermore, we found that RIP expression is induced after infection with pathogens and provided, for the first time, transcriptomic evidence of parasite SRL depurination. This evidence suggests a possible role of these foreign genes as immune effectors in insects.