The DNA virus Invertebrate iridescent virus 6 is a target of the Drosophila RNAi machinery

Abstract

RNA viruses in insects are targets of an RNA interference (RNAi)-based antiviral immune response, in which viral replication intermediates or viral dsRNA genomes are processed by Dicer-2 (Dcr-2) into viral small interfering RNAs (vsiRNAs). Whether dsDNA virus infections are controlled by the RNAi pathway remains to be determined. Here, we analyzed the role of RNAi in DNA virus infection using Drosophila melanogaster infected with Invertebrate iridescent virus 6 (IIV-6) as a model. We show that Dcr-2 and Argonaute-2 mutant flies are more sensitive to virus infection, suggesting that vsiRNAs contribute to the control of DNA virus infection. Indeed, small RNA sequencing of IIV-6-infected WT and RNAi mutant flies identified abundant vsiRNAs that were produced in a Dcr-2-dependent manner. We observed a highly uneven distribution with strong clustering of vsiRNAs to small defined regions (hotspots) and modest coverage at other regions (coldspots). vsiRNAs mapped in similar proportions to both strands of the viral genome, suggesting that long dsRNA derived from convergent overlapping transcripts serves as a substrate for Dcr-2. In agreement, strand-specific RT-PCR and Northern blot analyses indicated that antisense transcripts are produced during infection. Moreover, we show that vsiRNAs are functional in silencing reporter constructs carrying fragments of the IIV-6 genome. Together, our data indicate that RNAi provides antiviral defense against dsDNA viruses in animals. Thus, RNAi is the predominant antiviral defense mechanism in insects that provides protection against all major classes of viruses.insect immunity | Iridoviridae | siRNA | antiviral immunity | small RNA profiling | next-generation sequencing

Involvement of Viral MicroRNA in the Regulation of Antiviral Apoptosis in Shrimp

“…Recently, it was revealed that hosts can use virus-derived siRNA or cellular miRNA to restrict viral propagation (18,(21)(22)(23)(24). In turn, a number of viruses, in particular DNA viruses, seem to have evolved mechanisms to express their own miRNAs and employ miRNA-mediated regulations to counter host antiviral responses (25)(26)(27).…”

The Transcriptome of the Baculovirus Autographa californica Multiple Nucleopolyhedrovirus in Trichoplusia ni Cells

“…siRNA is subsequently loaded into a RNA-induced silencing complex (RISC) that cleaves the targeted RNA (91). While RNAi is typically thought of as a mechanism directed against RNA viruses, several recent reports (92)(93)(94) demonstrated the presence of siRNAs directed against insect dsDNA viruses (invertebrate iridovirus 6 [IIV-6] and the baculovirus Helicoverpa armigera single nucleopolyhedrovirus [HaSNPV]). In both cases, Dicer-2 (the primary RNase associated with the insect RNAi response) was associated with production of siRNAs, and in both cases, hotspots of RNAi were identified in the viral genome.…”

piRNA pathway is not required for antiviral defense in Drosophila melanogaster

“…IIV-6 and FHV are not natural Drosophila viruses. Nevertheless, both are able to replicate in D. melanogaster under experimental conditions (49)(50)(51). IIV-6 is commonly used as a DNA virus model, and we thought that vpiRNAs could originate from a DNA source, as is the case for endogenous piRNAs.…”