The piRNA pathway is required for nucleopolyhedrovirus replication in Lepidoptera

Abstract

The Piwi‐interacting RNA (piRNA) pathway has been shown to be involved in the antiviral defense against RNA viruses, especially in mosquitoes, but its universality has been questioned. Here, we used the Bombyx mori nucleopolyhedrovirus (BmNPV) ‐infected silkworm as a model to explore the effects of the key factors of piRNA pathway, BmAgo3 and Siwi, on replication of a large DNA virus (belonging to the family of Baculoviridae). We demonstrated that BmAgo3 and Siwi could promote the replication of BmNPV through both overexpression and knockdown experiments in BmN cell lines and silkworm larvae. In addition, we also studied the effect of PIWI‐class genes on Autographa californica nucleopolyhedrovirus (AcMNPV) replication in the Spodoptera frugiperda cell line Sf9. By knocking down the expression of PIWI‐class genes in Sf9, we found that Piwi‐like‐1 and Piwi‐like‐2‐3 could inhibit AcMNPV replication, while Piwi‐like‐4‐5 promoted virus replication. Our study provides compelling evidence that the piRNA pathway affects host infection by exogenous viruses in Lepidoptera. Also, our results reflect the diversity of the roles of PIWI‐class genes in virus infection of the host across species. This study is the first to explore the interaction of PIWI‐class proteins with DNA viruses, providing new insights into the functional roles of the piRNA pathway.

Multi-omics study and ncRNA regulation of anti-BmNPV in silkworms, Bombyx mori: an update

“…Regulatory non-coding RNAs can be divided into short, medium, and long non-coding RNAs according to different lengths. Short-stranded noncoding RNAs mainly include piRNA, siRNA, and miRNA ( Feng et al, 2021 ; Xia et al, 2022 ). The three are similar in length but work in different ways.…”

“…The three are similar in length but work in different ways. piRNA mainly interacts with the piwi protein and mediates the silencing of transposon genes ( Feng et al, 2021 ; Xia et al, 2022 ); siRNA, on the other hand, as double-stranded RNA, binds in vivo to become RISC complexes, silences target genes, often imported by foreign genes, may be viruses ( Zhao S. et al, 2022 ). While microRNAs are mainly synthesized in the nucleus, where precursor genes are first cleaved by the Drosha enzyme to form precursor miRNA (pri-miRNA), which is then transported out of the nucleus by Exportin 5, and finally cleaved by the Dicer enzyme in the cytoplasm to form mature miRNA ( MacRae et al, 2006 ), miRNA is also related to RISC complexes, it is a single strand, and binding to the target gene only exists at the 3′ end, siRNA can bind and silence the target gene in all segments of the gene.…”

What Are the Functional Roles of Piwi Proteins and piRNAs in Insects?

“…Interestingly, an antisense piRNA that targets Siwi becomes downregulated during BmNPV infection, reinforcing the idea of an active involvement of the piRNA pathway during BmNPV infection [ 203 ]. In concordance with this, knockdown and over-expression studies indicated that Siwi and BmAgo3 can promote BmNPV replication in silkworm cells, which is, however, consistent with a proviral instead of an antiviral role [ 204 ]. During baculovirus infection, a reorganization of the cellular nuclear chromatin takes place concomitant with the formation of the virogenic stroma, the site of virus genome DNA replication [ 205 , 206 ].…”

“…While in mammals the role of the piRNA pathway in the regulation of cancer cell function has received wide interest [ 278 ], its involvement in virus infection remains understudied [ 279 ], which could be related to the preferential expression of Piwi proteins in the germline [ 280 ]. Interestingly, the Piwi proteins Aub and Ago3 have recently been shown to have a proviral role during the infection of BmNPV ( Baculoviridae ) in silkworm larvae (discussed in Section 4.4 ; [ 204 ]). It can be speculated that the Piwi proteins have a role in the stabilization of transposon mobilization that could interfere with faithful viral genome replication.…”

“…Nevertheless, EVEs in the Bombyx genome are enriched in piRNA clusters and give rise to piRNAs with a ping-pong signature. While Bombyx contains only two Piwi genes, S. frugiperda encodes five Piwi members of which two underwent a recent duplication [ 204 ]. The number of EVEs in S. frugiperda is comparable with Ae.…”