Analysis of luciferase dsRNA production during baculovirus infection of Hi5 cells: RNA hairpins expressed by very late promoters do not trigger gene silencing

Stimulation of IRES-Dependent Translation by Rocaglamide A Increases the Replication and Virulence of Cricket Paralysis Virus in Lepidopteran Insect Cells

The discovery that infections of viruses are pervasive among insects has considerable potential for future applications, such as new strategies for pest control through the manipulation of virus-host interactions. However, few studies can be found that aim to minimize (for beneficial insects) or maximize (for pests) virus impact or virulence. Viruses generally employ molecular mechanisms that deviate from the cells' to increase their replication efficiency and to avoid the immune response. In this research, a screening system is presented for the detection of molecules that interfere with the internal ribosomal entry site (IRES) of Cricket paralysis virus (Dicistroviridae) which has been well characterized in previous research. Over-expression and RNAi experiments identified the importance of eIF4A, a component of the cap-dependent translation initiation complex, to modify the activity of IRES-mediated translation. Application of Rocaglamide A (RocA), a natural product from Aglaia plants and inhibitor of eIF4A, resulted in strong stimulation of IRES-mediated translation in reporter assays as well as increased CrPV genome replication and virion production in lepidopteran Hi5 cells. At 100 nM of RocA, dsRNA molecules accumulated in infected cells, corresponding to full-length genome (9.5 kb) and a smaller fragment (0.8 kb) with unknown function. Treatment of silkworm larvae with RocA by injection or topically was highly toxic while no strong stimulation of CrPV infection could be observed. The prospect of the use of rocaglamates as insecticides and enhancers of CrPV infection is discussed together with its potential impact on mammalian cells.

The piRNA pathway is required for nucleopolyhedrovirus replication in Lepidoptera

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.

Plant and insect virus-like particles: emerging nanoparticles for agricultural pest management

Virus-like particles (VLPs) represent a biodegradable, biocompatible nanomaterial made from viral coat proteins that can improve the delivery of antigens, drugs, nucleic acids, and other substances, with most applications in human and veterinary medicine. Regarding agricultural viruses, many insect and plant virus coat proteins have been shown to assemble into VLPs accurately. In addition, some plant virus-based VLPs have been used in medical studies. However, to our knowledge, the potential application of plant/insect virus-based VLPs in agriculture remains largely underexplored. This review focuses on why and how to engineer coat proteins of plant/insect viruses as functionalized VLPs, and how to exploit VLPs in agricultural pest control. The first part of the review describes four different engineering strategies for loading cargo at the inner or the outer surface of VLPs depending on the type of cargo and purpose. Second, the literature on plant and insect viruses the coat proteins of which have been confirmed to self-assemble into VLPs is reviewed. These VLPs are good candidates for developing VLP-based agricultural pest control strategies. Lastly, the concepts of plant/insect virus-based VLPs for delivering insecticidal and antiviral components (e.g., double-stranded RNA, peptides, and chemicals) are discussed, which provides future prospects of VLP application in agricultural pest control. In addition, some concerns are raised about VLP production on a large scale and the short-term resistance of hosts to VLP uptake. Overall, this review is expected to stimulate interest and research exploring plant/insect virus-based VLP applications in agricultural pest management. © 2023 Society of Chemical Industry.

dsRNase1 contribution to dsRNA degradation activity in the Sf9 cells conditioned medium

RNA interference (RNAi) is inefficient in lepidopteran insects, including Spodoptera frugiperda. RNase activity in the lumen and hemocoel is known to contribute to low RNAi efficiency in these insects. Conditioned medium from Sf9 cells developed from ovaries of S. frugiperda shows high dsRNA degradation activity. But the enzymes responsible for this activity have not been identified. The nuclease genes that are highly expressed in Sf9 cells, REase, RNaseT2, and dsRNase1, were identified. Knockdown of dsRNase1 in Sf9 cells resulted in a reduction of dsRNA degradation activity in the Sf9 cells conditioned medium. Knockdown of dsRNase1 also increased RNAi efficiency in Sf9 cells. The results from these studies identified a major player in dsRNA degradation activity in the Sf9 cells conditioned medium. We also describe an efficient system that can be used to identify other genes responsible for dsRNA degradation and RNAi efficiency in Sf9 cells.