Expressing MicroRNA Bantam Sponge Drastically Improves the Insecticidal Activity of Baculovirus via Increasing the Level of Ecdysteroid Hormone in Spodoptera exigua Larvae

Abstract

Bantam is a conserved miRNA highly expressed in insects. We previously showed that the antisense inhibitor (antagomiR) of bantam improved the infection by baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) in Spodoptera exigua and S. litura larvae. Here, we constructed a recombinant AcMNPV (vPH-banS) expressing bantam sponge, an mRNA containing eight antisense binding sites for bantam. Infection with wild type AcMNPV (WT) or the control recombinant virus vPH resulted in a significant increase of bantam level, whereas infection with vPH-banS led to an approximately 40% reduction of bantam in both Sf9 cells and S. exigua larvae. Although, comparable production of budded virus and polyhedra were detected in vPH-banS-, vPH-, and WT-infected Sf9 cells, vPH-banS showed remarkably increased insecticidal activity in S. exigua larvae. The 50% lethal concentration and the median lethal time of vPH-banS was only 1/40 and 1/2, respectively, of both vPH and WT. Further analysis showed that the level of molting hormone 20-hydroxyecdysone (20E) was significantly higher in larvae infected with vPH-banS than those infected with vPH or WT. This was confirmed by the result that the larvae treated with bantam inhibitor also had a markedly increased 20E level. Moreover, feeding larvae with 20E increased the virus-mediated mortality, whereas feeding with juvenile hormone partially reverted the high insecticidal effect of vPH-banS. Together, our results revealed that vPH-banS infection suppresses the level of bantam, and in turn elevates level of 20E in infected insects, resulting in increased susceptibility to baculovirus infection. Our study provided a novel approach to improve a baculovirus bio-insecticide by interfering with a key homeostasis-regulating miRNA of the host.

microRNA‐34‐5p encoded by Spodoptera frugiperda regulates the replication and infection of Autographa californica multiple nucleopolyhedrovirus by targeting odv‐e66, ac78 and ie2

“…Four miR‐34‐5p precursors were connected in tandem to ensure high expression of mature miR‐34‐5p. This method has been verified previously 25,41 . In our study, we found for the first time that miR‐34‐5p overexpression inhibited the production of infectious budded virions, inhibited viral DNA replication and promoted host DNA replication.…”

“…A conserved miRNA bantam was found to regulate the proliferation of AcMNPV, but the target is uncertain. 24,25 In preliminary work using next-generation sequencing analysis, we found that multiple miRNAs encoded by S. frugiperda, including miR-34-5p, were differentially expressed during AcMNPV infection. The downregulated miR-34-5p attracted our attention.…”

“…However, there are few studies on whether S. frugiperda miRNAs are involved in regulating baculovirus replication. A conserved miRNA bantam was found to regulate the proliferation of AcMNPV, but the target is uncertain 24,25 …”

microRNA-92a regulates the expression of aphid bacteriocyte-specific secreted protein 1

“…Recent attempts have been made to develop miRNAs as tools for pest control (reviewed in [25]), either by engineering miRNAs for insecticidal activities [39] or by silencing insect defensive miRNAs [40]. Here we have validated the role of miR-92a in regulation of the orphan, bacteriocyte-expressed gene SP1 , a gene that encodes a secreted protein that has been argued to be important for symbiotic function.…”

MicroRNA-Mediated Host-Pathogen Interactions Between Bombyx mori and Viruses

“…MiRNA bantam affects baculovirus-host interaction by regulating 20E. Reduction in bantam level results in an increased level of 20E, resulting in high mortality in virus-infected S. exigua (Ran et al, 2018). Bmo-miR-390 effectively downregulates the expression of BmNPV-cg30 in BmNPV-infected BmN cells.…”