Bombyx mori Tetraspanin A (BmTsp.A) is a facilitator in BmNPV invasion by regulating apoptosis

BmADARa cooperatively inhibits BmNPV proliferation through the interaction of its dsRBD2 with BmDcr-2-DEXHc in silkworm, Bombyx mori

Adenosine deaminases that act on RNA (ADARs) are RNA editing enzymes capable of converting adenosine into inosine at specific sites within double-stranded RNA (dsRNA), widely distributed across various animal species. Dicer (Dcr), a member of the RNase III family and a crucial component of the RNA-induced silencing complex (RISC), allows ADAR to participate in innate immunity through Dcr-2 in Drosophila. Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the viruses that can cause substantial economic losses to the sericulture industry upon infecting silkworm. Knocking down the expression of BmDcr-2 in silkworm enhances the proliferation of BmNPV. Our previous research revealed the existence of a predominantly expressed subtype, ADARa, in silkworm (BmADARa), which shares homology with Drosophila ADAR. It remains unclear whether BmADARa can also participate in innate immunity through BmDcr-2. Initially, through bacterial challenge experiments, we found that BmADARa exhibited the highest responsiveness to BmNPV stimulation. Further studies demonstrated that BmADARa, in conjunction with BmDcr-2-DEXHc (DEAD-box helicase domain), collectively inhibits the proliferation of BmNPV. BmADARa interacts with the DEXHc domain of BmDcr-2 through its dsRNA binding domain 2 (dsRBD2), thereby enhancing its ability to inhibit BmNPV proliferation. These results lay a foundation for the study of the function and molecular mechanism of BmADARa in innate immunity, and provide a new experimental ideas for antiviral research in B. mori.

N-acetylglucosaminyl 1-phosphate transferase (GPT) is a facilitator in Bombyx mori Nucleopolyhedrovirus proliferation

GPT is a conserved ER-resident transmembrane protein that catalyzes the initial step of protein N-glycosylation in vertebrates. However, to date, there have been no reports on GPT in silkworms. In the present study, we identified a GPT ortholog in the B. mori genome. Spatiotemporal expression profiles showed that BmGPT was highly expressed in the majority of silkworm's organs. BmGPT regulates multiple cellular processes such as cell viability, proliferation, and cell death. In addition, BmGPT overexpression increased BmNPV proliferation in BmN cells, whereas BmGPT inhibition by siRNA or a chemical inhibitor suppressed BmNPV proliferation both in vitro and in vivo. These results suggested that BmGPT facilitates BmNPV proliferation by regulating cell proliferation and apoptosis. This study identifies a potential molecular target for BmNPV prevention and for silkworm breeding.

The humoral immune response of the lepidopteran model insect, silkworm Bombyx mori L., to microbial pathogens

Insects are valuable models for studying innate immunity and its role in combating infections. The silkworm Bombyx mori L., a well-studied insect model, is susceptible to a range of pathogens, including bacteria, fungi, viruses, and microsporidia. Their susceptibility makes it a suitable model for investigating host-pathogen interactions and immune responses against infections and diseases. This review focuses on the humoral immune response and the production of antimicrobial peptides (AMPs), the phenoloxidase (PO) system, and other soluble factors that constitute the primary defense of silkworms against microbial pathogens. The innate immune system of silkworms relies on pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMPs), which then activate various immune pathways including Imd, Toll, JAK/STAT, and RNA interference (RNAi). Their activation triggers the secretion of AMPs, enzymatic defenses (lysozyme and PO), and the generation of reactive oxygen species (ROS). Collectively, these pathways work together to neutralize and eliminate pathogens, thereby contributing to the defense mechanism of silkworms. Understanding the innate immunity of silkworms can uncover conserved molecular pathways and key immune components shared between insects and vertebrates. Additionally, it can provide valuable insights for improving sericulture practices, developing strategies to control diseases affecting silk production, and providing a theoretical foundation for developing pest control measures.

Immune system modulation & virus transmission during parasitism identified by multi-species transcriptomics of a declining insect biocontrol system

BACKGROUND

The Argentine stem weevil (ASW, Listronotus bonariensis) is a significant pasture pest in Aotearoa New Zealand, primarily controlled by the parasitoid biocontrol agent Microctonus hyperodae. Despite providing effective control of ASW soon after release, M. hyperodae parasitism rates have since declined significantly, with ASW hypothesised to have evolved resistance to its biocontrol agent. While the parasitism arsenal of M. hyperodae has previously been investigated, revealing many venom components and an exogenous novel DNA virus Microctonus hyperodae filamentous virus (MhFV), the effects of said arsenal on gene expression in ASW during parasitism have not been examined. In this study, we performed a multi-species transcriptomic analysis to investigate the biology of ASW parasitism by M. hyperodae, as well as the decline in efficacy of this biocontrol system.

RESULTS

The transcriptomic response of ASW to parasitism by M. hyperodae involves modulation of the weevil's innate immune system, flight muscle components, and lipid and glucose metabolism. The multispecies approach also revealed continued expression of venom components in parasitised ASW, as well as the transmission of MhFV to weevils during parasitism and some interrupted parasitism attempts. Transcriptomics did not detect a clear indication of parasitoid avoidance or other mechanisms to explain biocontrol decline.

CONCLUSIONS

This study has expanded our understanding of interactions between M. hyperodae and ASW in a biocontrol system of critical importance to Aotearoa-New Zealand's agricultural economy. Transmission of MhFV to ASW during successful and interrupted parasitism attempts may link to a premature mortality phenomenon in ASW, hypothesised to be a result of a toxin-antitoxin system. Further research into MhFV and its potential role in ASW premature mortality is required to explore whether manipulation of this viral infection has the potential to increase biocontrol efficacy in future.