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Silkworm (Bombyx mori) is not only an economic insect but also a model organism for life science research. Bombyx mori nucleopolyhedrovirus (BmNPV) disease is a major infectious disease in the world's sericulture industry. The cocoon loss caused by this disease accounts for more than 60% of the total loss caused by all silkworm diseases. To date, there has been no effective solution for preventing and treating this disease. The most effective measure is to breed disease-resistant varieties. The quickest way to breed disease-resistant varieties is to apply genetic modification. However, this requires that we obtain disease resistance genes and know the mechanism of disease resistance. Since the discovery of disease-resistant resources in 1989, scholars in the sericulture industry around the world have been inspired to search for resistance genes. In the past two decades, with the help of multi-omics technologies, screening of resistance genes, gene localization, protein modification, virus–host interactions, etc., researchers have found some candidate genes that have been proposed to function at the cellular or individual level. Several disease-resistant varieties have been obtained and used in production through hybrid breeding, RNA interference, and genetic modification. This article summarizes and reviews the discovery of and research advances related to silkworm resistance to BmNPV. It is anticipated that the review will inspire scientific researchers to continue searching for disease resistance genes, clarify the molecular mechanism of silkworm disease resistance, and promote disease-resistant silkworm breeding. [ABSTRACT FROM AUTHOR]

Interacting with cell surface attachment factors or receptors is the first step for virus infection. Glycans cover a thick layer on eukaryotic cells and are potential targets of various viruses. Bombyx mori nuclear polyhedrosis viruses (BmNPV) is a baculovirus that causes huge economic loss to the sericulture industry but the mechanism of infection is unclear. Looking for potential host receptors for the virus is an important task. In this study, we investigated the role of glycosaminoglycan (GAG) modifications, including heparan sulfate (HS) and chondroitin sulfate (CS), during BmNPV infection. Enzymatic removal of cell surface HS and CS effectively inhibited BmNPV infection and replication. Exogenous HS and CS can directly bind to BmNPV virion in solution and act as neutralizers for viral infection. Furthermore, the expression of enzymes involved in GAG biosynthesis was upregulated in the BmNPV susceptible silkworm after virus administration, but down-regulated in the resistant strain after virus treatment, suggesting that BmNPV was able to utilize host cell machinery to promote the biosynthesis of GAGs. This study demonstrated HS and CS as important attachment factors that facilitate the viral entry process, and targeting HS and CS can be an effective means of inhibiting BmNPV infection. • BmNPV infection was suppressed after cell surface heparin sulfate and chondroitin sulfate were reduced. • Heparan sulfate and chondroitin sulfate can directly bind to BmNPV in solution. • GAG biosynthesis was promoted in the susceptible silkworm but suppressed in the resistant strain upon BmNPV treatment. [ABSTRACT FROM AUTHOR]

Interacting with cell surface attachment factors or receptors is the first step for virus infection. Glycans cover a thick layer on eukaryotic cells and are potential targets of various viruses. Bombyx mori nuclear polyhedrosis viruses (BmNPV) is a baculovirus that causes huge economic loss to the sericulture industry but the mechanism of infection is unclear. Looking for potential host receptors for the virus is an important task. In this study, we investigated the role of glycosaminoglycan (GAG) modifications, including heparan sulfate (HS) and chondroitin sulfate (CS), during BmNPV infection. Enzymatic removal of cell surface HS and CS effectively inhibited BmNPV infection and replication. Exogenous HS and CS can directly bind to BmNPV virion in solution and act as neutralizers for viral infection. Furthermore, the expression of enzymes involved in GAG biosynthesis was upregulated in the BmNPV susceptible silkworm after virus administration, but down-regulated in the resistant strain after virus treatment, suggesting that BmNPV was able to utilize host cell machinery to promote the biosynthesis of GAGs. This study demonstrated HS and CS as important attachment factors that facilitate the viral entry process, and targeting HS and CS can be an effective means of inhibiting BmNPV infection. • BmNPV infection was suppressed after cell surface heparin sulfate and chondroitin sulfate were reduced. • Heparan sulfate and chondroitin sulfate can directly bind to BmNPV in solution. • GAG biosynthesis was promoted in the susceptible silkworm but suppressed in the resistant strain upon BmNPV treatment. [ABSTRACT FROM AUTHOR]

The silkworm Bombyx mori ( B. mori ), a lepidopteran model organism, has become an important model for molecular biology researches with its genome completely sequenced. Silkworms confront different types of virus diseases, mainly including those caused by Bombyx mori nucleopolyhedrovirus (BmNPV), Bombyx mori densovirus type 1 (BmDNV-1), Bombyx mori bidesovirus (BmBDV) which was termed as Bombyx mori densovirus type 2 (BmDNV-2) or Bombyx mori parvo-like virus (BmPLV) before in sericulture. B. mori offers excellent models to study the molecular mechanisms of insect innate immune responses to viruses. A variety of molecules and pathways have been identified to be involved in the immune responses in the silkworm to viruses, such as the antimicrobial peptides, prophenoloxidase-activating system, apoptosis, ROS, small RNA and related molecules. Here in this review, we summarize the current research advances in molecules involved in silkworm anti-virus pathways. Moreover, taking BmNPV as an example, we proposed a schematic model of molecules and pathways involved in silkworm immune responses against virus infection. We hope this review can facilitate further study of antiviral mechanisms in silkworm, and provide a reference for virus diseases in other organisms. [ABSTRACT FROM AUTHOR]

It is unclear how, or to what extent, baculovirus DNA that has been damaged by ultraviolet (UV) light is repaired during infection and replication. In our previous study, expression of Bombyx mori nucleopolyhedrovirus (BmNPV) ORF Bm65, a homolog of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac79, correlated with decreased inactivation of virus by UV irradiation. In the current study, we accumulated more evidence pointing to a role for Bm65 in repair of UV-induced DNA damage. The localization of Bm65 was studied using enhanced green fluorescent protein (EGFP) fusion constructs expressed in BmN cells transfected with a Bm65 expression plasmid. The results indicate that Bm65-EGFP accumulates in the nucleus. A host cell reactivation assay showed that Bm65 significantly increased the expression of UV-damaged mCherry reporter gene. An assay measuring cyclobutane pyrimidine dimers (CPDs) in UV-irradiated BmN cells found that CPD quantity was decreased in cells transfected with a Bm65 expression plasmid. We also showed that after UVC treatment, the viability of Bm65-transfected cells was higher than that of egfp-transfected cells. These results suggest that Bm65 may be involved in the repair of baculovirus DNA that has been damaged by UV light. [ABSTRACT FROM AUTHOR]

[Display omitted] • Trends of metabolite levels in silkworm hemolymph upon BmNPV treatment were revealed. • BmNPV reprogrammed metabolic pathways involving trehalose, glutamine, and tryptophan. • Tryptophan inhibited BmNPV replication while glutamine promoted it. • Trehalose and riboflavin affected BmNPV replication in a complex manner. Elucidating the mechanism of infection of Bombyx mori nuclear polyhedrosis virus (BmNPV) and host antiviral response remains a major scientific task in sericulture. Virus invasion causes a series of antiviral immune responses in the host, and successful infection leads to massive changes in the host's physiological and biochemical state. Current research mainly focuses on silkworm genes and proteins associated with viral infection and resistance, but little is known regarding the host metabolic pathways that the virus utilizes for optimal replication. In this work, key metabolites involved in viral infection were identified, including trehalose, riboflavin, tryptophan, tyrosine, and phenylalanine. The genes associated with metabolite biosynthesis and catabolism were analyzed, and their expression levels were found to be largely consistent with their respective metabolite levels before and after viral treatment in both strains. The screened metabolites were further investigated for their roles in viral replication using exogenous metabolite addition into the culture medium. The results showed that tryptophan effectively inhibited BmNPV replication, while glutamine promoted viral replication in a dose-dependent manner. Trehalose and riboflavin exhibited a complex effect on BmNPV replication. This study outlines the critical metabolites and metabolic pathways required for BmNPV to proliferate and infect the host, indicting the potential of metabolite-based treatment for viral inhibition. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) light is one of the factors that causes baculovirus inactivation. However, little is known about the response of baculoviruses to UV light. In the present study, Bombyx mori nucleopolyhedrovirus ( Bm NPV) orf 65 (Bm65), the homolog of Autographa californica nucleopolyhedrovirus orf 79 (Ac79), a predicted endonuclease, was analyzed. Preliminary results indicated that Bm65 mainly accumulated within the nucleus and could improve the survival rate of Escherichia coli ( E . coli ) and Bm NPV BVs after UV radiation, suggesting that Bm65 was involved in the repair of UV-induced DNA damage. [ABSTRACT FROM AUTHOR]

Orf101 ( Bm101) of Bombyx mori nucleopolyhedrovirus (BmNPV) is a highly conserved gene in lepidopteran nucleopolyhedroviruses, but its function remains unknown. In this study, Bm101 was characterized. Transcripts of Bm101 were detected from 24 through 96 h post infection (h p.i.) by RT-PCR. The corresponding protein was also detected from 24 to 96 h p.i. in BmNPV-infected BmN cells by Western blot analysis using a polyclonal antibody against Bm101. Western blot assay of occlusion-derived virus and budded virus (BV) preparations revealed that Bm101 encodes a 28-kDa structural protein that is associated with BV and is located in the envelope fraction of budded virions. In addition, confocal analysis showed that the protein was localized in the cytosol and cytoplasmic membrane in virus-infected cells. In conclusion, the available data suggest that Bm101 is a functional ORF of BmNPV and encodes a protein expressed in the late stage of the infection cycle that is associated with the BV envelope. [ABSTRACT FROM AUTHOR]

The Bm111 of Bombyx mori nucleopolyhedrovirus (BmNPV) encodes a small polypeptide (70 amino acids) of which the function remains unknown. To characterize its function, multiple sequence alignments were performed, and the predicted protein was found to share amazingly high (98 %) sequence identity with the Bombyx mandarina nucleopolyhedrovirus ORF110 (Boma110) but negligible with proteins of other insect viruses, indicating the close relationship between these two NPVs with silkworm larvae. The transcription of Bm111 was detected as early as 3 hpi in BmNPV-infected BmN cells, suggesting it is an early gene. To investigate the role of Bm111 in baculovirus life cycle, a Bm111-knockout virus was constructed by bacmid recombination in Escherichia coli. The results showed that knockout of the Bm111 did not affect the replication of virus DNA, but significantly extended the death time of infected silkworm larvae compared to the wild-type or rescued viruses. We also successfully expressed the recombinant protein Bm111 in E. coli to provide sufficient material for subsequent studies. Taken together, our data indicate that Bm111 only affects the virulence of BmNPV, but not its replication. [ABSTRACT FROM AUTHOR]

Recombinant adeno-associated virus (AAV) vectors have broad application prospects in the field of gene therapy. The establishment of low-cost and large-scale manufacturing is now the general agenda for industry. The baculovirus-insect cell/larva expression system has great potential for these applications due to its scalability and predictable biosafety. To establish a more efficient production system, Bombyx mori pupae were used as a new platform and infected with recombinant Bombyx mori nuclear polyhedrosis virus (BmNPV). The production of a chimeric recombinant adeno-associated virus (rAAV) serotype 2/human bocavirus type-1 (HBoV1) vector was used to evaluate the efficiency of this new baculovirus expression vector (BEV)–insect expression system. For this purpose, we constructed two recombinant BmNPVs, which were named rBmNPV/AAV2Rep-HBoV1Cap and rBmNPV/AAV2ITR-eGFP. The yields of rAAV2/HBoV1 derived from the rBmNPV/AAV2Rep-HBoV1Cap and rBmNPV/AAV2ITR-eGFP co-infected BmN cells exceeded 2 × 104 vector genomes (VG) per cell. The rBmNPV/AAV2Rep-HBoV1Cap and rBmNPV/AAV2ITR-eGFP can express stably for at least five passages. Significantly, rAAV2/HBoV1 could be efficiently generated from BmNPV-infected silkworm larvae and pupae at average yields of 2.52 × 1012 VG/larva and 4.6 × 1012 VG/pupa, respectively. However, the vectors produced from the larvae and pupae had a high percentage of empty particles, which suggests that further optimization is required for this platform in the future. Our work shows that silkworm pupae, as an efficient bioreactor, have great potential for application in the production of gene therapy vectors. [ABSTRACT FROM AUTHOR]

• Baculovirus proliferation inhibition was observed in BmNPV-resistant silkworm strains. • Virus gene transcription was significantly inhibited in resistant silkworm tissues. • Insect innate immunity responses contribute to BmNPV resistance at varying levels. • Antiviral activity of BmSOCS2 on BmNPV proliferation inhibition evidenced in vitro. The resistance of silkworm to infection by Bombyx mori nuclear polyhedrosis virus (BmNPV) is a main focus of sericultural research. Previously, a BmNPV-resistant strain, NB, was identified among a collection of Chinese silkworm strains in our lab. To better understand the molecular mechanism of NB strain resistance, the patterns of host immune response gene transcription in resistant (NB) and susceptible (306) strains were examined. Quantative real-time PCR (qRT-PCR) revealed that multiple insect innate immune signaling pathways (Toll, Imd and JAK/STAT) were strongly activated upon infection with BmNPV. Notably, Suppressor of cytokine signaling 2 (BmSOCS2) mRNA expression was significantly up-regulated in midgut tissues of the resistant NB strain, suggesting that the BmSOCS2 gene product may be involved in host immune defense against BmNPV infection. A significant inhibition of BmNPV replication was also observed in BmN cells transfected with a vector encoding BmSOCS2. The results suggest that BmSOCS2 is a key gene involved in the resistance of the NB silkworm strain to BmNPV infection. [ABSTRACT FROM AUTHOR]