Identification of a PP2A gene in Bombyx mori with antiviral function against B. mori nucleopolyhedrovirus

Histone acetyltransferase BmMOF inhibits the proliferation of the Bombyx mori nucleopolyhedrovirus by targeting Bmp53

Bombyx mori nucleopolyhedrovirus (BmNPV) infection is a critical disease in silkworms (Bombyx mori), yet the molecular mechanism underlying the defense of Bombyx mori against BmNPV infection remains elusive. The histone acetyltransferase MOF plays a crucial role in cellular stress response and apoptosis. Nevertheless, its function in Bombyx mori is yet to be fully elucidated. Here, we demonstrated that BmMOF positively regulates the resistance of silkworm BmN cells to BmNPV by targeting a Bombyx mori homolog of the apoptosis-inducing factor Bmp53. Overexpression of BmMOF led to the suppression of BmNPV proliferation and the enhancement of cellular antiviral responses, conversely, RNA interference targeting BmMOF promoted viral proliferation, resulting in an opposite effect. Additionally, the application of the acetyltransferase inhibitor MG149 and the mutated BmMOF acetyltransferase active site K257R revealed that BmMOF is capable of acetylating H4K16 in BmN cells, and its acetylation function plays a crucial role in inhibiting virus proliferation. Further analyses showed that BmMOF interacted with Bmp53 and catalyzes its acetylation, thereby inducing the apoptosis-mediated antiviral immune response in BmN cells upon infection with BmNPV. These findings provided a new molecular target for antiviral immunity and information for comprehending the mechanism of host-virus interaction in silkworms.

BmWARS inhibits BmNPV infection via the PI3K-Akt pathway

Bombyx mori Tryptophanyl-tRNA synthetase (BmWARS) belongs to the family of Ic-like aminoacyl-tRNA synthetases (aaRSs), whose specific recognition of the substrate Trp, tRNA, maintains the fidelity of protein synthesis. In this study, BmWARS was cloned and characterized from the midgut of the silkworm, Bombyx mori, resulting in an open reading frame (ORF) with a full length of 1,149 bp, which can encode 382 Aa. BmWARS is localized in the cytoplasm, and is expressed in all tissues of the silkworm, with higher expression in the testis, ovary, silk gland and malpighian tubule. The expression of BmWARS was significantly up-regulated in the midgut and silk gland after infection with Bombyx mori nuclear polyhedrosis virus (BmNPV). In addition, overexpression of BmWARS inhibited BmNPV infection and replication extremely significantly, while interference with BmWARS expression promoted BmNPV infection and replication. Analysis of the immune pathways in which BmWARS may be involved revealed that the expression of the key genes of the PI3K-Akt pathway, BmPI3K, BmAkt, BmPDK1, BmeIF4E, BmS6, and p-Akt protein was significantly reduced, whereas the expression of BmPTEN, BmFoxO, and BmCaspase9 was significantly increased in the cells that overexpressed BmWARS and were infected with BmNPV. Meanwhile, the results of the study interfering with the expression of BmWARS were completely opposite to those of the study overexpressing BmWARS. This is the first report that BmWARS has antiviral effects in Bombyx mori. Moreover, BmWARS inhibits BmNPV infection and replication in Bombyx mori cells by promoting apoptosis and inhibiting cell proliferation.

Bombyx mori PAT4 gene inhibits BmNPV infection and replication through autophagy

Proton-assisted amino acid transporter 4 (PAT4) is a member of the solute carrier (SLC) 36 family, which mediates the transmembrane transport of amino acids and their derivatives. However, the function of PAT4 in Bombyx mori is not clear. In this study, BmPAT4 was cloned and identified using PCR technology. Its open reading frame (ORF) includes 1,395 bp, encoding 464 amino acid (Aa). Moreover, the sequence of BmPAT4 has the highest similarity with wild Bombyx.mandarina, Spodoptera frugiperda and Spodoptera litura, and it has ten transmembrane domains. BmPAT4 was localized in the cell membrane and expressed in all tissues of the silkworm. After Bombyx mori nuclear polyhedrosis virus (BmNPV) infection, the expression of BmPAT4 in midgut, hemolymph and fat body was significantly up-regulated. In addition, overexpression of BmPAT4 in BmN cells could significantly inhibit the proliferation of BmNPV, and the expression of several genes in autophagy pathway decreased significantly. On the contrary, down-regulation of BmPAT4 expression by RNA interference can promote BmNPV replication and proliferation, and the expression of key genes in autophagy pathway is significantly increased. This is the first time to report that BmPAT4 has an antiviral effect in silkworm. Moreover, the silkworm activates BmTORC1 via BmPAT4, which inhibits autophagy in silkworm cells, resulting in a lack of energy and raw materials for BmNPV infection and replication in cells.

A novel digestive protease chymotrypsin-like serine contributes to anti-BmNPV activity in silkworm (Bombyxmori)

Serine proteases (SPs) are important proteases in the digestive system of lepidopteran insects. They play important roles in protein digestion, coagulation, signal transduction, hormone activation, inflammation and development. Blood-borne pyosis caused by Bombyx mori nuclear polyhedrosis virus (BmNPV) has caused serious harm to sericulture. At present, the scientific problems of BmNPV infection and silkworm resistance to BmNPV infection have been the focus of many scientists, but the molecular mechanism needs further research and exploration. Based on the results of label-free quantitative protein proteomics of the midgut digestive juice of different resistant strains in our laboratory, we successfully screened a differentially expressed candidate protein (DEP), B. mori chymotrypsin-like serine protease (BmCLSP), and comprehensively analyzed the biological characteristics and anti-BmNPV function of BmCLSP. The open reading frame (ORF) of BmCLSP is 891 bp, encoding 296 amino acid residues. The analysis of the domain structure showed that there was a signal peptide and a trypsin-like serine protease domain, Tryp_SPC, in the BmCLSP protein. Semi-quantitative and real-time fluorescence quantitative PCR analysis showed that the BmCLSP gene was highly expressed in the fifth instar larvae of silkworm, and specifically expressed in the midgut. The expression level of BmCLSP in the BmNPV resistant strain A35 was higher than that in the sensitive strain P50. Virus amplification analysis showed that the relative expression level of VP39 was significantly lower than that of the control group after infection of silkworm larvae and BmN cells with BmNPV treated with recombinant BmCLSP at an appropriate concentration. Furthermore, our overexpression of BmCLSP in BmN cells significantly inhibited the expansion of BmNPV. In summary, the results of this study indicate that BmCLSP has anti-BmNPV activity in silkworm, and can significantly inhibit the proliferation of BmNPV in silkworm. It offers a promising avenue for silkworm anti-virus breeding.

Bombyx mori Metal Carboxypeptidases12 (BmMCP12) Is Involved in Host Protection Against Viral Infection

Baculoviruses, the largest studied insect viruses, are highly pathogenic to host insects. Bombyx mori nucleopolyhedrovirus (BmNPV) is the main cause of nuclear polyhedrosis of silkworm, a viral disease that causes significant economic losses to the sericulture industry. The anti-BmNPV mechanism of the silkworm has not yet been characterized. Carboxypeptidase is an enzyme that is involved in virtually all life activities of animals and plants. Studies have shown that the carboxypeptidase family is related to insect immunity. There are few reports on the role of carboxypeptidase in the defense of silkworms against pathogen invasion. In this study, we identified the homologous gene Bombyx mori metal carboxypeptidases12 (BmMCP12) related to mammalian carboxypeptidase A2 (CPA2) and found that BmMCP12 had a Zn-pept domain. The BmMCP12 gene was primarily located in the cytoplasm and was highly expressed in the midgut of silkworms, and the expression level in BmN-SWU1 cells was upregulated after infection with BmNPV. After overexpression of the BmMCP12 gene, quantitative real-time (qRT)-PCR and Western blots showed that BmMCP12 could inhibit BmNPV replication, whereas knockout of the gene had the opposite effect. In addition, we constructed transgenic silkworm strains with a knockout of BmMCP12, and the transgenic strains had reduced resistance to BmNPV. These findings deepen the functional study of silkworm carboxypeptidase and provide a new target for BmNPV disease prevention in silkworms.

The Bombyx mori G protein β subunit 1 (BmGNβ1) gene inhibits BmNPV infection

G protein β subunit 1 (GNβ1) has several functions, including cell growth regulation, the control of second messenger levels, and ion channel switching. Previous transcriptome analyses in our laboratory have shown that BmGNβ1 transcription is reduced following infection with Bombyx mori nucleopolyhedrovirus (BmNPV), but it is unknown what role this gene may have in the host response to BmNPV infection. In this study, the BmGNβ1 gene was cloned using the RACE method. After BmNPV infection, BmGNβ1 was downregulated in Baiyu strains in tissues such as the hemolymph and midgut. Indirect immunofluorescence showed that BmGNβ1 was localized to the cytoplasm. We further constructed a BmGNβ1-pIZ/V5-His-mCherry overexpression plasmid and designed siRNA to evaluate the role of BmGNβ1 in host response to infection. The results showed that BmGNβ1 overexpression inhibited BmNPV proliferation, while knockdown of BmGNβ1 was correlated with increased BmNPV proliferation. The siRNA-mediated reduction of BmGNβ1 was correlated with an increase in BmNPV infection of BmN cells, increased BmNPV vp39 transcription, and reduced survival time of BmNPV-infected B. mori. Overexpression of BmGNβ1 in BmN cells was also correlated with apoptosis and a modification in transcript levels of genes involved in host response to BmNPV infection (PI3K, AKT, Bmp53, BmFOXO, Caspase-1, Bmp21, BmPKN and BmCREB), suggesting that BmGNβ1 may influence the apoptotic host response of infected B. mori through the PI3K-AKT pathway. This study provides potential targets and theoretical support for breeding BmNPV-resistant silkworm varieties.

Bombyx mori triose-phosphate transporter protein inhibits Bombyx mori nucleopolyhedrovirus infection by reducing the cell glycolysis pathway

Bombyx mori triose-phosphate transporter protein (BmTPT) is a member of the solute carrier (SLC) family. Its main function is to transport triose phosphate between intracellular and extracellular. In this study, BmTPT was cloned and characterised from the fat body of the silkworm Bombyx mori, resulting in an open reading frame (ORF) with a full length of 936 bp, which can encode 311 amino acid residues and has eight transmembrane structural domains. BmTPT was distributed throughout the cell and deposited the most in the nucleus, and is expressed in all tissues of Bombyx mori. Bombyx mori nucleopolyhedrovirus (BmNPV) infection significantly up-regulated BmTPT expression in immune tissue fat bodies. In addition, overexpression of BmTPT significantly inhibited BmNPV infection and markedly reduced the expression of enzymes related to the cellular glycolytic pathway; on the contrary, down-regulation of BmTPT expression by RNA interference resulted in robust replication of BmNPV and a significant increase in the expression of enzymes related to the cellular glycolytic pathway. This is the first report that BmTPT has antiviral effect in silkworm, and also could result in a lack of energy and raw materials for BmNPV replication and infection through down-regulation of the cellular glycolytic pathway.

BmNPV Bm60 is a key target gene used by a resistant strain of Bombyx mori to inhibit BmNPV proliferation

Bombyx mori nucleopolyhedrovirus (BmNPV) is a pathogen that causes significant losses to the silkworm industry. Numerous antiviral genes and proteins have been identified by studying silkworm resistance to BmNPV. However, the molecular mechanism of silkworm resistance to BmNPV is unclear. We analyzed the differences between the susceptible strain 871 and a near-isogenic resistant strain 871C. The survival of strain 871C was significantly greater than that of 871 after oral and subcutaneous exposure to BmNPV. Strain 871C exhibited a nearly 10,000-fold higher LD50 for BmNPV compared to 871. BmNPV proliferation was significantly inhibited in all tested tissues of strain 871C using HE strain and fluorescence analysis. Strain 871C exhibited cellular resistance to BmNPV rather than peritrophic membrane or serum resistance. Strain 871C suppressed the expression of the viral early gene Bm60. This led to the inhibition of BmNPV DNA replication and late structural gene transcription based on the cascade regulation of baculovirus gene expression. Bm60 could also interact with the viral DNA binding protein and alkaline nuclease, as well as host proteins Methylcrotonoyl-CoA carboxylase subunit alpha, mucin-2-like protein, and 30 K-8. Overexpression of 30 K-8 significantly inhibited BmNPV proliferation. These results increase understanding of the molecular mechanism behind silkworm resistance to BmNPV and suggest targets for the breeding of resistant silkworm strains and the controlling pest of Lepidoptera.

BmSPP is a virus resistance gene in Bombyx mori

Introduction

Signal peptide peptidase (SPP) is an intramembrane protease involved in a variety of biological processes, it participates in the processing of signal peptides after the release of the nascent protein to regulate the endoplasmic reticulum associated degradation (ERAD) pathway, binds misfolded membrane proteins, and aids in their clearance process. Additionally, it regulates normal immune surveillance and assists in the processing of viral proteins. Although SPP is essential for many viral infections, its role in silkworms remains unclear. Studying its role in the silkworm, Bombyx mori , may be helpful in breeding virus-resistant silkworms.

Methods

First, we performed RT-qPCR to analyze the expression pattern of BmSPP. Subsequently, we inhibited BmSPP using the SPP inhibitor 1,3-di-(N-carboxybenzoyl-L-leucyl-L-leucylaminopropanone ((Z-LL)2-ketone) and downregulated the expression of BmSPP using CRISPR/Cas9 gene editing. Furthermore, we assessed the impact of these interventions on the proliferation of Bombyx mori nucleopolyhedrovirus (BmNPV).

Results

We observed a decreased in the expression of BmSPP during viral proliferation. It was found that higher concentration of the inhibitor resulted in greater inhibition of BmNPV proliferation. The down-regulation of BmSPP in both in vivo and in vitro was found to affect the proliferation of BmNPV. In comparison to wild type silkworm, BmSPPKO silkworms exhibited a 12.4% reduction in mortality rate.

Discussion

Collectively, this work demonstrates that BmSPP plays a negative regulatory role in silkworm resistance to BmNPV infection and is involved in virus proliferation and replication processes. This finding suggests that BmSPP servers as a target gene for BmNPV virus resistance in silkworms and can be utilized in resistance breeding programs.

Ras3 in Bombyx mori with antiviral function against B. mori nucleopolyhedrovirus

Bombyx mori ras protein3 (BmRas3) is a small molecular protein in the GTPase superfamily, which has the activity of binding guanosine nucleotides and GTP enzymes. It acts as a molecular switch by coupling extracellular signal to different cellular response through the conversion between Ras-GTP conformation and Ras-GDP conformation, thus regulating signal pathways responsible for cell growth, migration, adhesion, survival and differentiation. However, few studies have been done on Ras3 in silkworm, and its function and mechanism are unclear. In this study, we found that the overexpression of BmRas3 inhibited the infection of BmNPV(B. mori nucleopolyhedrovirus), while knockdown of BmRas3 could promote the infection of BmNPV. In addition, after the BmRas3 in silkworm larvae was knockdown, the anti-BmNPV ability of silkworm decreased and the survival rate of silkworm was affected. Additionly in the cells with BmRas3 overexpression, the transcription level of BmMapkk6 、BmP38、BmJNK、BmERK1/2 and BmERK5 were significantly increased after BmNPV infection, and the transcript levels of BmMapkk6、BmP38、BmJNK、BmERK1/2 and BmERK5 were also inhibited to varying degrees This is the first report on the antiviral effect of BmRas3 in silkworm, which provides a new direction for further study on the anti-BmNPV mechanism of silkworm and screening and cultivation of anti-BmNPV silkworm strain.

Bombyx mori nucleopolyhedrovirus induces BmFABP1 downregulation to promote viral proliferation

Fatty acid binding proteins (FABPs) play an important role as endogenous cytoprotectants. However, studies on FABPs in invertebrates are scarce. Previously, we discovered Bombyx mori fatty acid binding protein 1 (BmFABP1) through co-immunoprecipitation. Here, we cloned and identified BmFABP1 from BmN cells. The results of immunofluorescence indicated that BmFABP1 was localized in the cytoplasm. The tissue expression profile of silkworms showed that BmFABP1 was expressed in all tissues except hemocytes. The expression level of BmFABP1 gradually decreases in BmN cells and B. mori larvae after infection with B. mori nucleopolyhedrovirus (BmNPV). Upregulation of BmFABP1 expression through overexpression or WY14643 treatment significantly inhibited the replication of BmNPV, while downregulation of BmFABP1 expression by RNA interference promoted the replication of BmNPV. The same results were obtained in experiments on silkworm larvae. These results suggest that BmNPV induces BmFABP1 downregulation to promote its proliferation and that BmFABP1 has a potential anti-BmNPV role. This is the first report on the antiviral effect of BmFABP1 in silkworms and provides new insights into the study of the FABP protein family. Also, it is important to study BmNPV resistance in silkworms to breed transgenic silkworms with BmNPV resistance.

The Mechanisms of Silkworm Resistance to the Baculovirus and Antiviral Breeding

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.

The digestive proteinase trypsin, alkaline A contributes to anti-BmNPV activity in silkworm (Bombyx mori)

Bombyx mori nucleopolyhedrovirus (BmNPV) is a serious pathogenic microorganism that causes tremendous loss to sericulture. Previous studies have found that some proteins of serine protease family in the digestive juice of B. mori larvae have anti-BmNPV activity. In our previous publication about proteome analysis of the digestive juice of B. mori larvae, the digestive enzyme trypsin, alkaline A (BmTA) was filtered as a differentially expressed protein possibly involved in BmNPV resistance. Here, the biological characteristics and anti-BmNPV functions of BmTA were comprehensively analysed. The cDNA sequence of BmTA had an ORF of 768 nucleotides encoding 255 amino acid residues. Domain architecture analysis showed that BmTA contained a signal peptide and a typical Tryp_SPc domain. Quantitative real-time PCR analysis showed that BmTA was highly expressed in the larval stages and specifically expressed in the midgut of B. mori larvae. The expression level of BmTA in BmNPV resistant strain A35 was higher than that in susceptible strain P50. After BmNPV infection, the expression of BmTA increased in both strains from 24 to 72 h. Virus amplification analysis showed that the relative levels of VP39 in B. mori larvae and BmN cells infected with the appropriate concentration of recombinant-BmTA-treated BmNPV were significantly lower than in the control groups. Moreover, overexpression of BmTA in BmN cells significantly inhibited the amplification of BmNPV. Taken together, the results of this study indicated that BmTA possessed anti-BmNPV activity in B. mori, which broadens the horizon for virus-resistant breeding of silkworms.

Advances in the Arms Race Between Silkworm and Baculovirus

Insects are the largest group of animals. Nearly all organisms, including insects, have viral pathogens. An important domesticated economic insect is the silkworm moth Bombyx mori. B. mori nucleopolyhedrovirus (BmNPV) is a typical baculovirus and a primary silkworm pathogen. It causes major economic losses in sericulture. Baculoviruses are used in biological pest control and as a bioreactor. Silkworm and baculovirus comprise a well-established model of insect–virus interactions. Several recent studies have focused on this model and provided novel insights into viral infections and host defense. Here, we focus on baculovirus invasion, silkworm immune response, baculovirus evasion of host immunity, and enhancement of antiviral efficacy. We also discuss major issues remaining and future directions of research on silkworm antiviral immunity. Elucidation of the interaction between silkworm and baculovirus furnishes a theoretical basis for targeted pest control, enhanced pathogen resistance in economically important insects, and bioreactor improvement.

Antimicrobial Peptides as Potential Antiviral Factors in Insect Antiviral Immune Response

Antimicrobial peptides (AMPs) with antiviral activity (antiviral peptides: AVPs) have become a research hotspot and already show immense potential to become pharmaceutically available antiviral drugs. AVPs have exhibited huge potential in inhibiting viruses by targeting various stages of their life cycle. Insects are the most speciose group of animals that inhabit almost all ecosystems and habitats on the land and are a rich source of natural AMPs. However, insect AVP mining, functional research, and drug development are still in their infancy. This review aims to summarize the currently validated insect AVPs, explore potential new insect AVPs and to discuss their possible mechanism of synthesis and action, with a view to providing clues to unravel the mechanisms of insect antiviral immunity and to develop insect AVP-derived antiviral drugs.

A Novel Digestive Proteinase Lipase Member H-A in Bombyx mori Contributes to Digestive Juice Antiviral Activity Against B. mori Nucleopolyhedrovirus

Previous studies have revealed that some proteins in Bombyx mori larvae digestive juice show antiviral activity. Here, based on the label-free proteomics data, BmLipase member H-A (BmLHA) was identified as being involved in the response to BmNPV infection in B. mori larvae digestive juice. In the present study, a gene encoding the BmLHA protein in B. mori was characterized. The protein has an open reading fragment of 999 bp, encoding a predicted 332 amino acid residue-protein with a molecular weight of approximately 35.9 kDa. The phylogenetic analysis revealed that BmLHA shares a close genetic distance with Papilio xuthus Lipase member H-A. BmLHA was highly expressed in the middle part of the B. mori gut, and the expression level increased with instar rising in larvae. There was higher expression of BmLHA in A35 than in P50 strains, and it was upregulated in both A35 and P50 strains, following BmNPV infection. The expression level of VP39 decreased significantly in appropriate recombinant-BmLHA-treated groups compared with the PBS-treated group in B. mori larvae and BmN cells. Meanwhile, overexpression of BmLHA significantly reduced the infectivity of BmNPV in BmN cells. These results indicated that BmLHA did not have digestive function but had anti-BmNPV activity. Taken together, our work provides valuable data for the clarification of the molecular characterization BmLHA and supplements research on proteins of anti-BmNPV activity in B. mori.