Inhibition of miR-274-3p increases BmCPV replication by regulating the expression of BmCPV NS5 gene in Bombyx mori

Bmo-miR-3351 modulates glutathione content and inhibits BmNPV proliferation by targeting BmGSTe6 in Bombyx mori

MicroRNAs (miRNAs) are small non-coding RNAs that play pivotal roles in the host response to invading pathogens. Among these pathogens, Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the main causes of substantial economic losses in sericulture, and there are relatively few studies on the specific functions of miRNAs in the B. mori-BmNPV interaction. Therefore, we conducted transcriptome sequencing to identify differentially expressed (DE) messenger RNAs (mRNAs) and miRNAs in the midgut of 2 B. mori strains (BmNPV-susceptible strain P50 and BmNPV-resistant strain A35) after BmNPV infection. Through correlation analysis of the miRNA and mRNA data, we identified a comprehensive set of 21 miRNAs and 37 predicted target mRNAs. Notably, miR-3351, which has high expression in A35, exhibited remarkable efficacy in suppressing BmNPV proliferation. Additionally, we confirmed that miR-3351 binds to the 3' untranslated region (3' UTR) of B. mori glutathione S-transferase epsilon 6 (BmGSTe6), resulting in its downregulation. Conversely, BmGSTe6 displayed an opposite expression pattern to miR-3351, effectively promoting BmNPV proliferation. Notably, BmGSTe6 levels were positively correlated with glutathione S-transferase activity, consequently influencing intracellular glutathione content in the infected samples. Furthermore, our investigation revealed the protective role of glutathione against BmNPV infection in BmN cells. In summary, miR-3351 modulates glutathione content by downregulating BmGSTe6 to inhibit BmNPV proliferation in B. mori. Our findings enriched the research on the role of B. mori miRNAs in the defense against BmNPV infection, and suggests that the antiviral molecule, glutathione, offers a novel perspective on preventing viral infection in sericulture.

MicroRNA-Mediated Host Immune Genes Manipulation Benefits AcMNPV Proliferation in Spodoptera frugiperda

Spodoptera frugiperda is a highly destructive migratory pest that threatens various crops globally. Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is an effective biocontrol agent against lepidopteran pests. Here, we explored the molecular mechanisms underlying the immune response to AcMNPV infection in S. frugiperda. RNA-seq and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analyses identified the Toll, IMD, and apoptosis pathways as primary immune responses. Investigation into AcMNPV-induced apoptosis in the S. frugiperda cell line (Sf9) revealed that the Toll pathway activated the JNK via the TRAF6 (TNF receptor-associated factor 6) adapter. In addition, AcMNPV-induced the differential expression of several host-encoded microRNAs (miRNAs), with significant negative regulatory effects, on S. frugiperda antiviral immune genes. RNAi and miRNA-mimic mediated silencing of these genes resulted in increased AcMNPV proliferation. Our findings reinforce the potential of AcMNPV as a potent biocontrol agent and further our understanding of developing biotechnology-based targeted pest control agents.

Integrated miRNA and transcriptome profiling to explore the molecular mechanism of Spodoptera frugiperda larval midgut in response to azadirachtin exposure

As a destructive agricultural pest, Spodoptera frugiperda has spread worldwide in the past few years. Azadirachtin, an environmentally friendly and most promising compound, showed adverse effects, including mortality and growth inhibition, against S. frugiperda. While the effects of azadirachtin on the midgut of this pest remain to be determined. In this study, structural damage was observed in the larval midguts of S. frugiperda with azadirachtin exposure. RNA-seq on the larval midguts with different azadirachtin treatments was performed. Compared to the control group, a total of 3344 and 4759 differentially expressed genes (DEGs) were identified in the midguts with 0.1 and 0.5 μg/g azadirachtin exposure, respectively. Among them, the DEGs encoding detoxification enzymes/proteins, immune-related proteins, digestion and absorption-related proteins, and transcript factors were further analyzed. High-throughput sequencing was also used for the identification of differentially expressed microRNAs in different treatments. A total of 153 conserved miRNAs and 147 novel miRNAs were identified, of which 11 and 29 miRNAs were affected by 0.1 and 0.5 μg/g azadirachtin treatments, respectively. The integrated analysis found that 13 and 178 miRNA versus mRNA pairs were acquired in the samples with 0.1 and 0.5 μg/g azadirachtin treatments, respectively. The results of high-throughput sequencing were confirmed by real-time quantitative polymerase chain reaction (RT-qPCR). These results provide useful information for revealing the molecular mechanism of S. frugiperda larval midgut in response to azadirachtin.

A cypovirus encoded microRNA negatively regulates the NF-κB pathway to enhance viral multiplication in Silkworm, Bombyx mori

MicroRNAs (miRNAs) are small non-coding RNAs that function as novel gene expression regulators at the post-transcriptional level. Not with standing that the biogenesis and function of miRNAs are well-understood in eukaryotes, little is known about RNA virus-encoded miRNAs. Bombyx mori cypovirus (BmCPV) is a double-stranded RNA virus with a segmented genome that causes cytoplasmic polyhedrosis disease in silkworm larvae. To date, the interaction between BmCPV and silkworm remains largely unclear. 22 candidate BmCPV-encoded miRNAs were identified in this study through small RNA sequencing, stem-loop RT-PCR and qRT-PCR. Then, generation and function analyses were conducted on one of the candidate miRNAs, BmCPV-miR-1, in the BmN cells and the silkworm larvae by RNA interference, quantitative PCR, dual-luciferase assay. Our results revealed that BmCPV-miR-1 was encoded by BmCPV genome RNA rather than the degraded fragments of the viral genome. Its generation depended on Dicer-1 and might also be correlated with Dicer-2, Argonaute-1 and Argonaute-2. Moreover, BmCPV-miR-1 could suppress the expression of the target gene, B. mori inhibitor of nuclear factor kappa-B kinase subunit beta (BmIKKβ), via binding to the target mRNA 3'-untranslated region, which fine-tuned the host NF-κB signaling pathway and consequently enhanced viral replication. Our results provide new evidence supporting the hypothesis that RNA viruses could generate miRNAs to modulate antiviral host defense.

Profiling of MicroRNAs in Midguts of Plutella xylostella Provides Novel Insights Into the Bacillus thuringiensis Resistance

The diamondback moth (DBM), Plutella xylostella, one of the most destructive lepidopteran pests worldwide, has developed field resistance to Bacillus thuringiensis (Bt) Cry toxins. Although miRNAs have been reported to be involved in insect resistance to multiple insecticides, our understanding of their roles in mediating Bt resistance is limited. In this study, we constructed small RNA libraries from midguts of the Cry1Ac-resistant (Cry1S1000) strain and the Cry1Ac-susceptible strain (G88) using a high-throughput sequencing analysis. A total of 437 (76 known and 361 novel miRNAs) were identified, among which 178 miRNAs were classified into 91 miRNA families. Transcripts per million analysis revealed 12 differentially expressed miRNAs between the Cry1S1000 and G88 strains. Specifically, nine miRNAs were down-regulated and three up-regulated in the Cry1S1000 strain compared to the G88 strain. Next, we predicted the potential target genes of these differentially expressed miRNAs and carried out GO and KEGG pathway analyses. We found that the cellular process, metabolism process, membrane and the catalytic activity were the most enriched GO terms and the Hippo, MAPK signaling pathway might be involved in Bt resistance of DBM. In addition, the expression patterns of these miRNAs and their target genes were determined by RT-qPCR, showing that partial miRNAs negatively while others positively correlate with their corresponding target genes. Subsequently, novel-miR-240, one of the differentially expressed miRNAs with inverse correlation with its target genes, was confirmed to interact with Px017590 and Px007885 using dual luciferase reporter assays. Our study highlights the characteristics of differentially expressed miRNAs in midguts of the Cry1S1000 and G88 strains, paving the way for further investigation of miRNA roles in mediating Bt resistance.

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

MicroRNAs (miRNAs), small non-coding RNAs of about 22 nucleotides, have been reported to regulate gene expression at the posttranscriptional level and are involved in several biological processes such as immunity, development, metabolism, and host-pathogen interactions. Apart from miRNAs encoded by the host, miRNAs produced by pathogens also regulate host genes to facilitate virus replication and evasion of the host defense responses. In recent years, accumulated studies suggest that viral infections alter the host miRNAs expression profile, and both cellular and viral miRNAs may play vital roles in host-pathogen interactions. Bombyx mori, one of the critical lepidopteran model species, is an economically important insect for silk production. The mechanism of interaction between B. mori and its pathogens and their regulation by miRNAs has been extensively studied. Therefore, in this review, we aim to highlight the recent information and understanding of the virus-encoding miRNAs and their functions in modulating viral and host (B. mori) genes. Additionally, the response of B. mori derived miRNAs to viral infection is also discussed. A detailed critical view about miRNAs’ regulatory roles in B. mori-virus interactions will help us understand molecular networks and develop a sustainable antiviral strategy.

Identification of long noncoding RNAs in silkworm larvae infected with Bombyx mori cypovirus

Bombyx mori cypovirus (BmCPV) is one of the most important pathogens causing severe disease to silkworm. Emerging evidence indicates that long noncoding RNAs (lncRNAs) play importantly regulatory roles in virus infection and host immune response. To better understand the interaction between silkworm, Bombyx mori and BmCPV, we performed a comparative transcriptome analysis on lncRNAs and mRNAs between the virus-infected and noninfected silkworm larvae midgut at two time points postinoculation. A total of 16,753 genes and 1845 candidate lncRNAs were identified, among which 356 messenger RNA (mRNAs) and 41 lncRNAs were differentially expressed (DE). Target gene prediction revealed that most of DEmRNAs (123) were coexpressed with 28 DElncRNAs, suggesting that the expression of mRNA is mainly affected through trans- regulation by BmCPV-induced lncRNAs, and a regulatory network of DElncRNAs and DEmRNAs was then constructed. According to the network, many genes involved in apoptosis, autophagy, and antiviral response, such as ATG3, PDCD6, IBP2, and MFB1, could be targeted by different DElncRNAs, implying the essential roles of these genes and lncRNAs in BmCPV infection. In all, our studies revealed for the first time the alteration of lncRNA expression in BmCPV-infected larvae and its potential influence on BmCPV replication, providing a new perspective for host-cypovirus interaction studies.

Insights Into the Antiviral Pathways of the Silkworm Bombyx mori

The lepidopteran model silkworm, Bombyx mori, is an important economic insect. Viruses cause serious economic losses in sericulture; thus, the economic importance of these viruses heightens the need to understand the antiviral pathways of silkworm to develop antiviral strategies. Insect innate immunity pathways play a critical role in the outcome of infection. The RNA interference (RNAi), NF-kB-mediated, immune deficiency (Imd), and stimulator of interferon gene (STING) pathways, and Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway are the major antiviral defense mechanisms, and these have been shown to play important roles in the antiviral immunity of silkworms. In contrast, viruses can modulate the prophenol oxidase (PPO), phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), and the extracellular signal-regulated kinase (ERK) signaling pathways of the host to elevate their proliferation in silkworms. In this review, we present an overview of the current understanding of the main immune pathways in response to viruses and the signaling pathways modulated by viruses in silkworms. Elucidation of these pathways involved in the antiviral mechanism of silkworms furnishes a theoretical basis for the enhancement of virus resistance in economic insects, such as upregulating antiviral immune pathways through transgenic overexpression, RNAi of virus genes, and targeting these virus-modulated pathways by gene editing or inhibitors.

Antiviral defense against Cypovirus 1 (Reoviridae) infection in the silkworm, Bombyx mori

Recent years have shown a large increase in studies of infection of the silkworm (Bombyx mori) with Cypovirus 1 (previously designated as B. mori cytoplasmic polyhedrosis virus), that causes serious damage in sericulture. Cypovirus 1 has a single-layered capsid that encapsulates a segmented double-strand RNA (dsRNA) genome which are attractive features for the establishment of a biotechnological platform for the production of specialized gene silencing agents, either as recombinant viruses or as viral-like particles with nonreplicative dsRNA cargo. For both combatting viral disease and application of Cypovirus-based pest control, however, a better understanding is needed of the innate immune response caused by Cypovirus infection of the midgut of lepidopteran larvae. Studies of deep sequencing of viral small RNAs have indicated the importance of the RNA interference pathway in the control of Cypovirus infection although many functional aspects still need to be elucidated and conclusive evidence is lacking. A considerable number of transcriptome studies were carried out that revealed a complex response that hitherto remains uncharacterized because of a dearth in functional studies. Also, the uptake mechanism of Cypovirus by the midgut cells remains unclarified because of contrasting mechanisms revealed by electron microscopy and functional studies. The field will benefit from an increase in functional studies that will depend on transgenic silkworm technology and reverse genetics systems for Cypovirus 1.

Over expression of bmo-miR-2819 suppresses BmNPV replication by regulating the BmNPV ie-1 gene in Bombyx mori

Bombyx mori nucleopolyhedrovirus (BmNPV) is a major pathogen that threatens the growth and sustainability of the sericulture industry. Accumulating studies in recent years suggest that insect viruses infection can change the host microRNAs (miRNAs) expression profile and both cellular and viral miRNAs play roles in host-pathogen interactions. Until now, the functional analysis of miRNA encoded by silkworm for host-virus interaction is limited. In this study, we validate the down-regulation of bmo-miR-2819 upon BmNPV infection by qRT-PCR and confirm the BmNPV immediately early 1 gene, ie-1 is one of the targets for bmo-miR-2819 based on the results of dual luciferase report assay. Overexpression of bmo-miR-2819 can significantly decline the abundance of IE-1 protein level in BmNPV-infected silkworm larvae. Further, the expression level of polyhedrin gene and VP39 protein of BmNPV in the infected larvae after applying bmo-miR-2819 mimics was significantly decreased comparing with that of larvae with mimic control. Our results suggest that overexpression of bmo-miR-2819 could suppress BmNPV replication by down-regulating the expression of BmNPV ie-1 gene, which demonstrate that cellular miRNAs could affect virus infection by regulating the expression of virus genes.