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Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the most serious pathogens restricting the sustainable development of the sericulture industry. Currently, there is no effective treatment for BmNPV infection in silkworms, and the mechanism underlying BmNPV resistance in silkworms is also not clear. In this study, comparative transcriptome analyses were carried out in midguts of two silkworm varieties, namely BaiyuN, which is a resistance variety, and Baiyu, which is a susceptible variety, at five different time points (i.e., 0, 1, 3, 6, and 9 h) post-BmNPV infection to detect the early-stage transcriptional changes in these silkworms. In total, 1911 and 1577 differentially expressed genes (DEGs) were identified in the Baiyu and BaiyuN varieties, respectively, involving a total of 48 metabolic pathways. Of these pathways, eight were shared by the Baiyu and BaiyuN varieties in response to BmNPV infection. Notably, four genes (i.e., BGIBMGA08815, BGIBMGA003935, BGIBMGA003571, BGIBMGA010059) were upregulated in the Baiyu variety while downregulated in the BaiyuN variety. The inhibited expression of these four genes in the resistant variety highlighted their potential roles in the resistance of early-stage viral replication. Thus, our study provided a new avenue for the further study of the mechanism underlying BmNPV infection in silkworms and the potential treatment of BmNPV infection. [ABSTRACT FROM AUTHOR]

Simple Summary: SariNPV is one of the main pathogens of Samia ricini and its infection of Samia ricini sericulture has caused significant economic losses to society. In this study, we aim to reveal the molecular mechanism of pathogen–host interactions in SariNPV-infected S. ricini through transcriptomic and proteomic analyses. Using RNA-sequencing and iTRAQ, we mapped the differentially expressed genes (DEGs) and proteins (DEPs) that are involved in the immune responses of S. ricini upon virus invasion. Based on our analyses, we identified specific DEGs and DEPs that are involved in various essential biological signaling pathways and immune-related pathways upon SariNPV invasion. These DEGs and DEPs play an important role in triggering host immune responses to pathogens. Our study provides molecular insights into host immune responses regarding pathogen invasion, in particular, the immune response mechanism and network of S. ricini in response to SariNPV infection. Samia ricini nucleopolyhedrovirus (SariNPV) is one of the main pathogens of S. ricini sericulture and its infection causes severe impacts on economic sericulture development. To explore and reveal the molecular mechanisms of S. ricini in response to SariNPV infection, we employed RNA sequencing (RNA-seq), adopting isobaric tags for relative and absolute quantitation (iTRAQ), and carried out combination analysis of the obtained differentially expressed genes (DEGs) and proteins (DEPs). Through transcriptome sequencing, a total of 2535 DEGs were detected, and with iTRAQ, 434 DEPs with significant expression difference were identified. Through correlation analysis, we found that the expression trends of 116 differentially expressed proteins were the same as those of differentially expressed genes (including 106 up-regulated and 10 down-regulated). Twenty-five key differentially expressed genes (proteins) involved in several signaling and immune related pathways (mainly involving Toll, Imd, Jak-STAT and Wnt signaling pathways, as well as other immune related pathways) were screened through real-time quantitative PCR. Our results, not only provide insights into the pathogenic mechanism of SariNPV infection in ricin silkworm and the immune response mechanism within the host, but also provide a significant contribution for identifying and preventing diseases caused by SariNPV. [ABSTRACT FROM AUTHOR]

Simple Summary: The hemolynamic septic disease in silkworms is caused by Bombyx mori nuclear polyhedrosis virus (BmNPV). It is the most severe viral disease that adversely affects the sericulture industry. Breeding BmNPV-resistant silkworm varieties is the most economic and effective solution. However, BmNPVs from different geographical strains have different pathogenicities. This brings the challenges of cultivating BmNPV-resistant silkworm varieties with wider adaptabilities. In this study, the genomes of two BmNPV strains (BmNPV ZJ and BmNPV YN) were sequenced and characterized to compare the difference in pathogenicity between the two strains. A total of 76 different genes in these two viruses were found with amino acid mutations. These included genes were associated with BmNPV replication and infection. In addition, the relative gene expression of the BmNPV YN strain was lower than that BmNPV ZJ. Thus, we speculate that the mutations in some genes may affect viral functions and may be the cause of the higher pathogenicity of BmNPV YN despite its lower proliferation rate. The present research provides new clues for further exploring the mechanism determining the difference in pathogenicity of different BmNPV strains. The pathogenicity of different concentrations of Bombyx mori nuclear polyhedrosis virus- Zhenjiang strain (BmNPV ZJ) and Yunnan strain (BmNPV YN) was assessed in Baiyu larvae. The structures of the two viral strains were observed by negative-staining electron microscopy, and their proliferation was examined by quantitative polymerase chain reaction (qPCR). The genomic sequences of these two viruses were obtained to investigate the differences in their pathogenicity. The lethal concentration 50 (LC50) of BmNPV ZJ against Baiyu larvae was higher than that of BmNPV YN, indicating a relatively more robust pathogenicity in BmNPV YN. Electron microscopic images showed that the edges of BmNPV YN were clearer than those of BmNPV ZJ. The qPCR analysis demonstrated significantly higher relative expressions of immediately early 1 gene (ie-1), p143, vp39, and polyhedrin genes (polh) in BmNPV ZJ than in BmNPV YN at 12–96 h. The complete genomes of BmNPV ZJ and BmNPV YN were, respectively, 135,895 bp and 143,180 bp long, with 141 and 145 coding sequences and 40.93% and 39.71% GC content. Considering the BmNPV ZJ genome as a reference, 893 SNP loci and 132 InDel mutations were observed in the BmNPV YN genome, resulting in 106 differential gene sequences. Among these differential genes, 76 (including 22 hub genes and 35 non-hub genes) possessed amino acid mutations. Thirty genes may have been related to viral genome replication and transcription and five genes may have been associated with the viral oral infection. These results can help in understanding the mechanisms of pathogenicity of different strains of BmNPV in silkworms. [ABSTRACT FROM AUTHOR]

Bombyx mori nucleopolyhedrovirus (BmNPV) is a silkworm disease that is especially harmful to cocoon production and seriously restricts sericultural development. Our laboratory successfully cultivated a new highly BmNPV-resistant silkworm variety, Huakang 2; however, its mechanism of BmNPV resistance remains unclear. To understand its resistance mechanism, we conducted a metabolomic and transcriptomic study of the midgut of silkworm varieties, Baiyu N and Baiyu after BmNPV infection. We identified 451 differential metabolites, which were mostly comprised of small molecules, such as saccharides, acids, amines, alcohols, and glycosides. We found that the primary differences in disease resistance between the silkworm varieties are metabolic-pathways, tryptophan metabolism, oxidative phosphorylation, ABC-transporters, beta-alanine metabolism, and phenylalanine metabolism. Combined analysis with transcriptomic data suggested that tryptophan metabolism and oxidative phosphorylation are closely related to the silkworms' BmNPV resistance. We hypothesize that the roles of the two metabolic pathways in the BmNPV resistance mechanism might be the following: Oxidative phosphorylation generates a large amount of adenosine triphosphate (ATP) in response to BmNPV infection to provide silkworms the energy required for establishing BmNPV resistance. Tryptophan metabolism then activates the aryl hydrocarbon receptor (AhR) through the exogenous virus BmNPV, which activates the silkworm's immune system to defeat BmNPV infections. [ABSTRACT FROM AUTHOR]

Fluoride tolerance is an important economic trait in sericulture, especially in some industrial development regions. Analyses of physiological changes involving structural damage to the insect body and molecular analyses of some related genes have focused on this area; however, the changes that occur at the metabolic level of silkworms after eating fluoride-contaminated mulberry leaves remain unclear. Here, metabonomic analysis was conducted using gas chromatography-mass spectrometry (GC-MS) to analyze the changes in midgut tissue after NaF stress using silkworm strains 733xin (susceptible stain) and T6 (strain resistant to fluoride), which were previously reported by our laboratory. Differential metabolomics analysis showed that both T6 and 733xin strains displayed complex responses after exposure to 200 mg/kg NaF. The purine metabolism and arginine and proline metabolic pathways of fluoride-tolerant strains reached significant levels, among which 3′-adenylic acid and hypoxanthine were significantly upregulated, whereas guanine, allantoic acid, xanthine, N-acetyl-L-glutamic acid, and pyruvate were significantly downregulated. These metabolic pathways may be related to the fluoride tolerance mechanism of NaF poisoning and tolerant strains. [ABSTRACT FROM AUTHOR]

The silkworm Dominant trimolting (Moltinism, M³) mutant undergoes three larval molts and exhibits precocious metamorphosis. In this study, we found that compared with the wild-type (WT) that undergoes four larval molts, both the juvenile hormone (JH) concentration and the expression of the JH-responsive gene Krüppel homolog 1 (Kr-h1) began to be greater in the second instar of the M³ mutant. A positional cloning analysis revealed that only the homeodomain transcription factor gene Sex combs reduced (Scr) is located in the genomic region that is tightly linked to the M³ locus. The expression level of the Scr gene in the brain-corpora cardiaca-corpora allata (Br-CC-CA) complex, which controls the synthesis of JH, was very low in the final larval instar of both the M³ and WT larvae, and exhibited a positive correlation with JH titer changes. Importantly, luciferase reporter analysis and electrophoretic mobility shift assay (EMSA) demonstrated that the Scr protein could promote the transcription of genes involved in JH biosynthesis by directly binding to the cis-regulatory elements (CREs) of homeodomain protein on their promoters. These results conclude that the homeodomain protein Scr is transcriptionally involved in the regulation of JH biosynthesis in the silkworm.