Bombyx mori nucleopolyhedrovirus Bm96 suppresses viral virulence in Bombyx mori larvae

GC-MS-based metabonomic analysis of silkworm haemolymph reveals four-stage metabolic responses to nucleopolyhedrovirus infection

Silkworm, Bombyx mori, an economically significant insect, plays a crucial role in silk production. However, silkworm breeding is highly susceptible to various pathogens, particularly the Bombyx mori nucleopolyhedrovirus (BmNPV), which poses a serious threat. Recent metabonomic studies have provided insights into the metabolic changes associated with BmNPV infection. BmNPV infection has obvious temporal characteristics. However, few studies have investigated the silkworms infected in different periods. This study employed gas chromatography-mass spectrometry (GC-MS) to perform a comprehensive analysis of haemolymph metabolites in silkworms at 48, 72, 96 and 120 h post-infection (h.p.i.). Through the integration of time-course analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, the study revealed distinct four-stage metabolic characteristics in the silkworm's response to BmNPV infection. At Stage 1 (48 h.p.i.), silkworms activate antioxidant defence mechanisms, with significant enrichment in metabolic pathways involving key antioxidants such as glutathione, to mitigate oxidative stress induced by viral invasion. By Stage 2 (72 h.p.i.), pathways related to amino acid metabolism and protein synthesis become active, indicating an increase in protein synthesis. In Stage 3 (96 h.p.i.), energy metabolism and substance transport pathways are significantly upregulated to support the rapid viral replication and the enhanced locomotor behaviour of silkworm. Finally, at Stage 4 (120 h.p.i.), there is a further enhancement of pathways related to energy metabolism, nucleic acid synthesis, and substance transport, which align with peak viral assembly and release. These findings contribute to an in-depth understanding of the biochemical basis of silkworm resistance to NPV.

BV/ODV-E26 is a conserved baculoviral inhibitory factor for optimizing viral virulence in lepidopteran hosts

Alphabaculoviruses induce abnormal behavior in lepidopteran larval hosts. A baculoviral gene, bv/odv-e26, is crucial for behavioral manipulation in Bombyx mori larvae by Bombyx mori nucleopolyhedrovirus (BmNPV). However, how bv/odv-e26 fulfills its role in this phenotype remains largely unknown. In this study, we found that the overexpression of BmNPV bv/odv-e26 delayed viral infection in cultured cells and decreased pathogenicity in B. mori larvae. We also discovered that homologs of bv/odv-e26 are conserved more widely in alphabaculoviruses than previously thought. The inhibitory activity was demonstrated in bv/odv-e26 homologs of phylogenetically close and distant baculoviruses, indicating conserved inhibitory function among alphabaculoviruses. Furthermore, locomotory analyses revealed that bv/odv-e26 increased larval locomotory activity but had little effect on the timing of abnormal behavior initiation. Collectively, our findings demonstrate that bv/odv-e26 is a baculoviral inhibitory factor that is widely conserved in the genus alphabaculovirus and may reduce viral virulence for successful host behavioral manipulation.

An electrochemical immunosensor based on hybrid self-assembled monolayers for rapid detection of Bombyx mori nucleopolyhedrovirus

Bombyx mori nucleopolyhedrovirus (BmNPV) is highly contagious and poses a serious threat to sericulture production. Because there are currently no effective treatments for BmNPV, a rapid and simple detection method is urgently needed. This paper describes an electrochemical immunosensor for the detection of BmNPV. The immunosensor was fabricated by covalently immobilizing anti-BmNPV, a biorecognition element, onto the surface of the working gold electrode via 11-mercaptoundecanoic acid (MUA)/β-mercaptoethanol (ME) hybrid self-assembled monolayers. Electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) were used to characterize the electrochemical performance and morphology of the immunosensor, respectively. Under optimum conditions, the developed immunosensor exhibited a linear response to BmNPV polyhedrin in the range of 1 × 102-1 × 108 fg/mL, with a low detection limit of 14.54 fg/mL. The immunosensor also exhibited remarkable repeatability, reproducibility, specificity, accuracy, and regeneration. Normal silkworm blood was mixed with BmNPV polyhedrin and analyzed quantitatively using this sensor, and the recovery was 92.31 %-100.61 %. Additionally, the sensor was used to analyze silkworm blood samples at different time points after BmNPV infection, and an obvious antigen signal was detected at 12 h post infection. Although this result agreed with that provided by the conventional polymerase chain reaction (PCR) method, the electroanalysis method established in this study was simpler, shorter in detection period, and lower in material cost. Furthermore, this innovative electrochemical immunosensor, developed for the ultra-sensitive and rapid detection of BmNPV, can be used for the early detection of virus-infected silkworms.

The Potential Biological Roles of Circular RNAs in the Immune Systems of Insects to Pathogen Invasion

Circular RNAs (circRNAs) are a newly discovered class of endogenously expressed non-coding RNAs (ncRNAs). They are highly stable, covalently closed molecules that frequently exhibit tissue-specific expression in eukaryotes. A small number of circRNAs are abundant and have been remarkably conserved throughout evolution. Numerous circRNAs are known to play important biological roles by acting as microRNAs (miRNAs) or protein inhibitors ('sponges'), by regulating the function of proteins, or by being translated themselves. CircRNAs have distinct cellular functions due to structural and production differences from mRNAs. Recent advances highlight the importance of characterizing circRNAs and their targets in a variety of insect species in order to fully understand how they contribute to the immune responses of these insects. Here, we focus on the recent advances in our understanding of the biogenesis of circRNAs, regulation of their abundance, and biological roles, such as serving as templates for translation and in the regulation of signaling pathways. We also discuss the emerging roles of circRNAs in regulating immune responses to various microbial pathogens. Furthermore, we describe the functions of circRNAs encoded by microbial pathogens that play in their hosts.

High-resolution analysis of baculovirus-induced host manipulation in the domestic silkworm, Bombyx mori

Many parasites manipulate host behaviour to enhance their transmission. Baculoviruses induce enhanced locomotory activity (ELA) combined with subsequent climbing behaviour in lepidopteran larvae, which facilitates viral dispersal. However, the mechanisms underlying host manipulation system are largely unknown. Previously, larval locomotion during ELA was summarized as the distance travelled for a few minutes at several time points, which are unlikely to characterize ELA precisely, as ELA typically persists for several hours. In this study, we modified a recently developed method using time-lapse recording to characterize locomotion of Bombyx mori larvae infected with B. mori nucleopolyhedrovirus (BmNPV) for 24 h at 3 s resolution. Our data showed that the locomotion of the mock-infected larvae was restricted to a small area, whereas the BmNPV-infected larvae exhibited a large locomotory area. These results indicate that BmNPV dysregulates the locomotory pattern of host larvae. Furthermore, both the mock- and BmNPV-infected larvae showed periodic cycles of movement and stationary behaviour with a similar frequency, suggesting the physiological mechanisms that induce locomotion are unaffected by BmNPV infection. In contrast, the BmNPV-infected larvae exhibited fast and long-lasting locomotion compared with mock-infected larvae, which indicates that locomotory speed and duration are manipulated by BmNPV.