Characteristic analysis of resistance to BmNPV in CVDAR strain of silkworm

Abstract:

[Objective] Bombyx mori nucleopolyhedrovirus (BmNPV) induced hematogenous sepsis is a common severe disease of silkworm, and there are few effective prevention and control methods. In this study, CVDAR andDaZao (lines with strong resistance to BmNPV) silkworm strains were used as experimental materials. By analyzing the resistance characteristics of CVDAR silkworm, the resistance mechanism of CVDAR to BmNPV was determined. [Methods] In this study, we found that the lethal dose of CVDAR strain to BmNPV infection was more than 10 times higher than that of DaZao through semi lethal dose analysis. Further HE staining was performed to analyze the changes of midgut tissues before and after the infection of CVDAR and DaZao strains, and analyzed the anti-BmNPV mechanism of the resistant CVDAR strain. [Results] The results showed that after 72 hours of infection with BmNPV, the nucleus of large intestinal cells was enlarged and the staining became lighter; after 96 hours, the nuclei continued to increase and tended to fall off. The CVDAR-resistant strains only had enlarged nuclei in part of midgut after 96 hours of infection, but they were well arranged. At the same time by fluorescence quantitative analysis of the CVDAR and DaZao strain proliferation after virus infection, combined with the analysis and comparison of the transcriptional levels of the representative virus genes in each period, no difference in virus copy number and viral genes transcription level between the resistant CVDAR strain and the DaZao strain were found between 0-12 h after BmNPV infection. However, 24 hours after infection, we found that the CVDAR of the resistant strain was significantly lower than that of the control strain, regardless of the number of viral copies or the transcriptional expression level of viral genes. [Conclusion] Our study demonstrated that during the first round of replication after oral addition of CVDAR, the transcription of midgut virus genes was not affected; and later the transcription level was reduced. The critical period for the inhibition of BmNPV proliferation by CVDAR strain was identified to be 24 h after BmNPV infection, laying a foundation for the analysis of the resistance mechanism.