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Involvement of Bombyx mori nucleopolyhedrovirus GP37 in the postmortem host liquefaction
Shota Fujimoto1, Kaito Fujimaki1, Susumu Katsuma2
1Department of Agrobiology and Bioresources, Utsunomiya University, Utsunomiya-shi, Tochigi, Japan.
Abstract:
GP37, a component protein of baculovirus particles, enhances the ability of occlusion-derived virions (ODV) to penetrate the peritrophic membrane of host insects. The GP37 of Bombyx mori nucleopolyhedrovirus (BmNPV Orf52, Bm52) localizes to the mitochondria of host cells throughout the course of infection. However, the specific role of BmNPV GP37 (BmGP37) within infected cells and larvae remains unclear. In this study, to investigate the function of BmGP37, a Bmgp37-deleted virus (Bmgp37D) was constructed by inserting an hsp70-lacZ cassette. No significant differences were found between Bmgp37D and the wild type virus (WT) in terms of viral genome replication or virulence in cultured cells. However, both LC50 and LD50 values of Bmgp37D were higher in B. mori larvae compared to those of WT, and the LT50 of Bmgp37D was significantly longer than that of WT. Notably, postmortem liquefaction, crucial for the environmental release of occlusion bodies, was severely lessened in Bmgp37D -infected larvae. Expression levels of viral chitinase and viral cathepsin, both of which are associated with larval disintegration, showed no significant difference between Bmgp37D and WT. Similarly, systemic infection levels did not differ between Bmgp37D and WT. These findings indicate that BmGP37 is a novel protein required for postmortem host liquefaction.
Insights
Bombyx mori nucleopolyhedrovirus GP37 protein is essential for postmortem liquefaction in infected larvae. Deleting this protein reduced larval disintegration, impacting occlusion body release.
Area of Science:
- Virology
- Insect Pathology
- Molecular Biology
Background:
- Baculovirus GP37 protein aids virion penetration of insect peritrophic membranes.
- Bombyx mori nucleopolyhedrovirus (BmNPV) GP37 (BmGP37) localizes to host mitochondria during infection.
- The precise function of BmGP37 within infected cells and larvae is not fully understood.
Purpose of the Study:
- To investigate the role of BmGP37 in BmNPV infection.
- To determine the necessity of BmGP37 for viral replication, virulence, and host liquefaction.
Main Methods:
- Construction of a BmGP37-deleted virus (Bmgp37D) using an hsp70-lacZ cassette.
- Comparison of Bmgp37D and wild-type (WT) BmNPV in cultured cells and B. mori larvae.
- Assessment of viral genome replication, virulence (LC50, LD50, LT50), and postmortem liquefaction.
Main Results:
- No significant differences in viral replication or virulence in cultured cells between Bmgp37D and WT.
- Bmgp37D exhibited higher LC50 and LD50 values and a longer LT50 in B. mori larvae compared to WT.
- Postmortem liquefaction was significantly reduced in larvae infected with Bmgp37D, without affecting chitinase/cathepsin expression or systemic infection levels.
Conclusions:
- BmGP37 is not essential for viral replication or systemic infection within B. mori.
- BmGP37 plays a crucial, novel role in facilitating postmortem host liquefaction for baculovirus.
- This finding highlights BmGP37's importance in the baculovirus life cycle for environmental dissemination.
