Involvement of Bombyx mori nucleopolyhedrovirus GP37 in the postmortem host liquefaction

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.