Bombyx mori nucleopolyhedrovirus F-like protein Bm14 affects the morphogenesis and production of occlusion bodies and the embedding of ODVs.

In group I nucleopolyhedrovirus such as Bombyx mori nucleopolyhedrovirus (BmNPV), the biological functions of F-like protein (Bm14) still remain elusive. Here, we found that the deletion of Bm14 reduced the production rate of infectious budded viruses in cell culture, delayed the lethal time of infected larvae by approximately 26 h, and produced less occlusion bodies (OBs). Scanning electron microscopy demonstrated that its disruption affected OB morphogenesis, forming irregular OBs with a pitted surface and irregular profiles. Moreover, almost 45% less DNA was present in OBs produced by Bm14-null virus. This reduction in DNA content was consistent with fewer virions embedded into OBs. The titers of occlusion-derived viruses was 7.5 times less in mutant OBs. Western blot analysis revealed that Bm14 is present in the envelope of both BV and ODV. Taken together, Bm14 is a viral factor that affects OB morphogenesis and production, and the number of ODVs occluded into OBs.