Autographa californica multiple nucleopolyhedrovirus odv-e25 (Ac94) is required for budded virus infectivity and occlusion-derived virus formation

Abstract

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) odv-e25 is a core gene found in all lepidopteran baculoviruses, but its function is unknown. In this study, we generated an odv-e25-knockout AcMNPV and investigated the roles of ODV-E25 in the baculovirus life cycle. The odv-e25 knockout was subsequently rescued by reinserting the odv-e25 gene into the same virus genome. Fluorescence microscopy showed that transfection with the odv-e25-null bacmid vAcBac(KO) was insufficient for propagation in cell culture, whereas the 'repair' virus vAcBac(RE) was able to function in a manner similar to that of the control vAcBac. We found that odv-e25 was not essential for the release of budded viruses (BVs) into culture medium, although the absence of odv-e25 resulted in a 100-fold lower viral titer at 24 h post-transfection (p.t.). Analysis of viral DNA replication in the absence of odv-e25 showed that viral DNA replication was unaffected in the first 24 h p.t. Furthermore, electron microscopy revealed that polyhedra were found in the nucleus, while mature occlusion-derived viruses (ODVs) were not found in the nucleus or polyhedra in odv-e25 null transfected cells, which indicated that ODV-E25 was required for the formation of ODV.