Summary auto-generated
This study examined whether polyhedrin proteins from different baculoviruses could functionally substitute for each other in generating viral occlusion bodies. Researchers created recombinant Autographa californica multinucleocapsid nucleopolyhedroviruses (AcMNPV) containing polyhedrin genes from either Buzura suppressaria single-nucleocapsid NPV (BusuNPV) or Spodoptera exigua MNPV (SeMNPV). The heterologous polyhedrin genes were highly expressed and produced paracrystalline occlusion bodies in infected cell nuclei. Remarkably, BusuNPV polyhedrin successfully occluded AcMNPV virions with infectivity comparable to wild-type virus, indicating occlusion is not specific to single-nucleocapsid versus multinucleocapsid viruses. However, SeMNPV polyhedrin produced abnormal pyramidal-shaped occlusion bodies containing far fewer virions, resulting in significantly reduced infectivity. These findings demonstrate that virion occlusion is a precisely controlled process involving polyhedrin-specific recognition, though other viral or host factors may also contribute to optimal occlusion body morphogenesis and function.
Key findings
- Heterologous polyhedrin from BusuNPV (single-nucleocapsid NPV) functionally replaced AcMNPV polyhedrin with normal virion occlusion and full infectivity, showing occlusion specificity is not dependent on nucleocapsid number
- SeMNPV polyhedrin produced aberrant pyramidal-shaped occlusion bodies with poor virion encapsidation and reduced infectivity in S. exigua larvae, indicating virion occlusion specificity depends on polyhedrin identity
- Polyhedrin nuclear localization and paracrystalline assembly domains are conserved across NPV species and function in heterologous viral backgrounds
- Sequence divergence between polyhedrin proteins correlates with efficiency of virion occlusion, with more distantly related polyhedrins showing reduced ability to occlude virions
- Virus-specific or host-specific factors beyond polyhedrin itself appear necessary for optimal occlusion body morphogenesis and virion encapsidation
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Abstract
The role of polyhedrin in the occlusion of virions was studied by substituting two heterologous polyhedrin-coding sequences, one from a multiple-nucleocapsid (M) nucleopolyhedrovirus (NPV) of Spodoptera exigua (Se) and one from a single-nucleocapsid (S) NPV of Buzura suppressaria (BusuNPV), into the genome of Autographa californica (Ac) MNPV. Both heterologous polyhedrin genes were highly expressed and polyhedra were produced in the nuclei of cells infected with the respective recombinant AcMNPVs. Polyhedra produced by the recombinant with BusuNPV polyhedrin showed normal occlusion of multiple- nucleocapsid virions and were equally as infectious to S. exigua larvae as were wild-type AcMNPV polyhedra. This indicates that virion occlusion is not specific with respect to whether the virions or polyhedrin are from an SNPV or MNPV. Polyhedra produced by the recombinant containing the SeMNPV polyhedrin had an altered morphology, being pyramidal rather than polyhedral in shape, and many fewer virions were occluded. These occlusion bodies were less infectious to S. exigua larvae than were those of wild-type AcMNPV. These results indicate that virion occlusion is a finely controlled process that is to some extent specific to the polyhedrin involved and may also require other viral or host factors for optimal morphogenesis.