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Molecular characterization of baculovirus Bombyx mori nucleopolyhedrovirus polyhedron mutants
S Katsuma1, Y Noguchi, T Shimada
1Department of Agricultural and Environmental Biology, University of Tokyo, Japan.
Abstract:
Four newly isolated and two previously isolated polyhedron mutants of Bombyx mori nucleopolyhedrovirus (BmNPV) were studied. Two polyhedron deficient mutants, #126 and #136, produced small uncrystallized particles of polyhedrin in the nuclei and cytoplasm of infected cells. Mutant #211 produced a large number of variably sized polyhedra in the nucleus and #220 produced a few large cuboidal polyhedra in the nucleus. Mutant #24 and #128 were previously isolated BmNPV mutants. Mutant #24 could not produce polyhedrin mRNA and polyhedra produced by mutant #128 lacked oral infectivity. Nucleotide sequence analysis indicated that five mutants (#126, #136, #211, #220 and #128) had amino acid substitutions in polyhedrin and mutant #24 had a point mutation only in the promoter region of the polyhedrin gene. Cotransfection experiments showed that the altered phenotypes were due to the mutations found in the polyhedrin gene regions. In mutants #126 and #136, amino acid sequences of the nuclear localization signal of polyhedrin were identical to those of wild-type BmNPV, suggesting that this sequence was necessary but not sufficient for nuclear localization of polyhedrin. Electron microscopic observation revealed that fewer occluded virions were contained in polyhedra of #128 and #220.
Insights
Mutations in the Bombyx mori nucleopolyhedrovirus (BmNPV) polyhedrin gene affect polyhedron formation and infectivity. These findings are crucial for understanding BmNPV pathogenesis and developing improved biocontrol agents.
Area of Science:
- Virology
- Molecular Biology
- Insect Pathology
Background:
- Bombyx mori nucleopolyhedrovirus (BmNPV) is a significant pathogen of silkworms, utilized in biological control.
- The polyhedrin protein is essential for forming occlusion bodies, which protect the virus.
- Understanding polyhedrin gene mutations is key to BmNPV's life cycle and infectivity.
Purpose of the Study:
- To characterize polyhedron-deficient mutants of BmNPV.
- To elucidate the role of specific polyhedrin gene mutations in polyhedron formation and viral infectivity.
- To investigate the necessity and sufficiency of the nuclear localization signal in polyhedrin.
Main Methods:
- Isolation and characterization of BmNPV polyhedron mutants.
- Nucleotide sequence analysis to identify mutations in the polyhedrin gene.
- Cotransfection experiments to confirm mutation-induced phenotypic changes.
- Electron microscopy to assess polyhedron structure and virion occlusion.
Main Results:
- Mutants exhibited varied defects in polyhedron formation, including small uncrystallized particles, variable sizes, or few cuboidal polyhedra.
- Mutant #24 lacked polyhedrin mRNA production due to a promoter mutation.
- Mutant #128 polyhedra showed reduced oral infectivity.
- Five mutants had amino acid substitutions in polyhedrin, while mutant #24 had a promoter mutation.
- Nuclear localization signal sequence was necessary but not sufficient for nuclear localization.
- Polyhedra in mutants #128 and #220 contained fewer occluded virions.
Conclusions:
- Mutations in the BmNPV polyhedrin gene directly impact polyhedron formation and virion occlusion.
- The polyhedrin promoter is critical for polyhedrin gene expression.
- Specific polyhedrin mutations can abolish oral infectivity, highlighting their importance in viral pathogenesis.
- Further research is needed to fully understand the nuclear import mechanism of polyhedrin.