The Operophtera brumata nucleopolyhedrovirus (OpbuNPV) represents an early, divergent lineage within genus Alphabaculovirus

Authors: Harrison, Robert - Bob; Rowley, Daniel; Mowery, Joseph; Bauchan, Gary; BURAND, JOHN - University Of Massachusetts

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2017
Publication Date: 10/21/2017
Citation: Harrison, R.L., Rowley, D.L., Mowery, J.D., Bauchan, G.R., Burand, J.P. 2017. The Operophtera brumata nucleopolyhedrovirus (OpbuNPV) represents an early, divergent lineage within genus Alphabaculovirus. Viruses. 9(10):307.

Interpretive Summary: The winter moth is an invasive pest of forests and fruit orchards in the northeastern USA. A virus that infects winter moth larvae, known as a baculovirus, has been identified. This baculovirus potentially can be developed into a natural biopesticide to be applied against the winter moth. However, the winter moth baculovirus does not seem to kill many winter moth larvae in the wild. To understand why this baculovirus is not more lethal, the virus-containing crystals (called occlusion bodies) produced by the winter moth baculovirus and used to spread baculovirus infection to other larvae were examined by electron microscopy. Also, the entire genomic DNA sequence of the baculovirus was determined and analyzed. The occlusion bodies produced by the winter moth baculovirus were discovered to include occlusion bodies produced by an entirely different kind of virus called a cypovirus. The baculovirus genomic DNA was found to have an unusually low level of variability. These two discoveries – the presence of a cypovirus mixed with the winter moth baculovirus, and the low level of variability in the baculovirus genome – may explain why the winter moth baculovirus does not cause as much mortality in winter moth larvae as expected. The information in this study contributes to progress towards developing ecologically safe and environmentally friendly virus-based insecticides to control damaging outbreaks of winter moth, and will be of interest to those in academia, government, and industry who work with insect viruses or with winter moth and its management.

Technical Abstract: Operophtera brumata nucleopolyhedrovirus (OpbuNPV) infects larvae of the winter moth, Operophtera brumata. As part of an effort to explore the pesticidal potential of OpbuNPV, an isolate of this virus from Massachusetts (USA), OpbuNPV-MA, was characterized by electron microscopy of OpbuNPV occlusion bodies (OBs) and by sequencing of the viral genome. The OBs of OpbuNPV-MA consisted of irregular polyhedra and contained virions consisting of a single rod-shaped nucleocapsid within each envelope. Presumptive cypovirus OBs were also detected in sections of the OB preparation. The OpbuNPV-MA genome assembly yielded a circular contig of 119,054 bp and was found to contain little genetic variation, with most polymorphisms occurring at a frequency of <6%. A total of 130 ORFs were annotated, including the 38 core genes of Baculoviridae, along with five homologous repeat (hr) regions. The results of BLASTp and phylogenetic analysis with selected ORFs indicated that OpbuNPV-MA is not closely related to other alphabaculoviruses. Phylogenies based on concatenated core gene amino acid sequence alignments placed OpbuNPV-MA on a basal branch lying outside other alphabaculovirus clades. These results indicate that OpbuNPV-MA represents a divergent baculovirus lineage that appeared early during the diversification of genus Alphabaculovirus.