Abstract
Operophtera brumata nucleopolyhedrovirus (OpbuNPV) infects the 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 open reading frames (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.
Highlights
Baculoviruses are rod-shaped, insect-specific viruses of family Baculoviridae that possess large (≥80 kbp) double-stranded circular DNA genomes [1]
We present an analysis of the occlusion bodies and genome sequence of an alphabaculovirus from the winter moth, Operophtera brumata (L.) (Lepidoptera: Geometridae)
Closer examination of the occlusion bodies (OBs) cross-sections revealed the presence of OBs that did not contain the rod-shaped virions typically observed in baculovirus OBs (Figure 2A)
Summary
Baculoviruses are rod-shaped, insect-specific viruses of family Baculoviridae that possess large (≥80 kbp) double-stranded circular DNA genomes [1]. Alphabaculoviruses— known as nucleopolyhedroviruses (NPVs)—infect larvae of order Lepidoptera (moths and butterflies) and produce visually distinctive polyhedra (or occlusion bodies, OBs) in host cells during replication [2,3]. The OBs are large enough to be visualized by light microscopy, and contain a type of virion referred to as the occlusion-derived virus (ODV). A second type of virion—the budded virus (BV)—is initially assembled and secreted from infected cells to spread infection to other tissues in the host. Progeny ODVs are later assembled and occluded into OBs, which are subsequently released after the death of the infected insect
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