Sequence Analysis and Organization of theNeodiprion abietisNucleopolyhedrovirus Genome

Abstract

Of 30 baculovirus genomes that have been sequenced to date, the only nonlepidopteran baculoviruses include the dipteran Culex nigripalpus nucleopolyhedrovirus and two hymenopteran nucleopolyhedroviruses that infect the sawflies Neodiprion lecontei (NeleNPV) and Neodiprion sertifer (NeseNPV). This study provides a complete sequence and genome analysis of the nucleopolyhedrovirus that infects the balsam fir sawfly Neodiprion abietis (Hymenoptera, Symphyta, Diprionidae). The N. abietis nucleopolyhedrovirus (NeabNPV) is 84,264 bp in size, with a G؉C content of 33.5%, and contains 93 predicted open reading frames (ORFs). Eleven predicted ORFs are unique to this baculovirus, 10 ORFs have a putative sequence homologue in the NeleNPV genome but not the NeseNPV genome, and 1 ORF (neab53) has a putative sequence homologue in the NeseNPV genome but not the NeleNPV genome. Specific repeat sequences are coincident with major genome rearrangements that distinguish NeabNPV and NeleNPV. Genes associated with these repeat regions encode a common amino acid motif, suggesting that they are a family of repeated contiguous gene clusters. Lepidopteran baculoviruses, similarly, have a family of repeated genes called the bro gene family. However, there is no significant sequence similarity between the NeabNPV and bro genes. Homologues of early-expressed genes such as ie-1 and lef-3 were absent in NeabNPV, as they are in the previously sequenced hymenopteran baculoviruses. Analyses of ORF upstream sequences identified potential temporally distinct genes on the basis of putative promoter elements.

Pathology of aGammabaculovirusin Its Natural Balsam Fir Sawfly (Neodiprion abietis) Host

“…Although still distantly, gammabaculoviruses are thought to be more closely related than deltabaculoviruses to alphabaculoviruses and betabaculoviruses [3]. However, gammabaculoviruses appear to lack an envelope fusion protein homolog [22,28,31] and, as a consequence, lack a budded virus (BV) phenotype common to the other three genera. Group I alphabaculoviruses, such as that of Autographa californica (AcMNPV), encode GP-64 [32] whereas group II NPVs, for example, Lymantria dispar LdMNPV, encode F-protein [33].…”

“…Unprecedented outbreaks of balsam fir sawfly populations on the island of Newfoundland (Newfoundland and Labrador (NL), Canada) [17] have led to the development, registration, commercialization, and use Psyche of an N. abietis-specific Gammabaculovirus (NeabNPV) [18][19][20][21]. The genome of NeabNPV has been sequenced [22], and the in vivo replication and transcription kinetics studied [23]. There is, however, a dearth of information on the pathology of sawfly NPVs in the literature, although they are thought to only infect the midgut epithelium of their hosts [24,25].…”

Recent Advances in Our Knowledge of Baculovirus Molecular Biology and Its Relevance for the Registration of Baculovirus-Based Products for Insect Pest Population Control

“…Progeny virions were occluded directly without the production of BVs (reviewed in Federici, 1997;Slack & Arif, 2007;Rohrmann, 2011). Sequence data from gammabaculoviruses failed to identify homologues to the alphabaculovirus fusion proteins, GP64 or F-protein (Duffy et al, 2006;Lauzon et al, 2006), indicating the absence of the BV phenotype. Also lacking in gammabaculoviruses are viral fibroblast growth factor (vfgf) homologues (Jehle et al, 2006), that have been shown to accelerate the establishment of systemic infections in alphabaculoviruses (Detvisitsakun et al, 2007;Passarelli, 2011).…”

“…In mosquito hosts, following the primary infection of the gastric caeca and posterior midgut by ODVs, deltabaculovirus BVs also spread the infection further from cell to cell but only to these same tissues (Moser et al, 2001). Sawfly gammabaculoviruses do not appear to have a BV phenotype (Duffy et al, 2006;Garcia-Maruniak et al, 2004;Lauzon et al, 2004) and OBs are only produced in the nuclei of midgut epithelial cells (Federici, 1997).…”

“…Rather than using the BV phenotype to propagate the initial infection to other midgut cells, the released OBs have been suggested to serve as inoculum for other gut cells (Rohrmann, 2011). Midgut cell lysis in sawflies, rather than being a hindrance to gammabaculoviruses, is utilized as a mechanism for dispersal and only hymenopteran baculoviruses encode a trypsin-like protein (Duffy et al, 2006;Lauzon et al, 2006) that is thought to aid this process (Rohrmann, 2011). Much of the horizontal transmission occurs while infected larvae are still alive and feeding because OBs are excreted in a virus-laden diarrhea that is infectious to other larvae (Federici, 1997).…”