The complete genome sequence of an alphabaculovirus from Spodoptera exempta, an agricultural pest of major economic significance in Africa.

Spodoptera exempta nucleopolyhedrovirus (SpexNPV) is a viral pathogen of the African armyworm, Spodoptera exempta (Lepidoptera: Noctuidae), a significant agricultural pest of cereal crops in Africa. SpexNPV has been evaluated as a potential insecticide for control of this pest and has served as the subject of research on baculovirus pathology and transmission. Occlusion bodies (OBs) of SpexNPV isolate 244.1 were examined, and the nucleotide sequence of the genome was determined and characterized. SpexNPV-244.1 OBs consisted of irregular polyhedra with a size and appearance typical for alphabaculoviruses. Virions within the polyhedra contained 1-8 nucleocapsids per unit envelope. The SpexNPV-244.1 genome was comprised of a 129,528 bp circular sequence, in which 139 ORFs were annotated. Five homologous regions (hrs) consisting of a variable number of 28-bp imperfect palindromes were identified in the genome. The genome sequence contained the 38 core genes of family Baculoviridae, as well as three ORFs unique to the SpexNPV sequence and one ORF that was apparently acquired by horizontal gene transfer with a betabaculovirus ancestor. Phylogenetic inference with core gene amino acid sequence alignments placed SpexNPV-244.1 in a lineage containing alphabaculoviruses of Spodoptera frugiperda and Spodopotera exigua which in turn is part of a larger group of alphabaculoviruses from the subfamily Noctuinae in the lepidopteran family Noctuidae. Kimura-2-parameter pairwise nucleotide distances indicated that SpexNPV-244.1 represented a different and previously unlisted species in the genus Alphabaculovirus. Gene parity plots indicated that the gene order of SpexNPV-244.l was extensively collinear with that of Spodoptera exigua NPV (SeMNPV). These plots also revealed a group of 17 core genes whose order was conserved in other alpha- and betabaculoviruses.

Biology and genomics of viruses within the genus Gammabaculovirus.

Hymenoptera is a very large and ancient insect order encompassing bees, wasps, ants and sawflies. Fossil records indicate that they existed over 200 million years ago and about 100 million years before the appearance of Lepidoptera. Sawflies have been major pests in many parts of the world and some have caused serious forest defoliation in North America. All baculoviruses isolated from sawflies are of the single nucleocapsids phenotype and appear to replicate in midgut cells only. This group of viruses has been shown to be excellent pest control agents and three have been registered in Canada and Britain for this purpose. Sawfly baculoviruses contain the smallest genome of all baculoviruses sequenced so far. Gene orders among sequenced sawfly baculoviruses are co-linear but this is not shared with the genomes of lepidopteran baculoviruses. One distinguishing feature among all sequenced sawfly viruses is the lack of a gene encoding a membrane fusion protein, which brought into question the role of the budded virus phenotype in Gammabaculovirus biology.

Sequence analysis of the Choristoneura occidentalis granulovirus genome.

The genome of the Choristoneura occidentalis granulovirus (ChocGV) isolated from the western spruce budworm, Choristoneura occidentalis, was sequenced completely. It was 104,710 bp long, with a 67.3% A+T content and contained 116 potential open reading frames (ORFs) covering 88.4% of the genome. Of these, 29 ORFs were conserved in all fully sequenced baculovirus genomes, 30 were GV-specific, 53 were present in some nucleopolyhedroviruses (NPVs) and/or GVs, three were common to ChocGV and Choristoneura fumiferana GV (ChfuGV) and one was so far unique. To date, ChocGV is the only GV identified that contains a homologue of the apoptosis inhibitor protein P35/P49, present in some group I NPVs. It is also the first GV without a Xestia c-nigrum GV ORF 26 homologue. Five homologous regions (hrs)/repeat regions, lacking typical NPV hr palindromes were identified. ChocGV hrs were similar to each other but not to other GV hrs. A 1.8 kb repeat region with a high A+T content (81%) and multiple repeats of 21-210 bp was found between choc36 and 37. This area resembled the non-homologous region origin of DNA replication (non-hr ori) identified in Cryptophlebia leucotreta GV (CrleGV) and Cydia pomonella GV (CpGV). Based on the mean amino acid identities of homologous proteins, ChocGV was closest to fully sequenced genomes CpGV (52.3%) and CrleGV (52.1%). The closest amino acid identity was to individual ORFs from the partially sequenced ChfuGV genome (97.2% in 38 ORFs). Phylogenetic analysis placed ChocGV in a clade with CrleGV and CpGV.