Comparative analysis of the complete genome sequences of Helicoverpa zea and Helicoverpa armigera single-nucleocapsid nucleopolyhedroviruses

A Renewed Appreciation of Helicoverpa armigera Nucleopolyhedrovirus BJ (Formerly Helicoverpa assulta Nucleopolyhedrovirus) with Whole Genome Sequencing

Helicoverpa assulta is a pest that causes severe damage to tobacco, pepper and other cash crops. A local strain of HearNPV-BJ (formerly Helicoverpa assulta nucleopolyhedrovirus (HeasNPV-DJ0031)) was isolated from infected H. assulta larvae in Beijing, which had been regarded as a new kind of baculovirus in previous studies. Describing the biological characteristics of the strain, including its external morphology, internal structure and the pathological characteristics of the infection of various cell lines, can provide references for the identification and function of the virus. HearNPV-BJ virion was defined as a single-nucleocapsid nucleopolyhedrovirus by scanning electron microscopy. QB-Ha-E-5 (H. armigera) and BCIRL-Hz-AM1 (H. zea) cell lines were sensitive to HearNPV-BJ. Undoubtedly modern developed sequencing technology further facilitates the increasing understanding of various strains. The whole genome sequence of the HearNPV-BJ was sequenced and analyzed. The HearNPV-BJ isolate genome was 129, 800 bp nucleotides in length with a G + C content of 38.87% and contained 128 open reading frames (ORFs) encoding predicted proteins of 50 or over 50 amino acids, 67 ORFs in the forward orientation and 61 ORFs in the reverse orientation, respectively. The genome shared 99% sequence identity with Helicoverpa armigera nucleopolyhedrovirus C1 strain (HearNPV-C1), and 103 ORFs had very high homology with published HearNPV sequences. Two bro genes and three hrs were found to be dispersed along the HearNPV-BJ genome. Three of the highest homologs, ORFs with HearNPV, were smaller due to the earlier appearance of the stop codon with unknown functions. P6.9 of HearNPV-BJ, a structural protein, is distinctly different from that of Autographa californica nucleopolyhedrovirus (AcMNPV); its homology with the corresponding gene in HearNPV-C1 was 93.58%. HearNPV-BJ contains 38 core genes identified in other baculoviruses, and phylogenetic analysis indicates HearNPV-BJ belongs to Alphabaculovirus Group II, same as HearNPV-C1. The resulting data provide a better understanding of virion structure, gene function and character of infection. By supplementing the whole-genome sequencing data and Kimura-2 model index, there is more evidence to indicate that HearNPV-BJ may be a variant of Helicoverpa armigera nucleopolyhedrovirus, which also deepens our understanding of the virus species demarcation criteria.

Genome sequence analysis of a Helicoverpa armigera single nucleopolyhedrovirus (HearNPV-TR) isolated from Heliothis peltigera in Turkey

The entire genome of Helicoverpa armigera single nucleopolyhedrovirus (HearNPV-TR) was sequenced, and compared to genomes of other existing isolates. HearNPV-TR genome is 130.691 base pairs with a 38.9% G+C content and has 137 open reading frames (ORFs) of ≥ 150 nucleotides. Five homologous repeated sequences (hrs) and two baculovirus repeated ORFs (bro-a and bro-b) were identified. Phylogenetic analysis showed that HearNPV-TR is closer to HaSNPV-C1, HaSNPV-G4, HaSNPV-AU and HasNPV. However, there are significant differences in hr3, hr5 regions and in bro-a gene. Pairwise Kimura-2 parameter analysis of 38 core genes sequences of HearNPV-TR and other Helicoverpa NPVs showed that the genetic distances for these sequences were below 0.015 substitutions/site. Genomic differences as revealed by restriction profiles indicated that hr3, hr5 regions and bro-a gene may play a role in the virulence of HearNPV-TR.

Biological and molecular characterization of two Anticarsia gemmatalis multiple nucleopolyhedrovirus clones exhibiting contrasting virulence

Baculovirus natural populations are known to be genetically heterogeneous and such genotypic diversity could have implications in the performance of biocontrol agents. The Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) has been widely used to control the velvetbean caterpillar, Anticarsia gemmatalis, in Brazil. In the present work, morphological and molecular analyses as well as the biological activity of AgMNPV genotypes derived from a Brazilian field isolate (AgMNPV-79) were carried out. The existence of genotypic variants in the population was confirmed by DNA restriction analysis. Although difference in virulence was observed among the variants, the most (Ag79-01) and the least (AgL-16) virulent clones do not show any morphological and cytopathological changes when compared to the most studied isolate (AgMNPV-2D). The complete genome analysis of the two viral clones showed the presence of single open reading frames (ORFs) of the pe-38 and he65 genes, which contrasts with the two split ORFs present in the genome of the AgMNPV-2D isolate. The viral clone AgL-16 has many variations in the ie-2 and pe-38 genes, which are transcription regulatory genes responsible for the regulation of viral early gene expression during insect cell infection. Furthermore, other genes showed alterations like the odv-e56, which have an essential role in the maturation and envelopment of the ODVs, and bro-a and bro-b genes which were fused to form a single ORF. For the Ag79-01, although the total number of single nucleotide variants (SNVs) was more prominent in the pe-38 gene, its genome showed very few modifications in comparison to the AgMNPV-2D genome.

Elucidating the genetic diversity of Phthorimaea operculella granulovirus (PhopGV)

Twelve complete genome sequences of Phthorimaea operculella granulovirus (PhopGV) isolates from four different continents (Africa, South America, Asia and Europe) were analysed after Illumina next-generation sequencing (NGS). The isolates have a circular double-stranded DNA genome that is 118 355 to 119 177 bp in length and all of them encode 130 open reading frames (ORFs). Analysis of single-nucleotide polymorphisms (SNPs) revealed a unique set of SNP positions for every tested isolate. The genome sequences of the investigated PhopGV isolates were classified into a new system of four (1-4) groups according to the presence of group-specific SNPs as well as insertions and deletions. These genome groups correlated with phylogenetic lineages inferred from minimum-evolution trees of the whole-genome consensus nucleotide sequences. All members of group 3 originated from the Mediterranean area, whereas the geographical origin and the group assignment did not correlate for isolates belonging to genome groups 1, 2 or 4. The high degree of coverage facilitated the determination of variant nucleotide frequencies. We conclude that the geographical isolates of PhopGV are genetically highly similar. On the other hand, they were rarely genetically homogenous and in most cases appeared to be mixtures of multiple genotypes.

ADAPTATION OF THE CORN EARWORM SINGLE NUCLEOCAPCIDE NUCLEOPOLYHEDROVIRUS (HELICOVERPA ZEA SNPV) FOR THE CONTROL OF THE COTTON BOLLWORM (HELICOVERPA ARMIGERA) POPULATION

Helicoverpa zea (Boddie, 1850) (Hz) single nucleocapcide nucleopolyhedrovirus (SNPV) was adapted to the cotton bollworm (Helicoverpa armigera, (Hübner, 1805) (Ha)) by five blind passages on larvae. The full genomic sequence of the resulting strain HS-18 has been determined (GenBank acc. №: KJ004000.1). Biological activity of the HS-18 strain is higher than the activity of all other Russian strains of NPV, as far as cotton bollworm strain HearSNPV-G4. HS-18-infected caterpillars at the 3-rd and 4-th ages died much faster than those infected with HearSNPV-G4 strain. A major difference of HS-18 genome is an 18 bp repeat in the RING-finger ORF that confirms high variability of this region. Three other insertions and seven base substitutions were observed earlier, while six base substitutions are new. Mutations are located at ORF42, lef-9, ORF58, VP39, PIF-4, P48, SOD, ORF111, ORF129 and ORF138 genes. Among all nucleotide mutation only one is synonymous. Thus we suppose the selective pressure to the virus. The resulting strain HS-18 is recommended as a biopesticide for controlling the number of cotton bollworm in cotton fields.

Lacanobia oleracea nucleopolyhedrovirus (LaolNPV): A new European species of alphabaculovirus with a narrow host range

During an insect sampling program in alfalfa crops near Montpellier, France in 2011, Lacanobia oleracea larvae were collected that died due to nucleopolyhedrovirus infection (LaolNPV). This virus was subjected to molecular and biological characterization. The virus was a multiple nucleocapsid NPV that showed similar restriction profiles to Mamestra configurata NPV-A (MacoNPV-A) but with significant differences. Polypeptide analysis demonstrated similar proteins in occlusion bodies and occlusion derived virions, to those observed in NPVs from Mamestra spp. Terminal sequencing revealed that the genome organization shared similarity with that of MacoNPV-A. The most homologous virus was MacoNPV-A 90/2 isolate (95.63% identity and 96.47% similarity), followed by MacoNPV-A 90/4 strain (95.37% and 96.26%), MacoNPV-B (89.21% and 93.53%) and M. brassicae MNPV (89.42% and 93.74%). Phylogenetic analysis performed with lef-8, lef-9, polh and a concatenated set of genes showed that LaolNPV and the Mamestra spp. NPVs clustered together with HaMNPV, but with a closer genetic distance to MacoNPV-A strains. The Kimura 2-parameter (K-2-P) distances of the complete genes were greater than 0.05 between LaolNPV and the MbMNPV/MacoNPV-B/HaMNPV complex, which indicates that LaolNPV is a distinct species. K-2-P distances were in the range 0.015–0.050 for comparisons of LaolNPV with MacoNPV-A strains, such that additional biological characteristics should be evaluated to determine species status. While MacoNPV-A was pathogenic to seven lepidopteran species tested, LaolNPV was only pathogenic to Chrysodeixis chalcites. Given these findings, Lacanobia oleracea nucleopolyhedrovirus should be considered as a new species in the Alphabaculovirus genus.

MetaGaAP: A Novel Pipeline to Estimate Community Composition and Abundance from Non-Model Sequence Data

Next generation sequencing and bioinformatic approaches are increasingly used to quantify microorganisms within populations by analysis of ‘meta-barcode’ data. This approach relies on comparison of amplicon sequences of ‘barcode’ regions from a population with public-domain databases of reference sequences. However, for many organisms relevant ‘barcode’ regions may not have been identified and large databases of reference sequences may not be available. A workflow and software pipeline, ‘MetaGaAP,’ was developed to identify and quantify genotypes through four steps: shotgun sequencing and identification of polymorphisms in a metapopulation to identify custom ‘barcode’ regions of less than 30 polymorphisms within the span of a single ‘read’, amplification and sequencing of the ‘barcode’, generation of a custom database of polymorphisms, and quantitation of the relative abundance of genotypes. The pipeline and workflow were validated in a ‘wild type’ Alphabaculovirus isolate, Helicoverpa armigera single nucleopolyhedrovirus (HaSNPV-AC53) and a tissue-culture derived strain (HaSNPV-AC53-T2). The approach was validated by comparison of polymorphisms in amplicons and shotgun data, and by comparison of predicted dominant and co-dominant genotypes with Sanger sequences. The computational power required to generate and search the database effectively limits the number of polymorphisms that can be included in a barcode to 30 or less. The approach can be used in quantitative analysis of the ecology and pathology of non-model organisms.

Whole genome sequence and comparative genomic sequence analysis of Helicoverpa armigera nucleopolyhedrovirus (HearNPV-L1) isolated from India

The whole genome of Helicoverpa armigera nucleopolyhedrovirus (HearNPV) from India, HearNPV-L1, was sequenced and analyzed, with a view to look for genes and/or nucleotide sequences that might be involved in the differences and virulence among other HearNPVs sequenced from other countries like SP1A (Spain), NNg1 (Kenya) and G4 (China). The entire nucleotide sequence of the HearNPV-L1 genome was 136,740 bp in length having GC content of 39.19% and contained 113 ORFs that could encode polypeptides with more than 50 amino acids (GenBank accession number KT013224). Two ORFs, viz., ORF 18 (300 bp) and ORF 19 (401 bp) identified were unique in HearNPV-L1 genome. Most of the HearNPV-L1 ORFs showed high similarity to NNg1, SP1A and G4 genomes. HearNPV-L1 genome contains 5 h (hr1-hr5), these regions were found 84-100% similar to hr region of NNg1, SP1A and G4 genomes. A total of four bro genes were observed in HearNPV-L1 genome, of which bro-a gene was 12 and 351 bp bigger than SP1A and G4 bro-a, respectively, while bro-b was 15 bp bigger SP1A and NNg1 bro-b, whereas 593 bp shorter than G4 bro-b, while bro-c was 12 bp shorter than NNg1, however bro-c was absent in G4 genome. HearNPV-L1 bro-d was 100% homologous to bro-d of SP1A, NNg1 and G4 genomes, respectively. The comparative analysis of HearNPV-L1 genome indicated that there are several other putative genes and nucleotide sequences that may be responsible for insecticidal activity in HearNPV-L1 isolate, however, further functional analysis of the hypothetical (putative) genes may help identifying the genes that are crucial for the virulence and insecticidal activity.

Characterization of two monoclonal antibodies, 38F10 and 44D11, against the major envelope fusion protein of Helicoverpa armigera nucleopolyhedrovirus

The envelope fusion protein F of baculoviruses is a class I viral fusion protein which play a significant role during virus entry into insect cells. F is initially synthesized as a precursor (F₀) and then cleaved into a disulfide-linked F₁ and F₂ subunits during the process of protein maturation and secretion. To facilitate further investigation into the structure and function of F protein during virus infection, monoclonal antibodies (mAbs) against the F₂ subunit of Helicoverpa armigera nucleopolyhedrovirus (HearNPV) (HaF) were generated. Two kinds of mAbs were obtained according to their different recognition epitopes: one kind of mAbs, as represented by 38F10, recognizes amino acid (aa) 85 to 123 of F₂ and the other kind, represented by 44D11, recognizes aa 148 to 173 of F₂. Western blot and immunofluorescence assay confirmed that both of the mAbs recognized the F protein expressed in HearNPV infected cells, however, only 44D11 could neutralize HearNPV infection. The results further showed that 44D11 may not interact with a receptor binding epitope, rather it was demonstrated to inhibit syncytium formation in cells expressing the HaF protein. The results imply that the monoclonal antibody 44D11 recognizes a region within HaF2 that may be involved in the F-mediated membrane fusion process.

Comparative Analysis of HaSNPV-AC53 and Derived Strains

Complete genome sequences of two Australian isolates of H. armigera single nucleopolyhedrovirus (HaSNPV) and nine strains isolated by plaque selection in tissue culture identified multiple polymorphisms in tissue culture-derived strains compared to the consensus sequence of the parent isolate. Nine open reading frames (ORFs) in all tissue culture-derived strains contained changes in nucleotide sequences that resulted in changes in predicted amino acid sequence compared to the parent isolate. Of these, changes in predicted amino acid sequence of six ORFs were identical in all nine derived strains. Comparison of sequences and maximum likelihood estimation (MLE) of specific ORFs and whole genome sequences were used to compare the isolates and derived strains to published sequence data from other HaSNPV isolates. The Australian isolates and derived strains had greater sequence similarity to New World SNPV isolates from H. zea than to Old World isolates from H. armigera, but with characteristics associated with both. Three distinct geographic clusters within HaSNPV genome sequences were identified: Australia/Americas, Europe/Africa/India, and China. Comparison of sequences and fragmentation of ORFs suggest that geographic movement and passage in vitro result in distinct patterns of baculovirus strain selection and evolution.

Complete Genome Sequences of Helicoverpa armigera Single Nucleopolyhedrovirus Strains AC53 and H25EA1 from Australia

We report here the genome sequences of two alphabaculoviruses of Helicoverpa spp. from Australia: AC53, used in the biopesticides ViVUS and ViVUS Max, and H25EA1, used in in vitro production studies.

Characterization of a new Helicoverpa armigera nucleopolyhedrovirus variant causing epizootic on a previously unreported host, Helicoverpa gelotopoeon (Lepidoptera: Noctuidae)

This paper reports the first biological and molecular characterization of a nucleopolyhedrovirus isolated from the soybean and cotton pest Helicoverpa gelotopoeon. Studies were performed following a virus outbreak in a rearing facility and in wild H. gelotopoeon populations in Córdoba, Argentina. Host identity was corroborated by partial sequencing of the COI gene. Scanning electron microscope observations of purified OBs revealed their polyhedral morphology and an average diameter of 0.89±0.14μm. Ultrathin sections of infected larvae examined by transmission electron microscopy showed the intranuclear occurrence of polyhedra and virus particles in fat body cells. Nucleocapsids were singly enveloped. Phylogenetic analysis of lef-8, lef-9, polh, orf5/5b and hr3-orf62 viral sequences identified this new NPV isolate (hereafter HegeSNPV) as a variant of Helicoverpa armigera nucleopolyhedrovirus (HearNPV). Furthermore, HegeSNPV was closely related to the so-called "HzSNPV Group" within HearNPV, although having particular characteristics.

A Novel Neurotoxin Gene ar1b Recombination Enhances the Efficiency of Helicoverpa armigera Nucleopolyhedrovirus as a Pesticide by Inhibiting the Host Larvae Ability to Feed and Grow

A recombinant Helicoverpa armigera nucleopolyhedrovirus (HearNPV), Ar1b-HearNPV, was constructed and identified as an improved bio-control agent of Helicoverpa armigera larvae. The HearNPV polyhedrin promoter was used to express the insect-specific neurotoxin gene, ar1b, which was originally isolated from the Australian funnel-web spider (Atrax robustus). RT-PCR and Western blotting analysis showed that both the ar1b transcript and protein were produced successfully in Ar1b-HearNPV-infected HzAM1 cells. In order to investigate the influence of foreign gene insertion in HearNPV, including the ar1b gene, chloramphenicol resistance gene, lacZ, kanamycin resistance gene, and the gentamicin resistance gene, two virus strains (HZ8-HearNPV and wt-HearNPV) were used as controls in the cell transfection analysis. As expected, foreign gene insertion had no impact on budded virus production and viral DNA replication. Both optical microscopy and electron microscopy observations indicated that the formation of the occlusion bodies of recombinant virus was similar to wild type virus. The Ar1b-HearNPV-infected H. armigera larvae exhibited paralysis and weight loss before dying. This recombinant virus also showed a 32.87% decrease in LT₅₀ assays compared with the wild type virus. Besides, Ar1b-HearNPV also inhibited host larval growth and diet consumption. This inhibition was still significant in the older instar larvae treated with the recombinant virus. All of these positive properties of this novel recombinant HearNPV provide a further opportunity to develop this virus strain into a commercial product to control the cotton bollworm.

Genomic Sequences of Five Helicoverpa armigera Nucleopolyhedrovirus Genotypes from Spain That Differ in Their Insecticidal Properties

Helicoverpa armigera nucleopolyhedrovirus (HearNPV) has proved effective as the basis for various biological insecticides. Complete genome sequences of five Spanish HearNPV genotypes differed principally in the homologous regions (hrs) and the baculovirus repeat open reading frame (bro) genes, suggesting that they may be involved in the phenotypic differences observed among genotypes.

Selection of a nucleopolyhedrovirus isolate from Helicoverpa armigera as the basis for a biological insecticide

BACKGROUND

The cotton bollworm, Helicoverpa armigera, is an insect that causes damage in a wide range of crops in Spain. Seven isolates of H. armigera single nucleopolyhedrovirus (HearSNPV) from the Iberian Peninsula were subjected to molecular and biological characterization and compared with a Chinese genotype (HearSNPV-G4).

RESULTS

The estimated sizes of the Iberian genomes varied between 116.2 and 132.4 kb, compared to 131.4 kb of the HearSNPV-G4 reference genome. Phylogenetic analysis based on the lef-8, lef-9 and polh genes revealed that the Iberian strains were more closely related to one another than to other HearSNPV isolates. Occlusion body (OB) concentration-mortality responses (LC50 values) did not differ significantly among Iberian isolates when tested against a Helicoverpa armigera colony from Oxford (UK). Despite being the fastest killing isolate, HearSNPV-SP1 was as productive as isolates with lower virulence, with an average yield of 3.1 × 10(9) OBs larva(-1) . OBs of HearSNPV-SP1 and HearSNPV-G4 were similarly pathogenic against a recently established colony from southern Spain, although HearSNPV-SP1 was faster killing than HearSNPV-G4 against a range of instars.

CONCLUSION

The insecticidal properties of HearSNPV-SP1 mean that this strain is likely to prove useful as the basis for a biological insecticide for control of Helicoverpa armigera in Spain.

Genomic sequence analysis of Helicoverpa armigera nucleopolyhedrovirus isolated from Australia

The complete genomic sequence of Helicoverpa armigera nucleopolyhedrovirus from Australia, HearNPV-Au, was determined and analyzed. The HearNPV-Au genome was 130,992 bp in size with a G+C content of 39 mol% and contained 134 predicted open reading frames (ORFs) consisting of more than 150 nucleotides. HearNPV-Au shared 94 ORFs with AcMNPV, HearSNPV-G4 and SeMNPV, and was most closely related to HearSNPV-G4. The nucleotide sequence identity between HearNPV-Au and HearSNPV-G4 genome was 99%. The major differences were found in homologous regions (hrs) and baculovirus repeat ORFs (bro) genes. Five hrs and two bro genes were identified in the HearNPV-Au genome. All of the 134 ORFs identified in HearNPV-Au were also found in HearSNPV-G4, except the homologue of ORF59 (bro) in HearSNPV-G4. The sequence data strongly suggested that HearNPV-Au and HearSNPV-G4 belong to the same virus species.

Comparative analysis of the genomes of Clostera anastomosis (L.) granulovirus and Clostera anachoreta granulovirus

Clostera anastomosis (L.) granulovirus (CaLGV) and Clostera anachoreta granulovirus (ClanGV) are both capable of infecting each other's native host insects. Despite this, we have little information on their genetic relationship. The complete nucleotide sequence of CaLGV was determined and compared with that of the genome of ClanGV. The circular, double-stranded DNA CaLGV genome (GenBank accession no. KC179784) had a G+C content of 46.7 % and was 101,818 bp in size (331 bp larger than the ClanGV genome). Overall, the CaLGV nucleotide sequence was found to be 90 % identical to that of ClanGV. It contained a total of 123 ORFs, 119 of which had ClanGV homologues, with an identical transcription direction and ORF organization. Seventy-five of the 119 ORFs showed 90 % or greater identity to their ClanGV homologues. CaLGV contained only a single identifiable homologous region (hrs)/repeat region (similar to ClanGV hr4). The mean frequency of nucleotide substitutions in the CaLGV/ClanGV coding regions was 8.33 %. CaLGV contained four unique ORFs (CaL23, CaL39, CaL48 and CaL92). Eight ORFs found in both CaLGV and ClanGV have no homologues in other baculoviruses. Intergenic regions of CaLGV and ClanGV occupied 6.6 % and 7 % of their respective genomes. CaLGV appears closer phylogenetically to ClanGV than to any other baculoviruses.

Determination and analysis of the genome sequence of Spodoptera littoralis multiple nucleopolyhedrovirus

The Spodoptera littoralis multiple nucleopolyhedrovirus (SpliMNPV), a pathogen of the Egyptian cotton leaf worm S. littoralis, was subjected to sequencing of its entire DNA genome and bioassay analysis comparing its virulence to that of other baculoviruses. The annotated SpliMNPV genome of 137,998 bp was found to harbor 132 open reading frames and 15 homologous repeat regions. Four unique genes not present in SpltMNPV were identified, as were 14 genes that were absent or translocated by comparison. Bioassay analysis of experimentally infected Spodoptera frugiperda revealed an extended killing time for SpliMNPV as compared to S. frugiperda MNPV (SfMNPV), but a level of mortality similar to that caused by infection with SfMNPV and superior to that of Autographa californica MNPV (AcMNPV). Although extensive similarity was observed between the genome structure and predicted translation products of SpliMNPV and Spodoptera litura MNPV (SpltMNPV), genetic distances between isolates of SpliMNPV and SpltMNPV suggest that they are in fact different species of genus Alphabaculovirus.

Genomic sequencing and analyses of HearMNPV--a new Multinucleocapsid nucleopolyhedrovirus isolated from Helicoverpa armigera

Background

HearMNPV, a nucleopolyhedrovirus (NPV), which infects the cotton bollworm, Helicoverpa armigera, comprises multiple rod-shaped nucleocapsids in virion(as detected by electron microscopy). HearMNPV shows a different host range compared with H. armigera single-nucleocapsid NPV (HearSNPV). To better understand HearMNPV, the HearMNPV genome was sequenced and analyzed.

Methods

The morphology of HearMNPV was observed by electron microscope. The qPCR was used to determine the replication kinetics of HearMNPV infectious for H. armigera in vivo. A random genomic library of HearMNPV was constructed according to the “partial filling-in” method, the sequence and organization of the HearMNPV genome was analyzed and compared with sequence data from other baculoviruses.

Results

Real time qPCR showed that HearMNPV DNA replication included a decreasing phase, latent phase, exponential phase, and a stationary phase during infection of H. armigera. The HearMNPV genome consists of 154,196 base pairs, with a G + C content of 40.07%. 162 putative ORFs were detected in the HearMNPV genome, which represented 90.16% of the genome. The remaining 9.84% constitute four homologous regions and other non-coding regions. The gene content and gene arrangement in HearMNPV were most similar to those of Mamestra configurata NPV-B (MacoNPV-B), but was different to HearSNPV. Comparison of the genome of HearMNPV and MacoNPV-B suggested that HearMNPV has a deletion of a 5.4-kb fragment containing five ORFs. In addition, HearMNPV orf66, bro genes, and hrs are different to the corresponding parts of the MacoNPV-B genome.

Conclusions

HearMNPV can replicate in vivo in H. armigera and in vitro, and is a new NPV isolate distinguished from HearSNPV. HearMNPV is most closely related to MacoNPV-B, but has a distinct genomic structure, content, and organization.

Complete sequence, analysis and organization of the Orgyia leucostigma nucleopolyhedrovirus genome

The complete genome of the Orgyia leucostigma nucleopolyhedrovirus (OrleNPV) isolated from the whitemarked tussock moth (Orgyia leucostigma, Lymantridae: Lepidoptera) was sequenced, analyzed, and compared to other baculovirus genomes. The size of the OrleNPV genome was 156,179 base pairs (bp) and had a G+C content of 39%. The genome encoded 135 putative open reading frames (ORFs), which occupied 79% of the entire genome sequence. Three inhibitor of apoptosis (ORFs 16, 43 and 63), and five baculovirus repeated ORFs (bro-a through bro-e) were interspersed in the OrleNPV genome. In addition to six direct repeat (drs), a common feature shared among most baculoviruses, OrleNPV genome contained three homologous regions (hrs) that are located in the latter half of the genome. The presence of an F-protein homologue and the results from phylogenetic analyses placed OrleNPV in the genus Alphabaculovirus, group II. Overall, OrleNPV appears to be most closely related to group II alphabaculoviruses Ectropis obliqua (EcobNPV), Apocheima cinerarium (ApciNPV), Euproctis pseudoconspersa (EupsNPV), and Clanis bilineata (ClbiNPV).

Baculovirus induced transcripts in hemocytes from the larvae of Heliothis virescens

Using RNA-seq digital difference expression profiling methods, we have assessed the gene expression profiles of hemocytes harvested from Heliothis virescens that were challenged with Helicoverpa zea single nucleopolyhedrovirus (HzSNPV). A reference transcriptome of hemocyte-expressed transcripts was assembled from 202 million 42-base tags by combining the sequence data of all samples, and the assembled sequences were then subject to BLASTx analysis to determine gene identities. We used the fully sequenced HzSNPV reference genome to align 477,264 Illumina sequence tags from infected hemocytes in order to document expression of HzSNPV genes at early points during infection. A comparison of expression profiles of control insects to those lethally infected with HzSNPV revealed differential expression of key cellular stress response genes and genes involved in lipid metabolism. Transcriptional regulation of specific insect hormones in baculovirus-infected insects was also altered. A number of transcripts bearing homology to retroviral elements that were detected add to a growing body of evidence for extensive invasion of errantiviruses into the insect genome. Using this method, we completed the first and most comprehensive gene expression survey of both baculoviral infection and host immune defense in lepidopteran larvae.

Comparative genomic sequence analysis of novel Helicoverpa armigera nucleopolyhedrovirus (NPV) isolated from Kenya and three other previously sequenced Helicoverpa spp. NPVs

A newly cloned Helicoverpa armigera nucleopolyhedrovirus (HearNPV) from Kenya, HearNPV-NNg1, has a higher insecticidal activity than HearNPV-G4, which also exhibits lower insecticidal activity than HearNPV-C1. In the search for genes and/or nucleotide sequences that might be involved in the observed virulence differences among Helicoverpa spp. NPVs, the entire genome of NNg1 was sequenced and compared with previously sequenced genomes of G4, C1 and Helicoverpa zea single-nucleocapsid NPV (Hz). The NNg1 genome was 132,425 bp in length, with a total of 143 putative open reading frames (ORFs), and shared high levels of overall amino acid and nucleotide sequence identities with G4, C1 and Hz. Three NNg1 ORFs, ORF5, ORF100 and ORF124, which were shared with C1, were absent in G4 and Hz, while NNg1 and C1 were missing a homologue of G4/Hz ORF5. Another three ORFs, ORF60 (bro-b), ORF119 and ORF120, and one direct repeat sequence (dr) were unique to NNg1. Relative to the overall nucleotide sequence identity, lower sequence identities were observed between NNg1 hrs and the homologous hrs in the other three Helicoverpa spp. NPVs, despite containing the same number of hrs located at essentially the same positions on the genomes. Differences were also observed between NNg1 and each of the other three Helicoverpa spp. NPVs in the diversity of bro genes encoded on the genomes. These results indicate several putative genes and nucleotide sequences that may be responsible for the virulence differences observed among Helicoverpa spp., yet the specific genes and/or nucleotide sequences responsible have not been identified.

Genetic and biological variation among nucleopolyhedrovirus isolates from the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

A PCR-based method was used to identify and distinguish among 40 uncharacterized nucleopolyhedrovirus (NPV) isolates from larvae of the moth Spodoptera frugiperda that were part of an insect virus collection. Phylogenetic analysis was carried out with sequences amplified from two strongly conserved loci (polh and lef-8) from the 40 isolates in the collection and from eight previously studied S. frugiperda NPV (SfMNPV) isolates. To further distinguish these isolates, analysis was also carried out with sequences from two less-conserved loci, hr4 and hr5. Phylogenetic inference from the sequence data could distinguish among several of the individual isolates and between different groups of isolates from Georgia (USA) and Colombia, South America. A stronger degree of bootstrap support for the phylogenetic trees was obtained with the hr4 and hr5 homologous repeat sequences. Sequencing and phylogenetic analysis detected a relatively high degree of larva-to-larva sequence divergence occurring among isolates of SfMNPV collected from the same field in Missouri, USA. Restriction endonuclease analysis of viral DNA from larvae infected with five isolates from Georgia, Missouri, Louisiana, Florida (USA), and Colombia allowed for further comparison with other previously reported isolates of SfMNPV. Bioassays with these five geographically distinct isolates detected minor differences in virulence. This study highlights the use of PCR to rapidly distinguish and characterize large numbers of historical baculovirus isolates from the same host using minimal quantities of material, and the use of sequences from homologous repeat regions to distinguish closely related isolates of the same NPV species.

A new nucleopolyhedrovirus strain (LdMNPV-like virus) with a defective fp25 gene from Lymantria xylina (Lepidoptera: Lymantriidae) in Taiwan

A new multiple nucleopolyhedrovirus strain was isolated from casuarina moth, Lymantria xylina Swinhoe, (Lepidoptera: Lymantriidae) in Taiwan. This Lymantria-derived virus can be propagated in IPLB-LD-652Y and NTU-LY cell lines and showed a few polyhedra (occlusion bodies) CPE in the infected cells. The restriction fragment length polymorphism (RFLP) profiles of whole genome indicated that this virus is distinct from LyxyMNPV and the virus genome size was approximately 139 kbps, which was smaller than that of LyxyMNPV. The molecular phylogenetic analyses of three important genes (polyhedrin, lef-8 and lef-9) were performed. Polyhedrin, LEF-8 and LEF-9 putative amino acid analyses of this virus revealed that this virus belongs to Group II NPV and closely related to LdMNPV than to LyxyMNPV. The phylogenetic distance analysis was further clarified the relationship to LdMNPV and this virus provisionally named LdMNPV-like virus. A significant deletion of a 44bp sequence found in LdMNPV-like virus was noted in the fp25k sequences of LdMNPV and LyxyMNPV and may play an important role in the few polyhedra CPE. In ultrastructural observations, the nuclei of the infected LD host cells contained large occlusion bodies (OBs), and few OBs, which presented as one or two OBs in a nucleus that was otherwise filled with free nuclocapsids and virions. We concluded that this LdMNPV-like virus is a new LdMNPV strain from L. xylina.

Structural divergence among genomes of closely related baculoviruses and its implications for baculovirus evolution

Baculoviruses are members of a large, well-characterized family of dsDNA viruses that have been identified from insects of the orders Lepidoptera, Hymenoptera, and Diptera. Baculovirus genomes from different virus species generally exhibit a considerable degree of structural diversity. However, some sequenced baculovirus genomes from closely related viruses are structurally very similar and share overall nucleotide sequence identities in excess of 95%. This review focuses on the comparative analysis of partial and complete nucleotide sequences from two groups of closely related baculoviruses with broad host ranges: (a) group I multiple nucleopolyhedroviruses (MNPVs) from a cluster including Autographa californica (Ac)MNPV, Rachiplusia ou (Ro)MNPV, and Plutella xylostella (Plxy)MNPV; and (b) granuloviruses (GVs) from a cluster including Xestia c-nigrum (Xecn)GV and Helicoverpa armigera (Hear)GV. Even though the individual viruses in these clusters share high nucleotide sequence identities, a significant degree of genomic rearrangement (in the form of insertions, deletions, and homologous recombination resulting in allelic replacement) is evident from alignments of their genomes. These observations suggest an important role for recombination in the early evolution and biological characteristics of baculoviruses of these two groups.

Genomic sequence analysis of the Illinois strain of the Agrotis ipsilon multiple nucleopolyhedrovirus

The Agrotis ipsilon multiple nucleopolyhedrovirus (AgipMNPV) is a group II nucleopolyhedrovirus (NPV) from the black cutworm, A. ipsilon, with potential as a biopesticide to control infestations of cutworm larvae. The genome of the Illinois strain of AgipMNPV was completely sequenced. The AgipMNPV genome was 155,122 nt in size and contained 163 open reading frames (ORFs), including 61 ORFs found among all lepidopteran baculoviruses sequenced to date. Phylogenetic inference placed AgipMNPV in a clade with group II NPVs isolated from larvae of Agrotis and Spodoptera species. Though closely related to the Agrotis segetum NPV (AgseNPV), AgipMNPV was found to be missing 15 ORFs present in the AgseNPV genome sequence, including two of the three AgseNPV enhancin genes. Remarkably few polymorphisms were identified in the AgipMNPV sequence even though an uncloned field isolate of this virus was sequenced. A genotype characterized by a 128-bp deletion in the ecdysteroid UDP-glucosyltransferase gene (egt) was identified in the AgipMNPV field isolate and among clonal isolates of AgipMNPV. The deletion in egt was not associated with differences in budded virus or occluded virus production among AgipMNPV clones in cell culture.

Genomic sequence analysis of a fast-killing isolate of Spodoptera frugiperda multiple nucleopolyhedrovirus

Six clones of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) were plaque-purified from field isolates collected in Missouri, USA. In bioassays, four of the plaque-purified isolates killed neonate S. frugiperda larvae more rapidly than the field isolates from which they were derived, with LT(50) values (mean time to kill 50 % of the test larvae) ranging from 34.4 to 49.7 h post-infection. The complete genomic sequence of one of these isolates, SfMNPV-3AP2, was determined and analysed. The SfMNPV-3AP2 genome was 131 330 bp with a G+C content of 40.2 %. A total of 144 open reading frames (ORFs) was identified and examined, including the set of 62 genes in common among lepidopteran nucleopolyhedrovirus genomes. Comparisons of ORF content, order and predicted amino acid sequences with other nucleopolyhedoviruses indicated that SfMNPV is part of a cluster of viruses within NPV group II that includes NPVs isolated from Spodoptera, Agrotis and Mamestra host species. SfMNPV-3AP2 shared a high degree of nucleotide sequence similarity with partial sequences from other SfMNPV isolates. Comparison of the SfMNPV-3AP2 genome sequence with a partial sequence from a Brazilian isolate of SfMNPV revealed that SfMNPV-3AP2 contained a deletion that removed parts of ORF sf27 and the gene encoding ecdysteroid UDP-glucosyltransferase (egt). An examination of the egt region in the other isolates revealed that the other five SfMNPV clones also contained deletions of varying length in this region. Variant genotypes with deletions extending around the egt gene have been reported previously from a Nicaraguan field isolate of SfMNPV, suggesting that the presence of such variants is a common feature of SfMNPV populations.

Genomic sequence analysis of a granulovirus isolated from the Old World bollworm, Helicoverpa armigera

The genome of a granulovirus isolated from the Old World bollworm, Helicoverpa armigera, was completely sequenced. The size of the Helicoverpa armigera granulovirus (HearGV) genome is 169,794 nt containing 179 open reading frames (ORFs), making it the second largest baculovirus genome analyzed to date. The genomes of HearGV and the Xestia c-nigrum GV (XecnGV) exhibit extensive sequence similarity and co-linearity, with both genomes containing the same nine homologous regions (hrs) with conserved structure and locations and sharing 167 open reading frames (ORFs). Phylogenetic inference and pairwise analysis of Kimura-2-parameter nucleotide distances for the lef-8, lef-9, and granulin genes indicate that HearGV is part of a cluster of granuloviruses typified by XecnGV. The HearGV genome contains all 62 ORFs found in common among other fully sequenced lepidopteran baculovirus genomes, as well as seven ORFs unique to HearGV. In addition, HearGV and XecnGV genomes share 20 ORFs not found among other baculovirus genomes sequenced to date. In addition to possessing ten ORFs with sequence similarity to baculovirus repeated ORFs (bro), the HearGV genome contains members of two other gene families with homologues in ascovirus, nucleopolyhedrovirus, and entomopoxvirus genomes. Alignment of the HearGV and XecnGV genome sequences revealed that HearGV is missing approximately 16.6 kbp of XecnGV-homologous sequence and contains approximately 8.2 kbp of sequence not found in the XecnGV genome.

Deletion of a Helicoverpa armigera nucleopolyhedrovirus gene encoding a virion structural protein (ORF107) increases the budded virion titre and reduces in vivo infectivity

The open reading frame Ha107 of Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HearNPV) encodes a putative protein of 51 kDa with homologues in a few group II NPVs and a granulovirus. Ha107 was transcribed as polyadenylated transcripts in infected HzAM1 insect cells. The transcripts were initiated at two distinct locations, one upstream of Ha106 (superoxide dismutase gene, sod) and the second upstream of Ha107. By Western blot analysis, two forms of the HA107 protein were detected in infected cells, a major polypeptide of 48 kDa and a minor one of 51 kDa. Western blot and immunoelectron microscopy analyses further showed that the HA107 protein was associated with the nucleocapsids of both budded virions (BVs) and occlusion-derived virions. A Ha107 knockout virus expressing enhanced green fluorescent protein and polyhedrin was constructed using bacmid technology. A one-step virus growth curve indicated that the BV titre of the knockout virus was significantly higher than that of the parental virus and a Ha107 repair virus. Bioassays indicated that the knockout virus was able to infect third-instar H. armigera larvae; however, its median lethal dose (LD50) was significantly higher than those of the parental virus and Ha107 repair virus. These data indicate that Ha107 encodes a non-essential structural protein of HearNPV virions and that deletion of this gene increases the BV titre and LD50 of the occluded virus.

The genome sequence of the multinucleocapsid nucleopolyhedrovirus of the Chinese oak silkworm Antheraea pernyi

The complete genome sequence of the Liaoning isolate of the Antheraea pernyi multinucleocapsid nucleopolyhedrovirus (AnpeMNPV) was determined. The viral genome size is 126,246 bp, relatively GC-rich (53.5% G+C), with 145 predicted open reading frames (ORFs) of more than 50 amino acids, accounting for more than 97% of the genome. 97% of the ORFs have predicted functions or homologues in other baculoviruses. There are six homologous repeat regions (hrs) and two bro homologues, which are associated with regions of genome instability. The virus lacks the p35 homologue but encodes two members of the inhibitors of apoptosis (iap) gene family. The presence of a gp64 homologue in the AnpeMNPV genome and results from gene parity plot and phylogenetic analysis using the 29 core baculovirus genes clearly classify AnpeMNPV as a group I NPV. The divergence of genome sequences in two geographical NPV isolates suggests of great genetic heterogeneity of baculovirus populations in nature.

Genome sequence of Leucania seperata nucleopolyhedrovirus

The nucleotide sequence of the Leucania seperata (Ls) Nucleopolyhedrovirus (LsNPV) genome has been determined and analyzed. The circular dsDNA genome contains 168041 bp, making it the largest NPV sequenced to date. The genome has a G + C content of 48.6% and encodes 169 predicted open reading frames (ORFs), one unique repeat region, and eight homologous repeat regions that are divided into two groups. Of the genome, 82.8% encodes predicted ORFs including five dispersal ORFs that have a large overlaps (range in 149 approximately 390 bp) with their adjacent ORFs, respectively such as expression factor 10, 11, 5, 2 (lef-10, lef-11, lef-5, lef-2), and telokin-like protein-20 (tlp-20); 4.4% is in repeat regions; the remaining 12.8% of the genome comprises nonrepeat intergenic regions. LsNPV encodes homologues of 133 ORFs identified previously in other baculoviruses. Other than 10 'baculovirus repeat ORFs' (bro) and two 'inhibitor of apoptosis' (iap) genes, no duplicated ORFs were found. LsNPV lacks a homologue of the ubiquitin gene, which has been found in all fully sequenced baculoviruses. Iap3 and p49, two genes were proven to be inhibitors of apoptosis by experiment, and are found in the LsNPV genome. It is not found in other baculoviruses that two kinds of inhibitors of apoptosis present in a baculovirus genome.

Genomic sequence analysis of a nucleopolyhedrovirus isolated from the diamondback moth, Plutella xylostella

The CL3 plaque isolate of Plutella xylostella multiple nucleopolyhedrovirus (PlxyMNPV-CL3) exhibits a high degree of genetic similarity with the Autographa californica MNPV (AcMNPV) but is significantly more virulent against the diamondback moth, P. xylostella, than AcMNPV. To identify genetic differences between PlxyMNPV-CL3 and AcMNPV that may account for the difference in virulence against P. xylostella, the genome sequence of the CL3 plaque isolate of PlxyMNPV was determined and compared to the genome sequence of AcMNPV isolate C6. The PlxyMNPV genome is 134,417 bp, 523 bp larger than the AcMNPV-C6 genome, and the nucleotide sequence is almost completely co-linear with that of AcMNPV-C6. Of the 153 open reading frames (ORFs) identified in PlxyMNPV, 151 had homologues in AcMNPV-C6, with a mean amino acid sequence identity of 98.5%. The PlxyMNPV genome possessed two features previously reported for other variants of AcMNPV: (1) an extra baculovirus repeated orf (bro) sequence located between the plxy29/ac30 and sod ORFs, and (2) the deletion of the AcMNPV pnk/pnl polynucleotide kinase/ligase gene. In addition, an 817 bp insert of unknown origin located between the fp25K and lef-9 genes was discovered. This insert contained two small ORFs and was detected in both tissue culture- and larvae-derived PlxyMNPV DNA by PCR. Finally, the PlxyMNPV-CL3 ie-2 gene encodes a product with a low level (37.3%) of amino acid sequence identity with the AcMNPV-C6 ie-2 product. PlxyMNPV-CL3 apparently acquired this variant ie2 gene by recombination with an undescribed nucleopolyhedrovirus.

Identification and functional analysis of the origins of DNA replication in the Cydia pomonella granulovirus genome

The entire genome of Cydia pomonella granulovirus (CpGV) was systematically screened for origins of DNA replication, using an infection-dependent DNA replication assay in the granulovirus-permissive Cydia pomonella cell line, Cp14R. All seven cosmids in an overlapping library that covered the CpGV genome were found to replicate in the assay. A genomic library of 32 overlapping plasmids was subsequently screened. Plasmids that replicated were in turn subcloned into 1-2 kbp overlapping fragments. Eleven subclones replicated, each containing at least one of the 13 single-copy 74-76 bp imperfect palindromes, previously identified in the CpGV genome as possible origins of replication. Genome fragments of 156 bp, each containing one of the 13 palindromes, were cloned to verify replication and provided confirmation that these 13 palindromes are the only origins of replication in the genome. A real-time PCR method was developed for the quantification of DNA replication, which eliminated the need for Southern blotting and hybridization. A set of deletion clones allowed further quantitative characterization of one of the palindromes. The previously proposed non-homologous region origin of replication did not replicate in the assay.

The Homingbac baculovirus cloning system: An alternative way to introduce foreign DNA into baculovirus genomes

An in vitro baculovirus cloning system has been developed for direct cloning of foreign DNA into baculovirus genomes. This system is called the "Homingbac system" because it uses homing endonucleases. The Homingbac system was engineered into the baculoviruses AcMNPV, BmNPV, PxMNPV, RoMNPV, HaSNPV and HzSNPV. All Homingbac viruses were designed to retain the polyhedra phenotype so that they could be inoculated per os to insects. This is the first time a common in vitro baculovirus cloning system has been made for multiple baculovirus species that include both groups I and II nucleopolyhedroviruses (NPVs). In this study, the Homingbac system was demonstrated by directly cloning a PCR-amplified beta-glucuronidase gene cassette into a parent Homingbac virus. This new collection of groups I and II NPV Homingbac viruses are a significant expansion of in vitro cloning technology and are new tools for making recombinant baculoviruses.

Proteins associated with Culex nigripalpus nucleopolyhedrovirus occluded virions

Occlusion-derived virions (ODVs) of the nucleopolyhedrovirus of Culex nigripalpus (CuniNPV) were purified by Ludox density gradient ultracentrifugation, and the proteins were separated by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Proteins were identified by using Edman sequencing, matrix-assisted laser desorption ionization-time of flight mass spectrometry, nanoelectrospray quadrupole time-of-flight mass spectrometry, or a combination of these methods. Half of the 44 polypeptide sequences identified in this analysis were unique open reading frames (ORFs) encoded by the CuniNPV genome and did not show similarity to any other sequences present in protein databases. Of the 22 polypeptides that showed similarities to other baculovirus-encoded proteins, only 17 sequences have previously been identified as structural proteins. The newly identified CuniNPV structural proteins cun058, cun059, cun087, cun106, and cun109 are homologues of Autographa californica nucleopolyhedrovirus (AcMNPV) ORFs 68, 62, 98, 81, and 2, respectively. The products of four genes, namely, lef-1 (cun045), alkaline exonuclease (cun054), helicase (cun089), and DNA polymerase (cun091), were not detected in the CuniNPV ODV preparations. These four genes are conserved among all annotated baculovirus genomes, and their homologues have been detected in the ODV of AcMNPV.

Genome sequence and organization of a nucleopolyhedrovirus that infects the tea looper caterpillar, Ectropis obliqua

The complete nucleotide sequence of Ectropis obliqua nucleopolyhedrovirus (EcobNPV), which infects the tea looper caterpillar, was determined and analyzed. The double stranded circular genome is composed of 131,204 bp and is 37.6% G+C rich. The analysis predicted 126 putative, minimally overlapping open reading frames (ORFs) with 150 or more nucleotides that together compose 89.8% of the genome. The remaining 10.2% constitute non-coding and three homologous regions. Comparison with previously sequenced baculoviruses indicated that three ORFs were unique to EcobNPV, while the remaining 123 ORFs shared identity with other baculovirus genes. In addition to two bro homologues, three other repeat ORFs, including dbp, p26, and odv-e66, were identified. Phylogenetic analysis indicated that each member of the paired ORFs was acquired independently. Gene parity plot analysis and percent identity of gene homologues suggested that EcobNPV is a Group II NPV, although its genomic organization was highly distinct.

Open reading frame 132 of Helicoverpa armigera nucleopolyhedrovirus encodes a functional per os infectivity factor (PIF-2)

Open reading frame 132 (Ha132) of Helicoverpa armigera nucleopolyhedrovirus (HearNPV) is a homologue of per os infectivity factor 2 (pif-2) of Spodoptera exigua multiple nucleopolyhedrovirus. Sequence analysis indicated that Ha132 encoded a protein of 383 aa with a predicted molecular mass of 44.5 kDa. Alignment of HA132 and its baculovirus homologues revealed that HA132 was highly conserved among baculoviruses, with 14 absolutely conserved cysteine residues. RT-PCR indicated that Ha132 was first transcribed at 24 h post-infection. Western blot analysis showed that a 43 kDa band was detectable in HearNPV-infected HzAM1 cells from 36 h post-infection. Western blots also indicated that HA132 was a component of the occlusion-derived virus, but not of budded virus. Deletion of Ha132 from HearNPV abolished per os infectivity, but had no effect on the infectivity of the budded virus phenotype.

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.

On the classification and nomenclature of baculoviruses: A proposal for revision

Recent evidence from genome sequence analyses demands a substantial revision of the taxonomy and classification of the family Baculoviridae. Comparisons of 29 baculovirus genomes indicated that baculovirus phylogeny followed the classification of the hosts more closely than morphological traits that have previously been used for classification of this virus family. On this basis, dipteran- and hymenopteran-specific nucleopolyhedroviruses (NPV) should be separated from lepidopteran-specific NPVs and accommodated into different genera. We propose a new classification and nomenclature for the genera within the baculovirus family. According to this proposal the updated classification should include four genera: Alphabaculovirus (lepidopteran-specific NPV), Betabaculovirus (lepidopteran-specific Granuloviruses), Gammabaculovirus (hymenopteran-specific NPV) and Deltabaculovirus (dipteran-specific NPV).

Genome sequence of an enhancin gene-rich nucleopolyhedrovirus (NPV) from Agrotis segetum: collinearity with Spodoptera exigua multiple NPV

The genome sequence of a Polish isolate of Agrotis segetum nucleopolyhedrovirus (AgseNPV-A) was determined and analysed. The circular genome is composed of 147,544 bp and has a G+C content of 45.7 mol%. It contains 153 putative, non-overlapping open reading frames (ORFs) encoding predicted proteins of more than 50 aa, together making up 89.8 % of the genome. The remaining 10.2 % of the DNA constitutes non-coding regions and homologous-repeat regions. One hundred and forty-three AgseNPV-A ORFs are homologues of previously reported baculovirus gene sequences. There are ten unique ORFs and they account for 3 % of the genome in total. All 62 lepidopteran baculovirus genes, including the 29 core baculovirus genes, were found in the AgseNPV-A genome. The gene content and gene order of AgseNPV-A are most similar to those of Spodoptera exigua (Se) multiple NPV and their shared homologous genes are 100 % collinear. Three putative enhancin genes were identified in the AgseNPV-A genome. In phylogenetic analysis, the AgseNPV-A enhancins form a cluster separated from enhancins of the Mamestra species NPVs.

Characterization of a Unique Gene ORF135 from Helicoverpa Armigera Single Nucleocapsid Nucleopolyhedrovirus

The ORF135 of Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HearSNPV)(Ha135) is one of the 20 genes that are unique to HearSNPV. Computer-assisted analysis revealed that four potential post translation modification sites, four transcription factor associated domains and a DNA binding protein domain were found in Ha135 amino acid sequence. Northern blot analysis of Ha135 indicated that Ha135 transcript was detected at 12 h.p.i. and remained detectable at up to 122 h.p.i. RT-PCR method was used to understand the temporal regulation of the transcript at earlier stages, the result showed that the Ha135 transcript was detected as early as 3 h p.i. suggesting that Ha135 was an early gene, which is in agreement with the early promoter motifs. The Ha135 protein was also detected at 12 h.p.i and remained detectable until 122 h.p.i. by western blot using an anti-Ha135 antiserum. The product of Ha135 was found to be about 29 kDa, bigger than the predicted 24 kDa molecular weight, suggesting that post translational modification of the Ha135 protein occur in host cells. The subcellular location was studied using EGFP-Ha135, which suggested that the Ha135 protein is primarily localized in the nucleus, which is compatible with several functional domains present in Ha135 amino acid sequence. Together, these results suggest the possibility that HearSNPV ORFI35 might be involved in viral DNA transcription and/or replication.

Identification of Spodoptera Litura Multicapsid Nucleopolyhedrovirus ORF97, A Novel Protein Associated with Envelope of Occlusion-derived Virus

Open reading frame (ORF) 97 of Spodoptera litura multicapsid nucleopolyhedrovirus (Splt97) is a member of 11k gene family (InterPro database accession number: IPR009313) in insect viruses, potentially encoding 112 amino acids with a predicted molecular weight of 13.2 kDa. Sequence analysis indicated that Splt97 has 8-50% amino acid identity with the homologues of other known baculoviruses including Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) ORF108. Splt97 transcription in SpltMNPV-infected Spli-221 cells was detected from 6 to 96 h postinfection (p.i.) and the mRNA start site was mapped within a consensus baculovirus early promoter motif (ACATT). Time course of Splt97 expression in SpltMNPV-infected cells showed that Splt97 was expressed from 48 through 96 h p.i. as a 13 kDa protein. Western blot analysis revealed that Splt97 was present in occlusion-derived virus (ODV). Furthermore, when ODV was fractionated into nucleocapsid and envelope components, Splt97 was shown to be present only in the envelope. These results suggested that Splt97 was a baculovirus ODV-associated protein.

HearSNPV orf83 encodes a late, nonstructural protein with an active chitin-binding domain

The ORF83 (ha83) of Helicoverpa armigera nucleopolyhedrovirus (HearSNPV) was characterized during the present study. Sequence analysis and chitin-binding assay revealed that Ha83 contained an active chitin-binding domain. Northern blot and Western blot analyses demonstrated that ha83 was expressed as a late gene and encoded a nonstructural protein of HearSNPV. Ha83 gene was transcribed beginning at 12h post-infection in infected Helicoverpa zea cells (HzAM1). Western blot analysis using a rabbit derived polyclonal antibody showed the product of ha83 in infected cells was a 20 kDa protein, in tune with the theoretical size of 18.8 kDa. The protein was first detected in the cytoplasm of infected HzAM1 cells at 12h p.i., and was transported later into the nucleus during infection.

Molecular identification and phylogenetic analysis of baculoviruses from Lepidoptera

PCR amplification of the highly conserved baculovirus genes late expression factor 8 (lef-8), late expression factor 9 (lef-9) and polyhedrin/granulin (polh/gran) combined with molecular phylogenetic analyses provide a powerful tool to identify lepidopteran-specific baculoviruses and to study their diversity. In the present investigation, we have improved the degenerate oligonucleotides and corroborated the approach that was recently described by Lange et al. (Lange, M., Wang, H., Zhihong, H., Jehle, J.A., 2004. Towards a molecular identification and classification system of lepidopteran-specific baculoviruses. Virology 325, 36-47.). Baculovirus DNA was isolated from 71 uncharacterized historic baculovirus samples, and partial gene sequences were amplified by using gene-specific degenerate PCR primers. The obtained PCR products were directly sequenced, and the deduced amino acid sequences were compiled and aligned with published sequences of these target genes. A phylogenetic tree of 117 baculoviruses was inferred using maximum parsimony and distance methods. Based on the comprehensive phylogenetic analysis of the partial lef-8, lef-9 and polh/gran genes, we propose a phylogenetic species criterion for lepidopteran-specific baculoviruses that uses the genetic distances of these genes for species demarcation.

Baculoviruses-- re-emerging biopesticides

Biological control of agricultural pests has gained importance in recent years due to increased pressure to reduce the use of agrochemicals and their residues in the environment and food. Viruses of a few families are known to infect insects but only those belonging to the highly specialized family Baculoviridae have been used as biopesticides. They are safe to people and wildlife, their specificity is very narrow. Their application as bioinsecticides was limited until recently because of their slow killing action and technical difficulties for in vitro commercial production. Two approaches for the wider application of baculoviruses as biopesticides will be implemented in future. In countries where use of genetically modified organisms is restricted, the improvements will be mainly at the level of diagnostics, in vitro production and changes in biopesticide formulations. In the second approach, the killing activity of baculoviruses may be augmented by genetic modifications of the baculovirus genome with genes of another natural pathogen. It is expected that the baculoviruses improved by genetic modifications will be gradually introduced in countries which have fewer concerns towards genetically modified organisms.

Characterization of ORF2 and its encoded protein of the Helicoverpa armigera nucleopolyhedrovirus

The open reading frame 2 (ha2) of the Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HaSNPV), a conserved gene in most baculoviruses from lepidopteran insects such as p78/83 of the Autographa californica MNPV, was characterized. It is 1,242 bp long and potentially encodes a 45.9 kDa. Ha2 is conserved among baculoviruses from lepidopteran insects. Ha2 transcripts were detected from 16 to 96 h post infection (hpi) of HzAM1 cells. Rabbit polyclonal antiserum against a GST-HA2 fusion protein reacted with three protein of 50, 46 and 35 kDa at 24-72 hpi of HzAM1 cells. Anti OpMNPV ORF2 (homologue of HA2) antibody reacted only with the 46 and 35 kDa proteins in HaSNPV-infected cells. These results demonstrate that Ha2 is modified at the mRNA or protein levels. Western blot analysis showed that only the 50 kDa product of HA2 is a structural component of proteins of both the budded virus (BV) and occlusion-derived virus (ODV) phenotypes. HA2-EGFP fusion protein showed that HA2 is localized primarily in the nucleus of HzAM1 infected cells. The HA2 was found to co-localize with actin by labelling of actin with Rhordamine-Phalloidin. In summary, the data indicated that HA2 is a structural protein and interacts with host cell actin.

Characterization of Spodoptera litura multicapsid nucleopolyhedrovirus 38.7 k protein, which contains a conserved BRO domain

Homology analysis revealed that Spodoptera litura multicapsid nucleopolyhedrovirus (SpltMNPV) 38.7 k protein has 22-83% amino acid identities with Ecotropis obliqua NPV, Mamestra configurata MNPV, Helicoverpa armigera SNPV, H. zea SNPV, S. exigua MNPV and S. littoralis MNPV 38.7 k proteins. Analysis of the relationship of these 38.7 k proteins indicated that they contain a conserved BRO-N domain, and SpltMNPV and SpliMNPV 38.7 k proteins also contain a motif found in all known viral and prokaryotic single-strand DNA binding proteins. RT-PCR results showed that SpltMNPV 38.7 k gene is transcribed actively at the late stage of infection and the mRNA start site was mapped within a consensus baculovirus late promoter motif (ATAAG). Western blot analysis revealed that the 38.7 k was expressed in infected S. litura cells as a 41 kDa form and this protein distributed in the nucleus of infected cells. Using a histone extraction protocol, SpltMNPV 38.7 k could be detected in the histone H1 fraction. Micrococcal nuclease treatment released SpltMNPV 38.7 k protein from the chromatin fraction, suggesting that its involvement in nucleosome structures. Furthermore, column chromatography using DNA-cellulose showed that SpltMNPV 38.7 k protein interacted with nucleic acids. It was proposed that SpltMNPV 38.7 k might function as a DNA-binding protein.