The origins of replication of granuloviruses

Genome Analysis of an Alphabaculovirus Isolated from the Larch Looper, Erannis ankeraria

The larch looper, Erannis ankeraria Staudinger (Lepidoptera: Geometridae), is one of the major insect pests of larch forests, widely distributed from southeastern Europe to East Asia. A naturally occurring baculovirus, Erannis ankeraria nucleopolyhedrovirus (EranNPV), was isolated from E. ankeraria larvae. This virus was characterized by electron microscopy and by sequencing the whole viral genome. The occlusion bodies (OBs) of EranNPV exhibited irregular polyhedral shapes containing multiple enveloped rod-shaped virions with a single nucleocapsid per virion. The EranNPV genome was 125,247 bp in length with a nucleotide distribution of 34.9% G+C. A total of 131 hypothetical open reading frames (ORFs) were identified, including the 38 baculovirus core genes and five multi-copy genes. Five homologous regions (hrs) were found in the EranNPV genome. Phylogeny and pairwise kimura 2-parameter analysis indicated that EranNPV was a novel group II alphabaculovirus and was most closely related to Apocheima cinerarium NPV (ApciNPV). Field trials showed that EranNPV was effective in controlling E. ankeraria in larch forests. The above results will be relevant to the functional research on EranNPV and promote the use of this virus as a biocontrol agent.

Genome Analysis of a Novel Clade b Betabaculovirus Isolated from the Legume Pest Matsumuraeses phaseoli (Lepidoptera: Tortricidae)

Matsumuraeses phaseoli is a Lepidopteran pest that primarily feeds on numerous species of cultivated legumes, such as Glycine and Phaseolus. It is widely distributed in northeast Asia. A novel granulovirus, designated as Matsumuraeses phaseoli granulovirus (MaphGV), was isolated from pathogenic M. phaseoli larvae that dwell in rolled leaves of Astragalus membranaceus, a Chinese medicinal herb. In this study, using next-generation sequencing, we report the complete genome of MaphGV. MaphGV genome comprises a double-stranded DNA of 116,875 bp, with 37.18% GC content. It has 128 hypothetical open reading frames (ORFs). Among them, 38 are baculovirus core genes, 18 are lepidopteran baculovirus conserved genes, and 5 are unique to Baculoviridae. MaphGV has one baculovirus repeat ORF (bro) and three inhibitors of apoptosis proteins (iap), including a newfound iap-6. We found two atypical baculoviral homologous regions (hrs) and four direct repeats (drs) in the MaphGV genome. Based on phylogenetic analysis, MaphGV belongs to Clade b of Betabaculovirus and is closely related to Cydia pomonellagranulovirus (CpGV) and Cryptophlebia leucotretagranulovirus (CrleGV). This novel baculovirus discovery and sequencing are invaluable in understanding the evolution of baculovirus and MaphGV may be a potential biocontrol agent against the bean ravaging pest.

Genomic analysis of an Argentinean isolate of Spodoptera frugiperda granulovirus reveals that various baculoviruses code for Lef-7 proteins with three F-box domains

A new isolate of the Spodoptera frugiperda granulovirus, SfGV ARG, was completely sequenced and analyzed. The SfGV ARG genome is 139,812 bp long and encodes 151 putative open reading frames. Of these ORFs, 56 were found in betabaculoviruses, 19 of which are present only in GVs closely related to SfGV. Seven ORFs found homologs in this small GV group and also in noctuid NPVs. ORF066 codes a 74 amino acid protein, overlapped with nudix gene, with several homologs in baculovirus, found by tblastn search. Comparison with the genome of the Colombian isolate SfGV VG008 resulted in SfGV being 1101 bp smaller and lacking a homologue of VG008 ORF084, which codes for Lef-7. However, we found that ORF051 shows remote homology to Lef-7 proteins. Moreover, analysis of ORF051 along with Lef-7 proteins coded by a group of noctuid specific GVs and NPVs indicated that Lef-7 proteins coded by these viruses include three F-box domains in contrast to the single one reported for AcMNPV Lef-7. SfGV ARG genome also contains a split photolyase as a distinct feature not found in VG008. BlastX analysis revealed that a complete photolyase is coded considering a putative frameshift in a poly-A tract, which resembles known slippery sequences involved in programmed ribosome frameshifting.

Genome analysis of a novel Group I alphabaculovirus obtained from Oxyplax ochracea

Oxyplax ochracea (Moore) is a pest that causes severe damage to a wide range of crops, forests and fruit trees. The complete genome sequence of Oxyplax ochracea nucleopolyhedrovirus (OxocNPV) was determined using a Roche 454 pyrosequencing system. OxocNPV has a double-stranded DNA (dsDNA) genome of 113,971 bp with a G+C content of 31.1%. One hundred and twenty-four putative open reading frames (ORFs) encoding proteins of >50 amino acids in length and with minimal overlapping were predicted, which covered 92% of the whole genome. Six baculoviral typical homologous regions (hrs) were identified. Phylogenetic analysis and gene parity plot analysis showed that OxocNPV belongs to clade “a” of Group I alphabaculoviruses, and it seems to be close to the most recent common ancestor of Group I alphabaculoviruses. Three unique ORFs (with no homologs in the National Center for Biotechnology Information database) were identified. Interestingly, OxocNPV lacks three auxiliary genes (lef7, ie-2 and pcna) related to viral DNA replication and RNA transcription. In addition, OxocNPV has significantly different sequences for several genes (including ie1 and odv-e66) in comparison with those of other baculoviruses. However, three dimensional structure prediction showed that OxocNPV ODV-E66 contain the conserved catalytic residues, implying that it might possess polysaccharide lyase activity as AcMNPV ODV-E66. All these unique features suggest that OxocNPV represents a novel species of the Group I alphabaculovirus lineage.

Genome Sequencing of the Behavior Manipulating Virus LbFV Reveals a Possible New Virus Family

Parasites are sometimes able to manipulate the behavior of their hosts. However, the molecular cues underlying this phenomenon are poorly documented. We previously reported that the parasitoid wasp Leptopilina boulardi which develops from Drosophila larvae is often infected by an inherited DNA virus. In addition to being maternally transmitted, the virus benefits from horizontal transmission in superparasitized larvae (Drosophila that have been parasitized several times). Interestingly, the virus forces infected females to lay eggs in already parasitized larvae, thus increasing the chance of being horizontally transmitted. In a first step towards the identification of virus genes responsible for the behavioral manipulation, we present here the genome sequence of the virus, called LbFV. The sequencing revealed that its genome contains an homologous repeat sequence (hrs) found in eight regions in the genome. The presence of this hrs may explain the genomic plasticity that we observed for this genome. The genome of LbFV encodes 108 ORFs, most of them having no homologs in public databases. The virus is however related to Hytrosaviridae, although distantly. LbFV may thus represent a member of a new virus family. Several genes of LbFV were captured from eukaryotes, including two anti-apoptotic genes. More surprisingly, we found that LbFV captured from an ancestral wasp a protein with a Jumonji domain. This gene was afterwards duplicated in the virus genome. We hypothesized that this gene may be involved in manipulating the expression of wasp genes, and possibly in manipulating its behavior.

The Complete Genome Sequence of a Second Distinct Betabaculovirus from the True Armyworm, Mythimna unipuncta

The betabaculovirus originally called Pseudaletia (Mythimna) sp. granulovirus #8 (MyspGV#8) was examined by electron microscopy, host barcoding PCR, and determination of the nucleotide sequence of its genome. Scanning and transmission electron microscopy revealed that the occlusion bodies of MyspGV#8 possessed the characteristic size range and morphology of betabaculovirus granules. Barcoding PCR using cytochrome oxidase I primers with DNA from the MyspGV#8 collection sample confirmed that it had been isolated from the true armyworm, Mythimna unipuncta (Lepidoptera: Noctuidae) and therefore was renamed MyunGV#8. The MyunGV#8 genome was found to be 144,673 bp in size with a nucleotide distribution of 49.9% G+C, which was significantly smaller and more GC-rich than the genome of Pseudaletia unipuncta granulovirus H (PsunGV-H), another M. unipuncta betabaculovirus. A phylogeny based on concatenated baculovirus core gene amino acid sequence alignments placed MyunGV#8 in clade a of genus Betabaculovirus. Kimura-2-parameter nucleotide distances suggested that MyunGV#8 represents a virus species different and distinct from other species of Betabaculovirus. Among the 153 ORFs annotated in the MyunGV#8 genome, four ORFs appeared to have been obtained from or donated to the alphabaculovirus lineage represented by Leucania separata nucleopolyhedrovirus AH1 (LeseNPV-AH1) during co-infection of Mythimna sp. larvae. A set of 33 ORFs was identified that appears only in other clade a betabaculovirus isolates. This clade a-specific set includes an ORF that encodes a polypeptide sequence containing a CIDE_N domain, which is found in caspase-activated DNAse/DNA fragmentation factor (CAD/DFF) proteins. CAD/DFF proteins are involved in digesting DNA during apoptosis.

The Complete Genome Sequence of Plodia Interpunctella Granulovirus: Evidence for Horizontal Gene Transfer and Discovery of an Unusual Inhibitor-of-Apoptosis Gene

The Indianmeal moth, Plodia interpunctella (Lepidoptera: Pyralidae), is a common pest of stored goods with a worldwide distribution. The complete genome sequence for a larval pathogen of this moth, the baculovirus Plodia interpunctella granulovirus (PiGV), was determined by next-generation sequencing. The PiGV genome was found to be 112, 536 bp in length with a 44.2% G+C nucleotide distribution. A total of 123 open reading frames (ORFs) and seven homologous regions (hrs) were identified and annotated. Phylogenetic inference using concatenated alignments of 36 baculovirus core genes placed PiGV in the “b” clade of viruses from genus Betabaculovirus with a branch length suggesting that PiGV represents a distinct betabaculovirus species. In addition to the baculovirus core genes and orthologues of other genes found in other betabaculovirus genomes, the PiGV genome sequence contained orthologues of the bidensovirus NS3 gene, as well as ORFs that occur in alphabaculoviruses but not betabaculoviruses. While PiGV contained an orthologue of inhibitor of apoptosis-5 (iap-5), an orthologue of inhibitor of apoptosis-3 (iap-3) was not present. Instead, the PiGV sequence contained an ORF (PiGV ORF81) encoding an IAP homologue with sequence similarity to insect cellular IAPs, but not to viral IAPs. Phylogenetic analysis of baculovirus and insect IAP amino acid sequences suggested that the baculovirus IAP-3 genes and the PiGV ORF81 IAP homologue represent different lineages arising from more than one acquisition event. The presence of genes from other sources in the PiGV genome highlights the extent to which baculovirus gene content is shaped by horizontal gene transfer.

Genome sequence of Perigonia lusca single nucleopolyhedrovirus: insights into the evolution of a nucleotide metabolism enzyme in the family Baculoviridae

The genome of a novel group II alphabaculovirus, Perigonia lusca single nucleopolyhedrovirus (PeluSNPV), was sequenced and shown to contain 132,831 bp with 145 putative ORFs (open reading frames) of at least 50 amino acids. An interesting feature of this novel genome was the presence of a putative nucleotide metabolism enzyme-encoding gene (pelu112). The pelu112 gene was predicted to encode a fusion of thymidylate kinase (tmk) and dUTP diphosphatase (dut). Phylogenetic analysis indicated that baculoviruses have independently acquired tmk and dut several times during their evolution. Two homologs of the tmk-dut fusion gene were separately introduced into the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) genome, which lacks tmk and dut. The recombinant baculoviruses produced viral DNA, virus progeny, and some viral proteins earlier during in vitro infection and the yields of viral occlusion bodies were increased 2.5-fold when compared to the parental virus. Interestingly, both enzymes appear to retain their active sites, based on separate modeling using previously solved crystal structures. We suggest that the retention of these tmk-dut fusion genes by certain baculoviruses could be related to accelerating virus replication and to protecting the virus genome from deleterious mutation.

Genome Sequencing and Analysis of Catopsilia pomona nucleopolyhedrovirus: A Distinct Species in Group I Alphabaculovirus

The genome sequence of Catopsilia pomona nucleopolyhedrovirus (CapoNPV) was determined by the Roche 454 sequencing system. The genome consisted of 128,058 bp and had an overall G+C content of 40%. There were 130 hypothetical open reading frames (ORFs) potentially encoding proteins of more than 50 amino acids and covering 92% of the genome. Among all the hypothetical ORFs, 37 baculovirus core genes, 23 lepidopteran baculovirus conserved genes and 10 genes conserved in Group I alphabaculoviruses were identified. In addition, the genome included regions of 8 typical baculoviral homologous repeat sequences (hrs). Phylogenic analysis showed that CapoNPV was in a distinct branch of clade “a” in Group I alphabaculoviruses. Gene parity plot analysis and overall similarity of ORFs indicated that CapoNPV is more closely related to the Group I alphabaculoviruses than to other baculoviruses. Interesting, CapoNPV lacks the genes encoding the fibroblast growth factor (fgf) and ac30, which are conserved in most lepidopteran and Group I baculoviruses, respectively. Sequence analysis of the F-like protein of CapoNPV showed that some amino acids were inserted into the fusion peptide region and the pre-transmembrane region of the protein. All these unique features imply that CapoNPV represents a member of a new baculovirus species.

Genome sequencing and analysis of a granulovirus isolated from the Asiatic rice leafroller, Cnaphalocrocis medinalis

The complete genome of Cnaphalocrocis medinalis granulovirus (CnmeGV) from a serious migratory rice pest, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), was sequenced using the Roche 454 Genome Sequencer FLX system (GS FLX) with shotgun strategy and assembled by Roche GS De Novo assembler software. Its circular double-stranded genome is 111,246 bp in size with a high A+T content of 64.8% and codes for 118 putative open reading frames (ORFs). It contains 37 conserved baculovirus core ORFs, 13 unique ORFs, 26 ORFs that were found in all Lepidoptera baculoviruses and 42 common ORFs. The analysis of nucleotide sequence repeats revealed that the CnmeGV genome differs from the rest of sequenced GVs by a 23 kb and a 17kb gene block inversions, and does not contain any typical homologous region (hr) except for a region of non-hr-like sequence. Chitinase and cathepsin genes, which are reported to have major roles in the liquefaction of the hosts, were not found in the CnmeGV genome, which explains why CnmeGV infected insects do not show the phenotype of typical liquefaction. Phylogenetic analysis, based on the 37 core baculovirus genes, indicates that CnmeGV is closely related to Adoxophyes orana granulovirus. The genome analysis would contribute to the functional research of CnmeGV, and would benefit to the utilization of CnmeGV as pest control reagent for rice production.

The Complete Genome of a New Betabaculovirus from Clostera anastomosis

Clostera anastomosis (Lepidoptera: Notodontidae) is a defoliating forest insect pest. Clostera anastomosis granulovirus-B (ClasGV-B) belonging to the genus Betabaculovirus of family Baculoviridae has been used for biological control of the pest. Here we reported the full genome sequence of ClasGV-B and compared it to other previously sequenced baculoviruses. The circular double-stranded DNA genome is 107,439 bp in length, with a G+C content of 37.8% and contains 123 open reading frames (ORFs) representing 93% of the genome. ClasGV-B contains 37 baculovirus core genes, 25 lepidopteran baculovirus specific genes, 19 betabaculovirus specific genes, 39 other genes with homologues to baculoviruses and 3 ORFs unique to ClasGV-B. Hrs appear to be absent from the ClasGV-B genome, however, two non-hr repeats were found. Phylogenetic tree based on 37 core genes from 73 baculovirus genomes placed ClasGV-B in the clade b of betabaculoviruses and was most closely related to Erinnyis ello GV (ErelGV). The gene arrangement of ClasGV-B also shared the strongest collinearity with ErelGV but differed from Clostera anachoreta GV (ClanGV), Clostera anastomosis GV-A (ClasGV-A, previously also called CaLGV) and Epinotia aporema GV (EpapGV) with a 20 kb inversion. ClasGV-B genome contains three copies of polyhedron envelope protein gene (pep) and phylogenetic tree divides the PEPs of betabaculoviruses into three major clades: PEP-1, PEP-2 and PEP/P10. ClasGV-B also contains three homologues of P10 which all harbor an N-terminal coiled-coil domain and a C-terminal basic sequence. ClasGV-B encodes three fibroblast growth factor (FGF) homologues which are conserved in all sequenced betabaculoviruses. Phylogenetic analysis placed these three FGFs into different groups and suggested that the FGFs were evolved at the early stage of the betabaculovirus expansion. ClasGV-B is different from previously reported ClasGV-A and ClanGV isolated from Notodontidae in sequence and gene arrangement, indicating the virus is a new notodontid betabaculovirus.

The complete sequence of the first Spodoptera frugiperda Betabaculovirus genome: a natural multiple recombinant virus

Spodoptera frugiperda (Lepidoptera: Noctuidae) is a major pest in maize crops in Colombia, and affects several regions in America. A granulovirus isolated from S. frugiperda (SfGV VG008) has potential as an enhancer of insecticidal activity of previously described nucleopolyhedrovirus from the same insect species (SfMNPV). The SfGV VG008 genome was sequenced and analyzed showing circular double stranded DNA of 140,913 bp encoding 146 putative ORFs that include 37 Baculoviridae core genes, 88 shared with betabaculoviruses, two shared only with betabaculoviruses from Noctuide insects, two shared with alphabaculoviruses, three copies of own genes (paralogs) and the other 14 corresponding to unique genes without representation in the other baculovirus species. Particularly, the genome encodes for important virulence factors such as 4 chitinases and 2 enhancins. The sequence analysis revealed the existence of eight homologous regions (hrs) and also suggests processes of gene acquisition by horizontal transfer including the SfGV VG008 ORFs 046/047 (paralogs), 059, 089 and 099. The bioinformatics evidence indicates that the genome donors of mentioned genes could be alpha- and/or betabaculovirus species. The previous reported ability of SfGV VG008 to naturally co-infect the same host with other virus show a possible mechanism to capture genes and thus improve its fitness.

Homologous region 1 of Plutella xylostella granulovirus functions as an enhancer for early gene expression

Homologous regions (hrs) contained in genomes of baculoviruses have been shown to function as origins of viral DNA replication in alphabaculoviruses and betabaculoviruses, and as enhancers for early gene expression in alphabaculoviruses. The hr sequences of betabaculoviruses differ substantially from the ones of alphabaculoviruses. The enhancing property of betabaculovirus hrs has not been reported. In this study, transient assays were performed to investigate the effects of Plutella xylostella granulovirus (PlxyGV) hr1 on early gene expression of the virus. It was shown that hr1 stimulated reporter gene expression from the promoters of four early genes--ie1, dnapol, lef1, and lef9--independent of additional viral gene expression. The PlxyGV ie1 was shown to repress reporter gene expression from all four early gene promoters in a Trichoplusia ni cell line, both in the presence and absence of hr.

The genome and occlusion bodies of marine Penaeus monodon nudivirus (PmNV, also known as MBV and PemoNPV) suggest that it should be assigned to a new nudivirus genus that is distinct from the terrestrial nudiviruses

BACKGROUND

Penaeus monodon nudivirus (PmNV) is the causative agent of spherical baculovirosis in shrimp (Penaeus monodon). This disease causes significant mortalities at the larval stage and early postlarval (PL) stage and may suppress growth and reduce survival and production in aquaculture. The nomenclature and classification status of PmNV has been changed several times due to morphological observation and phylogenetic analysis of its partial genome sequence. In this study, we therefore completed the genome sequence and constructed phylogenetic trees to clarify PmNV's taxonomic position. To better understand the characteristics of the occlusion bodies formed by this marine occluded virus, we also compared the chemical properties of the polyhedrin produced by PmNV and the baculovirus AcMNPV (Autographa californica nucleopolyhedrovirus).

RESULTS

We used next generation sequencing and traditional PCR methods to obtain the complete PmNV genome sequence of 119,638 bp encoding 115 putative ORFs. Phylogenetic tree analysis showed that several PmNV genes and sequences clustered with the non-occluded nudiviruses and not with the baculoviruses. We also investigated the characteristics of PmNV polyhedrin, which is a functionally important protein and the major component of the viral OBs (occlusion bodies). We found that both recombinant PmNV polyhedrin and wild-type PmNV OBs were sensitive to acid conditions, but unlike the baculoviral OBs, they were not susceptible to alkali treatment.

CONCLUSIONS

From the viral genome features and phylogenetic analysis we conclude that PmNV is not a baculovirus, and that it should be assigned to the proposed Nudiviridae family with the other nudiviruses, but into a distinct new genus (Gammanudivirus).

Genome sequence and analysis of Buzura suppressaria nucleopolyhedrovirus: a group II Alphabaculovirus

The genome of Buzura suppressaria nucleopolyhedrovirus (BusuNPV) was sequenced by 454 pyrosequencing technology. The size of the genome is 120,420 bp with 36.8% G+C content. It contains 127 hypothetical open reading frames (ORFs) covering 90.7% of the genome and includes the 37 conserved baculovirus core genes, 84 genes found in other baculoviruses, and 6 unique ORFs. No typical baculoviral homologous repeats (hrs) were present but the genome contained a region of repeated sequences. Gene Parity Plots revealed a 28.8 kb region conserved among the alpha- and beta-baculoviruses. Overall comparisons of BusuNPV to other baculoviruses point to a distinct species in group II Alphabaculovirus.

Genome of Epinotia aporema granulovirus (EpapGV), a polyorganotropic fast killing betabaculovirus with a novel thymidylate kinase gene

BACKGROUND

Epinotia aporema (Lepidoptera: Tortricidae) is an important pest of legume crops in South America. Epinotia aporema granulovirus (EpapGV) is a baculovirus that causes a polyorganotropic infection in the host larva. Its high pathogenicity and host specificity make EpapGV an excellent candidate to be used as a biological control agent.

RESULTS

The genome of Epinotia aporema granulovirus (EpapGV) was sequenced and analyzed. Its circular double-stranded DNA genome is 119,082 bp in length and codes for 133 putative genes. It contains the 31 baculovirus core genes and a set of 19 genes that are GV exclusive. Seventeen ORFs were unique to EpapGV in comparison with other baculoviruses. Of these, 16 found no homologues in GenBank, and one encoded a thymidylate kinase. Analysis of nucleotide sequence repeats revealed the presence of 16 homologous regions (hrs) interspersed throughout the genome. Each hr was characterized by the presence of 1 to 3 clustered imperfect palindromes which are similar to previously described palindromes of tortricid-specific GVs. Also, one of the hrs (hr4) has flanking sequences suggestive of a putative non-hr ori. Interestingly, two more complex hrs were found in opposite loci, dividing the circular dsDNA genome in two halves. Gene synteny maps showed the great colinearity of sequenced GVs, being EpapGV the most dissimilar as it has a 20 kb-long gene block inversion. Phylogenetic study performed with 31 core genes of 58 baculoviral genomes suggests that EpapGV is the baculovirus isolate closest to the putative common ancestor of tortricid specific betabaculoviruses.

CONCLUSIONS

This study, along with previous characterization of EpapGV infection, is useful for the better understanding of the pathology caused by this virus and its potential utilization as a bioinsecticide.