Sequence analysis of the Spodoptera litura multicapsid nucleopolyhedrovirus genome

Genome characteristics and the ODV proteome of a second distinct alphabaculovirus from Spodoptera litura

BACKGROUND

Spodoptera litura is a harmful pest that feeds on more than 80 species of plants, and can be infected and killed by Spodoptera litura nucleopolyhedrovirus (SpltNPV). SpltNPV-C3 is a type C SpltNPV clone, that was observed and collected in Japan. Compared with type A or type B SpltNPVs, SpltNPV-C3 can cause the rapid mortality of S. litura larvae.

METHODS

In this study, occlusion bodies (OBs) and occlusion-derived viruses (ODVs) of SpltNPV-C3 were purified, and OBs were observed by scanning electron microscopy (SEM). ODVs were observed under a transmission electron microscope (TEM).

RESULTS

Both OBs and ODVs exhibit morphological characteristics typical of nucleopolyhedroviruses (NPVs).The genome of SpltNPV-C3 was sequenced and analyzed; the total length was 148,634 bp (GenBank accession 780,426,which was submitted as SpltNPV-II), with a G + C content of 45%. A total of 149 predicted ORFs were found. A phylogenetic tree of 90 baculoviruses was constructed based on core baculovirus genes. LC‒MS/MS was used to analyze the proteins of SpltNPV-C3; 34 proteins were found in the purified ODVs, 15 of which were core proteins. The structure of the complexes formed by per os infectivity factors 1, 2, 3 and 4 (PIF-1, PIF-2, PIF-3 and PIF-4) was predicted with the help of the AlphaFold multimer tool and predicted conserved sequences in PIF-3. SpltNPV-C3 is a valuable species because of its virulence, and the analysis of its genome and proteins in this research will be beneficial for pest control efforts.

Whole genome analysis of a novel Spodoptera exigua nucleopolyhedrovirus isolate (SeMNPV-IR) to Iran

Baculoviruses are successful microbial control agents used in the biological control of agricultural pest species, especially in the order Lepidoptera. The beet armyworm, Spodoptera exigua is a popular agricultural pest in the world. S exigua larvae, which are active in the all-summer period, cause economic losses by damaging many crops in agricultural production areas. This article aims to analyze the full genome of Spodoptera exigua multiple nucleopolyhedroviruses from Iran (SeMNPV-IR) and to determine the geographical difference between the strains at the genomic level. The full genome of SeMNPV-IR is 135.764 base pairs in length that contained 136 open reading frames (ORFs), and 43.92% G + C content. The seven homologous repeated (hr) regions were identified. In the results of genome-wide phylogenetic analysis, it was determined that the SeMNPV-IR genome isolated from Iran was interestingly close to the genome of the US and Korea isolates. However, there are significant differences in the two hypothetical (Orf 83 and Orf 104) genes. The SeMNPV-IR has a unique homolog repeat region (hr1, 96 bp) that is not found in other SeMNPV genomes, and it also differs in terms of the hr2 region. In silico restriction endonuclease analysis by StuI and SacII enzymes show that there were significant differences between all geographic isolates of SeMNPV.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11756-023-01399-2.

Natural Coinfection between Novel Species of Baculoviruses in Spodoptera ornithogalli Larvae

Spodoptera ornithogalli (Guenée) (Lepidoptera: Noctuidae) is an important pest in different crops of economic relevance in America. For its control, strategies that include chemicals are usually used; so, the description of entomopathogens would be very useful for the formulation of biopesticides. In this regard, two different baculoviruses affecting S. ornithogalli were isolated in Colombia, with one of them being an NPV and the other a GV. Ultrastructural, molecular, and biological characterization showed that both isolates possess the 38 core genes and are novel species in Baculoviridae, named as Spodoptera ornithogalli nucleopolyhedrovirus (SporNPV) and Spodoptera ornithogalli granulovirus (SporGV). The bioassays carried out in larvae of S. ornithogalli and S. frugiperda showed infectivity in both hosts but being higher in the first. In addition, it was observed that SporGV potentiates the insecticidal action of SporNPV (maximum value in ratio 2.5:97.5). Both viruses are individually infective but coexist in nature, producing mixed infections with a synergistic effect that improves the performance of the NPV and enables the transmission of the GV, which presents a slowly killing phenotype.

Toxicity of Bioactive Molecule Andrographolide against Spodoptera litura Fab and Its Binding Potential with Detoxifying Enzyme Cytochrome P450

Spodoptera litura Fab. is a polyphagous pest causing damage to many agriculture crops leading to yield loss. Recurrent usage of synthetic pesticides to control this pest has resulted in resistance development. Plant-derived diterpenoid compound andrographolide was isolated from the leaves of Andrographis paniculata. It was analysed by gas chromatography-mass spectroscopy and quantified by HPLC. Nutritional indices and digestive enzymatic profile were evaluated. Third, fourth and fifth instar larvae were treated with different concentrations of andrographolide. At 3, 6 and 9 ppm-treated concentrations the larvae showed decreased RGR, RCR, ECI, ECD values with adverse increase in AD. The digestive enzymes were significantly inhibited when compared with control. Conspicuously, andrographolide showed pronounced mortality of S. litura by inhibition of enzyme secretion and intake of food. The binding ability of andrographolide with CYTP450 showed high affinity with low binding energy. Andrographolide has the potential to be exploited as a biocontrol agent against S. litura as an eco-friendly pesticide.

VP39 of Spodoptera litura multicapsid nucleopolyhedrovirus cannot efficiently rescue the nucleocapsid assembly of vp39-null Autographa californica multiple nucleopolyhedrovirus

Background

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) vp39 is conserved in all sequenced baculovirus genomes. In previous studies, VP39 has been identified as the major capsid structure protein of baculoviruses and found to be essential for nucleocapsid assembly. The nucleocapsid composition and structure of Group I and II NPVs of the Alphabaculovirus genus are very similar. It is not clear whether the major capsid structure protein VP39 of Group I NPVs is functionally identical to or substitutable with the Group II NPV VP39. In this study, the function of Group II Spodoptera litura MNPV (SpltMNPV) VP39 in Group I AcMNPV was characterized.

Methods

Sequence alignment of AcMNPV VP39 and SpltMNPV VP39 was performed using Clustal X and edited with GeneDoc. To determine whether VP39 of Group I NPVs can be functionally substituted by Group II NPV VP39, a vp39-null AcMNPV (vAcvp39KO) and a vp39-pseudotyped AcMNPV (vAcSpltvp39:FLAG), in which the Group I AcMNPV vp39 coding sequence was replaced with that of SpltMNPV from Group II NPVs, were constructed via homologous recombination in Escherichia coli. Using an anti-FLAG monoclonal antibody, immunoblot analysis was performed to examine SpltMNPV VP39 expression. Fluorescence and light microscopy were used to monitor viral replication and infection. Viral growth curve analysis was performed using a fifty percent tissue culture infective dose (TCID₅₀) endpoint dilution assay. Viral morphogenesis was detected using an electron microscope.

Results

Sequence alignment indicated that the N-termini of AcMNPV VP39 and SpltMNPV VP39 are relatively conserved, whereas the C-terminus of SpltMNPV VP39 lacks the domain of amino acid residues 306–334 homologous to AcMNPV VP39. Immunoblot analysis showed that SpltMNPV VP39 was expressed in vAcSpltvp39:FLAG. Fluorescence and light microscopy showed that vAcSpltvp39:FLAG did not spread by infection. Viral growth curve analysis confirmed a defect in infectious budded virion production. Electron microscopy revealed that although masses of abnormally elongated empty capsid structures existed inside the nuclei of Sf9 cells transfected with vAcSpltvp39:FLAG, no nucleocapsids were observed.

Conclusion

Altogether, our results demonstrated that VP39 from SpltMNPV cannot efficiently substitute AcMNPV VP39 during nucleocapsid assembly in AcMNPV.

Efficacy of Entomopathogenic Nematodes Against the Tobacco Cutworm, Spodoptera litura (Lepidoptera: Noctuidae)

Spodoptera litura (F.) is an obnoxious cosmopolitan pest that causes serious damage to different economic crops. Entomopathogenic nematodes (EPN) have the potential to control the S. litura larvae. Fifteen EPN isolates were screened, and Steinernema sp. 64-2, four isolates of S. carpocapsae (Weiser), S. longicaudum (Shen & Wang) X-7, and two isolates of H. indica (Poinar, Karunaka & David) were found to cause higher mortality of the second, third, and fourth instars of S. litura than the other tested isolates, with larval mortality rates > 90% after 48 h of exposure. An exposure rate of 12.5 infective juveniles per larva was enough for S. carpocapsae A24, All, and G-R3a-2 and S. longicaudum X-7 to cause 100% mortality of the second instar, and for S. longicaudum X-7 and H. indica 212-2 to cause 100% mortality of the third instar. Five EPN isolates were tested on their virulence at different temperatures and found that all the five EPN isolates performed well against the S. litura larvae at 25 and 30°C, but were not active at 10 and 15°C. Two S. carpocapsae isolates (All and Mex) were virulent against the S. litura larvae at lower temperatures. The five tested EPN isolates were also found to have the ability to infect and kill the pupae of S. litura in the laboratory. The present study further proves that EPN are effective at controlling S. litura, which may partially substitute the use of chemical insecticides, thus reduce the overuse of chemical insecticides.

Identification of Loci Associated with Enhanced Virulence in Spodoptera litura Nucleopolyhedrovirus Isolates Using Deep Sequencing

Spodoptera litura is an emerging pest insect in cotton and arable crops in Central Asia. To explore the possibility of using baculoviruses as biological control agents instead of chemical pesticides, in a previous study we characterized a number of S. litura nucleopolyhedrovirus (SpltNPV) isolates from Pakistan. We found significant differences in speed of kill, an important property of a biological control agent. Here we set out to understand the genetic basis of these differences in speed of kill, by comparing the genome of the fast-killing SpltNPV-Pak-TAX1 isolate with that of the slow-killing SpltNPV-Pak-BNG isolate. These two isolates and the SpltNPV-G2 reference strain from China were deep sequenced with Illumina. As expected, the two Pakistani isolates were closely related with >99% sequence identity, whereas the Chinese isolate was more distantly related. We identified two loci that may be associated with the fast action of the SpltNPV-Pak-TAX1 isolate. First, an analysis of rates of synonymous and non-synonymous mutations identified neutral to positive selection on open reading frame (ORF) 122, encoding a viral fibroblast growth factor (vFGF) that is known to affect virulence in other baculoviruses. Second, the homologous repeat region hr17, a putative enhancer of transcription and origin of replication, is absent in SpltNPV-Pak-TAX1 suggesting it may also affect virulence. Additionally, we found there is little genetic variation within both Pakistani isolates, and we identified four genes under positive selection in both isolates that may have played a role in adaptation of SpltNPV to conditions in Central Asia. Our results contribute to the understanding of the enhanced activity of SpltNPV-Pak-TAX1, and may help to select better SpltNPV isolates for the control of S. litura in Pakistan and elsewhere.

Identification of Multiple Replication Stages and Origins in the Nucleopolyhedrovirus of Anticarsia gemmatalis

To understand the mechanism of replication used by baculoviruses, it is essential to describe all the factors involved, including virus and host proteins and the sequences where DNA synthesis starts. A lot of work on this topic has been done, but there is still confusion in defining what sequence/s act in such functions, and the mechanism of replication is not very well understood. In this work, we performed an AgMNPV replication kinetics into the susceptible UFL-Ag-286 cells to estimate viral genome synthesis rates. We found that the viral DNA exponentially increases in two different phases that are temporally separated by an interval of 5 h, probably suggesting the occurrence of two different mechanisms of replication. Then, we prepared a plasmid library containing virus fragments (0.5-2 kbp), which were transfected and infected with AgMNPV in UFL-Ag-286 cells. We identified 12 virus fragments which acted as origins of replication (ORI). Those fragments are in close proximity to core genes. This association to the core genome would ensure vertical transmission of ORIs. We also predict the presence of common structures on those fragments that probably recruit the replication machinery, a structure also present in previously reported ORIs in baculoviruses.

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.

Complete Genome Sequence of an Alphabaculovirus from the Southern Armyworm, Spodoptera eridania

We report the complete genome sequence of a baculovirus from the moth Spodoptera eridania, the southern armyworm. The genome sequence is 149,090 bp and exhibits the greatest degree of sequence similarity with genomes from alphabaculoviruses isolated from other moths of the genus Spodoptera.

We report the complete genome sequence of a baculovirus from the moth Spodoptera eridania, the southern armyworm. The genome sequence is 149,090 bp and exhibits the greatest degree of sequence similarity with genomes from alphabaculoviruses isolated from other moths of the genus Spodoptera.

The complete genome sequence of a second alphabaculovirus from the true armyworm, Mythimna unipuncta: implications for baculovirus phylogeny and host specificity

The Mythimna unipuncta nucleopolyhedrovirus isolate KY310 (MyunNPV-KY310) is an alphabaculovirus isolated from a true armyworm (Mythimna unipuncta) population in Kentucky, USA. Occlusion bodies of this virus were examined by electron microscopy and the genome sequence was determined by 454 pyrosequencing. MyunNPV-KY310 occlusion bodies consisted of irregular polyhedra measuring 0.8-1.8 µm in diameter and containing multiple virions, with one to six nucleocapsids per virion. The genome sequence was determined to be 156,647 bp with a nucleotide distribution of 43.9% G+C. 152 ORFs and six homologous repeat (hr) regions were annotated for the sequence, including the 38 core genes of family Baculoviridae and an additional group of 26 conserved alphabaculovirus genes. BLAST queries and phylogenetic inference confirmed that MyunNPV-KY310 is most closely related to the alphabaculovirus Leucania separata nucleopolyhedrovirus isolate AH1, which infects Mythimna separata. In contrast, MyunNPV-KY310 did not exhibit a close relationship with Mythimna unipuncta nucleopolyhedrovirus isolate #7, an alphabaculovirus from the same host species. MyunNPV-KY310 lacks the gp64 envelope glycoprotein, which is a characteristic of group II alphabaculoviruses. However, this virus and five other alphabaculoviruses lacking gp64 are placed outside the group I and group II clades in core gene phylogenies, further demonstrating that viruses of genus Alphabaculovirus do not occur in two monophyletic clades. Potential instances of MyunNPV-KY310 ORFs arising by horizontal transfer were detected. Although there are now genome sequences of four different baculoviruses from M. unipuncta, comparison of their genome sequences provides little insight into the genetic basis for their host specificity.

Complete genome sequence analysis of the Malacosoma neustria nucleopolyhedrovirus from Turkey

The lackey moth, Malacosoma neustria (Linnaeus, 1758), a worldwide pest, causes extensive economic losses particularly on hazelnut, plum, oak, poplar, and willow trees. A baculovirus, Malacosoma neustria nucleopolyhedrovirus (ManeNPV-T2), has been isolated from the larvae collected in Turkey and appears to have a potential as a microbial control agent. In this study, we describe the complete genome sequence of ManeNPV-T2 and compare it to other sequenced baculovirus genomes. The ManeNPV-T2 genome is a circular double-stranded DNA molecule of 130,202 bp, has 38.2% G + C, and is predicted to contain 131 putative open reading frames (ORFs) each with a coding capacity of more then 50 amino acids. There are 27 ORFs with unknown function of which 6 are unique to ManeNPV-T2. Eleven homologous regions (hrs) and two bro genes (bro-a and bro-b) were identified in the genome. There are two homologues of chaB and nicotinamide riboside kinase-1 genes, separated from themselves with a few nucleotides. Additionally, ac145, thought to be per os infectivity factor (pif) gene, is also found as two homologues. All 38 core genes are found in the ManeNPV-T2 genome. The phylogenetic tree of ManeNPV-T2 in relation to 50 other baculoviruses whose genomes have been completely sequenced showed ManeNPV-T2 to be closely related to the group II NPVs. This study expands our knowledge on baculoviruses, describes the characterization ManeNPV, and ultimately contributes to the registration of this virus as a microbial pesticide.

Characterization and functional assay of apsup (Lyxy105) from Lymantria xylina multiple nucleopolyhedrovirus (LyxyMNPV)

The baculoviral anti-apoptotic genes, p35 and iap (inhibitor of apoptosis), play important roles in the initiation of viral infection. Recently, a new anti-apoptotic gene (apoptosis suppressor, apsup) was identified in Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV). An apsup homolog gene, Lyxy105 (ly-apsup), was also predicted in the Lymantria xylina multiple nucleopolyhedrovirus (LyxyMNPV) genome. In this study, we attempt to perform a gene expression analysis and a functional assay of ly-apsup to demonstrate its anti-apoptotic activity and identify the functional domain of this protein. The transcription of the ly-apsup gene region was detected from 12 h post-infection (hpi) and increased significantly after 24-72 hpi. Comparison of the putative amino acid sequences to those of 18 baculoviral homolog proteins showed high amino acid identity to the LdMNPV sequences. Moreover, five conserved protein domains (named as domains I-V) were found. Therefore, protein functional assays were conducted on full-length proteins and different truncation clones. The overexpression of each clone was confirmed by western blot analysis, and the data revealed that a cleavage of ~ 5 kDa at the N-terminal region of the full-length, domains I-IV (1-241) and I-III (1-178), proteins occurred. The results of the functional analysis showed that full-length Ly-apsup and Ly-apsup with domain I (1-70) could inhibit Drosophila-RPR protein (D-RPR)-induced and actinomycin D (ActD)-induced apoptoses. In addition, the domains I and I-II (1-126) regions showed higher anti-apoptotic activity than the other domains in both D-RPR-induced and ActD-induced cell apoptoses. In conclusion, domain I of Ly-apsup may play an important role in the anti-apoptotic activity of this protein; cleavage of the Ly-apsup N-terminus may lead to decreased anti-apoptotic activity.

Genotype assembly, biological activity and adaptation of spatially separated isolates of Spodoptera litura nucleopolyhedrovirus

The cotton leafworm Spodoptera litura is a polyphagous insect. It has recently made a comeback as a primary insect pest of cotton in Pakistan due to reductions in pesticide use on the advent of genetically modified cotton, resistant to Helicoverpa armigera. Spodoptera litura nucleopolyhedrovirus (SpltNPV) infects S. litura and is recognized as a potential candidate to control this insect. Twenty-two NPV isolates were collected from S. litura from different agro-ecological zones (with collection sites up to 600 km apart) and cropping systems in Pakistan to see whether there is spatial dispersal and adaptation of the virus and/or adaptation to crops. Therefore, the genetic make-up and biological activity of these isolates was measured. Among the SpltNPV isolates tested for speed of kill in 3rd instar larvae of S. litura, TAX1, SFD1, SFD2 and GRW1 were significantly faster killing isolates than other Pakistani isolates. Restriction fragment length analysis of the DNA showed that the Pakistan SpltNPV isolates are all variants of a single SpltNPV biotype. The isolates could be grouped into three genogroups (A-C). The speed of kill of genogroup A viruses was higher than in group C according to a Cox' proportional hazards analysis. Sequence analysis showed that the Pakistan SpltNPV isolates are more closely related to each other than to the SpltNPV type species G2 (Pang et al., 2001). This suggests a single introduction of SpltNPV into Pakistan. The SpltNPV-PAK isolates are distinct from Spodoptera littoralis nucleopolyhedrovirus. There was a strong correlation between geographic spread and the genetic variation of SpltNPV, and a marginally significant correlation between the latter and the cropping system. The faster killing isolates may be good candidates for biological control of S. litura in Pakistan.

A betabaculovirus DNA polymerase cannot substitute for the DNA polymerase of the alphabaculovirus Autographa californica nucleopolyhedrovirus

DNA polymerase (DNApol) is present in all baculoviruses and plays a crucial role in viral DNA replication. Previously we showed that the DNApol of the alphabaculovirus group II Spodoptera litura nucleopolyhedrovirus (SpltNPV) could partially substitute for the DNApol of a group I alphabaculovirus, Autographa californica multiple nucleopolyhedrovirus (AcMNPV). However, it is not known if a betabaculovirus DNApol could subsititute for the alphabaculovirus DNApol in AcMNPV. In this report, DNApol of the betabaculovirus Pieris rapae granulovirus (PiraGV) was inserted into a dnapol-null AcMNPV bacmid, creating Bac-AcΔpol:PrPol. The repair virus did not spread to neighboring cells; virus growth curve and real-time PCR revealed that the PiraGV dnapol substitution abrogated AcMNPV DNA replication and virus production. Immunofluorescence microscopy showed that PiraGV DNApol could be expressed and localized to the nucleus. Collectively, our results suggested that the alphabaculovirus AcMNPV DNApol could not be replaced by a DNApol from the betabaculovirus, PiraGV.

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.

Characterization and Growing Development of Spodoptera exigua (Lepidoptera: Noctuidae) Larvae Infected by Heliothis virescens ascovirus 3h (HvAV-3h)

Spodoptera exigua (Hübner) is a very serious worldwide pest capable of causing severe economic losses in numerous agricultural crops. The need for an effective, highly virulent, pathogenic microorganism for use as a biological control agent against S. exigua larvae is particularly important. Heliothis virescens ascovirus 3 h (HvAV-3h)-containing hemolymph with a titer of 9.58 × 10(12) genome copies per ml was used to inoculate S. exigua larvae per os with a 1.06 × 10(10) dosage per larva for the first- to second instar and 9.58 × 10(9) genome copies per larva for the third- to fifth instars. Intrahemocoelic injections were also used with a dosage of 1.53 × 10(9) genome copies per larva for third- to fifth instar. The postinjection mortality, body weight, and food intake of the S. exigua larvae were observed and recorded. The corrected mortality rates for the first- through fifth instar inoculated per os were 21.88 ± 0.98, 22.22 ± 4.00, 8.89 ± 4.01, 6.66 ± 3.33, and 8.89 ± 2.94%, respectively. The early instars were significantly easier to infect with virus compared to the later instar. The corrected mortality of the third, fourth, and fifth instars inoculated by injection was 96.58 ± 3.42, 98.83 ± 1.17, and 97.78 ± 2.22%, respectively. Compared to the healthy larval population, survival time of the diseased larval population was considerably extended. In addition, food intake was greatly reduced, and the body weight remained fairly constant in the third- and fourth instar. The body weight declined in the fifth instar corresponding to a reduction in food intake.

The Host Specificities of Baculovirus per os Infectivity Factors

Baculoviruses are insect-specific pathogens with a generally narrow host ranges. Successful primary infection is initiated by the proper interaction of at least 8 conserved per os infectivity factors (PIFs) with the host's midgut cells, a process that remains largely a mystery. In this study, we investigated the host specificities of the four core components of the PIF complex, P74, PIF1, PIF2 and PIF3 by using Helicoverpa armigera nucleopolyhedrovirus (HearNPV) backbone. The four pifs of HearNPV were replaced by their counterparts from a group I Autographa californica multiple nucleopolyhedrovirus (AcMNPV) or a group II Spodoptera litura nucleopolyhedrovirus (SpltNPV). Transfection and infection assays showed that all the recombinant viruses were able to produce infectious budded viruses (BVs) and were lethal to H. armigera larvae via intrahaemocoelic injection. However, feeding experiments using very high concentration of occlusion bodies demonstrated that all the recombinant viruses completely lost oral infectivity except SpltNPV pif3 substituted pif3-null HearNPV (vHaBacΔpif3-Sppif3-ph). Furthermore, bioassay result showed that the median lethal concentration (LC50) value of vHaBacΔpif3-Sppif3-ph was 23-fold higher than that of the control virus vHaBacΔpif3-Hapif3-ph, indicating that SpltNPV pif3 can only partially substitute the function of HearNPV pif3. These results suggested that most of PIFs tested have strict host specificities, which may account, at least in part, for the limited host ranges of baculoviruses.

Developmental response of Spodoptera litura Fab. to treatments of crude volatile oil from Piper betle L. and evaluation of toxicity to earthworm, Eudrilus eugeniae Kinb

Evaluations of biological effects of (Pb-CVO) the crude volatile oil of Piper betle leaves on the tobacco cutworm Spodoptera litura were conducted. Pb-CVO was subjected to GC-MS analysis and twenty vital compounds were isolated from the betel leaf oil. Pb-CVO was tested at four different concentrations (0.25, 0.5, 1.0 and 1.5%) against S. litura. The treated insects exhibited dose depended mortality. The mortality rate was significantly higher at the 1.0 and 1.5% Pb-CVO. The LC50 (Lethal concentration) were observed at 0.48% Pb-CVO. Larval and pupal durations increased in all treatment concentrations (0.25, 0.3, 0.4 and 0.5%) whereas, pupal weight decreased compared to control. Adult longevity of S. litura was reduced in all treatments but predominantly in the 0.4 and 0.5% Pb-CVO. Correspondingly, mean fecundity rate was reduced at all concentrations compared to control. Histological studies of larvae mid-gut profiles of S. litura were severely damaged in 1.0 and 1.5% and showed abnormalities in mid-gut cells with 0.25 and 0.5% Pb-CVO treatments. Earthworm toxicity illustrated that 0.1% of chemical insecticides (monocrotophos and cypermethrin) varied widely in their contact toxicities compared to 0.5 and 1.0% Pb-CVO and control in both contact filter paper and artificial soil test. These findings suggest that twenty essential compounds of betel leaf oil were significant inhibitors of the development and caused behavioral changes of S. litura. Treatment with betel leaf oil at these concentrations had no adverse effect on earthworm populations.

Generating a host range-expanded recombinant baculovirus

As baculoviruses usually have a narrow insecticidal spectrum, knowing the mechanisms by which they control the host-range is prerequisite for improvement of their applications as pesticides. In this study, from supernatant of culture cells transfected with DNAs of an Autographa californica multiple nucleopolyhedrovirus (AcMNPV) mutant lacking the antiapoptotic gene p35 (vAc(∆P35)) and a cosmid representing a fragment of Spodoptera exigua nucleopolyhedrovirus (SeMNPV), a viral strain was plaque-purified and named vAcRev. vAcRev had a broader host range than either vAc(∆P35) or SeMNPV parental virus, being able to infect not only the permissive hosts of its parental viruses but also a nonpermissive host (Spodoptera litura). Genome sequencing indicated that vAcRev comprises a mixture of two viruses with different circular dsDNA genomes. One virus contains a genome similar to vAc(∆P35), while in the other viral genome, a 24.4 kbp-fragment containing 10 essential genesis replaced with a 4 kbp-fragment containing three SeMNPV genes including a truncated Se-iap3 gene. RNA interference and ectopic expression assays found that Se-iap3 is responsible for the host range expansion of vAcRev, suggesting that Se-iap3 inhibits the progression of apoptosis initiated by viral infection and promotes viral propagation in hosts both permissive and non-permissive for AcMNPV and SeMNPV.

The complete genome of a baculovirus isolated from an insect of medical interest: Lonomia obliqua (Lepidoptera: Saturniidae)

Lonomia obliqua (Lepidoptera: Saturniidae) is a species of medical importance due to the severity of reactions caused by accidental contact with the caterpillar bristles. Several natural pathogens have been identified in L. obliqua, and among them the baculovirus Lonomia obliqua multiple nucleopolyhedrovirus (LoobMNPV). The complete genome of LoobMNPV was sequenced and shown to have 120,022 bp long with 134 putative open reading frames (ORFs). Phylogenetic analysis of the LoobMNPV genome showed that it belongs to Alphabaculovirus group I (lepidopteran-infective NPV). A total of 12 unique ORFs were identified with no homologs in other sequenced baculovirus genomes. One of these, the predicted protein encoded by loob035, showed significant identity to an eukaryotic transcription terminator factor (TTF2) from the Lepidoptera Danaus plexippus, suggesting an independent acquisition through horizontal gene transfer. Homologs of cathepsin and chitinase genes, which are involved in host integument liquefaction and viral spread, were not found in this genome. As L. obliqua presents a gregarious behavior during the larvae stage the impact of this deletion might be neglectable.

Rescue of dnapol-null Autographa californica multiple nucleopolyhedrovirus with DNA polymerase (DNApol) of Spodoptera litura nucleopolyhedrovirus (SpltNPV) and identification of a nuclear localization signal in SpltNPV DNApol

DNA polymerase (DNApol) is highly conserved in all baculoviruses and plays an essential role in viral DNA replication. It determines the fidelity of baculovirus DNA replication by inserting the correct nucleotides into the primer terminus and proofreading any mispaired nucleotides. DNApols of groups I and II of the genus Alphabaculovirus in the family Baculoviridae share many common structural features. However, it is not clear whether a group I Autographa californica multiple nucleopolyhedrovirus (AcMNPV) DNApol can be substituted by a group II NPV DNApol. Here we report the successful generation of AcMNPV dnapol-null virus being rescued by a group II Spodoptera litura NPV (SpltNPV) dnapol (Bac-AcΔPol : Slpol). Viral growth curves and quantitative real-time PCR showed that the dnapol replacement reduced the level of viral production and DNA replication of Bac-AcΔPol : SlPol compared with WTrep, a native dnapol insertion in an AcMNPV dnapol-null virus. Light microscopy showed that production of occlusion bodies for Bac-AcΔPol : Slpol was reduced. We also identified a nuclear localization signal (NLS) for the SpltNPV DNApol C terminus at residues 827-838 by mutational analysis and confocal microscopy. Multiple point substitution of SpltNPV DNApol NLS abrogated virus production and viral DNA replication. Overall, these data suggested that the NLS plays an important role in SpltNPV DNApol nuclear localization and that SpltNPV DNApol cannot efficiently substitute the AcMNPV DNApol in AcMNPV.

Transcriptome Analysis of the SL221 Cells at the Early Stage during Spodoptera litura Nucleopolyhedrovirus Infection

Spodoptera litura (S. litura) is one of the most destructive agricultural pests worldwide. There is urgent need for a nuclear polyhedrosis virus that is specific to S. litura. To date, there have been no reports regarding the responses of S. litura cells to early Spodoptera litura nucleopolyhedrovirus (SpltNPV) infection due to the lack of a reference genome and transcriptome for S. litura. In this study, a cell transcriptome from the host S. litura was assembled and used for Illumina strand-specific RNA sequencing (RNA-seq) to generate 99180 unigenes, representing the 18 hour infection cycle. More than 2000 S. litura genes were significant differentially regulated throughout the infection. The levels of viral mRNAs began to increase dramatically at 6 hpi, and this increase continued throughout the remainder of the infection. We focused on the expression of genes related to stress responses, apoptosis, metabolic enzymes and host cell innate immune system. A small subset of genes related to host stress response, especially for 62 ones being able to annotated as enzyme, ligand and receptor genes, were observed to be specifically differentially expressed at 6 hpi. At 18 hpi, 104 unigenes were continuously significantly changing from 0 hpi to 18 hpi, considered to be viral multiplication related genes, including 3 annotated SL221 unigenes and 81 viral genes, such as tetraspanin and iap gene. This information and further studies on the regulation of host gene expression by baculovirus infection at early stage will provide the tools needed to enhance the utility of this virus as an effective insecticide.

Perylenediimide-cored cationic nanocarriers deliver virus DNA to kill insect pests

The narrow infection range of insect virus restricts its use for the control of broad range of pests. A cationic fluorescent nanocarrier delivery system was successfully applied to broaden the host range of an insecticidal virus DNA, which should contributes to the organic and green food production.

The chitinase C gene PsChiC from Pseudomonas sp. and its synergistic effects on larvicidal activity

Pseudomonas sp. strain TXG6-1, a chitinolytic gram-negative bacterium, was isolated from a vegetable field in Taixing city, Jiangsu Province, China. In this study, a Pseudomonas chitinase C gene (PsChiC) was isolated from the chromosomal DNA of this bacterium using a pair of specific primers. The PsChiC gene consisted of an open reading frame of 1443 nucleotides and encoded 480 amino acid residues with a calculated molecular mass of 51.66 kDa. The deduced PsChiC amino acid sequence lacked a signal sequence and consisted of a glycoside hydrolase family 18 catalytic domain responsible for chitinase activity, a fibronectin type III-like domain (FLD) and a C-terminal chitin-binding domain (ChBD). The amino acid sequence of PsChiCshowed high sequence homology (> 95%) with chitinase C from Serratia marcescens. SDS-PAGE showed that the molecular mass of chitinase PsChiC was 52 kDa. Chitinase assays revealed that the chitobiosidase and endochitinase activities of PsChiCwere 51.6- and 84.1-fold higher than those of pET30a, respectively. Although PsChiC showed little insecticidal activity towards Spodoptera litura larvae, an insecticidal assay indicated that PsChiC increased the insecticidal toxicity of SpltNPV by 1.78-fold at 192 h and hastened death. These results suggest that PsChiC from Pseudomonas sp. could be useful in improving the pathogenicity of baculoviruses.

Comparative study of two thioredoxins from common cutworm (Spodoptera litura): cloning, expression, and functional characterization

Thioredoxins (Trxs) are a ubiquitous family of antioxidant enzymes that are involved in protecting organisms against various oxidative stresses. Here, we cloned and characterized two thioredoxins, named SlTrx1 and SlTrx2, from the common cutworm Spodoptera litura. SlTrx1 and SlTrx2, respectively, consist of 988 and 606 bp full-length cDNA with 318 and 447 bp open reading frames encoding 106 and 149 amino acid residues. Furthermore, the N-terminal region of SlTrx2 contains a predicted mitochondrial localization signal (33 amino acids). A phylogenetic relationship analysis revealed that SlTrx1 is in the cytosolic thioredoxin Trx1 cluster, whereas SlTrx2 is in the mitochondrial thioredoxin Trx2 cluster. Recombinant SlTrx1 (14 kDa) and SlTrx2 (16 kDa), expressed in baculovirus-infected insect Sf9 cells, demonstrated insulin disulfide reductase activity at the same optimum temperature and pH value of 35 °C and 7.0, respectively, in vitro. During S. litura development, we found that SlTrx1 and SlTrx2 had similar transcript expression patterns and were constitutively expressed in the epidermis, fat body, and midgut, with the highest expression occurring in the sixth-instar larval stage in the epidermis and midgut. In addition, both SlTrx1 and SlTrx2 mRNA were up-regulated in S. litura after injection with H2O2, cumene hydroperoxide, indoxacarb, and metaflumizone. These results suggest that SlTrx1 and SlTrx2 function as potent antioxidant enzymes, and provide a molecular basis for the roles SlTrx1 and SlTrx2 during development and the oxidative stress response of S. litura.

Baculovirus induces host cell aggregation via a Rho/Rok-dependent mechanism

Several baculoviruses can induce host cell aggregation during infection; however, the molecular basis remains unknown. The Rho family of small GTPases, including Rho1, Racs and Cdc42, plays important roles in cell migration and cell-cell contact. Activated GTPases target actin polymerization to discrete sites on the plasma membrane, thereby inducing membrane protrusions. In this study, we demonstrated that Spodoptera litura nucleopolyhedrovirus (SpltNPV) infection induced the amoeboid movement and aggregation of SpLi-221 cells in vitro. The amount of Rho1-GTP increased in the infected cells, which suggested that Rho1 was activated upon infection. RNA interference and superinfection of dominant-negative recombinants revealed that the SpltNPV-induced SpLi-221 cell aggregation was dependent on the Rho1, but not Racs or Cdc42, signalling pathway. Inhibition of Rho-associated protein kinase (Rok) activity by the inhibitor Y-27632 significantly reduced SpLi-221 cell aggregation. Silencing Rho1 expression with RNA interference decreased SpltNPV propagation by approximately 40 % in vitro, when SpLi-221 cells were infected at a low, but not high, m.o.i., suggesting that the SpltNPV-induced cell aggregation may benefit SpltNPV spread.

Identification of a conserved non-protein-coding genomic element that plays an essential role in Alphabaculovirus pathogenesis

Highly homologous sequences 154-157 bp in length grouped under the name of "conserved non-protein-coding element" (CNE) were revealed in all of the sequenced genomes of baculoviruses belonging to the genus Alphabaculovirus. A CNE alignment led to the detection of a set of highly conserved nucleotide clusters that occupy strictly conserved positions in the CNE sequence. The significant length of the CNE and conservation of both its length and cluster architecture were identified as a combination of characteristics that make this CNE different from known viral non-coding functional sequences. The essential role of the CNE in the Alphabaculovirus life cycle was demonstrated through the use of a CNE-knockout Autographa californica multiple nucleopolyhedrovirus (AcMNPV) bacmid. It was shown that the essential function of the CNE was not mediated by the presumed expression activities of the protein- and non-protein-coding genes that overlap the AcMNPV CNE. On the basis of the presented data, the AcMNPV CNE was categorized as a complex-structured, polyfunctional genomic element involved in an essential DNA transaction that is associated with an undefined function of the baculovirus genome.

Analysis of the genome of a Korean isolate of the Pieris rapae granulovirus enabled by its separation from total host genomic DNA by pulse-field electrophoresis

BACKGROUND

Most traditional genome sequencing projects involving viruses include the culture and purification of the virus particles. However, purification of virions may yield insufficient material for traditional sequencing. The electrophoretic method described here provides a strategy whereby the genomic DNA of the Korean isolate of Pieris rapae granulovirus (PiraGV-K) could be recovered in sufficient amounts for sequencing by purifying it directly from total host DNA by pulse-field gel electrophoresis (PFGE).

METHODOLOGY/PRINCIPAL FINDINGS

The total genomic DNA of infected P. rapae was embedded in agarose plugs, treated with restriction nuclease and methylase, and then PFGE was used to separate PiraGV-K DNA from the DNA of P. rapae, followed by mapping of fosmid clones of the purified viral DNA. The double-stranded circular genome of PiraGV-K was found to encode 120 open reading frames (ORFs), which covered 92% of the sequence. BLAST and ORF arrangement showed the presence of 78 homologs to other genes in the database. The mean overall amino acid identity of PiraGV-K ORFs was highest with the Chinese isolate of PiraGV (~99%), followed up with Choristoneura occidentalis ORFs at 58%. PiraGV-K ORFs were grouped, according to function, into 10 genes involved in transcription, 11 involved in replication, 25 structural protein genes, and 15 auxiliary genes. Genes for Chitinase (ORF 10) and cathepsin (ORF 11), involved in the liquefaction of the host, were found in the genome.

CONCLUSIONS/SIGNIFICANCE

The recovery of PiraGV-K DNA genome by pulse-field electrophoretic separation from host genomic DNA had several advantages, compared with its isolation from particles harvested as virions or inclusions from the P. rapae host. We have sequenced and analyzed the 108,658 bp PiraGV-K genome purified by the electrophoretic method. The method appears to be generally applicable to the analysis of genomes of large viruses.

p13 from group II baculoviruses is a killing-associated gene

p13 gene was first described in Leucania separata multinuclear polyhedrosis virus (Ls-p13) several years ago, but the function of P13 protein has not been experimentally investigated to date. In this article, we indicated that the expression of p13 from Heliothis armigera single nucleocapsid nucleopolyhedrovirus (Ha-p13) was regulated by both early and late promoter. Luciferase assay demonstrated that the activity of Ha-p13 promoter with hr4 enhancer was more than 100 times in heterologous Sf9 cells than that in nature host Hz-AM1 cells. Both Ls-P13 and Ha-P13 are transmembrane proteins. Confocal microscopic analysis showed that both mainly located in the cytoplasm membrane at 48 h. Results of RNA interference indicated that Ha-p13 was a killing-associated gene for host insects H. armigera. The AcMNPV acquired the mentioned killing activity and markedly accelerate the killing rate when expressing Ls-p13. In conclusion, p13 is a killing associated gene in both homologous and heterologous nucleopolyhedrovirus. [BMB Reports 2012; 45(12): 730-735]

RNAi-mediated knockdown of catalase causes cell cycle arrest in SL-1 cells and results in low survival rate of Spodoptera litura (Fabricius)

Deregulated reactive oxygen species (ROS) production can lead to the disruption of structural and functional integrity of cells as a consequence of reactive interaction between ROS and various biological components. Catalase (CAT) is a common enzyme existing in nearly all organisms exposed to oxygen, which decomposes harmful hydrogen peroxide, into water and oxygen. In this study, the full length sequence that encodes CAT-like protein from Spodoptera litura named siltCAT (GenBank accession number: JQ_663444) was cloned and characterized. Amino acid sequence alignment showed siltCAT shared relatively high conservation with other insect, especially the conserved residues which defined heme and NADPH orientation. Expression pattern analysis showed that siltCAT mRNA was mainly expressed in the fat body, midgut, cuticle and malpighian tube, and as well as over last instar larvae, pupa and adult stages. RNA interference was used to silence CAT gene in SL-1 cells and the fourth-instar stage of S. litura larvae respectively. Our results provided evidence that CAT knockdown induced ROS generation, cell cycle arrest and apoptosis in SL-1 cells. It also confirmed the decrease in survival rate because of increased ROS production in experimental groups injected with double-stranded RNA of CAT (dsCAT). This study implied that ROS scavenging by CAT is important for S. litura survival.

Molecular and immunohistochemical characterization of the chitinase gene from Pieris rapae granulovirus

The chitinase gene of baculoviruses is expressed in the late phase of virus replication in insects and possesses high exo- and endochitinase activity, which can hydrolyze chitin in the body of the insect, thus promoting terminal host liquefaction. Alphabaculovirus viral chitinases (vChitA) have been well analyzed, but information regarding viral chitinases from betabaculoviruses is limited. Whole-genome sequencing of a Korean isolate of Pieris rapae GV (PiraGV-K) predicted a putative chitinase gene corresponding to ORF10. The PiraGV-K chitinase gene had a coding sequence of 1,761 bp, encoding a protein of 586 amino acid (aa) residues, including an 18-aa putative signal peptide. Time course induction pattern observed by SDS-PAGE and subsequent Western blot with anti-PiraGV-K chitinase antibody revealed the cleavage of the signal peptide from the intact chitinase. Edman sequencing analysis was further conducted to confirm the exact nature of the mature chitinase, and the N-terminal amino acid sequence (KPGAP) exactly matched the sequence following the signal peptide sequence. The transcriptomics of PiraGV-K chitinase in infected P. rapae larvae, examined by real-time PCR, revealed a significant 75-fold increase after four days of feeding with PiraGV-K-treated leaves, with a subsequent decline at the later stages of infection. Confocal microscopic analysis showed that PiraGV-K chitinase possibly exists as a secreted protein, with strong chitinase-specific signals in fat body cells and integument at four days postinfection. Furthermore, immunogold labeling and electron microscopy studies localized the PiraGV-K chitinase in the cytoplasm and sparsely within vacuolar structures in the fat body apart from the extensive aggregation in the cuticular lining of the integument.

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.

Phylogenetic analysis of Bombyx mori nucleopolyhedrovirus polyhedrin and p10 genes in wild isolates from Guangxi Zhuang Autonomous Region, China

Bombyx mori nucleopolyhedrovirus (BmNPV) is a severe pathogen that seriously impacts the sericulture industry. In this study, 45 wild BmNPV isolates were collected from different silkworm-raising regions in China's Guangxi Zhuang Autonomous Region. Two highly expressed very late genes from each isolate, polyhedrin and p10, were sequenced and subjected to phylogenetic analysis. The polyhedrin gene was found to be highly conserved, while the p10 gene was more variable frequently harboring point mutations and displaying variations in codon use without obvious codon bias. The BmNPV isolates from Guangxi were separated into three main clades, I, II, and III, according to the p10 gene phylogenetic tree. The geographical distribution of clade I isolates in Guangxi showed a concentrated pattern and that of clade II isolates showed a connected pattern. Clade III isolates were irregularly scattered throughout Guangxi. Local transmission of this pathogen clearly occurred in the silkworm-raising regions in Guangxi. This study may provide some data on BmNPV transmission in the silkworm-raising regions and be helpful in devising strategies for the prevention and control of BmNPV disease.

Seamless replacement of Autographa californica multiple nucleopolyhedrovirus gp64 with each of five novel type II alphabaculovirus fusion sequences generates pseudotyped virus that fails to transduce mammalian cells

Autographa californica multiple nucleopolyhedrovirus (AcMNPV), a member of the type I alphabaculoviruses, is able to transduce and deliver a functional gene to a range of non-host cells, including many mammalian lines and primary cells, a property mediated by the envelope fusion protein GP64. AcMNPV is non-cytopathic and inherently replication deficient in non-host cells. As such, AcMNPV represents a possible new class of gene therapy vector with potential future clinical utility. Whilst not a problem for in vitro gene delivery, the broad tropism displayed for non-host cells is less desirable in a gene therapy vector. The fusion protein F of type II alphabaculoviruses can substitute functionally for GP64, and such pseudotyped viruses display a severely impaired capacity for non-host-cell transduction. Thus, surface decoration of such an F-pseudotyped AcMNPV with cell-binding ligands may restore transduction competence and generate vectors with desirable cell-targeting characteristics. By seamlessly swapping the native gp64 coding sequence with each of five sequences encoding different F proteins, a set of F-pseudotyped AcMNPV was generated. This report details their relative abilities both to functionally replace GP64 in viral growth and to transduce human Saos-2 and HeLa cells. All five supported viable infections in insect cell cultures and one, the Mamestra configurata NPV (MacoNPV) F pseudotype, could be amplified to titres close to those of native AcMNPV. In contrast, none was able to transduce the Saos-2 and HeLa cell lines. The robust support provided by MacoNPV F in virus production makes the corresponding pseudotype a viable scaffold to display surface ligands to direct selective mammalian cell targeting.

Identification of a new Bombyx mori nucleopolyhedrovirus and analysis of its bro gene family

The highly pathogenic Bombyx mori nucleopolyhedrovirus (BmNPV) has caused severe damages to sericulture in many countries, and the relationship between the pathogenicity of various BmNPV strains and their geographical evolution has been the topic of our interest. In this study, we isolated a new BmNPV strain from Thailand (BmNPV-Thai), based on the sequences of its conservative genes p10, p35, polh, egt and vp39. The BmNPV-Thai appears to have baculovirus repeated ORF (bro) genes different from four other well-known BmNPV strains of China (GD, CQ1), Japan (T3), and France (SC7); It only has bro-a, bro-c, and bro-d, but not bro-b and bro-e genes. These bro genes are localized only in the two subgroups highly homologous to their counterparts and their encoded BRO proteins differ mainly at their N-terminal amino acid residues. Phylogenetic analysis indicates that the evolution of the bro genes of the five BmNPV strains is not obviously associated with their geographic locations.

Genomic sequence analysis of granulovirus isolated from the tobacco cutworm, Spodoptera litura

BACKGROUND

Spodoptera litura is a noctuid moth that is considered an agricultural pest. The larvae feed on a wide range of plants and have been recorded on plants from 40 plant families (mostly dicotyledons). It is a major pest of many crops. To better understand Spodoptera litura granulovirus (SpliGV), the nucleotide sequence of the SpliGV DNA genome was determined and analyzed.

METHODOLOGY/PRINCIPAL FINDINGS

The genome of the SpliGV was completely sequenced. The nucleotide sequence of the SpliGV genome was 124,121 bp long with 61.2% A+T content and contained 133 putative open reading frames (ORFs) of 150 or more nucleotides. The 133 putative ORFs covered 86.3% of the genome. Among these, 31 ORFs were conserved in most completely sequenced baculovirus genomes, 38 were granulovirus (GV)-specific, and 64 were present in some nucleopolyhedroviruses (NPVs) and/or GVs. We proved that 9 of the ORFs were SpliGV specific.

CONCLUSIONS/SIGNIFICANCE

The genome of SpliGV is 124,121 bp in size. One hundred thirty-three ORFs that putatively encode proteins of 50 or more amino acid residues with minimal overlap were determined. No chitinase or cathepsin genes, which are involved in the liquefaction of the infected host, were found in the SpliGV genome, explaining why SpliGV-infected insects do not degrade in a typical manner. The DNA photolyase gene was first found in the genus Granulovirus. When phylogenic relationships were analyzed, the SpliGV was most closely related to Trichoplusia ni granulovirus (TnGV) and Xestia c-nigrum granulovirus (XecnGV), which belong to the Type I-granuloviruses (Type I-GV).

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).

Quantitative proteomics of Spodoptera frugiperda cells during growth and baculovirus infection

Baculovirus infection of Spodoptera frugiperda cells is a system of choice to produce a range of recombinant proteins, vaccines and, potentially, gene therapy vectors. While baculovirus genomes are well characterized, the genome of S. frugiperda is not sequenced and the virus-host molecular interplay is sparsely known. Herein, we describe the application of stable isotope labeling by amino acids in cell culture (SILAC) to obtain the first comparative proteome quantitation of S. frugiperda cells during growth and early baculovirus infection. The proteome coverage was maximized by compiling a search database with protein annotations from insect species. Of interest were differentially proteins related to energy metabolism, endoplasmic reticulum and oxidative stress, yet not investigated in the scope of baculovirus infection. Further, the reduced expression of key viral-encoded proteins early in the infection cycle is suggested to be related with decreased viral replication at high cell density culture. These findings have implications for virological research and improvement of baculovirus-based bioprocesses.

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.

Baculovirus: molecular insights on their diversity and conservation

The Baculoviridae is a large group of insect viruses containing circular double-stranded DNA genomes of 80 to 180 kbp. In this study, genome sequences from 57 baculoviruses were analyzed to reevaluate the number and identity of core genes and to understand the distribution of the remaining coding sequences. Thirty one core genes with orthologs in all genomes were identified along with other 895 genes differing in their degrees of representation among reported genomes. Many of these latter genes are common to well-defined lineages, whereas others are unique to one or a few of the viruses. Phylogenetic analyses based on core gene sequences and the gene composition of the genomes supported the current division of the Baculoviridae into 4 genera: Alphabaculovirus, Betabaculovirus, Gammabaculovirus, and Deltabaculovirus.

Sequence comparison between three geographically distinct Spodoptera frugiperda multiple nucleopolyhedrovirus isolates: Detecting positively selected genes

The complete genomic sequence of a Nicaraguan plaque purified Spodoptera frugiperda nucleopolyhedrovirus (SfMNPV) genotype SfMNPV-B was determined and compared to previously sequenced isolates from United States (SfMNPV-3AP2) and Brazil (SfMNPV-19). The genome of SfMNPV-B (132,954bp) was 1623bp and 389bp larger than that of SfMNPV-3AP2 and SfMNPV-19, respectively. Genome size differences were mainly due to a deletion located in the SfMNPV-3AP2 egt region and small deletions and point mutations in SfMNPV-19. Nucleotide sequences were strongly conserved (99.35% identity) and a high degree of predicted amino acid sequence identity was observed. A total of 145 open reading frames (ORFs) were identified in SfMNPV-B, two of them (sf39a and sf110a) had not been previously identified in the SfMNPV-3AP2 and SfMNPV-19 genomes and one (sf57a) was absent in both these genomes. In addition, sf6 was not previously identified in the SfMNPV-19 genome. In contrast, SfMNPV-B and SfMNPV-19 both lacked sf129 that had been reported in SfMNPV-3AP2. In an effort to identify genes potentially involved in virulence or in determining population adaptations, selection pressure analysis was performed. Three ORFs were identified undergoing positive selection: sf49 (pif-3), sf57 (odv-e66b) and sf122 (unknown function). Strong selection for ODV envelope protein genes indicates that the initial infection process in the insect midgut is one critical point at which adaptation acts during the transmission of these viruses in geographically distant populations. The function of ORF sf122 is being examined.

Genomic sequencing and analyses of Lymantria xylina multiple nucleopolyhedrovirus

BACKGROUND

Outbreaks of the casuarina moth, Lymantria xylina Swinehoe (Lepidoptera: Lymantriidae), which is a very important forest pest in Taiwan, have occurred every five to 10 years. This moth has expanded its range of host plants to include more than 65 species of broadleaf trees. LyxyMNPV (L. xylina multiple nucleopolyhedrovirus) is highly virulent to the casuarina moth and has been investigated as a possible biopesticide for controlling this moth. LdMNPV-like virus has also been isolated from Lymantria xylina larvae but LyxyMNPV was more virulent than LdMNPV-like virus both in NTU-LY and IPLB-LD-652Y cell lines. To better understand LyxyMNPV, the nucleotide sequence of the LyxyMNPV DNA genome was determined and analysed.

RESULTS

The genome of LyxyMNPV consists of 156,344 bases, has a G+C content of 53.4% and contains 157 putative open reading frames (ORFs). The gene content and gene order of LyxyMNPV were similar to those of LdMNPV, with 151 ORFs identified as homologous to those reported in the LdMNPV genome. Two genes (Lyxy49 and Lyxy123) were homologous to other baculoviruses, and four unique LyxyMNPV ORFs (Lyxy11, Lyxy19, Lyxy130 and Lyxy131) were identified in the LyxyMNPV genome, including a gag-like gene that was not reported in baculoviruses. LdMNPV contains 23 ORFs that are absent in LyxyMNPV. Readily identifiable homologues of the gene host range factor-1 (hrf-1), which appears to be involved in the susceptibility of L. dispar to NPV infection, were not present in LyxyMNPV. Additionally, two putative odv-e27 homologues were identified in LyxyMNPV. The LyxyMNPV genome encoded 14 bro genes compared with 16 in LdMNPV, which occupied more than 8% of the LyxyMNPV genome. Thirteen homologous regions (hrs) were identified containing 48 repeated sequences composed of 30-bp imperfect palindromes. However, they differed in the relative positions, number of repeats and orientation in the genome compared to LdMNPV.

CONCLUSION

The gene parity plot analysis, percent identity of the gene homologues and a phylogenetic analysis suggested that LyxyMNPV is a Group II NPV that is most closely related to LdMNPV but with a highly distinct genomic organisation.

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.

Baculovirus genes affecting host function

Baculoviruses are insect-specific viruses. These large DNA viruses encode many genes in addition to those required to replicate and build new virions. These auxiliary genes provide selective advantages to the virus for invading and infecting host insects. Eight of these genes, which help the virus overcome insect defenses against invasion, are discussed. These include genes whose products help the virus traverse physical or physiological barriers and those that overcome host immune defenses.