Proteomic Analysis of Mamestra Brassicae Nucleopolyhedrovirus Progeny Virions from Two Different Hosts

A sensitive assay for scrutiny of Autographa californica multiple nucleopolyhedrovirus genes using CRISPR-Cas9

Baculoviruses have very large genomes and previous studies have demonstrated improvements in recombinant protein production and genome stability through the removal of some nonessential sequences. However, recombinant baculovirus expression vectors (rBEVs) in widespread use remain virtually unmodified. Traditional approaches for generating knockout viruses (KOVs) require several experimental steps to remove the target gene prior to the generation of the virus. In order to optimize rBEV genomes by removing nonessential sequences, more efficient techniques for establishing and evaluating KOVs are required. Here, we have developed a sensitive assay utilizing CRISPR-Cas9-mediated gene targeting to examine the phenotypic impact of disruption of endogenous Autographa californica multiple nucleopolyhedrovirus (AcMNPV) genes. For validation, 13 AcMNPV genes were targeted for disruption and evaluated for the production of GFP and progeny virus - traits that are essential for their use as vectors for recombinant protein production. The assay involves transfection of sgRNA into a Cas9-expressing Sf9 cell line followed by infection with a baculovirus vector carrying the gfp gene under the p10 or p6.9 promoters. This assay represents an efficient strategy for scrutinizing AcMNPV gene function through targeted disruption, and represents a valuable tool for developing an optimized rBEV genome. KEY POINTS: [Formula: see text] A method to scrutinize the essentiality of baculovirus genes was developed. [Formula: see text] The method uses Sf9-Cas9 cells, a targeting plasmid carrying a sgRNA, and a rBEV-GFP. [Formula: see text] The method allows scrutiny by only needing to modify the targeting sgRNA plasmid.

Utility of Alternative Promoters for Foreign Gene Expression Using the Baculovirus Expression Vector System

The baculovirus expression vector system (BEVS) is a widely used platform for recombinant protein production for use in a wide variety of applications. Of particular interest is production of virus-like particles (VLPs), which consist of multiple viral proteins that self-assemble in strict stoichiometric ratios to mimic the structure of a virus but lacks its genetic material, while a significant amount of effort has been spent on optimizing expression ratios by co-infecting cells with multiple recombinant BEVs and modulating different process parameters, co-expressing multiple foreign genes from a single rBEV may offer more promise. However, there is currently a lack of promoters available with which to optimize co-expression of each foreign gene. To address this, previously published transcriptome data was used to identify promoters that have incrementally lower expression profiles and compared by expressing model cytoplasmic and secreted proteins. Bioinformatics was also used to identify sequence determinants that may be important for late gene transcription regulation, and translation initiation. The identified promoters and bioinformatics analyses may be useful for optimizing expression of foreign genes in the BEVS.

Coocclusion of Helicoverpa armigera Single Nucleopolyhedrovirus (HearSNPV) and Helicoverpa armigera Multiple Nucleopolyhedrovirus (HearMNPV): Pathogenicity and Stability in Homologous and Heterologous Hosts

Helicoverpa armigera single nucleopolyhedrovirus (HearSNPV) is a virulent pathogen of lepidopterans in the genera Heliothis and Helicoverpa, whereas Helicoverpa armigera multiple nucleopolyhedrovirus (HearSNPV) is a different virus species with a broader host range. This study aimed to examine the consequences of coocclusion of HearSNPV and HearMNPV on the pathogenicity, stability and host range of mixed-virus occlusion bodies (OBs). HearSNPV OBs were approximately 6-fold more pathogenic than HearMNPV OBs, showed faster killing by approximately 13 h, and were approximately 45% more productive in terms of OB production per larva. For coocclusion, H. armigera larvae were first inoculated with HearMNPV OBs and subsequently inoculated with HearSNPV OBs at intervals of 0–72 h after the initial inoculation. When the interval between inoculations was 12–24 h, OBs collected from virus-killed insects were found to comprise 41–57% of HearSNPV genomes, but the prevalence of HearSNPV genomes was greatly reduced (3–4%) at later time points. Quantitative PCR (qPCR) analysis revealed the presence of HearSNPV genomes in a small fraction of multinucleocapsid ODVs representing 0.47–0.88% of the genomes quantified in ODV samples, indicating that both viruses had replicated in coinfected host cells. End-point dilution assays on ODVs from cooccluded mixed-virus OBs confirmed the presence of both viruses in 41.9–55.6% of wells that were predicted to have been infected by a single ODV. A control experiment indicated that this result was unlikely to be due to the adhesion of HearSNPV ODVs to HearMNPV ODVs or accidental contamination during ODV band extraction. Therefore, the disparity between the qPCR and end-point dilution estimates of the prevalence of mixed-virus ODVs likely reflected virus-specific differences in replication efficiency in cell culture and the higher infectivity of pseudotyped ODVs that were produced in coinfected parental cells. Bioassays on H. armigera, Spodoptera frugiperda and Mamestra brassicae larvae revealed that mixed-virus OBs were capable of infecting heterologous hosts, but relative potency values largely reflected the proportion of HearMNPV present in each mixed-virus preparation. The cooccluded mixtures were unstable in serial passage; HearSNPV rapidly dominated during passage in H. armigera whereas HearMNPV rapidly dominated during passage in the heterologous hosts. We conclude that mixed-virus coocclusion technology may be useful for producing precise mixtures of viruses with host range properties suitable for the control of complexes of lepidopteran pests in particular crops, although this requires validation by field testing.

Cd exposure-triggered metabolic disruption increases the susceptibility of Lymantria dispar (Lepidoptera: Erebidae) larvae to Mamestra brassicae nuclear polyhedrosis virus: A multi-omics study

Biological control is an environmentally friendly and effective pest control strategy, but it is often affected by a variety of abiotic factors in the pest control area. Here, the susceptibility of gypsy moth larvae to Mamestra brassicae nuclear polyhedrosis virus (MbNPV) under Cd treatment at the low and high dosages was investigated, and the mechanism of Cd stress affecting virus susceptibility of gypsy moth larvae was analyzed from a metabolic perspective by combining transcriptome and metabolome of the larval fat body. Our results showed that the mortality of MBNPV infection on gypsy moth larvae pre-exposed to Cd was significantly higher than that of larvae without Cd pre-exposure, and the joint effects of Cd exposure and virus infection on larval mortality were demonstrated to be synergistic. Transcriptome analysis revealed that amino acid and carbohydrate transport and metabolism accounted for most of the differently expressed genes in the low Cd and high Cd treatment groups. Consistent with the transcriptome results, metabolome analysis also showed that most metabolites affected by Cd exposure were involved in amino acid and carbohydrate metabolism. Function analysis showed that the contents of several amino acids (e.g. tryptophan and tyrosine) with antioxidant properties were significantly increased in Cd-treated gypsy moth larvae. Taken together, Cd exposure as an environmental factor, promotes the susceptibility of gypsy moth larvae to MbNPV, and metabolic disruption, especially amino acids and carbohydrates-related metabolism, is responsible for the increased susceptibility of gypsy moth larvae to virus under Cd stress.

Genetic Variation and Biological Activity of Two Closely Related Alphabaculoviruses during Serial Passage in Permissive and Semi-Permissive Heterologous Hosts

Phylogenetic analyses suggest that Mamestra brassicae multiple nucleopolyhedrovirus (MbMNPV) and Helicoverpa armigera multiple nucleopolyhedrovirus (HearMNPV) may be strains of the same virus species. Most of the studies comparing their biological activities have been performed in their homologous hosts. A comparison of host range and stability in alternative hosts was performed. The host range of these viruses was compared using high concentrations of inoculum to inoculate second instars of six species of Lepidoptera. One semi-permissive host (Spodoptera littoralis) and one permissive host (S. exigua) were then selected and used to perform six serial passages involving a concentration corresponding to the ~25% lethal concentration for both viruses. Restriction endonuclease analysis showed fragment length polymorphisms in every host-virus system studied. In S. littoralis, serial passage of MbMNPV resulted in decreased pathogenicity and an increase in speed-of-kill, whereas no significant changes were detected for HearMNPV with respect to the initial inoculum. In contrast, both viruses showed a similar trend in S. exigua. These results highlight the low genetic diversity and a high phenotypic stability of HearMNPV with respect to the original inoculum after six successive passages in both insect hosts. This study concludes that host-baculovirus interactions during serial passage are complex and the process of adaptation to a novel semi-permissive host is far from predictable.

Protein composition of the occlusion bodies of Epinotia aporema granulovirus

Within family Baculoviridae, members of the Betabaculovirus genus are employed as biocontrol agents against lepidopteran pests, either alone or in combination with selected members of the Alphabaculovirus genus. Epinotia aporema granulovirus (EpapGV) is a fast killing betabaculovirus that infects the bean shoot borer (E. aporema) and is a promising biopesticide. Because occlusion bodies (OBs) play a key role in baculovirus horizontal transmission, we investigated the composition of EpapGV OBs. Using mass spectrometry-based proteomics we could identify 56 proteins that are included in the OBs during the final stages of larval infection. Our data provides experimental validation of several annotated hypothetical coding sequences. Proteogenomic mapping against genomic sequence detected a previously unannotated ac110-like core gene and a putative translation fusion product of ORFs epap48 and epap49. Comparative studies of the proteomes available for the family Baculoviridae highlight the conservation of core gene products as parts of the occluded virion. Two proteins specific for betabaculoviruses (Epap48 and Epap95) are incorporated into OBs. Moreover, quantification based on emPAI values showed that Epap95 is one of the most abundant components of EpapGV OBs.

Proteomic analysis of the Heliothis virescens ascovirus 3i (HvAV-3i) virion

Ascoviruses are enveloped, circular, double-stranded DNA viruses that can effectively control the appetite of lepidopteran larvae, thereby reducing the consequent damage and economic losses to crops. In this study, the virion of a sequenced Heliothis virescens ascovirus 3i (HvAV-3i) strain was used to perform proteomic analysis using both in-gel and in-solution digestion. A total of 81 viral proteins, of which 67 were associated with the virions, were identified in the proteome of HvAV-3i virions. Among these proteins, 23 with annotated functions were associated with DNA/RNA metabolism/transcription, virion assembly, sugar and lipid metabolism, signalling, cellular homoeostasis and cell lysis. Twenty-one viral membrane proteins were also identified. Some of the minor 'virion' proteins identified may be non-virion contaminants of viral proteins synthesized during replication, identified by more recent and highly sensitive methods. The extensive identification of the ascoviral proteome will establish a foundation for further investigation of ascoviral replication and infection.

Protein composition analysis of polyhedra matrix of Bombyx mori nucleopolyhedrovirus (BmNPV) showed powerful capacity of polyhedra to encapsulate foreign proteins

Polyhedra can encapsulate other proteins and have potential applications as protein stabilizers. The extremely stable polyhedra matrix may provide a platform for future engineered micro-crystal devices. However, the protein composition of the polyhedra matrix remains largely unknown. In this study, the occlusion-derived virus (ODV)-removed BmNPV polyhedra matrix fraction was subjected to SDS-PAGE and then an LC-ESI-MS/MS analysis using a Thermo Scientific Q Exactive mass spectrometer. In total, 28 host and 91 viral proteins were identified. The host components were grouped into one of six categories, i.e., chaperones, ubiquitin and related proteins, host helicases, cytoskeleton-related proteins, RNA-binding proteins and others, according to their predicted Pfam domain(s). Most viral proteins may not be essential for polyhedra assembly, as evidenced by studies in the literature showing that polyhedra formation occurs in the nucleus upon the disruption of individual genes. The structural role of these proteins in baculovirus replication will be of significant interest in future studies. The immobilization of enhanced green fluorescent protein (eGFP) into the polyhedra by fusing with the C-terminus of BM134 that is encoded by open reading frame (ORF) 134 suggested that the polyhedra had a powerful capacity to trap foreign proteins, and BM134 was a potential carrier for incorporating proteins of interest into the polyhedra.