AcMNPV ac143 (odv-e18) is essential for mediating budded virus production and is the 30th baculovirus core gene

162

169

Baculoviruses produce two progeny phenotypes during their replication cycles. The occlusion-derived virus (ODV) is responsible for initiating primary infection in the larval midgut, and the budded virus (BV) phenotype is responsible for the secondary infection. The proteomics of several baculovirus ODVs have been revealed, but so far, no extensive analysis of BV-associated proteins has been conducted. In this study, the protein composition of the BV of Autographa californica nucleopolyhedrovirus (AcMNPV), the type species of baculoviruses, was analyzed by various mass spectrometry (MS) techniques, including liquid chromatographytriple quadrupole linear ion trap (LC-Qtrap), liquid chromatography-quadrupole time of flight (LC-Q-TOF), and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF). SDS-PAGE and MALDI-TOF analyses showed that the three most abundant proteins of the AcMNPV BV were GP64, VP39, and P6.9. A total of 34 viral proteins associated with the AcMNPV BV were identified by the indicated methods. Thirteen of these proteins, PP31, AC58/59, AC66, IAP-2, AC73, AC74, AC114, AC124, chitinase, polyhedron envelope protein (PEP), AC132, ODV-E18, and ODV-E56, were identified for the first time to be BV-associated proteins. Western blot analyses showed that ODV-E18 and ODV-E25, which were previously thought to be ODV-specific proteins, were also present in the envelop fraction of BV. In addition, 11 cellular proteins were found to be associated with the AcMNPV BV by both LC-Qtrap and LC-Q-TOF analyses. Interestingly, seven of these proteins were also identified in other enveloped viruses, suggesting that many enveloped viruses may commonly utilize certain conserved cellular pathways.During the baculovirus infection cycle, two progeny virion phenotypes are produced, the budded virus (BV) and the occlusion-derived virus (ODV). The two phenotypes are genotypically identical, but each has characteristic structural components to accommodate its respective functions (37). ODVs are responsible for initiating primary infections in the midgut epithelial cells of susceptible hosts, while BVs are responsible for spreading the virus among cells and tissues in the host (48). At the early stage of the infection, the nucleocapsids are transported through the nuclear membranes and migrate across the cytosol to the cell membrane, where the virus buds out (BV). BVs acquire an envelope of virus-encoded proteins as they bud out of the cell membrane (50). In the late stages of the infection, the nucleocapsids within the nucleus are enveloped with a lipid bilayer that resembles, but is not identical to, the inner nuclear membrane (8, 37). Therefore, it is generally believed that the BV and ODV share the same components of the nucleocapsid but differ in their envelopes. However, detailed structures of the BV and ODV have not been elucidated totally.The availability of genome sequences has facilitated proteomic analyses of baculoviruses, especially by mass spectrometry (MS)-based techniques. Since Braunagel et al. fir...

Section: Discussionsupporting

confidence: 84%

Proteomics of the Autographa californica Nucleopolyhedrovirus Budded Virions

Wang

Deng

Hou

et al. 2010

162

169

“…We demonstrated here that ac93 and odv-e25 were conserved among all baculoviruses and were baculovirus core genes, thus increasing the total number of core genes from 31 to 33 and designating p33-ac93-odv-e25 as the third core gene cluster (13,27,33). The failure to identify ac93 and odv-e25 homologs in hymenopteran and dipteran baculoviruses by BLAST searches might simply be because they are too highly divergent to be identified by this technique (1,13,18,33).…”

Section: Discussionmentioning

confidence: 91%

“…Based on phylogenetic evidence, genomic composition, and morphological characteristics, the family Baculoviridae is divided into four genera: Alphabaculovirus (lepidopteran-specific NPVs), Betabaculovirus (lepidopteranspecific Granuloviruses), Gammabaculovirus (hymenopteranspecific NPVs), and Deltabaculovirus (dipteran-specific NPVs) (16). Despite the diversity in the genetic content present in different baculovirus genomes, a set of 31 genes present in all of the sequenced baculovirus genomes has been identified and assigned as the baculovirus core genes; p33 (ac92) is one of these genes (13,16,27,33). Ac92 is associated with both BV and ODV (4,7,30,32,44).…”

mentioning

confidence: 99%

Identification of Autographa californica Nucleopolyhedrovirus ac93 as a Core Gene and Its Requirement for Intranuclear Microvesicle Formation and Nuclear Egress of Nucleocapsids

Yuan

Huang

Wei

et al. 2011

Autographa californica nucleopolyhedrovirus (AcMNPV) orf93 (ac93) is a highly conserved uncharacterized gene that is found in all of the sequenced baculovirus genomes except for Culex nigripalpus NPV. In this report, using bioinformatics analyses, ac93 and odv-e25 (ac94) were identified as baculovirus core genes and thus p33-ac93-odv-e25 represent a cluster of core genes. To investigate the role of ac93 in the baculovirus life cycle, an ac93 knockout AcMNPV bacmid was constructed via homologous recombination in Escherichia coli. Fluorescence and light microscopy showed that the AcMNPV ac93 knockout did not spread by infection, and titration assays confirmed a defect in budded virus (BV) production. However, deletion of ac93 did not affect viral DNA replication. Electron microscopy indicated that ac93 was required for the egress of nucleocapsids from the nucleus and the formation of intranuclear microvesicles, which are precursor structures of occlusionderived virus (ODV) envelopes. Immunofluorescence analyses showed that Ac93 was concentrated toward the cytoplasmic membrane in the cytoplasm and in the nuclear ring zone in the nucleus. Western blot analyses showed that Ac93 was associated with both nucleocapsid and envelope fractions of BV, but only the nucleocapsid fraction of ODV. Our results suggest that ac93, although not previously recognized as a core gene, is one that plays an essential role in the formation of the ODV envelope and the egress of nucleocapsids from the nucleus.

“…Notably, the link between these two genes was also conserved in baculoviruses. To date, three core gene clusters whose relative positions are conserved in all of the sequenced baculovirus genomes have been identified (31)(32)(33). One of these contained a set of four genes, i.e., dnahel, pif-4, 38k, and lef-5.…”

Section: Resultsmentioning

confidence: 99%

Brown Planthopper Nudivirus DNA Integrated in Its Host Genome

Cheng

Lou

et al. 2014

The brown planthopper (BPH), Nilaparvata lugens (Hemiptera:Delphacidae), is one of the most destructive insect pests of rice crops in Asia. Nudivirus-like sequences were identified during the whole-genome sequencing of BPH. PCR examination showed that the virus sequences were present in all of the 22 BPH populations collected from East, Southeast, and South Asia. Thirty-two of the 33 nudivirus core genes were identified, including 20 homologues of baculovirus core genes. In addition, several gene clusters that were arranged collinearly with those of other nudiviruses were found in the partial virus genome. In a phylogenetic tree constructed using the supermatrix method, the original virus was grouped with other nudiviruses and was closely related to polydnavirus. Taken together, these data indicated that the virus sequences belong to a new member of the family Nudiviridae. More specifically, the virus sequences were integrated into the chromosome of its insect host during coevolution. This study is the first report of a large double-stranded circular DNA virus genome in a sap-sucking hemipteran insect. IMPORTANCEThis is the first report of a large double-stranded DNA virus integrated genome in the planthopper, a plant sap-sucking hemipteran insect. It is an exciting addition to the evolutionary story of bracoviruses (polydnaviruses), nudiviruses, and baculoviruses. The results on the virus sequences integrated in the chromosomes of its insect host also represent a story of successful coevolution of an invertebrate virus and a plant sap-sucking insect. Brown planthoppers (BPH) (Nilaparvata lugens) are insect herbivores that feed mainly on rice. They damage rice plants by sucking sap from the vascular bundle and by transmitting the rice ragged stunt virus (RRSV) and rice grassy stunt virus (RGSV) (1). In addition, three commensal viruses have been characterized in BPH, i.e., Nilaparvata lugens reovirus (NLRV) (2), himetobi P virus (HiPV), and Nilaparvata lugens commensal X virus (NLCXV) (3). Recently, an iflavirus found in the honeydews of BPH was reported as Nilaparvata lugens honeydew virus 1 (NLHV-1) (4). These viruses infect BPH without visible symptoms, raising the question of how the insect host copes with various foreign microbes.In our study on the whole genome sequence of BPH, sequences that likely belonged to a previously unknown virus were identified (5). Homology analysis indicated that the sequences came from an uncharacterized virus that was related to the family Nudiviridae. Nudiviruses (Latin nudi ϭ naked) are a highly diverse group of invertebrate viruses that have rod-shaped nucleocapsids and large, double-stranded DNA (dsDNA) genomes. They were once described as "nonoccluded baculoviruses" but were later excluded from the family Baculoviridae (6). These baculovirus-like particles have been reported in a wide range of host species of insects and other arthropods (7, 8); however, although related to baculoviruses, they form a distinct lineage.To date, only a few nudiviruses have been well ...