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Baculoviruses are large dsDNA viruses that are virulent pathogens of certain insect species. In a natural host, Trichoplusia ni, infection by the model baculovirus Autographa californica Multiple Nucleopolyhedrovirus (AcMNPV) begins when the occluded form of the virus disassembles in the midgut and virions infect midgut epithelial cells to establish the primary phase of the infection. To better understand the primary phase of the AcMNPV infection cycle, newly molted 5 th instar T. ni larvae were orally infected with AcMNPV occlusion bodies and transcriptional responses of the T. ni midgut were analyzed at various times from 0-72 hours post infection, using RNA-Seq analysis and a T. ni reference genome. The numbers of differentially expressed host genes increased as the infection progressed, and we identified a total of 3,372 differentially expressed T. ni transcripts in the AcMNPV-infected midgut. Genes encoding orthologs of HMG176, atlastin, and CPH43 were among the most dramatically upregulated in response to AcMNPV infection. A number of cytochrome P450 genes were downregulated in response to infection. We also identified the effects of AcMNPV infection on a large variety of genes associated with innate immunity. This analysis provides an abundance of new and detailed information on host responses to baculovirus infection during the primary phase of the infection in the midgut, and will be important for understanding how baculoviruses establish productive infections in the organism. IMPORTANCE Baculoviruses are virulent pathogens of a number of important insect pest species. In the host Trichoplusia ni , infection begins in the midgut when infectious virions of the occulsion derived virus (ODV) phenotype enter and subsequently replicate in cells of the midgut epithelium. A second virion phenotype (budded virus or BV) is produced there and BV mediates systemic infection of the animal. Most prior detailed studies of baculovirus infections have focused on BV infections of cultured cells. In this study, we examined the transcriptional responses of the T. ni midgut to infection by ODV of the baculovirus AcMNPV, and identified a variety of host genes that respond dramatically to viral infection. Understanding transcriptional responses of the host midgut to viral infection is critically important for understanding the biphasic infection in the animal as a whole.
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Host permissiveness to baculovirus influences time‐dependent immune responses and fitness costs
Abstract Insects possess specific immune responses to protect themselves from different types of pathogens. Activation of immune cascades can inflict significant developmental costs on the surviving host. To characterize infection kinetics in a surviving host that experiences baculovirus inoculation, it is crucial to determine the timing of immune responses. Here, we investigated time‐dependent immune responses and developmental costs elicited by inoculations from each of two wild‐type baculoviruses,Autographa californicamultiple nucleopolyhedrovirus (AcMNPV) andHelicoverpa zeasingle nucleopolyhedrovirus (HzSNPV), in their common hostH. zea. AsH. zeais a semi‐permissive host of AcMNPV and fully permissive to HzSNPV, we hypothesized there are differential immune responses and fitness costs associated with resisting infection by each virus species. Newly molted 4th‐instar larvae that were inoculated with a low dose (LD15) of either virus showed significantly higher hemolymph FAD‐glucose dehydrogenase (GLD) activities compared to the corresponding control larvae. Hemolymph phenoloxidase (PO) activity, protein concentration and total hemocyte numbers were not increased, but instead were lower than in control larvae at some time points post‐inoculation. Larvae that survived either virus inoculation exhibited reduced pupal weight; survivors inoculated with AcMNPV grew slower than the control larvae, while survivors of HzSNPV pupated earlier than control larvae. Our results highlight the complexity of immune responses and fitness costs associated with combating different baculoviruses.
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- Award ID(s):
- 1645548
- PAR ID:
- 10361123
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Insect Science
- Volume:
- 28
- Issue:
- 1
- ISSN:
- 1672-9609
- Page Range / eLocation ID:
- p. 103-114
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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