Effective oral infection is set off by interaction of a group of conserved per os infectivity factors (PIFs) with larval midgut columnar epithelial cells. We constructed pseudotyped viruses by substituting pif1, pif2 or pif3 genes of Helicoverpa armigera nucleopolyhedrovirus (HearNPV) with their homologs from Mamestra bracissae multiple nucleopolyhedrovirus and tested their infectivity to tissue culture cells and to larvae. Transfection and infection assays revealed that all recombinant viruses generated infectious budded virus in both cell culture and in larvae. Electron microscopy showed synthesized occlusion body and occlusion derived virus (ODV) were morphologically indistinguishable from those of the parental virus. By contrast, feeding assays revealed that pseudotyped viruses could not rescue oral infectivity except for pif3 pseudotyped virus that only partially rescued oral infectivity but at a mortality rate much lower than that of the parental HearNPV. Consistent with the bioassay result, PIF complex was detected in ODVs of pif3 pseudotyped virus only but not in pif1 or pif2 pseudotyped viruses. Our results suggest that PIF complex is essential for oral infectivity, and in the formation of the PIF complex, PIF1, 2 are virus-specific while PIF3 does not appear to be as specific and can function in heterologous environment, albeit to a much more limited extent.
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This work was supported by grants from the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (grant No. QYZDJ-SSW-SMC021), the National Natural Science Foundation of China (grants No. 31621061 and 31130058), the Virology Key Frontier Science Program of State Key Laboratory of Virology (grant No. klv-2016-03), and the National Key R&D Program of China (2017YFD0200400). This research study was sponsored by CAS-TWAS President’s Fellowship for International PhD Students. We acknowledge the technical support and core facility of Wuhan institute of Virology for technical assistance.
ZHH and MLW designed the study; GAM performed most of the experiments; XW, HYZ, NZ and CC participated in the experiments; GAM, LJ, FD and HLW analyzed the data; GAM, ZHH and MLW wrote and finalized the manuscript. All authors read and approved the manuscript.
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Makalliwa, G.A., Wang, X., Zhang, H. et al. HearNPV Pseudotyped with PIF1, 2, and 3 from MabrNPV: Infectivity and Complex Stability. Virol. Sin. 33, 187–196 (2018). https://doi.org/10.1007/s12250-018-0014-5
- Oral infectivity
- per os infectivity factors (PIFs)
- PIF complex