Abstract
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.
Highlights
Baculoviruses are insect-specific large DNA viruses, which have important applications in the areas of insect pesticides, protein expression and gene therapy [1,2,3]
The data reveal that Spodoptera litura nucleopolyhedrovirus (SpltNPV) PIF3 only partially substituted the function of Helicoverpa armigera nucleopolyhedrovirus (HearNPV) PIF3. These results suggested that, the pifs are conserved in baculoviruses, substitution of individual HearNPV pifs with homologues from Autographa californica multiple nucleopolyhedrovirus (AcMNPV) or SpltNPV did not yield a virus with efficient oral infectivity, indicating the role of per os infectivity factors (PIFs) proteins in host specificity
We studied the host specificity of HearNPV p74, pif1, pif2 and pif3 by substituting with their counterparts from AcMNPV or SpltNPV
Summary
Baculoviruses are insect-specific large DNA viruses, which have important applications in the areas of insect pesticides, protein expression and gene therapy [1,2,3]. The PIF complex is likely to play an important role in virus entry into midgut epithelial cells of susceptible insect larvae [24]. Previous studies showed that P74, PIF1 and PIF2 are involved in the binding of ODV onto midgut cells [12, 26]. Bioassay results demonstrated that most recombinant viruses lost their oral infectivity completely, except SpltNPV pif substituted pif3-null HearNPV (vHaBacΔpif3-Sppif3-ph) which retained only partial oral infectivity. These results revealed the involvement of PIF proteins in host specificities of baculovirus
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