Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2004
Publication Date: 6/15/2004
Citation: Lapointe, R., Popham, H.J., Straschil, U., Goulding, D., O'Reilly, D.R., Olszewski, J.A. 2004. Characterization of two autographa californica nucleopolyhedrovirus proteins, ac145 and ac150, which affect oral infectivity in a host dependent manner. Journal of Virology. 78:6439-6448. Interpretive Summary: Insect baculoviruses are useful for the control of pest insects in place of pesticides. Understanding how these viruses infect insects and how to use this understanding to expand their host range are important for their commercialization. One baculovirus that infects many different species of pest caterpillars was found to have two genes in it that were similar to a gene found in a different family of insect viruses called entomopoxviruses. The location and function of the proteins produced from these two genes within the virus was studied in the old world cotton bollworm baculovirus. Removal of these genes from the virus caused the resulting virus to greatly lose potency against the budworm but only slightly lowered the potency against the cabbage looper. This work will benefit scientists working in the field of baculoviruses. The identification of two new genes involved in the infection of a baculovirus allows us to identify which genes are necessary for infection in different species of insects and will eventually allow us to tailor a virus for the control of specific target pests.
Technical Abstract: The genome of the baculovirus AcMNPV contains two homologues, orf145 and orf150, of the Heliothis armigera Entomopoxvirus (HaEPV) 11K gene. Polyclonal antibodies raised against the Ac145 or Ac150 proteins were utilised to demonstrate that they are expressed from late to very late times of infection and are within the nucleus of infected Sf-21 cells. Transmission electron microscopy coupled with immunogold labeling of Ac145 found this protein within the nucleus in areas of nucleocapsid assembly and maturation, along with some association with the enveloped bundles of virions within the developing occlusion bodies (OBs). Ac150 was found to be mainly associated with enveloped bundles of virions within OBs, and also with those not yet occluded. Both Ac145 and Ac150 were found to be present in BV as well as OBs. Both orf145 and orf150 were deleted from the AcMNPV genome, singly or together, and these deletion mutants were assessed for oral infectivity both in Trichoplusia ni and Heliothis virescens larvae. The deletion of either gene individually led to either a small or non-significant drop in infectivity, compared to wild-type AcMNPV infection of each host. However, deletion of both genes gave a recombinant virus with a moderate (T. ni; 6.8-fold) to drastic (H. virescens; 43-fold) reduction in infectivity compared to wt virus. Intrahaemocoelic injection of BV from the double-deletion virus into H. virescens larvae is as infectious to this host as wt BV, indicating that Ac145 and Ac150 play a role in primary oral infection of AcMNPV, the extent of which is host-dependent.