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Host Response to Baculovirus infection in Helicoverpa armigera

Final Activity Report Summary - REBACHA (Host Response to Baculovirus infection in Helicoverpa armigera)

Baculoviruses are large DNA viruses infecting invertebrates, mainly insects from the orders Lepidoptera, Hymenoptera and Diptera. They are used to control insect pests replacing chemical insecticides. The main limitations of baculovirus wide use are a long time they need to stop the larvae feeding as well as their high specificity towards insect species. Much research effort have been undertaken to overcome these limitations. Introducing in baculovirus genome foreign genes coding for toxins, hormones or enzymes is one of the strategies used to improve their characteristics as bioinsecticide. In the present project we aimed to identify host genes involved in the response to baculovirus infection and explored the possibility of employing these genes to improve baculovirus infectivity.

Among the genes regulated after baculovirus (HearNPV) infection in Helicoverpa armigera larvae we identified a midgut protein, HaCDA5a that showed a homology to chitin deacetylase-like protein. HaCDA5a was shown to strongly bind chitin as well as to increase peritrophic membrane (PM) permeability. Bioassays showed that administered orally NPV expressing HaCDA5a is more virulent that the virus non-expressing this protein however there was no change in virulence when both viruses were injected intrahemocoelically. These findings showed that HaCDA5a most likely acts on PM while the virus enters the midgut and revealed the possibility of baculovirus improvement by expression of the host genes.

Another gene that was identified to be involved in the midgut response to baculovirus infection was cellular repressor of E1A stimulated genes (creg). Up to date no CREG-like proteins have been characterized from insects. H. armigera creg showed around 30% similarity to human creg and around 70% similarity to other lepidopteran cregs. Its up-regulation due to baculovirus infection has been shown by means of real-time RT-PCR in H. armigera larvae and H. armigera derived cells, HzAM1 and HzGUT. A virus was constructed expressing Ha-creg. Bioassays showed as expected that creg-expressing virus caused lower mortality in larvae when compared to mortality of the virus non-expressing this protein. We expect that up-regulation of creg in larvae infected with the virus may form a part of response to the infection by inhibiting cell growth and hence diminishing virus replication. Its silencing by RNA interference is planned.

Obtained results add to the general knowledge of host genes involved in the insect response to the pathogens as well as reveal that this knowledge can successfully be employed for improving virus characteristics for use in biocontrol.