Canadian Forest Service Publications

Characterization of the polydnaviral 'T. rostrale virus' (TrV) gene family: TrV1 expression inhibits in vitro cell proliferation. 2013. Djoumad, A.; Dallaire, F.; Lucarotti, C.J.; Cusson, M. J. Gen. Virol. 94:1134-1144.

Year: 2013

Issued by: Laurentian Forestry Centre

Catalog ID: 34664

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1099/vir.0.049817-0

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Tranosema rostrale ichnovirus (TrIV) is a polydnavirus (PDV) transmitted by the endoparasitic wasp T. rostrale to its host Choristoneura fumiferana during oviposition. PDV genes are expressed in infected caterpillars, causing physiological disturbances that promote the survival of the developing endoparasite. The previously sequenced genome of TrIV contains ~86 genes organized in multigene families and distributed on multiple segments of circular dsDNA. Among these, the 'T. rostrale virus' (TrV) family comprises seven genes that are absent in other PDV genomes examined to date and whose function(s) remain(s) unknown. Here, we initiated a functional analysis of the TrV family using qPCR, transfection and RNAi approaches. TrV family genes were weakly expressed in wasp ovaries, but some displayed high transcript abundance in parasitized caterpillars. Whilst TrV1 was the most highly transcribed TrV gene in infected caterpillars, transcript levels for TrV5 and TrV6 were nearly undetectable, indicating that they may be pseudogenes. Temporal and tissue-specific patterns of transcript abundance were similar for all expressed TrV family genes, indicative of an apparent lack of difference in function or tissue specificity. Infection of Cf-203 and Sf-21 insect cells with TrIV led to a dose-dependent inhibition of cell proliferation with no sign of apoptosis. Whilst similar inhibition was observed following transfection of cells with a cloned genome segment carrying the TrV1 gene, RNA interference targeting TrV1 largely restored cell growth in TrIV-infected cells, indicating that TrV1 expression was responsible for the observed inhibition. We suggest that TrV genes may contribute to host developmental disruption by interfering with host-cell proliferation during parasitism.

Plain Language Summary

Some wasps use their stinger to lay an egg under the skin of caterpillars. This egg contains a larva that will feed on the caterpillar’s inner tissues. Just before the end of its larval development, the wasp will leave its host and transform itself into an adult wasp. The parasitic life of the egg and larva exhibits a characteristic allowing them to bypass the host’s immune response. To help it in this process, the wasp has a powerful ally, a virus, which it transmits to the caterpillar when it lays its egg. In the caterpillar, the virus expresses genes that produce a reduced immune response by the host. This virus belongs to the polydnavirus group, which contains two subgroups: bracoviruses and ichnoviruses, which are associated with the Braconidae and Ichneumonidae wasp families, respectively. However, ichnoviruses do not form a homogenous group since two very distinct lines have been identified, but the characterization of one of these lines is based on the study of a single virus, the one transmitted by the Glypta fumiferanae wasp to the spruce budworm. As part of this study, we have isolated a second ichnovirus from this line, which is produced by the Apophua simplicipes wasp and transmitted to the obliquebanded leafroller. This study highlighted characteristics that are common in both viruses, thus demonstrating that the first description is likely representative of all viruses in this line.