Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 24, 2002
Publication Date: N/A
Interpretive Summary: Barley yellow dwarf viruses (BYDVs) cause the most damaging virus disease of cereal crops. The viruses are spread from infected to healthy plants by aphids. Previous experiments have shown that insecticides can reduce the incidence of BYDV infection in oat and wheat fields by limiting spread of the viruses from initially infected plants. The aphids that transmit BYDVs also can be infected with viruses that reduce their longevity and fecundity. One of these insect viruses, Rhopalosiphum padi virus (RhPV), infects the aphid species that are the most common vectors of BYDVs in the central United States. RhPV infects a relatively narrow range of insects, which makes it suitable for use as a biological control agent that could replace chemical insecticides for controlling aphids in cereal crops. As a first step towards developing biological insecticides based on RhPV, we have determined how RhPV expresses the proteins that package and protect its small chromosome. The results of these experiments showed that RhPV employs a very unusual strategy to express its genes. This information will be useful to other scientists who are interested in developing virus-based insecticides and others who are studying basic mechanisms of gene expression. These experiments may allow researchers to design modified viral chromosomes that could be used as highly targeted biological insecticides.
Technical Abstract: The RNA genome of Rhopalosiphum padi virus (RhPV), like other members of the Dicistroviridae, contains two open reading frames that are preceded by internal ribosome entry sites (IRESs). To compare the activities of the two RhPV IRESs in insect cells, a system was established for the in vivo transcription and translation of plasmid templates containing the IRESs. In this system, the two RhPV IRESs directed initiation of translation from bicistronic plasmids with equal efficiency. Competition was observed between the two IRESs when they were in cis in a bicistronic plasmid. A mutation that disrupted the 3'-proximal pseudoknot of the intergenic IRES reduced translation initiation in vivo. Similarly, mutations in the RhPV IG-IRES disrupted its ability to bind 80S particles in vitro. The two IRESs preferentially labeled proteins of different masses in UV-cross-linking experiments illustrating the different translation initiation mechanisms employed by the two elements.