The genome of the vast majority of plant viruses consists of RNA. This genome encodes one or more proteins that act as subunits of an enzyme complex, the "RNA-dependent RNA-polymerase" (RdRp) or "replicase, that is responsible for the replication of the viral RNA. Available evidence indicates that, in addition to viral proteins, these replicases also contain subunits encoded by the plant genome. Despite 25 years of research, the composition of a viral replicase or the function of host proteins in the enzyme complex is not known for any plant (or animal) RNA virus. Sequence similarities between viral replicase proteins indicate an evolutionary relationship between the enzymes of different viruses and suggest that different viruses make use of similar host proteins to replicate their RNA genome.
The first objective of this proposal is to identify the host subunits in the replicases of three plant viruses, representing the two major superfamilies of plant viruses. The interaction between virus and host proteins will be studied by a number of novel techniques including the yeast two-hybrid system, novel reporter genes and protein tags that permit the purification of replicases by affinity column chromatography. In addition, hoSt proteins interacting specifically with viral RNAs will be identified by a newly developed technique for screening cDNA libraries. The proposal will focus the research of leading experts in the respective fields from four European countries (NL, GB, ES, GR) on common virus/plant interactions.
Identification of host proteins involved in the synthesis of viral RNA will represent a major break-through in understanding the replication mechanism of RNA viruses and will offer targets for the engineering of plants with a broad resistance to virus infection. Transformation of plants with these (mutant) host genes will complement current strategies to obtain plants with a highly specific virus-resistance by transformation of plants with viral sequences.
In addition to replicases induced by virus infection, plants contain an RdRp activity that is detectable in non-infected plants. The host RdRp appears to be associated with a RNase activity and is believed to play a role in the phenomenon of RNA-mediated resistance of plants to viruses. This resistance is based on the activation of a host activity that specifically degrades transgenic viral RNA and homologous genomic RNA of an infecting virus, and may resemble the phenomenon of co-suppression of host gene expression.
The second objective of this proposal is to identify plant genes encoding components of the host RdRp/RNase complex or other factors involved in RNA-mediated resistance to virus infection. Identification of these genes by transposon tagging will shed light on the function of the host RdRp in noninfected plants and will increase the efficacy of strategies to engineer RNA-mediated resistance to virus infection in plants.
The results accruing from both objectives will be promoted where appropriate by the commercial partner in this proposal. The benefits of this proposal include increased crop yield and quality, and a reduction of the use of pesticides that are currently being applied to control the vectors that transmit viruses from plant to plant.
Funding SchemeCSC - Cost-sharing contracts
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