Testing novel anti-viral strategies in plants

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ssRNA viruses are major pathogens infecting plants and cause severe reductions in crop yields. Viruses are thus a significant threat to efforts to expand and secure the world's food supply. In addition, viruses and virus-like particles (VLPs) are important as potential chimeric vaccines, e.g. against cancer, and as nanoscale containers in applications such as diagnostic imaging and targeted drug delivery. A number of these applications involve VLPs produced in plants - Molecular Pharming. This proposal sets out to test directly a novel anti-viral strategy in plants exploiting fundamental insights into the mechanisms of virus assembly and disassembly. The new concept arises due to our realization that assembly in many ssRNA viruses is mediated by packaging signal (PS)-coat protein interactions. The PSs are regions of the cognate genomes that both bind sequence-specifically to coat proteins and thereby improve the yield, rate and/or fidelity of assembly. These ideas are revising the paradigm in the field which assumes there is no selectivity of genome encapsidation. In addition a second approach towards the same goal arises due to the growing recognition that such viruses extrude their genomes as linear molecules from their capsids as one of the earliest steps in infection. We have shown that for at least some of these viruses their protein containers are not truly icosahedral, a unique site being created associated with minor structural proteins and one end of the genomic RNA. Clearly disrupting the formation of such unique sites would have seriously deleterious effects on infection. We are proposing to identify vital RNA sequences/motifs within a few test plant viruses that are involved in PS-mediated assembly and early RNA uncoating. These RNA fragments will be co-expressed in plants during viral infection and the consequences for viral titre assayed. Reductions in viral titre will be direct proof of our hypotheses and open novel anti-viral opportunities.

Pathways to impact: RNA viruses are major threats to human & animal health, as well as to crop yields. For example, Foot and Mouth Disease Virus (FMDV) has recently been the cause of substantial economic damage to UK farming and exports. Novel ways to control such pathogens are therefore urgently required. Our goal here is to demonstrate that the viral genomic RNAs are viable drug targets because of their vital cooperative roles in assembly and disassembly, and that small molecules can be used to inhibit such processes. We will also establish a medium throughput screening assay for such compounds. Obtaining direct support from UK BigPharma is currently difficult because most of them have moved their anti-viral programmes abroad. One benefit of the work proposed will be to demonstrate that the basic innovative science that can improve such applied programmes is actively being developed in the UK. The work proposed is very timely since the Universities of York Helsinki & Leeds have just filed a patent on the potential utility of interfering with the PS-CP interactions that form the core of the new approach. Work carried out under the auspices of this grant during Year 1 will therefore be part of the exemplification of these claims. It is vital to establish that the PS-mediated assembly mechanism is functional in vivo and the best way to achieve this is in plants. This has an immediate potential practical value, and one of us (GL, BBSRC Innovator of the Year, 2012) is perfectly placed to publicise our work to industry.

Advance in knowledge base: Our recent discoveries highlight the importance of understanding the roles of viral RNA genomes in assembly and disassembly. The PS-mediated mechanism and the realisation that "icosahedral" virus capsids are not completely symmetrical are at the cutting edge of basic structural virology. They potential transform our ability to interfere with conserved and vital aspects of these viral lifecycles and have obvious potential application.

Benefit to other disciplines: The outcomes of the experiments planned here will be of widespread benefit for virologists working on the molecular mechanism of viral infection and assembly in the field of ssRNA viruses.

Dissemination of results: Our work will be published in appropriate international journals and presented at the international meetings for which travel funds are sought. Targeted discussions with industry will also be held at appropriate points during the grant period, i.e. especially during Year 3 when the results from plant infections will become known.

Social and economic impact: Many important scientific advances are only found to be useful many years after the original discovery. The work here proposes to test the inferences from novel insights into fundamental biological processes. It is both required to confirm that such mechanisms are operating in vivo and to demonstrate that there could be direct benefits in the medium term for improved novel anti-viral strategies.