Characterise the expression of an inhibitor of virus replication and determine its role in resistance to viruses.
Identify the mechanism by which CMV neutralises a resistance specific to TMV.
Determine the role of the RNA-dependent RNA polymerase in the above resistance responses.
Characterise the mechanism of replicase-mediated resistance to PVY.
Establish whether the use of the CaMV 35S promoter poses risks to the environment.
Examine the role of the CMV 2b protein in recombination, movement and disease.
Map functional domains on the PLRV capsid protein and read-through protein involved in particle assembly, movement and transmission.
Satellite RNA and pathogenicty This work delineated the sequences of the satellite RNAs of cucumber mosaic virus (CMV) that were responsible for elicitation of necrosis in tomato and those sequences that controlled chlorosis in tobacco as well as (white vs. yellow) chlorosis in tomato. The necrosis was shown to involve a small structural domain in the satellite RNA, while chlorosis depended on interactions between the CMV helper virus and the satellite RNA.
Molecular and cellular biology of cucumber mosaic virus (CMV) The complete genome sequence and organisation of a subgroup I strain of CMV was determined and the first biologically active cDNA clones of CMV were generated. Sequence domains were identified involved in host range, pathogenicity, virus movement, and replication of satellite RNAs. The subcellular distribution of all five CMV-encoded proteins was determined. The major viral movement protein was characterised and various properties of these proteins were identified, including separate roles in movement between different cell types. The separate roles for the capsid protein in cell to cell and long distance movement of the genomic and defective CMV RNAs were described. The role of the 2b gene in virus movement and synergy with potyviruses was characterised.
Molecular biology of tobacco mosaic virus (TMV)
The sequence relationships of various tobamoviruses were established by hybridisation technology prior to the availability of their sequences, with the latter confirming the former relationships. TMV was shown to consist of a population of sequences, some very closely related to the master sequence, but others showing considerable differences and were carried along with the dominant master strain. A fifth gene in TMV was identified, based initially on the presence of a novel dsRNA corresponding to a ssRNA also found on polyribosomes. The encoded protein was a redundant part of the virus replicase, but since the protein has not been found in vivo, its existence and role are still controversial. This is also the case for a sixth TMV gene, encoding a small 4-5 kDa protein, which was characterised genetically and shown to be involved in pathogenicity in some hosts and was associated with plasmodesmata and nuclei.
Resistance and resistance breakage Pathogen-derived resistance to CMV was established using sequences from either of the two viral-encoded replication proteins. The mechanism of resistance was characterised and shown not to be due to RNA silencing. The expression of CMV RNA 1 also was shown to neutralize a basal resistance mechanism operating against TMV-derived virus vectors in N gene tobacco. This novel resistance was identified to operate at temperatures permissive for infection of N gene tobacco by wild type TMV. The natural resistance of cowpeas to most strains of CMV was shown to be due to an inhibition response that could be separated from the hypersensitive response and the viral sequences important for breaking of the restriction response and elicitation of the apoptotic response were identified.
Dietrich, C., Miller, J., McKenzie, G., Palkovics, L., Balazs, E., Palukaitis, P. and Maiss, E. 2007. No recombination detected in artificial potyvirus mixed infections and between potyvirus derived transgenes and heterologous challenging potyviruses. Environmental Biosafety Research 6, 207-218.
Chung, B.-N., Canto, T. and Palukaitis, P. 2007. Stability of recombinant plant viruses containing genes of unrelated plant viruses. Journal of General Virology 88, 1347-1355.
Lewsey, M., Robertson, F.C., Canto, T, Palukaitis, P. and Carr, J.P. 2007. Selective targeting of miRNA-regulated plant development by a viral counter-silencing protein. The Plant Journal50, 240-252.
Kaplan, I.B., Lee, L., Ripoll, D.R., Palukaitis, P., Gildow, F. and Gray, S.M. 2007. Point mutations in the potato leafroll virus major capsid protein alter virion stability and aphid transmission. Journal of General Virology88, 1821-1830.
Shams-Bakhsh, M., Canto, T. and Palukaitis. P. 2007. Enhanced resistance and neutralization of defense responses by suppressors of RNA silencing. Virus Research 130, 103-109.
Choi, S.K., Palukaitis, P., Min, B.E., Lee, M.Y., Choi, J.K. and Ryu, K.H. 2005. Cucumber mosaic virus 2a polymerase and 3a movement proteins independently affect both virus movement and the timing of symptom development in zucchini squash. Journal of General Virology86, 1213-1222.
Canto, T. and Palukaitis, P. 2005. Subcellular distribution of mutant movement proteins of Cucumber mosaic virus fused to green fluorescent proteins. Journal of General Virology86, 1223-1228.
Shi, B-J., Palukaitis, P. and Symons, R.H. 2005. The conserved 5' termini of RNAs 1 and 2 of Tomato aspermy virus are dispensable for infection but affect virulence. Virus Genes 30, 181-191.
Lee, L., Kaplan, I.B., Ripoll, D.R., Liang, D., Palukaitis, P. and Gray, S.M. 2005. A surface loop of the potato leafroll virus coat protein is involved in virion assembly, systemic movement, and aphid transmission. Journal of Virology 79, 1207-1214.
Kaplan, I.B., Lee, K-C., Canto, T., Wong, S-M. and Palukaitis, P. 2004. Host-specific encapsidation of a defective RNA 3 of Cucumber mosaic virus. Journal of General Virology 85, 3757-3763.
Canto. T., MacFarlane, S.A. and Palukaitis, P. 2004. ORF6 of Tobacco mosaic virus is a determinant of viral pathogenicity in Nicotiana benthamiana. Journal of General Virology 85, 3123-3133.
Wang, Y., Tzfira, T., Gaba, V., Citovsky, V., Palukaitis, P. and Gal-On, A. 2004. Functional analysis of the Cucumber mosaic virus 2b protein: pathogenicity and nuclear localization. Journal of General Virology 85, 3135-3147.
Andreev, I.A., Kim, S.H., Kalinina, N.O., Rakitina, D.V., Fitzgerald, A.G., Palukaitis, P. and Taliansky, M.E. 2004. Molecular interactions between a plant virus movement protein and RNA: force spectroscopy investigation. Journal of Molecular Biology 339, 1041-1047.
Liang, D., Gray, S.M., Kaplan, I. and Palukaitis, P. 2004. Site-directed mutagenesis and generation of chimeric viruses by homologous recombination in yeast to facilitate analysis of plant-virus interactions. Molecular Plant-Microbe Interactions 17, 571-576.