Scottish Crop Research Institute, Dundee, DD2 5DA, UK.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
Resistance to Tobacco mosaic virus (TMV) mediated by the tobacco N gene involves a cell death response, as well as a distinct inhibition response. The latter prevents the spread of further infection by virus located outside the dead tissues via several pathways, two of which are activated by salicylic acid (SA) and two of which are SA-independent. The SA-dependent responses involve the stimulation of the host RNA-dependent RNA polymerase 1 (RdRp-1) and a separate pathway involving alternative oxidase. The SA-independent responses involve the induction of an inhibitor of virus replication (IVR), as well as the transcription factor ERF5, which was shown to be involved in reducing local infection by TMV and preventing systemic infection. The SA-dependent response is known to induce systemic acquired resistance (SAR). Inhibition of expression of either RdRp-1 or IVR by RNAi in N gene tobacco did not significantly affect resistance to TMVmovement in the inoculated leaves, but did permit limited systemic infection, similar to plants in which SA accumulation had been compromised by transgenic expression of a bacterial salicylate hydroxylase gene. By contrast, SA-induced SAR against infection by TMV was compromised in the RNAi transgenic lines inhibiting expression of either RdRp-1 or IVR. An SA-independent response could be neutralised by the expression of the cucumber mosaic virus 1a protein, which was found to bind to ERF5. The relationship between these various resistance responses inhibiting infection by TMV and the effects of virus infection on the expression of various defence-related plant genes will be presented.
