Virus resistance in plants, like that to other pathogens, is often conferred by major dominant genes and can be described in tenns of gene for gene interactions between the host and the pathogen.
Several genes have been identifled in Solanum species that confer resistance to potato virus X (PVX) . These include Nb and Nx, which confer hypersensitive response (HR) against group 2 and group 3 strains of PVX, respectively, and the Rx genes, which confer extreme resistance to most strains of PVX.
The aim of this project is the cloning of the ND gene in order to study the molecular mechanism of natural resistance conferred by virus-host interaction and the processes activated in the resistant plant that lead to suppression of virus accumulation.
An analysis of Nb resistance will be undertaken using a PVX group 2 strain and the Nb cultivar Pentland Ivory (genotype Nb nb nb nb). Nb is a single dominant gene, which has recently been mapped to chromosome V in potato, in a region where there is also another virus resistance gene (Ex2) and a Plytophtora infestans resistance gene.
In order to obtain a high resolution genetic map around Nb, more than 2000 segregating progeny of a resistant self cross will be screened with flanking markers Plants with recombination events close to NB will be identified and the relationship between genetic and physical distance will be established. These recombinants will be used to order further markers generated by amplified fragment length polymorphism (AFLP) and/or bacterial artificial chromosome (BAC)-walking strategies. Finally, a large genomic library from cv Pentland Ivory will be screened to identify clones carrying the targeted gene. The identity of tile Nb gene will be confirmed by complementation in transgenic plants.