The broad-spectrum tospovirus resistance gene Sw-5 of tomato is a homolog of the root-knot nematode resistance gene Mi

We used a positional cloning approach to isolate the Sw-5 disease resistanc e locus of tomato. Complementation experiments with overlapping cosmid clon es enabled us to demonstrate that Sw-5 is a single gene locus capable of re cognizing several tospovirus isolates and species. Analysis of the predicte d Sw-5 protein suggests that it is a cytoplasmic protein, with a potential nucleotide binding site (NBS) domain and a C-terminal end consisting of leu cine-rich repeats (LRRs), Based on its structural features, Sw-5 belongs to the class of NBS-LRR resistance genes that includes the tomato Mi, 12, and Prf genes; the Arabidopsis RPM1 gene; and the plant potato virus X resista nce gene Rr. The overall similarity between the Sw-5 and Mi proteins of tom ato suggests that a shared or comparable signal transduction pathway leads to both virus and nematode resistance in tomato. The similarity also suppor ts the hypothesis that Sw-5 provides resistance via a hypersensitive respon se. Sw-5 is a member of a loosely clustered gene family in the telomeric re gion of chromosome 9. Members of this family map to other regions of chromo some 9 and also to chromosome 12, where several fungal, virus, and nematode genes have been mapped, suggesting that paralogs of Sw-5 may have evolved to provide different resistance specificities.