Sh. Brommonschenkel et al., The broad-spectrum tospovirus resistance gene Sw-5 of tomato is a homolog of the root-knot nematode resistance gene Mi, MOL PL MICR, 13(10), 2000, pp. 1130-1138
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.