Arabidopsis thaliana: A source of candidate disease-resistance genes for Brassica napus

Common structural and amino acid motifs among cloned plant disease-resistan ce genes (R genes), have made it possible to identify putative disease-resi stance sequences based on DNA sequence identity. Mapping of such R-gene hom ologues will identify candidate disease-resistance loci to expedite map-bas ed cloning strategies in complex crop genomes. Arabidopsis thaliana express ed sequence tags (ESTs) with homology to cloned plant R genes (R-ESTs), wer e mapped in both A. thaliana and Brassica napus to identify candidate R-gen e loci and investigate intergenomic collinearity. Brassica R-gene homologou s sequences were also mapped in B. napus. In total, 103 R-EST loci and 36 B rassica R-gene homologous loci were positioned on the N-fo-61-9 B. napus ge netic map, and 48 R-EST loci positioned on the Columbia x Landsberg A. thal iana map. The mapped loci identified collinear regions between Arabidopsis and Brassica which had been observed in previous comparative mapping studie s; the detection of syntenic genomic regions indicated that there was no ap parent rapid divergence of the identified genomic regions housing the R-EST loci.