Characterisation of disease resistance gene-like sequences in Brassica oleracea L.

Several cloned disease resistance genes from a wide range of plant species are known to share conserved regions with similar structural motifs. Degene rate primers based on conserved sequences of the nucleotide binding site of the genes RPS2, N and L6 were used for polymerase chain reaction (PCR) amp lification from genomic DNA of two doubled haploid lines of Brassica olerac ea. Sequences of amplified products were highly variable, but most of them showed similarity to known disease resistance genes, including RPS5, RPS2 a nd N, and to disease resistance gene-like sequences (RGLs) from different s pecies. Primers based on B. oleracea sequences amplified five groups of RGL s. Products were mapped through cleaved amplified polymorphic sequence assa ys onto four different linkage groups of B. oleracea. PCR amplification fro m cDNA and allele analysis indicated that four locus-specific RGL fragments are expressed in cauliflower. Screening of a B, oleracea bacterial artific ial chromosome library (BAC) with four B. oleracea RGL probes identified a small number of clones, suggesting that the four RGLs may not be highly cop ied. Screening of a BAC library of A. thaliana with the same probes identif ied clones that mapped onto four different chromosomes. These map positions correspond to known disease resistance loci of A, thaliana.