Expression, mapping, and genetic variability of Brassica napus disease resistance gene analogues

Numerous sequences analogous to resistance (R) genes exist in plant genomes and could be involved in resistance traits. The aim of this study was to i dentify a large number of Brassica napus sequences related to R genes and a lso to test the adequacy of specific PCR-based tools for studying them. Dif ferent consensus primers were compared for their efficiency in amplifying r esistance-gene analogues (RGAs) related to the nucleotide-binding-site subg roup of R genes. Specific primers were subsequently designed to fine-study the different RGAs and we tested their efficiency in three species related to B. napus: Brassica oleracea, Brassica rapa, and Arabidopsis thaliana. Fo rty-four B. napus RGAs were identified. Among 29 examined, at least one-thi rd were expressed. Eighteen RGAs were mapped on 10 of the 19 B. napus linka ge groups. The high variability within these sequences permitted discrimina tion of each genotype within a B. napus collection. The RGA-specific primer s amplified RGAs in the B. oleracea and B. rapa genomes, but the sequences appear to be poorly conserved in A. thaliana. Specific RGA primers are a pr ecise tool for studying known-sequence RGAs. These sequences represent inte resting markers that could be correlated with resistance traits in B. napus or related Brassica genomes.