MAP POSITIONS OF 47 ARABIDOPSIS SEQUENCES WITH SEQUENCE SIMILARITY TODISEASE RESISTANCE GENES

Map positions have been determined for 42 non-redundant Arabidopsis ex pressed sequence tags (ESTs) showing similarity to disease resistance genes (R-ESTs), and for three Pto-like sequences that were amplified w ith degenerate primers. Employing a PCR-based strategy, yeast artifici al chromosome (YAC) clones containing the EST sequences were identifie d. Since many YACs have been mapped, the locations of the R-ESTs could be inferred from the map positions of the YACs. R-EST clones that exh ibited ambiguous map positions were mapped as either cleavable amplifi able polymorphic sequence (CAPS) or restriction fragment length polymo rphism (RFLP) markers using F-8 (Ler x Col-0) recombinant inbred (RI) lines. In all cases but two, the R-ESTs and Pto-like sequences mapped to single, unique locations. One R-EST and one Pto-like sequence each mapped to two locations. Thus, a total of 47 loci were identified in t his study. Several R-ESTs occur in clusters suggesting that they may h ave arisen via gene duplication events. Interestingly, several R-ESTs map to regions containing genetically defined disease resistance genes . Thus, this collection of mapped R-ESTs may expedite the isolation of disease resistance genes. As the cDNA sequencing projects have identi fied an estimated 63% of Arabidopsis genes, a very large number of R-E STs (similar to 95), and by inference disease resistance genes of the leucine-rich repeat-class probably occur in the Arabidopsis genome.