Molecular analysis of a complex resistance locus in the common bean, Phaseolus vulgaris L.

The imperfect fungus Colletotrichum lindemuthianum is the causal agent of the anthracnose disease of the common bean, Phaseolus vulgaris L. Studies on the inheritance of resistance to this pathogen led to the definition of several major genes for resistance in the plant. Recombinant inbred lines (RILs), issued from a cross between extremely polymorphic parents representating the two major gene pools, BAT93 (Mesoamerican) and Jalo EEP558 (Andean), were used to map anthracnose resistance genes. A complex locus containing several clustered resistance genes, from either Andean or Mesoamerican origin, was identified on the B14 linkage group. Degenerate oligonucleotide primers, deduced from conserved domains of the Nucleotide Binding Site (NBS) regions of the two Arabidopsis RPM1, RPS2 and the tobacco N disease resistance genes were used to amplify related sequences in common bean. The sequencing of the PCR products obtained from BAT93 and Jalo EEP558 genotypes indicated that at least 3 subfamilies of sequences, containing the different NBS domains conserved among RPS2, RPM1 and N resistance genes, coexist in these genotypes. They correspond to low- or moderately low-copy number sequences, as expected for resistance genes. One of these subfamilies of NBS-containing sequences was located within the clustered resistance genes previously identified in the linkage group B14. The NBS-containing sequences are, now, used to screen both genomic and cDNA libraries. The candidate resistance genes will be sequenced and used in transformation experiments in order to confirm their function and to identify their specificity. (Texte intégral)