IDENTIFICATION OF R-GENE HOMOLOGOUS DNA FRAGMENTS GENETICALLY LINKED TO DISEASE RESISTANCE LOCI IN ARABIDOPSIS-THALIANA

Disease resistance in plants is a desirable economic trait. A number o f disease resistance genes from various plant species have been cloned so far. The gene products of some of these can be distinguished by th e presence of an N-terminal nucleotide binding site and a C-terminal s tretch of leucine-rich repeats. Although these gene products are struc turally related, the DNA sequences are poorly conserved. Only parts of the nucleotide binding site share enough DNA identity to design prime rs for polymerase chain reaction amplification of related DNA sequence s. Such primers were used to amplify different resistance-gene-like (R GL) DNA fragments from Arabidopsis thaliana accessions Landsberg erect a and Columbia. Almost all cloned DNA fragments were genetically close ly linked with known disease resistance loci. Most RGL fragments were found in a clustered or dispersed multi-copy sequence organization, su pporting the supposed correlation of RGL sequences and disease resista nce loci.