MAP-BASED CLONING OF A GENE SEQUENCE ENCODING A NUCLEOTIDE-BINDING DOMAIN AND A LEUCINE-RICH REGION AT THE CRE3 NEMATODE RESISTANCE LOCUS OF WHEAT

The Cre3 gene confers a high level of resistance to the root endoparas itic nematode Heterodera avenae in wheat. A DNA marker cosegregating w ith H. avenae resistance was used as an entry point for map-based clon ing of a disease resistance gene family at the Cre3 locus. Two related gene sequences have been analysed at the Cre3 locus. One, identified as a cDNA clone, encodes a polypeptide with a nucleotide binding site (NBS) and a leucine-rich region; this member of the disease resistance gene family is expressed in roots. A second Cre3 gene sequence, clone d as genomic DNA, appears to be a pseudogene, with a frame shift cause d by a deletion event. These two genes, related to members of the cyto plasmic NBS - leucine rich repeat class of plant disease resistance ge nes were physically mapped to the distal 0.06 fragment of the long arm of wheat chromosome 2D and cosegregated with nematode resistance.