Targeted mapping of rye chromatin in wheat by representational difference analysis.

A targeted mapping strategy using representational difference analysis (RDA) was employed to isolate new restriction fragment length polymorphism probes for the long arm of chromosome 6 in rye (6RL), which carries a gene for resistance to Hessian fly larvae. Fragments from the 6RL arm were specifically isolated using a 'Chinese Spring' (CS) wheat - rye ditelosomic addition line (CSDT6RL) as tester, and CS and (or) CS4R as the driver for the genomic subtraction. Three RDA experiments were performed using BamHI amplicons, two of which were successful in producing low-copy clones. All low-copy clones were confirmed to have originated from 6RL, indicating substantial enrichment for target sequences. Two mapping populations, both of which are derived from a cross between two similar wheat-rye translocation lines, were used to map five RDA probes as well as five wheat probes. One of the populations was prescreened for recombinants by C-banding analysis. Fifteen loci, including seven new RDA markers, were placed on a map of the distal half of 6RL. The Hessian fly resistance gene was localized by mapping and C-banding analysis to approximately the terminal 1% of the arm. The utility of RDA as a method of targeted mapping in cereals and prospects for map-based cloning of the resistance gene are discussed.