DIRECT ISOLATION OF CDNA SEQUENCES FROM SPECIFIC CHROMOSOMAL REGIONS OF THE TOMATO GENOME BY THE DIFFERENTIAL DISPLAY TECHNIQUE

The differential display technique was originally developed for the is olation of differentially expressed genes from eukaryotic tissues. We have adapted this technique for the isolation of cDNA markers from spe cific regions of the tomato genome. For this purpose, differential dis play was performed on RNA extracted from leaf tissue of nearly isogeni c lines for the Tm-2a gene of tomato. On average, one out of 20 primer combinations resulted in a polymorphism at the cDNA level. When used as hybridization probes, all of these cDNA fragments were single or lo w copy and all of them were polymorphic on Southern hybridizations usi ng DNA from the isogenic lines. Genetic mapping revealed in each case at least one locus in the introgressed segment on chromosome 9 of toma to. Thus, this technique might provide a way for the direct isolation of transcribed sequences from specific regions of any animal or plant genome for which such lines exist.