Comparative analysis of polymorphism and chromosomal location of tomato microsatellite markers isolated from different sources

Previously isolated tomato (Lycopersicon esculentum) microsatellite markers were mainly clustered in the centromeric heterochromatin and not located in euchromatic regions. To achieve a more-uniform distribution of microsatellite markers for genome mapping purposes, a set of tomato microsatellite markers containing dinucleotide simple sequence repeats were developed by screening genomic libraries enriched for single-copy sequences, and screening the tomato EST database. The tomato microsatellites isolated in these ways were characterized by combinations of different types of repeated motifs and they were polymorphic in a set of L. esculentum varieties detecting up to four alleles. A total of 20 markers were placed on the genetic map of tomato. Interestingly, all markers isolated from genomic libraries enriched for single-copy sequences by PstI-pre-digestion mapped into the centromeric regions. The majority of markers derived from EST sequences contained predominantly AT microsatellites and were located in euchromatic regions.