The physical and genomic organization of microsatellites in sugar beet

Microsatellites, tandem arrays of short (2-5 bp) nucleotide motifs, are present in high numbers in most eukaryotic genomes. We have characterized the physical distribution of microsatellites on chromosomes of sugar beet (Beta vulgaris L.). Each microsatellite sequence shows a characteristic genomic distribution and motif-dependent dispersion, with site-specific amplification on one to seven pairs of centromeres or intercalary chromosomal regions and weaker, dispersed hybridization along chromosomes. Exclusion of some microsatellites from 18S-5.8S-25S rRNA gene sites, centromeres, and intercalary sites was observed. In-gel and in situ hybridization patterns are correlated, with highly repeated restriction fragments indicating major centromeric sites of microsatellite arrays. The results have implications for genome evolution and the suitability of particular microsatellite markers for genetic mapping and genome analysis.