Long tomato microsatellites are predominantly associated with centromeric regions

Microsatellites as genetic markers are used in many crop plants. Major criteria for their usability as molecular markers include that they are highly polymorphic and evenly spread throughout a genome. In tomato, it has been reported that long arrays of tetranucleotide microsatellites containing the motif GATA are highly clustered around the centromeres of all chromosomes. In this study, we have isolated tomato microsatellites containing long arrays (> 20 repeats) of the dinucleotide motifs GA, GT, AT, as well as GATA, assessed their variability within Lycopersicon esculentum varieties and mapped them onto a genetic map of tomato. The investigated microsatellite markers exhibited between 1 and 5 alleles in a diverse set of L. esculentum lines. Mapping of the microsatellites onto the genetic map of tomato demonstrates that, as previously shown, GATA microsatellites are highly clustered in the regions of the tomato centromeres. Interestingly, the same centromeric location was now found for long dinucleotide microsatellite markers. Because of this uneven distribution, genetic mapping of the entire tomato genome using long dinucleotide microsatellites will be very difficult to achieve and microsatellite markers with shorter arrays of microsatellites could be more suitable for mapping experiments albeit their lower level of polymorphism. Some microsatellite markers described in this study might provide a useful tool to study the molecular structure of tomato centromeric regions and for variety identification.