Plant & Animal Genomes XIV Conference

January 14-18, 2006
Town & Country Convention Center
San Diego, CA

Locating Centromeres On The Tomato Linkage Map

Song-Bin Chang , Stephen M. Stack

  Department of Biology, Colorado State University, Fort Collins, CO 80523-1878

Determining the precise location of centromeres on linkage maps of plants and animals is hampered by suppression of crossing over in centromeres and pericentric heterochromatin. As a result, the locations of centromeres on linkage maps can be given only as approximations unless the genome of an organism has been completely sequenced or its chromosomes have been dissected minutely with breaks. Here we report a new and precise method of locating centromeres on the linkage map of tomato (Solanum lycopersicum). First, we identified a repeated sequence called TGR4 that we showed by FISH to be located specifically at the centromeres of all twelve tomato chromosomes. Indeed, the repeat is located in the centromeres of all chromosomes in the Solanum subsection Lycopersicon. A labeled TGR4 probe was then hybridized to filters carrying a HindIII tomato BAC library with 129,024 clones and 15 genome equivalents. 5542 BACs were identified that carry the TGR4 sequence. Because some of these BACs with TGR4 repeats also have mapped sequences, these mapped sequences must reside at centromeres. This assumption is supported by FISH localization of one of these mapped sequences to the centromere of chromosome 1. Using this approach, specific mapped loci have been identified at eleven of the twelve tomato centromeres, thereby precisely indicating the positions of these centromeres on the tomato linkage map. This technique should be applicable to locating centromeres on the linkage maps of other species where BAC libraries are available and repeated sequences have been identified at centromeres.