TGR4, a novel tomato centromere-specific retrotransposon
Song-Bin Chang and Stephen M. Stack Department of Biology, Colorado State University, Fort Collins, CO 80523-1878
Centromeres are sites on chromosomes where spindle microtubules attach to move chromosomes in mitosis and meiosis. In plants, centromere-specific DNA sequences consist of tandem repeats 150-180 bp in length and Ty3-Gypsy type long terminal repeat (LTR) retrotransposons (Jiang et al. 2003). In spite of the conserved nature of centromere function, the sequence of centromere repeats varies between different plant groups. Here we report a new Ty3-Gypsy type retrotransposon called TGR4 that is found exclusively in the centromeres of all tomato (Solanum lycopersicum) chromosomes. Fig. 1a illustrates fluorescent in situ hybridization (FISH) using TGR4 as a probe on a spread of the twelve tomato pachytene bivalents. The signals at the centromeres vary in brightness, implying differing numbers of the TGR4 sequence on different chromosomes.
Figure 1. TGR4 loci after FISH (e.g., arrows) on (a) tomato (Solanum lycopersicum VFNT pachytene chromosomes and on (b) metaphase chromosomes of S. chilense.
When TGR4 is used as a probe for FISH on metaphase chromosome spreads from other solanaceous species, hybridization occurred exclusively at centromeres in members of the section Lycopersicon (Fig. 1b, Fig. 2). More distantly related solanaceous species, including S. tuberosum, showed no hybridization, suggesting that TGR4 arose in the common ancestor of the section Lycopersicon.
Figure 2. A combined phylogenetic tree based on Bohs and Olmstead, (1997) and Spooner et al. (2005). Among the species investigated above, the TGR4 centromere-specific retrotransposon is confined to the section Lycopersicon (black box).
Acknowledgements. Seeds were supplied by the Tomato Genetics Resource Center (TGRC) at the University of California at Davis. This research was supported by NSF grant DBI-0421634
References:
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