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(American Journal of Botany. 2006;93:814-823.)
© 2006 Botanical Society of America, Inc.

Cell Biology

Minisatellite telomeres occur in the family Alliaceae but are lost in Allium1

Eva Sykorová, Jirí Fajkus7, Marie Mezníková, Kar Yoong Lim, Kamila Neplechová, Frank R. Blattner, Mark W. Chase and Andrew R. Leitch7

2 Institute of Biophysics, Czech Academy of Sciences, Královopolská 135, 61265 Brno, Czech Republic; 3 Department of Functional Genomics and Proteomics, Masaryk University, Kotlárská 2, 61137 Brno, Czech Republic; 4 School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK; 5 Department of Taxonomy, Institute of Plant Genetics and Crop Plant Research, Corrensstraße 3, D-06466 Gatersleben, Germany; 6 Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK

ABSTRACT

Although telomere sequences are considered to be highly conserved, there are switch-points in plant telomere evolution that are congruent with species' phylogenies. When Asparagales diverged, the Arabidopsis-type telomeric minisatellite repeat (TTTAGGG)n was first replaced by a human-type (TTAGGG)n repeat, and both were lost in Allium cepa (Alliaceae). We aimed to discover (1) when this loss occurred during divergence of Alliaceae and, (2) if (TTAGGG)n repeats were replaced by other known telomeric minisatellites. Slot-blot hybridization, fluorescent in situ hybridization, BAL31 digestion, asymmetric PCR, and cloning were used to identify and localize candidate telomeric sequences in species of Nothoscordum, Miersia, Ipheion, Tulbaghia, Gethyum, Gilliesia, Leucocoryne, Tristagma, and representatives of the three major Allium clades. Alliaceae genera other than Allium have human (TTAGGG)-type telomeric repeats that form telomeres. In Allium, only Tetrahymena-type (TTGGGG) repeats were ubiquitous in the genome, but they were not localized to telomeres. Likewise, the consensus telomeric repeats in Arabidopsis, human, Bombyx (TTAGG), Chlamydomonas (TTTTAGGG), and Oxytricha (TTTTGGGG) are absent in Allium telomeres. Alliaceae with human-type telomeres share telomere structures with related Asparagales species. We demonstrate that in the Allium ancestor human-type telomeric repeats were lost from telomeres and were not replaced by any investigated alternative minisatellite repeats. However, human and other types of minisatellite telomeric repeats are interspersed in some Allium genomes and their genomic signatures coincide with Allium clades.

Key Words: alternative telomeres • Asparagales • asymmetric PCR • FISH • minisatellites • onion • slot-blot hybridization • telomere evolution






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