Interstitial telomeric sites and Robertsonian translocations in species of Ipheion and Nothoscordum (Amaryllidaceae)
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The genera Nothoscordum and Ipheion (Allioideae, Amaryllidaceae) are cytologically characterized by a dysploid series with variable numbers of metacentric and acrocentric chromosomes typical of karyotypes rearranged by Robertsonian translocations (RT). Since they have large chromosomes, low diploid numbers, and possess two telomeric motifs [the vertebrate-type (TTAGGG) n and the Arabidopsis-type (TTTAGGG) n ] they are suitable for investigating the occurrence and possible role of interstitial telomeric sites (ITS) associated with RT. We analyzed the distributions of telomeric sites in 12 species of Nothoscordum and Ipheion and found that both telomeric probes colocalized in all chromosome termini. Cloning and sequencing PCR products obtained using both telomeric primers simultaneously revealed long stretches of (TTAGGG) n and (TTTAGGG) n sequences together with degenerated telomeric sequences. Most acrocentric chromosomes have a 45S rDNA site at the terminal region of the short arms adjacent to the most distal telomeric sites. Telomeric signals were found at all chromosome ends, but ITS were also detected in a few proximal and subterminal regions in some Nothoscordum species. Although RT are common in this group of plants, our findings suggest that proximal positioning of telomeric motifs are not necessarily related to that kind of rearrangement. Rather, transposition of telomeric sequences followed by amplification, could better explain the presence of (TTAGGG) n and (TTTAGGG) n repeats at those sites. Furthermore, a few small interstitial sites found in some Nothoscordum species indicate that dispersion of these sequences was not restricted to the proximal region.
KeywordsAsparagales Interstitial telomeric sites Ipheion Nothoscordum Robertsonian translocations 45S rDNA
The authors wish to thank the Brazilian agencies Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à Ciência e Tecnologia de Pernambuco (FACEPE - APQ-2008-2.02/12) for financial support and a grant to G.S. by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).
- Crosa O (1972) Estudios cariología en el género Nothoscordum (Liliaceae). Bol Fac Agron Uruguay 122:3–8Google Scholar
- Guerra M, Felix LP (2000) O cariótipo de Nothoscordum pulchellum (Alliaceae) com ênfase na heterocromatina e sítios de DNAr. Bol Soc Argent Bot 35:283–289Google Scholar
- Ijdo JW, Wells RA, Baldini A, Reeders ST (1991) Improved telomere detection using a telomere repeat probe (TTAGGG)n generated by PCR. Nucleic Acids Res 13:17Google Scholar
- Kearse M, Moir R, WilsonA Stones-Havas S, Cheung M, Sturrock S, Buxton S, Cooper A, Markowitz S, Duran C, Thierer T, Ashton B, Mentijes P, Drummond A (2012) Geneious Basic: an integrated and extendable desktop software platform for the organization and analysis of sequence data. Bioinformatics 28:1647–1649CrossRefPubMedPubMedCentralGoogle Scholar
- Ocalewicz K (2012) Genomic distribution of telomeric DNA sequences—What do we learn from fish about telomere evolution? In: Reviews on Selected topics of telomere biology. Intech Open Access Publisher pp 271–294Google Scholar
- Ruiz-Herrera A, Robinson TJ (2008) Evolutionary plasticity and cancer breakpoints in human chromosome 3. Bio Essays 30:1126–1137Google Scholar