Telomere and 45S rDNA sequences are structurally linked on the chromosomes in Chrysanthemum segetum L.
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Some reports have shown that nucleolar organizer regions are located at the telomeric region and have a structural connection with telomeres at the cellular level in many organisms. In this study, we found that all 45S ribosomal DNA (rDNA) signals were located at telomeric regions on the chromosomes in Chrysanthemum segetum L., and the 45S rDNA showed distinct signal patterns on different metaphase chromosome spreads. The bicolor fluorescence in situ hybridization experiment on the extended fibers revealed that telomere repeats were structurally connected with or interspersed into rDNA sequences. The close cytological structure relation between rDNA and telomere sequences led us to use PCR with combinations of the telomere primer and the rDNA primer to obtain some fragments, which were flanked by different rDNA and telomere primer sequences. One representative clone CHS2 contains closely connected rDNA and telomere sequences, suggesting that the telomere sequence invaded into the conserved rDNA sequence. In addition, the sequences of some PCR clones were flanked by the single telomeric primer sequence or the rDNA primer sequence. These results suggested that homologous recombination occurred between tandem repeat units of rDNA sequences or telomere repeats at the chromosome terminus.
KeywordsTelomere rDNA Chrysanthemum segetum L. Fluorescence in situ hybridization
Alternative lengthening of telomeres
Fluorescence in situ hybridization
Interstitial telomere repeats
Internal transcribed spacer
Nucleolar organizer regions
This work was supported by the NSFC (nos. 30870261 and 30771204), the National Genetically Modified Organism Breeding Major Project (no. 200908010-008B), the Research Fund for the Doctoral Program of Higher Education (no. 20090141110031), and the Fundamental Research Funds for the Central Universities (no. 3081003).
Conflict of interest
The authors declare that they have no conflict of interest.
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