The Isolation Of Telomeric DNA Sequences In G Arboreum And G. Raimondii

Telomeres are complexes of DNA and protein at the ends of linear eukaryotic chromosomes that prevent chromosome fusion and degradation of chromosome ends. Telomeric DNA sequence contains a simple telomere repeat sequence (TR) and telomere-associated sequence (TAS) which has a role to protect the ends of chromosomes. The TR sequences are highly conservation in plants. Not like TR, TAS showed a highly variation and species specificity, by which we can identify specific chromosome. The research of telomere sequence has an important role for construction of artificial chromosome, chromosome localization and the analysis of the origin and evolution of the genome sequence. In this study, two different methods were used to clone the telomere sequence of G. arboreum and diploid cotton Group D. The comparative analysis of the sequence and FISH signal distributions on chromosomes in group A and AD were conducted:1. Isolation of telomere associated sequence--TAS-1in G. arboreum. FISH results showed that all the signals of TAS-1were localized at the end of each chromosome in G. arboreum. Sequencing analysis of the TAS-1showed that the A/T content is66.6%; it contain10tandem repeat sequence one copy of TTTAGGG and one unknown interspersed repetitive. sequence.2. The distribution of TAS-1was different in G. arboreum, G. hirsutum and G. barbadense. By FISH, we revealed that TAS-1had a high copy number in G. arboreum due to the bright signals in each of chromosome end. Whereas it showed a relative low copy number in G. hirsutum because of the weak signals; it is interesting that it has a strong fluorescence signal points at the ends of a pair of unknown homologous chromosomes in G. hirsutum. In G. barbadense, the weakest fluorescence signal compared with the other two species indicated that the lowest copy number.3. By restriction fragment length measurement (TRF), we estimated the average length of telomeres were range from10kb to20kb in G. arboreum.4. Isolation of telomeric sequence of G. raimondii. Based on whole genome acquisition, we obtained ten telomere associated sequences from the D diploid cotton. Sequence analysis indicated that most of them were degraded of Arabidopsis telomeric repeat.5. FISH analysis showed that there were different distributions in G. arboreum and G. hirsutum. The results indicate that the distributions of the TTTAGGG repeat were similar in the AD and A species. However, degraded arrays have a different distribution on either AD and A species or different chromosome of them.