Investigation of distal repetitive sequences in the genus allium
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The telomere is a DNA/protein structure required to maintain the ends of linear chromosomes.
Usually the DNA component comprises a highly conserved tandemly repeated
minisatellite sequence. In most plants the minisatellite sequence is typically present in several
hundred copies at each chromosome end, and is extended primarily by telomerase, which
adds telomere repeats to the 3’ end. In the plant genus Allium, which contains around 700
species, there is an absence of typical telomeric DNA repeats. It is of great interest to determine
what sequence or sequences have replaced the ancestral repeats and how they are
lengthened.
A range of molecular cloning methods were used to isolate candidate telomere sequences
from the genomes of two diverged species, Allium cernuum and Allium cepa. I analyse
several putative telomere sequences, isolated in this work and by others, but no proven
candidate sequence has emerged. Nevertheless, one of those sequences, 35S ribosomal DNA
(rDNA) encoding 35S rRNA, proved to have a structure that is previously not described for
plants. I show that some units have a Ty1/copia retrotransposon fragment in the intergenic
spacer region. Sequence analysis indicates that there was a single insertion followed by
amplification, probably involving homogenisation mechanisms. Furthermore, I show high
levels of rDNA length heterogeneity and rDNA unit divergence both within species and
across the genus, respectively.
Authors
Chester, MichaelCollections
- Theses [4490]