WEISS, HANNA1*, HARRY SCHERTHAN2, CHANG GEE JANG1, MARTIN PFOSSER1, and DIETER SCHWEIZER3. 1Department of Higher Plant Systematics and Evolution, Institute of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria; 2Max-Planck-Institute for Molecular Genetics, Ihnestrasse 73, D-14195 Berlin, Germany; 3Department of Cell Biology and Genetics, Institute of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria. - Othocallis siberica (Hyacinthaceae) - a plant with vertebrate-type telomeric sequences.
Telomeres play an important role in maintaining chromosome structure
and genome integrity. In most organisms telomeres are composed of
G-rich short tandemly repeated sequences that are maintained by a
conserved repair mechanism involving telomerase. Plant telomeric DNA,
as first identified in Arabidopsis thaliana, is characterized
by the sequence 3’(-TTTAGGG-)5’, while e.g., vertebrates possess
3’(-TTAGGG-)5’ repeats at their chromosome termini. Additionally, both
in plants and animals, a considerable amount of simple repeat variants
have been detected besides dominant repeat motifs. Several plant
genera, all belonging to monocotyledonous order Asparagales (e.g.,
Allium, Aloe), were reported to lack typical TTTAGGG
repeats at chromosome ends. It was speculated that in this plant group
the alternative, recombination-based pathway of telomere maintenance
might be present. However, within this group, typical
Arabidopsis-type telomere repeats were found in two species of
Ornithogalum (Hyacinthanceae), and the re-gain of those
sequences has been suggested (Adams et al. 2001, Proc. Royal Soc.
Biol. Sci., 268). In order to test the presence of G-rich telomeric
repeats in other members of this order, we employed FISH with
different probes of telomeric repeats in Othocallis siberica
(Scilla siberica s.l., Hyacinthaceae). Using FISH with a PNA
probe (CCCATT)3, and using two types of plant telomeric
repeats (TTTAGGG)7 and (TTTAGGG)28-43, and the
vertebrate-type repeats (TTAGGG)33-50, it was found that
vertebrate telomere probes preferentially localized to O.
siberica telomeres. Additionally, human-type probes detected
polymorphic interstitial and terminal amplified telomeric sites.
Arabidopsis-type telomeric probes hybridised to amplified
interstitial sites and, at best, to a few chromosome ends only. Using
single primer PCR with various telomeric repeats we amplified, cloned,
and sequenced fragments containing the telomeric sequence. One clone
contained exclusively “human-type” telomeric repeats with TTAGGG in a
long, almost uninterrupted stretch of 40 repeats. The implication of
the results for models of plant telomere architectures will be
discussed.
Key words: cloning, fluorescence in situ hybridization, human-type telomeric repeats (TTAGGG), Hycinthaceae, Othocallis siberica, sequencing