(to
KOMUGI Home) (go
to WIS List) (go
to NO.76 Contents)
Wheat Information
Service
Number 76: 61- 62 (1993)
Synthesis
of telomere repetitive sequences at the broken ends in common wheat
chromosomes
H. Tsujimoto
Kihara Institute for Biological Research, Yokohama City
University, Mutsukawa 3-122-20, Minami-ku, Yokohama
232, Japan
Telomeres of chromosomes possess special repetitive DNA sequences. In
higher plants, Richard and Ausubel (1988) have first cloned the
sequence from Arabidopsis thaliana and revealed that they
mainly Consisted of repeats of 5'-CCCTAAA-3'. In situ
hybridization using the sequences of Arabidopsis made signals
on the chromosomal termini of tomato, barley and wheat, indicating
high conservation of the sequences among the species of higher plants
(Ganal et al 1991, Wang et al 1991, Murata et al 1992).
In yeast and human, the telomere repetitive sequence are known to be
synthesized by telomerase but not by ordinary DNA polymerase. The
numbers of the repeats are retained as a metabolic balance between
the synthesis by the telomerase and the loss of terminal bases that
results from every semiconservative DNA replication (reviewed by
Blackburn 1991).
The purpose of this study is to investigate synthesis of the telomere
sequences at the broken ends of chromosomes. For this study, common
wheat is a suitable material because 'gametocidal genes' that induce
chromosome breakage only in a specific developmental stage are
available (Tsujimoto and Tsunewaki 1985, reviewed by Endo 1990). It
is possible therefore to obtain broken chromosomes at various periods
after the chromosomes had been broken. In situ hybridization
probed by the telomere repetitive sequences to these broken
chromosomes will indicate when, in the developmental stage, the
broken ends acquire the telomere sequences.
Hybridization using the biotin-labeled probe of the Arabidopsis
telomere sequences (pAtT4) and subsequent amplification by an
antibody detected prominent signals at all the telomeres of the
normal chromosomes and also the broken ends of the telocentric and
deletion chromosomes that had passed through more than one generation
since the appearance. However, no complete signals such as found in
normal telomeres were not observed at the broken ends that had been
produced during the former gametogenesis and thus passed through only
the stages of gametogenesis, fertilization, embryogenesis and root
development (Fig.1).
These findings clearly indicate that a certain time or stage is
required for synthesis of the telomere repetitive sequences with a
complete length. Nevertheless, because the broken ends without
complete telomere sequences had been already healed, restoration of
the normal complement of telomere sequences is not necessary for
healing of broken ends.
References
Blackburn EH (1991) Structure and function of telomeres. Nature
350:569-573.
Endo TR (1990) Gametocidal chromosomes and their induction of
chromosome mutations in wheat. Jpn J Genet 65: 135-152.
Ganal MW, Lapitan NLV, Tanksley SD (1991) Macrostructure of tomato
telomeres. Plant Cell 3: 87-94.
Murata M, Nakata N, Yasumuro Y (1992) Origin and molecular structure
of the midget chromosomes in a common wheat with rye cytoplasm.
Genome (in press).
Richard EJ, Ausubel FM (1988) Isolation of higher eukaryotic telomere
from Arabidopsis thaliana. Cell 53: 127-136.
Tsujimoto H, Tsunewaki, K (1985) Gametocidal genes in wheat and its
relatives. II. Suppression of chromosome 3C gametocidal gene of
Aegilops triuncialis. Genome 27: 178-185.
Wang S, Lapitan NLV, Tsuchiya T (1991) Characterization of telomere
in Hordeum vulgare chromosomes by in situ
hybridization. I. Normal diploid barley. Jpn J Genet 66:
313-316.
(go
to KOMUGI Home) (go
to WIS List) (go
to NO.76 Contents)