Telomeres and centromeres are the most important functional elements in plant chromosomes, as in other eukaryotic chromosomes. Both elements are in general composed of repetitive DNA sequences, and binding or associated proteins. Recent findings showed that the telomere DNA sequences are conserved among all plant species except Allium and related species, and that they form high-order complexes together with special proteins for maintaining the functions. Although centromere-specific DNA sequences have been isolated in a wide range of plant species, almost no conservation was found in their DNA sequences. Exceptions are cereal centromeres, which contain common Ty3/gypsy-type retrotransposon-like sequences. Recently, homologues to the genes encoding mammalian centromere proteins (CENPs) have been identified in maize and A. thaliana. This indicates that high-order structures of centromeres or kinetochore assemblies are conserved among eukaryotic organisms. The 180-bp centromeric repeat family of Arabidopsis thaliana is strongly suggested to play important roles for centromere functions. Since the organization of this family is similar to that of human alpha-satellite family, it is likely to be possible to build Arabidopsis thaliana artificial chromosomes (AtAC) with the same strategies used for constructing mammalian artificial chromosomes.
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