ORGANIZATION AND EVOLUTION OF THE SUBTELOMERIC REGIONS OF THE RYE CHROMOSOMES
E.V. Evtushenko,1 E.A. Elisafenko,2 A.V. Vershinin 1,*
1 Institute of Molecular and Cellular Biology SB RAS and 2 Institute of Cytology and Genetics SB RAS, Novosibirsk;
* e-mail: avershin@mcb.nsc.ru
The subtelomeric regions are particularly dynamic and variable parts in the evolution of the eukaryotic genomes. A specific feature of the rye (Secale) chromosomes is large
heterochromatin blocks at the arms of all seven pairs of chromosomes. Within the genus Secale, an interspecific variation in the genome size reaches nearly 15% between
Secale cereale (cultivated rye) and the ancient species Secale silvestre and an increase in the size of subtelomeric heterochromatin regions is the main contributor to these
differences. Earlier works have demonstrated that the subtelomeric heterochromatin of rye is enriched for a few multicopy tandemly organized DNA families which form the long arrays
of monomers. Here we aimed to clarify the fine large-scale organization and mutual arrangement within the tandem arrays of these families and the flanking genomic nonarray DNA.
Restriction analysis of the BAC clones containing genetic material of the short arm of the first rye chromosome (1RS) showed that within arrays the bulk of monomers is organized in the
specific higher-order repeat units (up to hexamers) which are generated in the central part of tandem arrays, while only monomers and dimers are present near the boundaries.
Sequencing of the genomic nonarray DNA flanking the tandem arrays has demonstrated that this DNA in the studied BAC clones consists completely of retrotransposons of various
classes which are also present in the wheat and barley genomes. Thus, only an explosive amplification of pSc200 and pSc250 monomers, on the background of a saturated mixture of
various retrotransposons, can be regarded as a specific molecular process in formation of subtelomeric heterochromatin during the divergence of rye genome from the common ancestor
of cereals. Evidently, this process resulted in the enlargement of subtelomeric heterochromatin of Secale cereale and an increasing of its genome size.
Key words: tandemly organized repetitive DNA sequences, BAC library, retrotransposons, subtelomeric heterochromatin, molecular organization and evolution
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