Instability of Subtelomeric Spelt1 Repeats of Wheat Species

Abstract

A new family of cereal telomeric tandem repeats was isolated, characterized, and designated Spelt1. The Spelt1 sequence is a highly species-specific repeat associated with the telomeric heterochromatin of Aegilops speltoides Boiss, in which its copy numbers vary from 1.5 × 10⁵ to 5.3 × 10⁵. In comparison to Ae. speltoides, the amount of the subtelomeric Spelt1 repeat in the tetraploid species is reduced by 50–1000 times and the number of localization sites on the chromosomes is decreased from 13 to 2 and more per haploid genome. The Spelt1 sequence was localized on chromosome arm 6BL of tetraploid wheat Triticum durum Desf. var. Langdon by dot-hybridization using D-genome disomic substitution lines.

An analysis of several accessions of Triticum and Aegilops species (86 diploid, 91 tetraploid, and 109 hexaploid) was performed using squash-dot hybridization with the Spelt1 sequence as a probe. The amounts of Spelt1 vary widely from less that 10² to 1.2 × 10⁴ in tetraploid and hexaploid species. Two tetraploid wheats, T. timopheevii Zhuk. and T. carthlicum Nevski, are exceptional endemic species and their restricted geographical distributions maintain the amounts of Spelt1 unaltered.

Thus, large subtelomeric blocks of the Spelt1 repeat are, for the most part, unstable within Triticum and Aegilops species and can be eliminated during the evolution and the formation of allopolyploid forms.