Organization and evolution of the 5S ribosomal RNA gene family in wheat and related species

Abstract

Variation in restriction fragments in nullisomic–tetrasomic and ditelosomic lines of Triticum aestivum 'Chinese Spring' and disomic and ditelosomic substitutions of chromosomes of diploid species Lophopyrum elongatum, T. monococcum ssp. aegilopoides, T. tauschii, and T. umbellulatum for 'Chinese Spring' chromosomes were used to identify chromosomal loci of 5S rRNA genes (5S DNA) in wheat and related species. These loci are on wheat chromosome arms 1BS, 1DS, 5AS, 5BS, and tentatively 5DS, T. m. aegilopoides chromosomes 1A and 5A, T. tauschii chromosomes 1D and 5D, and T. umbellulatum chromosome 5U. In diploid L. elongatum a locus was detected on chromosome arm 1ES. In most genomes, the locus on chromosome 1 contains 5S DNA subfamily with short spacers and the locus on chromosome 5 contains 5S DNA subfamily with long spacers. Only a few genomes were found to be potential exceptions to this rule. Concerted evolution of the 5S DNA loci was examined in several genomes. It appeared that homogenization of spacers occurs predominantly within a locus. A scenario of the evolution of polyploid wheats and relationships among diploid species in Triticum are proposed from the observed variation among 5S DNA loci.Key words: Triticum, Lophopyrum, gene mapping, concerted evolution, wheat evolution, DNA methylation.