[Comparative analysis of sequences of the 5S rDNA NTS in wild close relatives of barley from Tibet of China].

Abstract

Tibet is a center of distribution and differentiation of genus Hordeum in China,and has a great deal of species resource. The sequences of the nontranscribed intergenic spacer (NTS) region of 5S nuclear ribosomal DNA was studied in 18 varieties of the close relative of wild barley (Hordeum spontaneum) from different geographical regions in Tibet and Turkmenistan. These sequences were determined by sequencing the clones of PCR products. Alignment of sequences revealed that the 5S rDNA NTS contained two comparatively conservative regions, A and B, and a variable TAG repeat (V). The number of TAG repeats varies from 4-17, also including several transitions and conversions (TAG-->TCG, TAG-->TAC). The total size of the conservative regions was from 168 -169 bp, and the sequence length variation was only 1 bp. The GC content (%) of the conservative sequence was 43.8% and the homologous of that nearly 98.2% -100%. The number of variable sites was 12 (7.1%). In general, there were more transitions than conversions in the variation sites,and the ratios of transition/conversion were 1.0 - 2.0. NTS polymorphism of 5S rDNA was mainly determined by polymorphism of TAG repeats. The molecular system-tree showed that the NTS should be a useful marker to classify the accessions in Hordeum.