Sequence variation of ITS1, 5.8S rDNA, and ITS2 regions in 45S rRNA genes and species relationship among the Hordeum species

초록

Nucleotide sequences from ITS1, 5.8S subunit, ITS2 of 45S rDNA were analyzed in 23 different Hordeum species. Although the lengths of the regions were relatively homogenous, the nucleotide sequences were variable between species. The sizes were approximately 206-222 bp in ITS1, 163-166 in 5.8S subunit, and 206-223 in ITS2 region, respectively. As expected, ITS regions showed more variation than the 5.8S rDNA subunit. Base substitution mutations were more frequent than in/del mutations and, as expected, transition mutations were more frequent than transversion mutation in the region. GC contents were mostly approximately 60% and there were no apparent pattern of GC content variation depending on the arid resistance or annual versus perennial species. In sequence divergence and identity and phylogenetic analyses, the clustering pattern did not follow the genome or Section classification. Although concerted evolution among the clones from the same species was found in most of the rDNA clones analyzed, H. procerum and H. tetraploidum showed two types of 45S rDNA sequences, H. procerum1 and H. procerum2, H. tetraploidum-1 and H. tetrapoidum-2, based on the ITS1 and ITS2 sequences. The H. procerum-2 and H. tetrapoidum2 types were not included in the clusters of the Hordeum species. Because similar inconsistencies of the clustering pattern were also reported by others, the genome and classification must be very complicated in the Hordeum species.

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