The 5S rRNA gene units in ancestral two-rowed barley (Hordeum spontaneum C. Koch) and bulbous barley (H. bulbosum L.): sequence analysis and phylogenetic relationships with the 5S rDNA units of cultivated barley (H. vulgare L.).

5S rRNA genes from several accessions of Hordeum spontaneum and Hordeum bulbosum, wild relatives of cultivated barley, Hordeum vulgare, have been amplified by the polymerase chain reaction, cloned, and sequenced. Evaluation of aligned sequences along with principal coordinate analysis demonstrates that the two classes of 5S rDNA sequences found in cultivated barley, and subclasses (groups) of these sequences, can also be found in its closest wild relatives. The two classes of units, formerly categorized as containing short or long 5S rDNA repeats, are distinguishable by the presence or absence of a TAG repeating unit. Sequence comparisons of individual clones (units) isolated from different species have allowed us to confirm that orthology exists for several groups. This demonstration of orthologous groups suggests that the 5S rDNA sequence may be useful for further phylogenetic analysis in the genus Hordeum and possibly in the Triticeae.