The 5S rRNA gene diversity in Kengyilia rigidula (Keng and SL Chen) JL Yang, Yen, and Baum (Poaceae : Triticeae): Possible contribution of the H genome to the origin of Kengyilia

Fifty-three units of 5S rDNA sequences from five accessions of Kengyilia ri gidula, a member of the tribe Triticeae that also includes wheat, barley, r ye, and their wild relatives, have been amplified by the polymerase chain r eaction (PCR), cloned, and sequenced. The genome of K. rigidula consists of three haplomes, St, P, and Y. An evaluation of the aligned sequences of th e diverse 53 different 5S DNA units yielded three 5S-unit classes. One unit class, Long S1, was assignable to the St haplome, one unit class, the Long P1, was assignable to the P haplome, and a third unit class, Long H1, was assignable to the H haplome. The last was expected to be assignable to the Y haplome, based on previous knowledge. Evolutionary scenarios are put forw ard to explain this finding. Among those possibilities is that the number o f copies of units assignable to the Y haplome is very small and difficult t o detect. Short units, reported earlier in K. alatavica, were not found in K. rigidula.