The 5S rDNA units in Kengyilia (Poaceae : Triticeae): diversity of the nontranscribed spacer and genomic relationships

The sequences of eighty 5S rDNA clones were obtained by polymerase chain re action (PCR) amplification of DNA from 12 accessions representing eight spe cies of Kengyilia. Orthologous sequences were grouped into five unit classe s: long P1, long S1, long {Y1, short P1, and short S1. Both the long P1 and long S1 classes are prevalent in Kengyilia, whereas the rest are rare. The short S1 class has not been described previously in other Kengyilia specie s. Two clones represent the long {Y1 class, with only one clone reported pr eviously in Kengyilia alatavica (Drobow) J.L. Yang, Yen & Baum and a single clone found in this investigation. The long H1 unit class reported earlier for Kengyilia rigidula (Keng and S.L. Chen) J.L. Yang, Yen & Baum, but not for K. alatavica, was not found in any of the eight species investigated. Therefore, its presence in K. rigidula may be the result of introgression f rom Elymus nutans Grisebach, an HS-genome species containing the long H1 un it class; the two are often found growing together and are known to yield s terile hybrids in those populations. The specific 5S DNA unit classes, exce pt for the ones that were found in very low frequency and in few samples, m ay have a potential not only as markers for the identification of haplomes but also of hybrids containing a combination of genomes. This investigation indicated, along with previous studies, that the 5S unit classes either fo rm integral parts of haplomes or remain conserved and identifiable within h aplomes originating from distant species, indicating that concerted evoluti on in the 5S gene plays only a partial role as an evolutionary force.