Variation in the restriction fragments of 18S–26S rRNA loci in South American Elymus (Triticeae)

Abstract

The repeat units of the 18S–5.8S–26S ribosomal genes (rDNA) of 15 South American and 6 Asiatic and North American species of Elymus were shown to vary between 8.7 and 11.3 kb among species. Interspecific variation in the EcoRI and BamHI cleavage sites was observed. BamHI restriction sites were present in the subrepeats in the intergenic spacers in rDNA from diploid Hordeum (H genome) and absent in the diploid Pseudoroegneria (S genome) and in nearly all the tetraploid species of Elymus (SH genomes). Tetraploid Elymus species have only two pairs of chromosomes with secondary constrictions similar to those found in Pseudoroegneria and a maximum of two different repeat unit length classes. These results suggest that the rDNA in the H genome was lost during the evolution of the tetraploid Elymus. However, the additional H genome present in the hexaploid Elymus with genome formula SSHHH′H′ still show active ribosomal genes. Nucleolar organizer activity was also observed in rDNA from both the S and H genomes in artificial SS × HH amphiploids, suggesting no complete nucleolar dominance (amphiplasty) between the S and H genomes.Key words: Elymus, ribosomal genes, RFLP, nucleolus.

Genome analysis of South American Elymus (Triticeae) and Leymus (Triticeae) species based on variation in repeated nucleotide sequences

“…Stronger hybridization intensity was also found in the H genome specific marker bands. These results confirm the S'HH-genome formula previously assigned to these species by studies of chromosome pairing in interspecific hybrids (Hunziker 1953(Hunziker , 1966Dewey 1972c;Seberg 1991) and variation in the BamHI sites of the rDNA (Dubcovsky et al 1992). Restriction fragments characteristic of the H-genome Hordeum species from the New World but absent in the three diploid species from the Old World (Hordeum bogdanii, Hordeum roshevitzii, and Hordeum brevisubulatum) were detected by hybridization with clones pHch3 (HaeIII), pHch950 (HaeIII), and pHchl.3 (AluI, but different from pHchl.3 HaeIII; Table 1).…”

“…Differences between E. erianthus and the other South American Elymus species were also suggested by their particular morphological characteristics (Nicora 1978;Seberg and Linde-Laursen 1996), unique restriction sites in the rDNA repeat unit (Dubcovsky et al 1992), and sequence variation in the chloroplast gene rbcL (Seberg and Linde-Laursen 1996). Both E. erianthus and E. mendocinus also differ from the South American Elymus species in their karyotype parameters (Lewis et al 1996).…”

Genetic diversity of rbcL gene in Elymus trachycaulus complex and their phylogenetic relationships to several Triticeae species

“…Southern blot hybridization of South American Elymus species using repeated nucleotide sequences (RNS) confirmed the absence of the H genome and suggested the absence of the St-genome from this South American polyploidy (Dubcovsky et al 1997). Differences between this species and other South American Elymus species were also suggested by their particular morphological characteristics (Nicora 1978;Seberg and Linde-Laursen 1996), unique restriction sites in the rDNA repeat unit (Dubcovsky et al 1992), and sequence variation in the rbcL gene (Seberg and Linde-Laursen 1996). The present study found that this species did not cluster with any Elymus species used in this study, supporting the conclusion of Seberg and Linde-Laursen (1996) and Dubcovsky et al (1997).…”

Interspecific polymorphism at non-coding regions of chloroplast, mitochondrial DNA and rRNA IGS region in Elymus species

“…Genomic analysis on hybrids of the different species has been a very useful approach, but this technique is not very informative when large phylogenetic distances are involved between species, and there exist gene(s) controlling chromosome pairing. Recently, molecular techniques have been applied to address some questions in Elymus (D ubcovsky and L ewis 1992; D ubcovsky et al 1997; S vitashev et al 1996, 1998; S un et al 1997). Consequently, a better understanding of the genus has been obtained, but the molecular information on Elymus is very limited, and many questions still remain to be addressed in the genus.…”