Isolation of a D-genome specific repeated DNA sequence from Aegilops squarrosa

A. Lane Rayburn, Bikram S. Gill

Research output: Contribution to journalArticlepeer-review


Three repeated sequence clones, pAS1(1.0 Kb), pAS2(1.8 Kb) and pAS12(2.5 Kb), were isolated from Aegilops squarrosa (Triticum tauschii). The inserts of the three clones did not hybridize to each other. Two of the clones, pAS2 and pAS12, contain repeated sequences which were distributed throughout the genome. The clone pAS1 sequence was more restricted and was located in specific areas on telomeres and certain interstitial sites along the chromosome length. This cloned sequence was also found to be restricted to the D genome at the level of in situ hybridization. The pAS1 sequence will be useful in chromosomal identification and phylogenetic analysis. All three clones will allow assessment of genome plasticity in Aegilops squarrosa. Nuclear DNA content varies over a range of 10,000 fold among all organisms (Nagl et al., 1983). Among angiosperms, at least a 65-fold range in genome size occurs in diploid species (Sparrow, Price and Underbrink, 1972; Bennett, Smith and Heslop-Harrison, 1982). This DNA variation has been reported within families, genera, and species (Rothfels et al., 1966; Rees and Jones, 1967; Miksche, 1968; Price, Chambers and Bachmann, 1981). Much of the interspecific variation in genome size among angiosperms appears to be due to amplification and/or deletion of DNA within chromosomes. The variation in genome size does not appear to result in changes in the number of coding genes (Nagl et al., 1983). While the number of coding genes, with the exception of rDNA in specific examples, appears to remain constant, the remaining non-coding regions are quite flexible. This non-coding DNA encompasses over 99% of the plant genome and consists of sequences that exist as multiple copies throughout the genome and are identified as repeated DNA sequences (Flavell et al., 1974). Flavell et al. (1974) have reported that increasing genome size in higher plants is associated with increasing repetitive DNA amounts. Subsequent reports have substantiated this correlation (Bachmann and Price, 1977; Narayan, 1982). In various cereals, heterochromatin, which has been demonstrated to be correlated with the location of specific repeated DNA sequences, has been positively correlated with genome size (Bennett, Gustafson and Smith, 1977; Rayburn et al., 1985). Furuta, Nishikawa and Makino (1975) found significant DNA content variation among different accessions of Aegilops squarrosa L. This species contains the D genome, a pivotal genome in several polyploid species and also found in hexaploid wheat (AABBDD). The importance of this genome to the study of bread wheat genomes makes the mechanism(s) of this genomic plasticity of particular interest. In order to determine which sequences are varying, one must first have a way to identify specific types of chromatin and/or DNA. Specific types of chromosome banding such as C- and N-banding have been used to identity types of chromatin in previous studies. C-banding of the D genome results in very lightly staining bands whose pattern is somewhat indistinct. N-banding alternatively has been shown to be useful in identifying certain chromosomes of hexaploid wheat but is limited by the lack of major bands in the D genome (Endo and Gill, 1984). Specific DNA sequences have been isolated from Triticum aestivum cultivar "Chinese Spring" (hexaploid wheat). However, these sequences are representatives of the A and/or B genomes of hexaploid wheat and are not found in significant quantities in the D genome (Hutchinson and Lonsdale, 1982). Various other repeated DNA sequences have been successfully isolated from rye (Bedbrook et al., 1980) and identified on rye chromosomes (Appels et al., 1981; Jones and Flavell, 1982). Certain of these sequences are found in wheat genomes, but the sequences are representative of only a minor fraction of the D genome (Bedbrook et al., 1980; Rayburn and Gill, 1985). The purpose of this report is to describe three distinct repeated DNA sequences isolated from A. squarrosa (D genome). Two clones appear to be distributed throughout the total genome, and the third clone is restricted to specific sites along the chromosomes. This latter clone will prove useful in cytologically defining the D genome chromosomes. These sequences appear representative of two types of repeated DNA genome organization: 1) sequences distributed throughout the genome and 2) specific arrays of repeated sequences. The availability of such repeated DNA sequence clones along with the known intraspecific DNA content variation in A. squarrosa will allow the study of genomic plasticity of this species.

Original languageEnglish (US)
Pages (from-to)102-109
Number of pages8
JournalPlant Molecular Biology Reporter
Issue number2
StatePublished - Jun 1986
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Plant Science


Dive into the research topics of 'Isolation of a D-genome specific repeated DNA sequence from Aegilops squarrosa'. Together they form a unique fingerprint.

Cite this