Journal Article

Comparative cytogenetic analysis of the genomes of the model grass <i>Brachypodium distachyon</i> and its close relatives

Elzbieta Wolny and Robert Hasterok

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 104, issue 5, pages 873-881
Published in print October 2009 | ISSN: 0305-7364
Published online July 2009 | e-ISSN: 1095-8290 | DOI:
Comparative cytogenetic analysis of the genomes of the model grass Brachypodium distachyon and its close relatives

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry


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Background and Aims

Brachypodium is a small genus of temperate grasses that comprises 12–15 species. Brachypodium distachyon is now well established as a model species for temperate cereals and forage grasses. In contrast to B. distachyon, other members of the genus have been poorly investigated at the chromosome level or not at all.


Twenty accessions comprising six species and two subspecies of Brachypodium were analysed cytogenetically. Measurements of nuclear genome size were made by flow cytometry. Chromosomal localization of 18–5·8–25S rDNA and 5S rDNA loci was performed by dual-colour fluorescence in situ hybridization (FISH) on enzymatically digested root-tip meristematic cells. For comparative phylogenetic analyses genomic in situ hybridization (GISH) applied to somatic chromosome preparations was used.

Key Results

All Brachypodium species examined have rather small genomes and chromosomes. Their chromosome numbers and genome sizes vary from 2n = 10 and 0·631 pg/2C in B. distachyon to 2n = 38 and 2·57 pg/2C in B. retusum, respectively. Genotypes with 18 and 28 chromosomes were found among B. pinnatum accessions. GISH analysis revealed that B. pinnatum with 28 chromosomes is most likely an interspecific hybrid between B. distachyon (2n = 10) and B. pinnatum (2n = 18). Two other species, B. phoenicoides and B. retusum, are also allopolyploids and B. distachyon or a close relative seems to be one of their putative ancestral species. In chromosomes of all species examined the 45S rDNA loci are distally distributed whereas loci for 5S rDNA are pericentromeric.


The increasing significance of B. distachyon as a model grass emphasizes the need to understand the evolutionary relationships in the genus Brachypodium and to ensure consistency in the biological nomenclature of its species. Modern molecular cytogenetic techniques such as FISH and GISH are suitable for comparative phylogenetic analyses and may provide informative chromosome- and/or genome-specific landmarks.

Keywords: 5S rDNA; 25S rDNA; B. distachyon; Brachypodium; FISH; flow cytometry; GISH; nuclear genome size; ribosomal RNA genes

Journal Article.  5263 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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