Comparative cytogenetic analysis of the genomes of the model grass Brachypodium distachyon and its close relatives

Abstract

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.

Intraspecific polymorphism of ribosomal DNA loci number and morphology in Brachypodium pinnatum and Brachypodium sylvaticum

“…To the best of our knowledge, the presence of two or three 35S rDNA loci in B. sylvaticum accessions has not been reported yet. However, this study along with the previous analysis [18] indicates that the most common number of 35S rRNA gene sites in this species is four. The results presented here confirmed the occurrence of intraspecific variation of 35S rDNA loci number in both analysed species.…”

“…two accessions with 2n = 18 and another two with 2n = 28 ( [18]. However, recent molecular studies contradict this hypothesis and suggest that both ancestral species had the chromosome number of 18 and some major rearrangements, e.g.…”

“…Such intraspecific variation in number and chromosomal distribution of rDNA loci has been reported in numerous plant genera, including Brassica, Raphanus, Sinapis [14], Pinus [15] and Sanguisorba [16]. The number and chromosomal distribution of rDNA loci have also been analysed in some species of Brachypodium [17,18]. This is a genus of temperate grasses, mostly Mediterranean and Eurosiberian, which comprises about 17 species [6,19].…”

“…This feature, along with a very small nuclear genome (~355 Mb/1C DNA), low number (2n = 10) of easily distinguishable chromosomes and some attractive biological traits, such as undemanding growth requirements, selffertility and short life cycle, have drawn attention to one of the representatives of the genus, B. distachyon, which has become an internationally recognised model organism [23][24][25]. Brachypodium species possess variable base chromosome numbers of 5, 7, 8, 9 and 10 [6, 26] and rather small genomes [18]. Our previous cytogenetic studies in Brachypodium species showed that the number of both 5S and 35S rDNA loci varies from 2 to 6, while their position in chromosomes is highly conserved, 5S rDNA loci always being localised in pericentromeric regions while 35S rDNA are distributed at the chromosomal termini [18].…”

“…Brachypodium species possess variable base chromosome numbers of 5, 7, 8, 9 and 10 [6, 26] and rather small genomes [18]. Our previous cytogenetic studies in Brachypodium species showed that the number of both 5S and 35S rDNA loci varies from 2 to 6, while their position in chromosomes is highly conserved, 5S rDNA loci always being localised in pericentromeric regions while 35S rDNA are distributed at the chromosomal termini [18]. However, it turned out in this study that the number of rDNA loci may differ within a species, as was observed in B. pinnatum and B. sylvaticum.…”