Journal Article

Evolution and taxonomic split of the model grass <i>Brachypodium distachyon</i>

Pilar Catalán, Jochen Müller, Robert Hasterok, Glyn Jenkins, Luis A. J. Mur, Tim Langdon, Alexander Betekhtin, Dorota Siwinska, Manuel Pimentel and Diana López-Alvarez

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 109, issue 2, pages 385-405
Published in print February 2012 | ISSN: 0305-7364
Published online January 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcr294
Evolution and taxonomic split of the model grass Brachypodium distachyon

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

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Background and Aims

Brachypodium distachyon is being widely investigated across the world as a model plant for temperate cereals. This annual plant has three cytotypes (2n =  10, 20, 30) that are still regarded as part of a single species. Here, a multidisciplinary study has been conducted on a representative sampling of the three cytotypes to investigate their evolutionary relationships and origins, and to elucidate if they represent separate species.

Methods

Statistical analyses of 15 selected phenotypic traits were conducted in individuals from 36 lines or populations. Cytogenetic analyses were performed through flow cytometry, fluorescence in situ hybridization (FISH) with genomic (GISH) and multiple DNA sequences as probes, and comparative chromosome painting (CCP). Phylogenetic analyses were based on two plastid (ndhF, trnLF) and five nuclear (ITS, ETS, CAL, DGAT, GI) genes from different Brachypodium lineages, whose divergence times and evolutionary rates were estimated.

Key Results

The phenotypic analyses detected significant differences between the three cytotypes and demonstrated stability of characters in natural populations. Genome size estimations, GISH, FISH and CCP confirmed that the 2n = 10 and 2n = 20 cytotypes represent two different diploid taxa, whereas the 2n = 30 cytotype represents the allotetraploid derived from them. Phylogenetic analysis demonstrated that the 2n = 20 and 2n = 10 cytotypes emerged from two independent lineages that were, respectively, the maternal and paternal genome donors of the 2n = 30 cytotype. The 2n = 20 lineage was older and mutated significantly faster than the 2n = 10 lineage and all the core perennial Brachypodium species.

Conclusions

The substantial phenotypic, cytogenetic and molecular differences detected among the three B. distachyon sensu lato cytotypes are indicative of major speciation processes within this complex that allow their taxonomic separation into three distinct species. We have kept the name B. distachyon for the 2n = 10 cytotype and have described two novel species as B. stacei and B. hybridum for, respectively, the 2n = 20 and 2n = 30 cytotypes.

Keywords: Brachypodium distachyon; Brachypodium stacei; Brachypodium hybridum; cytogenetics; evolutionary systematics; nomenclature; speciation

Journal Article.  15359 words.  Illustrated.

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

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