Journal Article

Evolution of genome size in <i>Carex</i> (Cyperaceae) in relation to chromosome number and genomic base composition

Ivana Lipnerová, Petr Bureš, Lucie Horová and Petr Šmarda

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 111, issue 1, pages 79-94
Published in print January 2013 | ISSN: 0305-7364
Published online November 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcs239
Evolution of genome size in Carex (Cyperaceae) in relation to chromosome number and genomic base composition

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

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Background and Aims

The genus Carex exhibits karyological peculiarities related to holocentrism, specifically extremely broad and almost continual variation in chromosome number. However, the effect of these peculiarities on the evolution of the genome (genome size, base composition) remains unknown. While in monocentrics, determining the arithmetic relationship between the chromosome numbers of related species is usually sufficient for the detection of particular modes of karyotype evolution (i.e. polyploidy and dysploidy), in holocentrics where chromosomal fission and fusion occur such detection requires knowledge of the DNA content.

Methods

The genome size and GC content were estimated in 157 taxa using flow cytometry. The exact chromosome numbers were known for 96 measured samples and were taken from the available literature for other taxa. All relationships were tested in a phylogenetic framework using the ITS tree of 105 species.

Key Results

The 1C genome size varied between 0·24 and 1·64 pg in Carex secalina and C. cuspidata, respectively. The genomic GC content varied from 34·8 % to 40·6 % from C. secalina to C. firma. Both genomic parameters were positively correlated. Seven polyploid and two potentially polyploid taxa were detected in the core Carex clade. A strong negative correlation between genome size and chromosome number was documented in non-polyploid taxa. Non-polyploid taxa of the core Carex clade exhibited a higher rate of genome-size evolution compared with the Vignea clade. Three dioecious taxa exhibited larger genomes, larger chromosomes, and a higher GC content than their hermaphrodite relatives.

Conclusions

Genomes of Carex are relatively small and very GC-poor compared with other angiosperms. We conclude that the evolution of genome and karyotype in Carex is promoted by frequent chromosomal fissions/fusions, rare polyploidy and common repetitive DNA proliferation/removal.

Keywords: Agmatoploidy; AT/GC ratio; chromosomal fusion and fission; chromosome numbers; DNA content; flow cytometry; GC content; karyotype; phylogeny; polyploidy; symploidy

Journal Article.  9236 words.  Illustrated.

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

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