Journal Article

The Ups and Downs of Genome Size Evolution in Polyploid Species of <i>Nicotiana</i> (Solanaceae)

I. J. Leitch, L. Hanson, K. Y. Lim, A. Kovarik, M. W. Chase, J. J. Clarkson and A. R. Leitch

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 6, pages 805-814
Published in print April 2008 | ISSN: 0305-7364
Published online January 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcm326
The Ups and Downs of Genome Size Evolution in Polyploid Species of Nicotiana (Solanaceae)

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

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Background

In studies looking at individual polyploid species, the most common patterns of genomic change are that either genome size in the polyploid is additive (i.e. the sum of parental genome donors) or there is evidence of genome downsizing. Reports showing an increase in genome size are rare. In a large-scale analysis of 3008 species, genome downsizing was shown to be a widespread biological response to polyploidy. Polyploidy in the genus Nicotiana (Solanaceae) is common with approx. 40 % of the approx. 75 species being allotetraploid. Recent advances in understanding phylogenetic relationships of Nicotiana species and dating polyploid formation enable a temporal dimension to be added to the analysis of genome size evolution in these polyploids.

Methods

Genome sizes were measured in 18 species of Nicotiana (nine diploids and nine polyploids) ranging in age from <200 000 years to approx. 4·5 Myr old, to determine the direction and extent of genome size change following polyploidy. These data were combined with data from genomic in situ hybridization and increasing amounts of information on sequence composition in Nicotiana to provide insights into the molecular basis of genome size changes.

Key Results and Conclusions

By comparing the expected genome size of the polyploid (based on summing the genome size of species identified as either a parent or most closely related to the diploid progenitors) with the observed genome size, four polyploids showed genome downsizing and five showed increases. There was no discernable pattern in the direction of genome size change with age of polyploids, although with increasing age the amount of genome size change increased. In older polyploids (approx. 4·5 million years old) the increase in genome size was associated with loss of detectable genomic in situ hybridization signal, whereas some hybridization signal was still detected in species exhibiting genome downsizing. The possible significance of these results is discussed.

Keywords: Genome downsizing; genome size; Nicotiana; polyploidy; sequence elimination; Solanaceae

Journal Article.  5767 words.  Illustrated.

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

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