The dynamic ups and downs of genome size evolution in Brassicaceae |
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Authors: | Lysak Martin A Koch Marcus A Beaulieu Jeremy M Meister Armin Leitch Ilia J |
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Institution: | * Department of Functional Genomics and Proteomics, Institute of Experimental Biology, Masaryk University, Brno, Czech Republic
Heidelberg Institute of Plant Sciences, Biodiversity and Plant Systematics, University of Heidelberg, Heidelberg, Germany
Department of Ecology and Evolutionary Biology, Yale University
Leibniz-Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany
|| Jodrell Laboratory, Royal Botanic Gardens, Kew, United Kingdom |
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Abstract: | Crucifers (Brassicaceae, Cruciferae) are a large family comprisingsome 338 genera and c. 3,700 species. The family includes importantcrops as well as several model species in various fields ofplant research. This paper reports new genome size (GS) datafor more than 100 cruciferous species in addition to previouslypublished C-values (the DNA amount in the unreplicated gameticnuclei) to give a data set comprising 185 Brassicaceae taxa,including all but 1 of the 25 tribes currently recognized. Evolutionof GS was analyzed within a phylogenetic framework based ongene trees built from five data sets (matK, chs, adh, trnLF,and ITS). Despite the 16.2-fold variation across the family,most Brassicaceae species are characterized by very small genomeswith a mean 1C-value of 0.63 pg. The ancestral genome size (ancGS)for Brassicaceae was reconstructed as anc1C = 0.50 pg. Approximately50% of crucifer taxa analyzed showed a decrease in GS comparedwith the ancGS. The remaining species showed an increase inGS although this was generally moderate, with significant increasesin C-value found only in the tribes Anchonieae and Physarieae.Using statistical approaches to analyze GS, evolutionary gainsor losses in GS were seen to have accumulated disproportionatelyfaster within longer branches. However, we also found that GShas not changed substantially through time and most likely evolvespassively (i.e., a tempo that cannot be distinguished betweenneutral evolution and weak forms of selection). The data revealan apparent paradox between the narrow range of small GSs overlong evolutionary time periods despite evidence of dynamic genomicprocesses that have the potential to lead to genome obesity(e.g., transposable element amplification and polyploidy). Toresolve this, it is suggested that mechanisms to suppress amplificationand to eliminate amplified DNA must be active in Brassicaceaealthough their control and mode of operation are still poorlyunderstood. |
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Keywords: | Brassicaceae Cruciferae Arabidopsis genome size evolution chromosomes phylogenetics polyploidy |
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