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Evolution of genome size in Brassicaceae
J Spencer Johnston1, Alan E Pepper, Anne E Hall
1Department of Entomology, Texas A and M University, College Station, TX 77843, USA. spencerj@tamu.edu
Annals of Botany
|December 15, 2004
Summary
The Brassicaceae family shows significant genome size evolution, with Arabidopsis thaliana having the smallest genome. This study reveals genome size changes across the family, including decreases and increases, and identifies ancient polyploidy events.
Area of Science:
- Plant genomics
- Evolutionary biology
- Cytogenetics
Background:
- Brassicaceae (mustard family) exhibits a wide diversity with ~340 genera and >3350 species.
- This family is known for its compact genome sizes, with DNA content ranging from 0.16 pg to 1.95 pg (1C).
- Despite extensive chromosomal changes, genome size has remained relatively narrow.
Purpose of the Study:
- To establish a cytological and molecular phylogenetic framework for Brassicaceae.
- To analyze genome size evolution within the Brassicaceae family using this framework.
- To investigate the relationship between phylogenetic divergence and genome size variation.
Main Methods:
- Flow cytometry was used to determine DNA content for 34 Brassicaceae species and 10 Arabidopsis thaliana ecotypes.
- Chromosome counts were performed for the selected species.
- The Internal Transcribed Spacer (ITS) region was amplified, sequenced, and analyzed using parsimony to infer phylogenetic relationships.
Main Results:
- Genome size (1C DNA content) varied 8-fold (0.16–1.31 pg) in the studied species, or 4.4-fold (0.16–0.71 pg) excluding polyploid Brassica species.
- Arabidopsis thaliana ecotypes displayed minimal variation in DNA content (0.16–0.17 pg).
- Phylogenetic analysis identified ancestral genome size and evolutionary trends.
Conclusions:
- The ancestral Brassicaceae genome size is estimated at approximately 1x = 0.2 pg.
- Arabidopsis thaliana possesses the smallest genome (1C = 0.16 pg) and likely represents an evolutionary genome size reduction.
- The study identified multiple instances of genome size increase and decrease across the family, including two ancient polyploidy events in Brassica.