Chromosome triplication found across the tribe Brassiceae
Abstract
We have used an ∼8.7-Mb BAC contig of Arabidopsis thaliana Chromosome 4 to trace homeologous chromosome regions in 21 species of the family Brassicaceae. Homeologs of this segment could be identified in all tested species. Painting of pachytene chromosomes of Calepina, Conringia, and Sisymbrium species (2n = 14, 16), traditionally placed in tribe Brassiceae, showed one homeologous copy of the Arabidopsis contig, while the remaining taxa of the tribe (2n = 14–30) revealed three, and three Brassica species (2n = 34, 36, and 38) and Erucastrum gallicum (2n = 30) had six copies corresponding to the 8.7-Mb segment. The multiple homeologous copies corresponded structurally to the Arabidopsis segment or were rearranged by inversions and translocations within the diploidized genomes. These chromosome rearrangements accompanied by chromosome fusions/fissions led to the present-day chromosome number variation within the Brassiceae. Phylogenetic relationships based on the chloroplast 5′-trnL (UAA)–trnF(GAA) region and estimated divergence times based on sequence data of the chalcone synthase gene are congruent with comparative painting data and place Calepina, Conringia, and Sisymbrium outside the clade of Brassiceae species with triplicated genomes. Most likely, species containing three or six copy pairs descended from a common hexaploid ancestor with basic genomes similar to that of Arabidopsis. The presumed hexaploidization event occurred after the Arabidopsis–Brassiceae split, between 7.9 and 14.6 Mya.
Footnotes
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[The following individuals kindly provided reagents, samples, or unpublished information as indicated in the paper: T. Ksiazczyk.]
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Article and publication are at http://www.genome.org/cgi/doi/10.1101/gr.3531105. Article published online before print in March 2005.
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↵4 Corresponding author. E-mail m.lysak{at}rbgkew.org.uk; fax 44 (0)20 8332 5310.
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- Accepted February 14, 2005.
- Received December 3, 2004.
- Cold Spring Harbor Laboratory Press