title: Chromosome triplication found across the tribe Brassiceae.
abstract: We have used an approximately 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.
authors.affiliation: Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom. m.lysak@rbgkew.org.uk
authors.forename: Martin A
authors.initials: MA
authors.lastname: Lysak
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Koch
authors.forename: Ales
authors.initials: A
authors.lastname: Pecinka
authors.forename: Ingo
authors.initials: I
authors.lastname: Schubert
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D019607:Brassicaceae / Q000235:genetics*; D007446:Chromosome Inversion; D020223:Chromosome Painting; D022202:Chromosomes, Artificial, Bacterial; D032461:Chromosomes, Plant; D004261:DNA Replication; D018744:DNA, Plant / Q000235:genetics*; D004171:Diploidy; D017404:In Situ Hybridization, Fluorescence; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D026801:Synteny; D014178:Translocation, Genetic
chemical_list: D018744:DNA, Plant