Ancestral Chromosomal Blocks Are Triplicated in Brassiceae Species with Varying Chromosome Number and Genome Size

Abstract

The paleopolyploid character of genomes of the economically important genus Brassica and closely related species (tribe Brassiceae) is still fairly controversial. Here, we report on the comparative painting analysis of block F of the crucifer Ancestral Karyotype (AK; n 5 8), consisting of 24 conserved genomic blocks, in 10 species traditionally treated as members of the tribe Brassiceae. Three homeologous copies of block F were identified per haploid chromosome complement in Brassiceae species with 2n 5 14, 18, 20, 32, and 36. In high-polyploid (n $ 30) species Crambe maritima (2n 5 60), Crambe cordifolia (2n 5 120), and Vella pseudocytisus (2n 5 68), six, 12, and six copies of the analyzed block have been revealed, respectively. Homeologous regions resembled the ancestral structure of block F within the AK or were altered by inversions and/or translocations. In two species of the subtribe Zillineae, two of the three homeologous regions were combined via a reciprocal translocation onto one chromosome. Altogether, these findings provide compelling evidence of an ancient hexaploidization event and corresponding whole-genome triplication shared by the tribe Brassiceae. No direct relationship between chromosome number and genome size variation (1.2-2.5 pg/2C) has been found in Brassiceae species with 2n 5 14 to 36. Only two homeologous copies of block F suggest a whole-genome duplication but not the triplication event in Orychophragmus violaceus (2n 5 24), and confirm a phylogenetic position of this species outside the tribe Brassiceae. Chromosome duplication detected in Orychophragmus as well as chromosome rearrangements shared by Zillineae species demonstrate the usefulness of comparative cytogenetics for elucidation of phylogenetic relationships.Approximately 240 cruciferous species of the Brassicaceae family classified into approximately 52 genera and sharing distinct morphological characters with the genus Brassica are taxonomically treated as the tribe Brassiceae (

Cross-Species Bacterial Artificial Chromosome–Fluorescence in Situ Hybridization Painting of the Tomato and Potato Chromosome 6 Reveals Undescribed Chromosomal Rearrangements

“…Cross-species multicolor BAC-FISH-a powerful tool for comparative genomics across Solanum: Crossspecies BAC-FISH was previously applied to Arabidopsis and related Brassicaceae species for demonstrating chromosomal evolutionary processes and rearrangements (Fransz et al 2000;Jackson et al 2000;Lysak et al 2005Lysak et al , 2006Lysak et al , 2007. In Solanum species chromosomal rearrangements have not been cytologically studied so far.…”

Fast Diploidization in Close Mesopolyploid Relatives ofArabidopsis

“…The unexpectedly detected WGD shared by the diploid Australian crucifer species is analogous to the mesopolyploid whole-genome triplication discerned in the tribe Brassiceae by comparative genetic mapping (Lagercrantz and Lydiate, 1996;Parkin et al, 2005) and by comparative cytogenetic analysis (Lysak et al, 2005(Lysak et al, , 2007Ziolkowski et al, 2006). Several lineagespecific WGD events thus far documented across the angiosperms (Tang et al, 2008;Jaillon et al, 2009;Soltis et al, 2009) represent only the tip of the iceberg, as potential other WGD events remain uncovered.…”

“…The steadily improving knowledge of crucifer genome evolution suggests that the duplication-diploidization process is ongoing and occurred several times across the family. In addition to the three aforemetioned paleopolyploid events, several Brassicaceae groups with diploid-like genomes have experienced additional, more recent WGD events, as exemplified by a whole-genome triplication (;8 to 15 mya) most likely promoting the diversification within the tribe Brassiceae (Lysak et al, 2005(Lysak et al, , 2007Parkin et al, 2005;Panjabi et al, 2008). Such duplications are younger than paleopolyploid events but older than neopolyploid speciation events (e.g., the origin of Arabidopsis suecica, Brassica napus, or Cardamine schulzii) and can be detected by comparative genetic and cytogenetic methods.…”

Different timing and spatial separation of parental chromosomes in intergeneric somatic hybrids between Brassica napus and Orychophragmus violaceus

“…The crucifer Orychophragmus violaceus (L.) O. E. Schulz (2n = 24, genomes OO), which is cultivated as an ornamental plant in China, is a tetraploid taxon that shares the common ancestor of Brassiceae but lacks the tribe-specific genome triplication event, suggesting a phylogenetic position outside of the tribe (Lysak et al, 2007). In the sexual intergeneric or even intertribal crosses between six cultivated Brassica species and O. violaceus, only hybrids with O. violaceus as the pollen parent have been obtained, and reciprocal crosses proved unsuccessful.…”