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 (
Desmodesmus species taxonomy is one of the most long-standing issues in green microalgal systematics due to problems associated with phenotypic plasticity. Whereas more recent species descriptions and identifications are mainly based on cell wall structures and the use of cultures, comparisons with molecular phylogenies are largely lacking. In this study, the phylogenetic relationships between 22 clones identified as Desmodesmus costatogranulatus (Skuja) E. H. Hegew. were assessed using ITS2 rDNA sequence data in combination with cell wall morphology. The unrooted ITS2 phylogeny showed that the clones cluster into five groups, which also differ in their cell wall structures. Therefore, the taxon is split into five species: D. costatogranulatus, D. elegans, D. fennicus, D. regularis, and D. ultrasquamatus. Compared with other Desmodesmus species, intraspecific sequence variation is extensive and may contain additional (pseudo)cryptic diversity. Compensatory base changes were nearabsent within the species and varied from one to 11 between species. Relationships among the species were unresolved. Despite this, they clustered together with the two other Desmodesmus species having a combination of small and large warts in a well-supported lineage. Remarkably, ITS2 sequence variation in this lineage is as high as between all other included Desmodesmus species, even though the morphology of its members is rather uniform.
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