Showing papers by "Martin A. Lysak published in 2012"
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TL;DR: In this article, the authors present the first in-depth information on chromosome numbers, rDNA in situ localization, genomic structure, and phylogenetic relationship within the unigeneric tribe Heliophileae.
Abstract: The unigeneric tribe Heliophileae includes ca. 90 Heliophila
species, all endemic to southern Africa. The tribe is
morphologically the most diverse Brassicaceae lineage in every
aspect of habit, foliage, flower and fruit morphology. Despite
this diversity, virtually nothing is known about its origin and
genome evolution. Here we present the first in-depth
information on chromosome numbers, rDNA in situ localization,
genome structure, and phylogenetic relationship within
Heliophileae. Chromosome numbers determined in 27 Heliophila
species range from 2n = 16 to 2n = ca. 88, but 2n = 20 and 22
prevail in 77% of the examined species. Chromosome-number
variation largely follows three major lineages (A, B, and C)
resolved in the ITS phylogeny. Clade A species mostly have a
chromosome number of 2n = 20, whereas 2n = 22 is the dominant
number in clade C (2n = 16 and 22 were counted in two diploid
species of clade B). The number and position of 5S and 45S rDNA
loci cannot be employed as phylogenetically informative
characters. Seven species with different chromosome number and
from the three ITS clades were analyzed by comparative
chromosome painting. In all species analyzed, 90% of painting
probes unveiled three homeologous chromosome regions in
Heliophila haploid chromosome complements. These results
suggest that all Heliophila species, and probably the entire
tribe Heliophileae, experienced a whole-genome triplication
(WGT) event. We hypothesize that the mesohexaploid ancestor
arose through hybridization between genomes resembling the
Ancestral Crucifer Karyotype with n = 8. The WGT has been
followed by species-specific chromosome rearrangements
(diploidization) resulting in descending dysploidy towards
extant quasi-diploid genomes. The WGT might have contributed to
diversification and species radiation in Heliophileae. To our
knowledge, this is the first study to document polyploidy as a
potential major mechanism for the radiation of a Cape plant
lineage.
33 citations
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TL;DR: Relationship data from the internal transcribed spacer mDNA and rbeL cpDNA regions were used to determine relationships of genera of Brassicaceae from Australia and New Zealand that were previously unassigned to a tribe, and the tribe Microlepidieae is expanded.
Abstract: Sequence data from the internal transcribed spacer (ITS) mDNA
and rbeL cpDNA regions were used to determine relationships of
genera of Brassicaceae from Australia and New Zealand (NZ) that
were previously unassigned to a tribe. Maximum likelihood
analysis of 71 ITS sequences identified a monophyletic clade of
Australian genera, including Carinavalva and Microlepidium that
had previously been assigned to the tribe Microlepidieae.
Pachycladon is not supported as monophyletic, comprising a
clade of the NZ species and another clade of the Tasmanian P.
radicatum. These two Pachycladon clades form a polytomy with
the Australian clade. Maximum likelihood analysis of the rbel,
region generally supports the ITS analysis with the Australian
genera forming a monophyletic clade with Pachycladon.
Arabidella is polyphyletic in the rbeL phylogeny as A.
eremigena is member of the Australian clade but A. trisecta is
placed in a sister clade that comprises mainly genera of tribe
Camelineae. As a result of these phylogenetic analyses the
tribe Microlepidieae is expanded and now includes 16 genera and
56 species endemic to Australia and New Zealand. Genera
included in the Microlepidieae are Arabidella, Ballantinia,
Blennodia, Carinavalva, Cuphonotus, Drabastrum, Geococcus,
Harmsiodoxa, Irenepharsus, Menkea, Microlepidium, Pachycladon,
Pachymitus, Phlegmatosperinum, Scambopus and Stenopetalum.
Whole-genome duplication has previously been shown to have
occurred in the ancestry of Arabidella, Ballantinia,
Pachycladon and Stenopetalum and is likely to be a defining
feature of the tribe Microlepidieae. Future research needs to
investigate circumscription of the Australian genera as there
is a predominance of closely related monotypic genera in the
Microlepidieae. With resolution of the tribal placement of
these Australian and New Zealand genera, ca. 94% (302) of the
321 genera in the family have been assigned to a tribe.
16 citations