diploidization
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Whole-genome duplications are widespread across land plant phylogenies and particularly frequent in ferns and angiosperms. Genome duplications spurred the evolution of key innovations associated with diversification in many angiosperm clades and lineages. Such diversifications are not initiated by genome doubling per se. Rather, differentiation of the primary polyploid populations through a range of processes results in post-polyploid genome diploidization. Structural diploidization gradually reverts the polyploid genome to one functionally diploid-like through chromosomal rearrangements which frequently result in dysploid changes. Dysploidies may lead to reproductive isolation among post-polyploid offspring and significantly contribute to speciation and cladogenetic events.
Mesopolyploid whole-genome duplication (WGD) was revealed in the ancestry of Australian Brassicaceae species with diploid-like chromosome numbers (n = 4 to 6). Multicolor comparative chromosome painting was used to reconstruct complete cytogenetic maps of the cryptic ancient polyploids. Cytogenetic analysis showed that the karyotype of the Australian Camelineae species descended from the eight ancestral chromosomes (n = 8) through allopolyploid WGD followed by the extensive reduction of chromosome number. Nuclear and maternal gene phylogenies corroborated the hybrid origin of the mesotetraploid ancestor and suggest that the hybridization event occurred approximately 6 to 9 million years ago. The four, five, and six fusion chromosome pairs of the analyzed close relatives of Arabidopsis thaliana represent complex mosaics of duplicated ancestral genomic blocks reshuffled by numerous chromosome rearrangements. Unequal reciprocal translocations with or without preceeding pericentric inversions and purported end-to-end chromosome fusions accompanied by inactivation and/or loss of centromeres are hypothesized to be the main pathways for the observed chromosome number reduction. Our results underline the significance of multiple rounds of WGD in the angiosperm genome evolution and demonstrate that chromosome number per se is not a reliable indicator of ploidy level.
Hybridization and genome doubling (allopolyploidy) have led to evolutionary novelties as well as to the origin of new clades and species. Despite the importance of allopolyploidization, the dynamics of postpolyploid diploidization (PPD) at the genome level has been only sparsely studied. The Microlepidieae (MICR) is a crucifer tribe of 17 genera and c. 56 species endemic to Australia and New Zealand. Our phylogenetic and cytogenomic analyses revealed that MICR originated via an intertribal hybridization between ancestors of Crucihimalayeae (n = 8; maternal genome) and Smelowskieae (n = 7; paternal genome), both native to the Northern Hemisphere. The reconstructed ancestral allopolyploid genome (n = 15) originated probably in northeastern Asia or western North America during the Late Miocene (c. 10.6-7 million years ago) and reached the Australian mainland via long-distance dispersal. In Australia, the allotetraploid genome diverged into at least three main subclades exhibiting different levels of PPD and diversity: 1.25-fold descending dysploidy (DD) of n = 15 → n = 12 (autopolyploidy → 24) in perennial Arabidella (3 species), 1.5-fold DD of n = 15 → n = 10 in the perennial Pachycladon (11 spp.) and 2.1-3.75-fold DD of n = 15 → n = 7-4 in the largely annual crown-group genera (42 spp. in 15 genera). These results are among the first to demonstrate multispeed genome evolution in taxa descending from a common allopolyploid ancestor. It is suggested that clade-specific PPD can operate at different rates and efficacies and can be tentatively linked to life histories and the extent of taxonomic diversity.
- MeSH
- biologická evoluce * MeSH
- Brassicaceae klasifikace genetika MeSH
- DNA rostlinná genetika MeSH
- fylogeneze MeSH
- genom rostlinný MeSH
- genová přestavba MeSH
- hybridizace genetická * MeSH
- malování chromozomů MeSH
- polyploidie * MeSH
- Publikační typ
- časopisecké články MeSH
- Geografické názvy
- Austrálie MeSH
- Nový Zéland MeSH
Meiotic chromosome segregation is critical for fertility across eukaryotes, and core meiotic processes are well conserved even between kingdoms. Nevertheless, recent work in animals has shown that at least some meiosis genes are highly diverse or strongly differentiated among populations. What drives this remains largely unknown. We previously showed that autotetraploid Arabidopsis arenosa evolved stable meiosis, likely through reduced crossover rates, and that associated with this there is strong evidence for selection in a subset of meiosis genes known to affect axis formation, synapsis, and crossover frequency. Here, we use genome-wide data to study the molecular evolution of 70 meiosis genes in a much wider sample of A. arenosa. We sample the polyploid lineage, a diploid lineage from the Carpathian Mountains, and a more distantly related diploid lineage from the adjacent, but biogeographically distinct Pannonian Basin. We find that not only did selection act on meiosis genes in the polyploid lineage but also independently on a smaller subset of meiosis genes in Pannonian diploids. Functionally related genes are targeted by selection in these distinct contexts, and in two cases, independent sweeps occurred in the same loci. The tetraploid lineage has sustained selection on more genes, has more amino acid changes in each, and these more often affect conserved or potentially functional sites. We hypothesize that Pannonian diploid and tetraploid A. arenosa experienced selection on structural proteins that mediate sister chromatid cohesion, the formation of meiotic chromosome axes, and synapsis, likely for different underlying reasons.
Background and Aims: Knowledge of diploid phylogeny and ecogeography provide a foundation for understanding plant evolutionary history, diversification patterns and taxonomy. The genus Anthoxanthum (vernal grasses, Poaceae) represents a taxonomically intricate polyploid complex with large phenotypic variation and poorly resolved evolutionary relationships. The aims of the study were to reveal: (1) evolutionary lineages of the diploid taxa and their genetic differentiation; (2) the past distribution of the rediscovered 'Mediterranean diploid'; and (3) possible migration routes of diploids in the Mediterranean. Methods: A combined approach involving sequencing of two plastid regions ( trnL-trnF and rpl32-trnL ), nrDNA ITS, rDNA FISH analyses, climatic niche characterization and spatio-temporal modelling was used. Key Results: Among the examined diploid species, only two well-differentiated evolutionary lineages were recognized: Anthoxanthum gracile and A. alpinum . The other taxa - A. aristatum, A. ovatum, A. maderense and the 'Mediterranean diploid' - form a rather intermixed group based on the examined molecular data. In situ rDNA localization enabled identification of the ancestral Anthoxanthum karyotype, shared by A. gracile and two taxa from the crown group. For the studied taxa, ancestral location probabilities for six discrete geographical regions in the Mediterranean were proposed and likely scenarios of gradual expansion from them were suggested. Modelling past and present distributions shows that the 'Mediterranean diploid' has already been occurring in the same localities for 120 000 years. Conclusions: Highly congruent results were obtained and dated the origin and first diversification of Anthoxanthum to the Miocene. The later divergence probably took place in the Pleistocene and started polyploid evolution within the genus. The most recent diversification event is still occurring, and incomplete lineage sorting prevents full diversification of taxa at the molecular level, despite clear separation based on climatic niches. The 'Mediterranean diploid' is hypothesized to be a possible relic of the most recent common ancestor of Anthoxanthum due to their sharing of ancestral features.
- MeSH
- biologická evoluce * MeSH
- diploidie * MeSH
- DNA chloroplastová genetika MeSH
- fylogeneze * MeSH
- lipnicovité klasifikace MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Středomoří MeSH
Polyploidization has played an important role in the evolution of vertebrates, particularly at the base of Teleostei-an enormously successful ray-finned fish group with additional genome doublings on lower taxonomic levels. The investigation of post-polyploid genome dynamics might provide important clues about the evolution and ecology of respective species and can help to decipher the role of polyploidy per se on speciation. Few studies have attempted to investigate the dynamics of repetitive DNA sequences in the post-polyploid genome using molecular cytogenetic tools in fishes, though recent efforts demonstrated their usefulness. The demonstrably monophyletic freshwater loach family Botiidae, branching to evolutionary diploid and tetraploid lineages separated >25 Mya, offers a suited model group for comparing the long-term repetitive DNA evolution. For this, we integrated phylogenetic analyses with cytogenetical survey involving Giemsa- and Chromomycin A3 (CMA3)/DAPI stainings and fluorescence in situ hybridization with 5S/45S rDNA, U2 snDNA and telomeric probes in representative sample of 12 botiid species. The karyotypes of all diploids were composed of 2n = 50 chromosomes, while majority of tetraploids had 2n = 4x = 100, with only subtle interspecific karyotype differences. The exceptional karyotype of Botia dario (2n = 4x = 96) suggested centric fusions behind the 2n reduction. Variable patterns of FISH signals revealed cases of intraspecific polymorphisms, rDNA amplification, variable degree of correspondence with CMA3+ sites and almost no phylogenetic signal. In tetraploids, either additivity or loci gain/loss was recorded. Despite absence of classical interstitial telomeric sites, large blocks of interspersed rDNA/telomeric regions were found in diploids only. We uncovered different molecular drives of studied repetitive DNA classes within botiid genomes as well as the advanced stage of the re-diploidization process in tetraploids. Our results may contribute to link genomic approach with molecular cytogenetic analyses in addressing the origin and mechanism of this polyploidization event.
- MeSH
- biologická evoluce * MeSH
- diploidie * MeSH
- fylogeneze MeSH
- karyotypizace MeSH
- máloostní klasifikace genetika MeSH
- ribozomální DNA genetika MeSH
- tandemové repetitivní sekvence * MeSH
- tetraploidie * MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Background and Aims: Apomixis or asexual seed reproduction is a key evolutionary mechanism in certain angiosperms providing them with reproductive assurance and isolation. Nevertheless, the frequency of apomixis is largely unknown, especially in groups with autonomous apomixis such as the diploid-polyploid genus Hieracium. Methods: Using flow cytometric analyses, we determined the ploidy level and reproductive pathways (sexual vs. apomictic) for 7616 seeds originating from 946 plants belonging to >50 taxa sampled at 130 sites across Europe. Key Results: Diploid seeds produced by diploids were formed exclusively by the sexual pathway after double fertilization of reduced embryo sacs. An absolute majority of tri- and tetraploid seeds (99.6 %) produced by tri- and tetrapolyploid taxa were formed by autonomous apomixis. Only 20 polyploid seeds (0.4 %) were formed sexually. These seeds, which originated on seven polyploid accessions of four taxa, were formed after fertilization of either unreduced embryo sacs through a so-called triploid bridge or reduced embryo sacs, and frequently resulted in progeny with an increased ploidy. In addition, the formation of seedlings with increased ploidy (4x and 6x) was found in two triploid plants. This is the first firm evidence on functional facultative apomixis in polyploid members of Hieracium sensu stricto (s.s.). Conclusions: The mode of reproduction in Hieracium s.s. is tightly associated with ploidy. While diploids produce seeds exclusively sexually, polyploids produce seeds by obligate or almost obligate apomixis. Strict apomixis can increase the reproductive assurance and this in turn can increase the colonization ability of apomicts. Nevertheless, our data clearly show that certain polyploid plants are still able to reproduce sexually and contribute to the formation of new cytotypes and genotypes. The finding of functional facultative apomicts is essential for future studies focused on evolution, inheritance and ecological significance of apomixis in this genus.
Vicia cracca diploids and autotetraploids are highly parapatric in Europe; tetraploids reside in western and northern part, whereas diploids occupy much drier south-eastern part. They meet together in a Central European contact zone. This distribution pattern raised questions about a transformative effect of polyploidization on plant performance and environmental tolerances. We investigated plant survival, growth, and seed production in two water regimes in a common garden experiment using seeds collected from five localities in the Central European contact zone where diploids and tetraploids occur in sympatry. Obtained data imply that tetraploids of V. cracca are not generally superior in performance to diploids. Significantly larger seeds from tetraploid mother plants collected in the field were not correlated with greater stature of the seedlings. Nonetheless, tetraploids might have a potential to out-compete diploids in the long run due to the tetraploids' ability of greater growth which manifested in the second year of cultivation. Considering the response of diploids and tetraploids to water supply, drought stressed tetraploids but not diploids produced a higher proportion of aborted seeds than watered ones, which implies that tetraploids are more drought susceptible than diploids. On the other hand, decreased plant height in drought stresses tetraploids, which simultaneously increased total seed production, may suggest that tetraploids have a greater ability to avoid local extinction under unfavourable conditions by enhancing biomass allocation into production of seeds at the cost of lower growth. The significant interaction between ploidy level and locality in several traits suggests possible polyfyletic origin of tetraploids and the necessity to clarify the history of the tetraploids in Europe.
- MeSH
- biomasa MeSH
- diploidie MeSH
- ploidie MeSH
- semena rostlinná genetika růst a vývoj MeSH
- semenáček genetika růst a vývoj MeSH
- sympatrie MeSH
- tetraploidie MeSH
- vikev genetika růst a vývoj MeSH
- zahrady MeSH
- Publikační typ
- časopisecké články MeSH
- Geografické názvy
- Evropa MeSH
BACKGROUND: The gibel carp is a fish species with dual reproduction modes, gynogenesis and sexual reproduction, coexisting in mixed diploid-polyploid populations. Following the Red Queen (RQ) assumption, asexual organisms are, due to their low genetic diversity, targets for parasite adaptation. Because MHC polymorphism is maintained by selection from parasites and sexual selection, MHC genes are considered as a suitable candidate for testing the RQ hypothesis. In this study, we investigated MHC variability and the selection pressure acting on MHC genes in sexual diploids and asexual triploids. In addition, we tested whether the asexual form of gibel carp suffers from higher parasite loads than the sexual form. RESULTS: At the population level, genotype and allelic diversity of MHC were reduced in gynogenetic triploids when compared to sexual diploids. Different patterns in positively selected sites (PSS) between gynogens and sexual gibel carp were also found. A weak difference in parasite species richness was found between sexual fish and gynogens. However, two common clones of gynogens were significantly more parasitized than sexual diploids or other gynogens with rare MHC genotypes. At the individual level, the higher number of alleles was not associated with higher parasitism in either sexual diploids or gynogens. CONCLUSIONS: The differences in MHC diversity between gynogenetic triploids and sexual diploids are in accordance with the hypothesis of sexually-mediated selection increasing MHC diversity and fulfil a prerequisite of the Red Queen hypothesis. The different patterns in PSS between gynogens and sexual gibel carp also suggest the potential role of sexual selection and supports parasite-mediated selection maintaining MHC diversity. We showed that the most common MHC genotypes of gynogenetic triploids are the target of parasite selection. Our results suggest that the MHC genotype in gibel carp is more important than allelic number for immunocompetence.
