Introgression allows polyploid species to acquire new genomic content from diploid progenitors or from other unrelated diploid or polyploid lineages, contributing to genetic diversity and facilitating adaptive allele discovery. In some cases, high levels of introgression elicit the replacement of large numbers of alleles inherited from the polyploid's ancestral species, profoundly reshaping the polyploid's genomic composition. In such complex polyploids, it is often difficult to determine which taxa were the progenitor species and which taxa provided additional introgressive blocks through subsequent hybridization. Here, we use population-level genomic data to reconstruct the phylogenetic history of Betula pubescens (downy birch), a tetraploid species often assumed to be of allopolyploid origin and which is known to hybridize with at least four other birch species. This was achieved by modeling polyploidization and introgression events under the multispecies coalescent and then using an approximate Bayesian computation rejection algorithm to evaluate and compare competing polyploidization models. We provide evidence that B. pubescens is the outcome of an autoploid genome doubling event in the common ancestor of B. pendula and its extant sister species, B. platyphylla, that took place approximately 178,000-188,000 generations ago. Extensive hybridization with B. pendula, B. nana, and B. humilis followed in the aftermath of autopolyploidization, with the relative contribution of each of these species to the B. pubescens genome varying markedly across the species' range. Functional analysis of B. pubescens loci containing alleles introgressed from B. nana identified multiple genes involved in climate adaptation, while loci containing alleles derived from B. humilis revealed several genes involved in the regulation of meiotic stability and pollen viability in plant species.

• Klíčová slova
• Allopolyploidy, Betula, autopolyploidy, gene flow, genomic polarization, homoeologs, interploidal, introgressive hybridization, polyploid phylogenetics, polyploidization simulation, reticulate evolution,
• MeSH
• alely * MeSH
• bříza * genetika   klasifikace   MeSH
• fylogeneze * MeSH
• genom rostlinný * MeSH
• genová introgrese MeSH
• hybridizace genetická MeSH
• polyploidie * MeSH
• Publikační typ
• časopisecké články MeSH

BACKGROUND AND AIMS: Dogroses (Rosa sect. Caninae) are mostly pentaploid, bearing 2n = 5x = 35 chromosomes in somatic cells. They evolved a unique form of asymmetrical meiosis characterized by two types of chromosomes: (1) chromosomes forming bivalents and distributed in the normal sexual way; and (2) chromosomes occurring as univalents and transferred by a female gamete only. In the mature pollen of pentaploid species, seven bivalent-derived chromosomes are transmitted to offspring, and 21 unpaired univalent chromosomes are eliminated during microsporogenesis. To discriminate between bivalent- and univalent-forming chromosomes, we studied histone H3 phosphorylation patterns regulating meiotic chromosome condensation and segregation. METHODS: We analysed histone modification patterns during male canina meiosis in two representative dogrose species, 5x Rosa canina and 5x Rosa rubiginosa, by immunohistochemical and molecular cytogenetics approaches. Immunostaining of meiotic cells included α-tubulin, histone H3 phosphorylation (H3S10p, H3S28p and H3T3p) and methylation (H3K4me3 and H3K27me3) marks. In addition, fluorescent in situ hybridization was carried out with an 18S rDNA probe. KEY RESULTS: In the first meiotic division, univalent chromosomes underwent equational division into chromatids, while homologues in bivalents were segregated as regular dyads. In diakinesis, bivalent chromosomes displayed strong H3 phosphorylation signals in proximal regions, spreading to the rest of the chromosome. In contrast, in univalents, the H3 phosphorylation signals were weaker, occurring mostly outside proximal regions largely overlapping with the H3K4me3 signals. Reduced phosphorylation was associated with relative under-condensation of the univalent chromosomes, particularly at early diakinesis. CONCLUSIONS: We hypothesize that the absence of pairing and/or recombination in univalent chromosomes negatively affects the histone H3 phosphorylation of their chromatin and perhaps the loading of meiotic-specific cohesins. This apparently destabilizes cohesion of sister chromatids, leading to their premature split in the first meiotic division.

• Klíčová slova
• Rosa genus, 18S ribosomal DNA, canina meiosis, dogroses, euchromatin and heterochromatin, fluorescence in situ hybridization, histone H3 phosphorylation, immunostaining, non-disjunction,
• MeSH
• chromozomy MeSH
• epigeneze genetická MeSH
• fosforylace MeSH
• histony * genetika   MeSH
• hybridizace in situ fluorescenční MeSH
• meióza * MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• histony * MeSH

Whole-genome duplication is a common mutation in eukaryotes with far-reaching phenotypic effects. The resulting morphological, physiological and fitness consequences and how they affect the survival probability of polyploid lineages are intensively studied, but little is known about the effect of genome doubling on the evolutionary potential of populations. Historically, it has been argued polyploids should be less able to adapt because gene duplication dilutes the effects of alleles, such that polyploids are less likely to evolve new adaptive gene complexes compared with diploids. In this paper, I investigate the short- and long-term consequences of genome doubling on the additive genetic variance of populations. To do so, I extended the classical models of quantitative traits under stabilizing selection to study the evolution of the additive variance of the trait under study after a shift from diploidy to tetraploidy. I found that, for realistic allele-dosage effects, polyploidization is associated with an initial decrease in adaptive potential. In the long term, the better masking of recessive deleterious mutations associated with polyploidy compensates for the initial decrease in additive variance. The time for the tetraploid populations to reach or exceed the additive variance of their diploid progenitors is generally lower than 200 generations. These results highlight that polyploidization per se has a negligible negative effect on the adaptive potential of populations in the short term, and a substantial positive effect in the long term.

• Klíčová slova
• additive variance, evolvability, polyploidy, quantitative genetics,
• MeSH
• diploidie * MeSH
• duplikace genu MeSH
• fenotyp MeSH
• lidé MeSH
• polyploidie * MeSH
• tetraploidie MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Deserts exert strong selection pressures on plants, but the underlying genomic drivers of ecological adaptation and subsequent speciation remain largely unknown. Here, we generated de novo genome assemblies and conducted population genomic analyses of the psammophytic genus Pugionium (Brassicaceae). Our results indicated that this bispecific genus had undergone an allopolyploid event, and the two parental genomes were derived from two ancestral lineages with different chromosome numbers and structures. The postpolyploid expansion of gene families related to abiotic stress responses and lignin biosynthesis facilitated environmental adaptations of the genus to desert habitats. Population genomic analyses of both species further revealed their recent divergence with continuous gene flow, and the most divergent regions were found to be centered on three highly structurally reshuffled chromosomes. Genes under selection in these regions, which were mainly located in one of the two subgenomes, contributed greatly to the interspecific divergence in microhabitat adaptation.

• Klíčová slova
• chromosomal structural variation, desert plants, microhabitat divergence, polyploidization,
• MeSH
• Brassicaceae klasifikace   genetika   fyziologie   MeSH
• ekosystém * MeSH
• fylogeneze MeSH
• fyziologická adaptace genetika   MeSH
• genom rostlinný * MeSH
• polyploidie MeSH
• vznik druhů (genetika) * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The establishment and success of polyploids are thought to often be facilitated by ecological niche differentiation from diploids. Unfortunately, most studies compared diploids and polyploids, ignoring variation in ploidy level in polyploids. To fill this gap, we performed a large-scale study of 11,163 samples from 1,283 populations of the polyploid perennial geophyte Allium oleraceum with reported mixed-ploidy populations, revealed distribution ranges of cytotypes, assessed their niches and explored the pattern of niche change with increasing ploidy level. Altogether, six ploidy levels (3x-8x) were identified. The most common were pentaploids (53.6%) followed by hexaploids (22.7%) and tetraploids (21.6%). Higher cytotype diversity was found at lower latitudes than at higher latitudes (>52° N), where only tetraploids and pentaploids occurred. We detected 17.4% of mixed-ploidy populations, usually as a combination of two, rarely of three, cytotypes. The majority of mixed-ploidy populations were found in zones of sympatry of the participating cytotypes, suggesting they have arisen through migration (secondary contact zone). Using coarse-grained variables (climate, soil), we found evidence of both niche expansion and innovation in tetraploids related to triploids, whereas higher ploidy levels showed almost zero niche expansion, but a trend of increased niche unfilling of tetraploids. Niche unfilling in higher ploidy levels was caused by a contraction of niche envelopes toward lower continentality of the climate and resulted in a gradual decrease of niche breadth and a gradual shift in niche optima. Field-recorded data indicated wide habitat breadth of tetraploids and pentaploids, but also a pattern of increasing synanthropy in higher ploidy levels. Wide niche breadth of tetra- and pentaploids might be related to their multiple origins from different environmental conditions, higher "age", and retained sexuality, which likely preserve their adaptive potential. In contrast, other cytotypes with narrower niches are mostly asexual, probably originating from a limited range of contrasting environments. Persistence of local ploidy mixtures could be enabled by the perenniality of A. oleraceum and its prevalence of vegetative reproduction, facilitating the establishment and decreasing exclusion of minority cytotype due to its reproductive costs. Vegetative reproduction might also significantly accelerate colonization of new areas, including recolonization of previously glaciated areas.

• Klíčová slova
• chromosome numbers, cytogeography, ecological niche, flow cytometry, geophytes, ploidy coexistence, polyploidy,
• Publikační typ
• časopisecké články MeSH

Angiosperms have become the dominant terrestrial plant group by diversifying for ~145 million years into a broad range of environments. During the course of evolution, numerous morphological innovations arose, often preceded by whole genome duplications (WGD). The mustard family (Brassicaceae), a successful angiosperm clade with ~4000 species, has been diversifying into many evolutionary lineages for more than 30 million years. Here we develop a species inventory, analyze morphological variation, and present a maternal, plastome-based genus-level phylogeny. We show that increased morphological disparity, despite an apparent absence of clade-specific morphological innovations, is found in tribes with WGDs or diversification rate shifts. Both are important processes in Brassicaceae, resulting in an overall high net diversification rate. Character states show frequent and independent gain and loss, and form varying combinations. Therefore, Brassicaceae pave the way to concepts of phylogenetic genome-wide association studies to analyze the evolution of morphological form and function.

• MeSH
• biologická evoluce * MeSH
• Brassicaceae klasifikace   genetika   MeSH
• celogenomová asociační studie MeSH
• fylogeneze MeSH
• genetická variace genetika   MeSH
• genom rostlinný genetika   MeSH
• molekulární evoluce * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Polyploids are species in which three or more sets of chromosomes coexist. Polyploidy frequently occurs in plants and plays a major role in their evolution. Based on their origin, polyploid species can be divided into two groups: autopolyploids and allopolyploids. The autopolyploids arise by multiplication of the chromosome sets from a single species, whereas allopolyploids emerge from the hybridization between distinct species followed or preceded by whole genome duplication, leading to the combination of divergent genomes. Having a polyploid constitution offers some fitness advantages, which could become evolutionarily successful. Nevertheless, polyploid species must develop mechanism(s) that control proper segregation of genetic material during meiosis, and hence, genome stability. Otherwise, the coexistence of more than two copies of the same or similar chromosome sets may lead to multivalent formation during the first meiotic division and subsequent production of aneuploid gametes. In this review, we aim to discuss the pathways leading to the formation of polyploids, the occurrence of polyploidy in the grass family (Poaceae), and mechanisms controlling chromosome associations during meiosis, with special emphasis on wheat.

• Klíčová slova
• Poaceae, chromosome pairing, homoeologous pairing, meiosis, polyploidy,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

BACKGROUND AND AIMS: Despite their abundant odd-ploidy (2n = 5x = 35), dogroses (Rosa sect. Caninae) are capable of sexual reproduction due to their unique meiosis. During canina meiosis, two sets of chromosomes form bivalents and are transmitted by male and female gametes, whereas the remaining chromosomes form univalents and are exclusively transmitted by the egg cells. Thus, the evolution of chromosomes is expected to be driven by their behaviour during meiosis. METHODS: To gain insight into differential chromosome evolution, fluorescence in situ hybridization was conducted for mitotic and meiotic chromosomes in four dogroses (two subsections) using satellite and ribosomal DNA probes. By exploiting high-throughput sequencing data, we determined the abundance and diversity of the satellite repeats in the genus Rosa by analysing 20 pentaploid, tetraploid and diploid species in total. KEY RESULTS: A pericentromeric satellite repeat, CANR4, was found in all members of the genus Rosa, including the basal subgenera Hulthemia and Hesperhodos. The satellite was distributed across multiple chromosomes (5-20 sites per mitotic cell), and its genomic abundance was higher in pentaploid dogroses (2.3 %) than in non-dogrose species (1.3 %). In dogrose meiosis, univalent chromosomes were markedly enriched in CANR4 repeats based on both the number and the intensity of the signals compared to bivalent-forming chromosomes. Single-nucleotide polymorphisms and cluster analysis revealed high intragenomic homogeneity of the satellite in dogrose genomes. CONCLUSIONS: The CANR4 satellite arose early in the evolution of the genus Rosa. Its high content and extraordinary homogeneity in dogrose genomes is explained by its recent amplification in non-recombining chromosomes. We hypothesize that satellite DNA expansion may contribute to the divergence of univalent chromosomes in Rosa species with non-symmetrical meiosis.

• Klíčová slova
• Rosa, chromosome evolution, dogroses, genetic recombination, meiosis, polyploidy, repeatome, satellite DNA,
• MeSH
• DNA rostlinná MeSH
• genom rostlinný MeSH
• hybridizace in situ fluorescenční MeSH
• lidé MeSH
• meióza MeSH
• polyploidie MeSH
• Rosa genetika   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA rostlinná MeSH

BACKGROUND AND AIMS: The origin of different cytotypes by autopolyploidy may be an important mechanism in plant diversification. Although cryptic autopolyploids probably comprise the largest fraction of overlooked plant diversity, our knowledge of their origin and evolution is still rather limited. Here we study the presumed autopolyploid aggregate of Aster amellus, which encompasses diploid and hexaploid cytotypes. Although the cytotypes of A. amellus are not morphologically distinguishable, previous studies showed spatial segregation and limited gene flow between them, which could result in different evolutionary trajectories for each cytotype. METHODS: We combine macroevolutionary, microevolutionary and niche modelling tools to disentangle the origin and the demographic history of the cytotypes, using chloroplast and nuclear markers in a dense population sampling in central Europe. KEY RESULTS: Our results revealed a segregation between diploid and hexaploid cytotypes in the nuclear genome, where each cytotype represents a monophyletic lineage probably homogenized by concerted evolution. In contrast, the chloroplast genome showed intermixed connections between the cytotypes, which may correspond to shared ancestral relationships. Phylogeny, demographic analyses and ecological niche modelling supported an ongoing differentiation of the cytotypes, where the hexaploid cytotype is experiencing a demographic expansion and niche differentiation with respect to its diploid relative. CONCLUSIONS: The two cytotypes may be considered as two different lineages at the onset of their evolutionary diversification. Polyploidization led to the occurrence of hexaploids, which expanded and changed their ecological niche.

• MeSH
• Aster genetika   MeSH
• biologická evoluce * MeSH
• biologické modely MeSH
• DNA chloroplastová analýza   MeSH
• fylogeneze * MeSH
• fylogeografie MeSH
• genetické markery MeSH
• mezerníky ribozomální DNA analýza   MeSH
• polyploidie * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Evropa MeSH
• Názvy látek
• DNA chloroplastová MeSH
• genetické markery MeSH
• mezerníky ribozomální DNA MeSH