Similar patterns of rDNA evolution in synthetic and recently formed natural populations of Tragopogon (Asteraceae) allotetraploids

<p>Abstract</p> <p>Background</p> <p><it>Tragopogon mirus </it>and <it>T. miscellus </it>are allotetraploids (2<it>n </it>= 24) that formed repeatedly during the past 80 years in eastern Washington and adjacent Idaho (USA) following the introduction of the diploids <it>T. dubius</it>, <it>T. porrifolius</it>, and <it>T. pratensis </it>(2<it>n </it>= 12) from Europe. In most natural populations of <it>T. mirus </it>and <it>T. miscellus</it>, there are far fewer 35S rRNA genes (rDNA) of <it>T. dubius </it>than there are of the other diploid parent (<it>T. porrifolius </it>or <it>T. pratensis</it>). We studied the inheritance of parental rDNA loci in allotetraploids resynthesized from diploid accessions. We investigate the dynamics and directionality of these rDNA losses, as well as the contribution of gene copy number variation in the parental diploids to rDNA variation in the derived tetraploids.</p> <p>Results</p> <p>Using Southern blot hybridization and fluorescent <it>in situ </it>hybridization (FISH), we analyzed copy numbers and distribution of these highly reiterated genes in seven lines of synthetic <it>T. mirus </it>(110 individuals) and four lines of synthetic <it>T. miscellus </it>(71 individuals). Variation among diploid parents accounted for most of the observed gene imbalances detected in F₁hybrids but cannot explain frequent deviations from repeat additivity seen in the allotetraploid lines. Polyploid lineages involving the same diploid parents differed in rDNA genotype, indicating that conditions immediately following genome doubling are crucial for rDNA changes. About 19% of the resynthesized allotetraploid individuals had equal rDNA contributions from the diploid parents, 74% were skewed towards either <it>T. porrifolius </it>or <it>T. pratensis</it>-type units, and only 7% had more rDNA copies of <it>T. dubius</it>-origin compared to the other two parents. Similar genotype frequencies were observed among natural populations. Despite directional reduction of units, the additivity of 35S rDNA locus number is maintained in 82% of the synthetic lines and in all natural allotetraploids.</p> <p>Conclusions</p> <p>Uniparental reductions of homeologous rRNA gene copies occurred in both synthetic and natural populations of <it>Tragopogon </it>allopolyploids. The extent of these rDNA changes was generally higher in natural populations than in the synthetic lines. We hypothesize that locus-specific and chromosomal changes in early generations of allopolyploids may influence patterns of rDNA evolution in later generations.</p

Rapid Chromosome Evolution in Recently Formed Polyploids in Tragopogon (Asteraceae)

Polyploidy, frequently termed "whole genome duplication", is a major force in the evolution of many eukaryotes. Indeed, most angiosperm species have undergone at least one round of polyploidy in their evolutionary history. Despite enormous progress in our understanding of many aspects of polyploidy, we essentially have no information about the role of chromosome divergence in the establishment of young polyploid populations. Here we investigate synthetic lines and natural populations of two recently and recurrently formed allotetraploids Tragopogon mirus and T. miscellus (formed within the past 80 years) to assess the role of aberrant meiosis in generating chromosomal/genomic diversity. That diversity is likely important in the formation, establishment and survival of polyploid populations and species.Applications of fluorescence in situ hybridisation (FISH) to natural populations of T. mirus and T. miscellus suggest that chromosomal rearrangements and other chromosomal changes are common in both allotetraploids. We detected extensive chromosomal polymorphism between individuals and populations, including (i) plants monosomic and trisomic for particular chromosomes (perhaps indicating compensatory trisomy), (ii) intergenomic translocations and (iii) variable sizes and expression patterns of individual ribosomal DNA (rDNA) loci. We even observed karyotypic variation among sibling plants. Significantly, translocations, chromosome loss, and meiotic irregularities, including quadrivalent formation, were observed in synthetic (S(0) and S(1) generations) polyploid lines. Our results not only provide a mechanism for chromosomal variation in natural populations, but also indicate that chromosomal changes occur rapidly following polyploidisation.These data shed new light on previous analyses of genome and transcriptome structures in de novo and establishing polyploid species. Crucially our results highlight the necessity of studying karyotypes in young (<150 years old) polyploid species and synthetic polyploids that resemble natural species. The data also provide insight into the mechanisms that perturb inheritance patterns of genetic markers in synthetic polyploids and populations of young natural polyploid species

Design and baseline characteristics of the finerenone in reducing cardiovascular mortality and morbidity in diabetic kidney disease trial

Background: Among people with diabetes, those with kidney disease have exceptionally high rates of cardiovascular (CV) morbidity and mortality and progression of their underlying kidney disease. Finerenone is a novel, nonsteroidal, selective mineralocorticoid receptor antagonist that has shown to reduce albuminuria in type 2 diabetes (T2D) patients with chronic kidney disease (CKD) while revealing only a low risk of hyperkalemia. However, the effect of finerenone on CV and renal outcomes has not yet been investigated in long-term trials. Patients and Methods: The Finerenone in Reducing CV Mortality and Morbidity in Diabetic Kidney Disease (FIGARO-DKD) trial aims to assess the efficacy and safety of finerenone compared to placebo at reducing clinically important CV and renal outcomes in T2D patients with CKD. FIGARO-DKD is a randomized, double-blind, placebo-controlled, parallel-group, event-driven trial running in 47 countries with an expected duration of approximately 6 years. FIGARO-DKD randomized 7,437 patients with an estimated glomerular filtration rate >= 25 mL/min/1.73 m(2) and albuminuria (urinary albumin-to-creatinine ratio >= 30 to <= 5,000 mg/g). The study has at least 90% power to detect a 20% reduction in the risk of the primary outcome (overall two-sided significance level alpha = 0.05), the composite of time to first occurrence of CV death, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for heart failure. Conclusions: FIGARO-DKD will determine whether an optimally treated cohort of T2D patients with CKD at high risk of CV and renal events will experience cardiorenal benefits with the addition of finerenone to their treatment regimen. Trial Registration: EudraCT number: 2015-000950-39; ClinicalTrials.gov identifier: NCT02545049

Transcription activity of rRNA genes correlates with a tendency towards intergenomic homogenization in Nicotiana allotetraploids

International audienceThis paper establishes relationships between two aspects of ribosomal DNA (rDNA) biology: epigenetic silencing of rDNA loci; and homogenization leading to concerted evolution. Here, we examined rDNA inheritance and expression patterns in three natural Nicotiana allopolyploids (closest living descendants of diploid parents are given), N. rustica (N. paniculata x N. undulata), N. tabacum (N. sylvestris x N. tomentosiformis) and N. arentsii (N. undulata x N. wigandioides), and synthetic F-1 hybrids and allopolyploids. The extent of interlocus rDNA homogenization decreased in the direction N. arentsii > N. tabacum > N. rustica. The persistence of parental rDNA units in one of the subgenomes was associated with their transcription inactivity and likely heterochromatization. Of synthetic hybrids and polyploids only N. paniculata x N. undulata showed strong uniparental transcriptional silencing of rDNA triggered already in F-1. Epigenetic patterns of expression established early in allopolyploid nucleus formation may render units susceptible or resistant to homogenization over longer time-frames. We propose that nucleolus-associated transcription leaves rDNA units vulnerable to homogenization, while epigenetically inactivated units, well-separated from the nucleolus, remain unconverted

Karyotype organisation of individuals of <i>T. mirus</i> from three populations (localities of each population are indicated in column 1).

<p>The parental origins of the chromosomes were determined by GISH. Chromosome nomenclature of homeologous groups (A–F) followed Ownbey and McCollum <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003353#pone.0003353-Ownbey2" target="_blank">[25]</a> and Pires <i>et al</i>. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003353#pone.0003353-Pires1" target="_blank">[24]</a>. Superscript letters indicate the genome origins of the chromosomes, du = <i>T. dubius</i>, po = <i>T. porrifolius</i>. Chromosomes carrying translocations are indicated by naming the chromosome according to the genomic origins of the centromeres, followed by the genome origins of the translocated segments. E-indicates chromosome set as expected from the diploid parents.</p

Karyotype organisation of individuals of <i>T. miscellus</i> from two populations (localities of each population are indicated in column 1).

<p>The parental origins of the chromosomes were determined by GISH. Chromosome nomenclature of homeologous groups (A–F) followed Ownbey and McCollum <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003353#pone.0003353-Ownbey2" target="_blank">[25]</a> and Pires <i>et al.</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003353#pone.0003353-Pires1" target="_blank">[24]</a>. Superscript letters indicate the genome origins of the chromosomes, du = <i>T. dubius</i>, pr = <i>T. pratensis</i>. Chromosomes carrying translocations are indicated as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003353#pone-0003353-t001" target="_blank">Table 1</a>. E-indicates parental chromosome set as expected from the diploid parent.</p

Pollen meiosis in synthetic <i>T. mirus.</i>

<p>(A,B) Feulgen staining showing in (A) 12 regular bivalents and (B) one quadrivalent (arrow) and bivalents in close association with each other and a nucleolus. (C–H). Fluorochrome colours and GISH probes are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003353#pone-0003353-g002" target="_blank">Figure 2</a>. (C–D) Note chromosome A^du in association with the nucleolus. Two bivalents, one from the <i>T. dubius</i> genome (yellow) and one from the <i>T. porrifolius</i> genome (orange), overlapped (arrow), perhaps occurring as a multivalent. (E–F). Note the rDNA and the bivalents carrying these genes associated with the nucleolus. A quadrivalent with two chromosomes of <i>T. dubius</i> origin and two of <i>T. porrifolius</i> origin occurring in a ring (arrow). (G–H) Note two bivalents (A^du and D^po) with rDNA associated with the nucleolus and the A^po bivalent with condensed rDNA unassociated with the nucleolus. N = nucleolus. Scale bar (C–H) is 10 µm.</p