Ales Kovarik

The Czech Academy of Sciences | AVCR · Institute of Biophysics

Number, position and structure of the 5S and 18S-5.8S-26S ribosomal DNA (rDNA) loci are important species characteristics. In recent decades, we have witnessed accumulation of rDNA data, and there is a need to compile, store and analyse this information, and to make it accessible to a broader scientific community. An online resource, accessible at...

Typically in plants, the 5S and 35S ribosomal DNA (rDNA) encoding two major ribosomal RNA species occur at separate loci. However, in some algae, bryophytes and ferns, they are at the same locus (linked arranged). Southern blot hybridisation, polymerase chain reactions (PCR), fluorescent in situ hybridisation, cloning and sequencing were used to re...

Ribosomal DNA (rDNA) loci encoding 5S and 45S (18S-5.8S-28S) rRNAs are important components of eukaryotic chromosomes. Here, we set up the animal rDNA database containing cytogenetic information about these loci in 1343 animal species (264 families) collected from 542 publications. The data are based on in situ hybridisation studies (both radioacti...

The pandemic caused by the spread of SARS-CoV-2 has led to considerable interest in its evolutionary origin and genome structure. Here, we analyzed mutation patterns in 34 human SARS-CoV-2 isolates and a closely related RaTG13 isolated from Rhinolophus affinis (a horseshoe bat). We also evaluated the CpG dinucleotide contents in SARS-CoV-2 and othe...

The classical model of concerted evolution states that hundreds to thousands of ribosomal DNA (rDNA) units undergo homogenization, making the multiple copies of the individual units more uniform across the genome than would be expected given mutation frequencies and gene redundancy. While the universality of this over 50-year-old model has been con...

The supernumerary mostly dispensable B chromosomes are nuclear components of about 15% of eukaryotic phyla. For a long time, B chromosomes have been studied, generating an enormous bulk of knowledge, diluted in the vastness of the scientific literature. In order to provide better access to this information, we created B-chrom ( www.bchrom.csic.es )...

This paper presents the latest update to the Plant rDNA database (Release 4.0), a valuable resource for researchers in the field of plant cytogenetics. The database provides information on the number, position, and arrangement of ribosomal DNA loci in plants, including angiosperms, gymnosperms, bryophytes, and pteridophytes. The new release include...

Accumulation and selection of nucleotides is one of the most challenging problems surrounding the origin of the first RNA molecules on our planet. In the current work we propose that guanosine 3',5' cyclic monophosphate could selectively crystallize upon evaporation of an acidic prebiotic pool containing various other nucleotides. The conditions of...

The ribosomal RNA genes (rDNA) are universal genome components with a housekeeping function, given the crucial role of ribosomal RNA in the synthesis of ribosomes and thus for life-on-Earth. Therefore, their genomic organization is of considerable interest for biologists, in general. Ribosomal RNA genes have also been largely used to establish phyl...

RNA modifications have been known for many years, but their function has not been fully elucidated yet. For instance, the regulatory role of acetylation on N4-cytidine (ac4C) in RNA can be explored not only in terms of RNA stability and mRNA translation but also in DNA repair. Here, we observe a high level of ac4C RNA at DNA lesions in interphase c...

Silicate glasses are ubiquitous on terrestrial planets wherever molten rock – generated by volcanism or impacts – is quenched by air or water. Hence, they provided ready and abundant reactive solid surfaces for prebiotic chemistry on the early Earth. Here, we show that rock glass composition determines basicity, which in turn modulates the outcome...

Nucleolar dominance (ND) is selective epigenetic silencing of 35-48S rDNA loci. In allopolyploids, it is frequently manifested at the cytogenetic level by the inactivation of nucleolar organiser region(s) (NORs) inherited from one or several evolutionary ancestors. Grasses are ecologically and economically one of the most important land plant group...

RNA modifications have been known for many years, but their function has not been fully elucidated yet. For instance, the regulatory role of acetylation on N4-cytidine (ac4C) in RNA should be explored not only from the view of regulation of RNA stability and mRNA translation but also during DNA repair. Here, we observe a pronounced positivity of ac...

Simple telomeric repeats composed of 6‐7 iterating nucleotide units are important sequences typically found at the ends of chromosomes. Here we analyzed their abundance and homogeneity in 42 gymnosperm (29 newly sequenced), 29 angiosperm (1 newly sequenced) and 8 bryophytes using bioinformatics, conventional cytogenetic and molecular biology approa...

In the original article, there was a mistake in Figure 3B as published. The gel lines were marked in an incorrect order. The corrected Figure 3B appears below. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.

During our initial phylogenetic study of the monocot genus Erythronium (Liliaceae), we observed peculiar eudicot‐type internal transcribed spacer (ITS) sequences in a dataset derived from genomic DNA of Erythronium dens‐canis . This raised the possibility of horizontal transfer of a eudicot alien ribosomal DNA (rDNA) into the Erythronium genome. In...

Three out of four RNA components of ribosomes are encoded by 45S ribosomal DNA (rDNA) loci, which are organized as long head-to-tail tandem arrays of nearly identical units, spanning several megabases of sequence. Due to this structure, the rDNA loci are the major sources of gaps in genome assemblies, and gene copy number, sequence composition, and...

The history of rDNA research started almost 90 years ago when the geneticist, Barbara McClintock observed that in interphase nuclei of maize the nucleolus was formed in association with a specific region normally located near the end of a chromosome, which she called the nucleolar organizer region (NOR). Cytologists in the twentieth century recogni...

The occurrence of horizontal gene transfer (HGT) in Eukarya is increasingly gaining recognition. Nuclear-to-nuclear jump of DNA between plant species at high phylogenetic distance and devoid of intimate association (e.g., parasitism) is still scarcely reported. Within eukaryotes, components of ribosomal DNA (rDNA) multigene family have been found t...

Plant genomes consist, to a considerable extent, of non-coding repetitive DNA. Several studies showed that phylogenetic signals can be extracted from such repeatome data by using among-species dissimilarities from the RepeatExplorer2 pipeline as distance measures. Here, we advanced this approach by adjusting the read input for comparative clusterin...

Nucleolar dominance (ND) is an epigenetic, developmentally regulated phenomenon that describes the selective inactivation of 35S rDNA loci derived from one progenitor of a hybrid or allopolyploid. The presence of ND was documented in an allotetraploid grass, Brachypodium hybridum (genome composition DDSS), which is a polyphyletic species that arose...

Heat, protons and a dry crystalline material are the three prerequisites for oligonucleotide synthesis from acid‐form 3′,5′‐cyclic guanosine monophosphate monomers. The process is believed to play a role in the abiotic generation of the most ancient RNA molecules on our planet. Now, we show that the reaction is acid‐catalyzed and that the facile cr...

The assembly of ancient informational polymers from nucleotide precursors is the central challenge of life’s origin on our planet. Among the possible solutions, dry polymerization of 3´,5´‐cyclic guanosine monophosphate (3´,5´‐cGMP) has been proposed as a candidate to create oligonucleotides of the length of 15‐20 nucleotides. However, the reported...

We report on a major update to the animal rDNA loci database, which now contains cytogenetic information for 45S and 5S rDNA loci in more than 2600 and 1000 species, respectively. The data analyses show the following: (i) A high variability in 5S and 45S loci numbers, with both showing 50-fold or higher variability. However, karyotypes with an extr...

Posttranscriptional RNA modifications, including the presence of methyl-6-adenosine (m6A), methyl-5-cytosine (m5C), or pseudo-uridine (Ψ), are known for over many years, but their functional properties have not been fully elucidated yet. Similarly, the regulatory role of N4-cytidine (ac4C) acetylation in RNA must be explored. Here, we observed PARP...

Genome sizes of eukaryotic organisms vary substantially, with whole genome duplications (WGD) and transposable element expansion acting as main drivers for rapid genome size increase. The two North American mudminnows, Umbra limi and U. pygmaea, feature genomes about twice the size of their sister lineage Esocidae (e.g., pikes and pickerels). Howev...

Template-free nonenzymatic polymerization of 3′,5′ cyclic nucleotides is an emerging topic of the origin of life research. In the last ten years, a number of papers have been published addressing various aspects of this process. These works evoked a vivid discussion among scientists working in the field of prebiotic chemistry. The aim of the curren...

This article comments on: Nicola Schmidt, Kathrin M. Seibt, Beatrice Weber, Trude Schwarzacher, Thomas Schmidt, and Tony Heitkam, Broken, silent, and in hiding: tamed endogenous pararetroviruses escape elimination from the genome of sugar beet (Beta vulgaris), Annals of Botany Volume 128, Issue 3, 26 August 2021, Pages 281–291, https://doi.org/10.1...

Previous studies on the polymerization of 3’,5’ cyclic guanosine monophosphate (cGMP) demonstrated the potential of the compound in the abiotic generation of the first oligonucleotide sequences on the early Earth. These experiments were conducted under idealized laboratory conditions that logically raises the question whether the same chemistry cou...

Genome sizes of eukaryotic organisms vary substantially, with whole genome duplications (WGD) and transposable element expansion acting as main drivers for rapid genome size increase. The two North American mudminnows, Umbra limi and U. pygmaea , feature genomes about twice the size of their sister lineage Esocidae (e.g., pikes and pickerels). Howe...

The genomic diversity of SARS-CoV-2 has been a focus during the ongoing COVID-19 pandemic. Here, we analyzed the distribution and character of emerging mutations in a data set comprising more than 95,000 virus genomes covering eight major SARS-CoV-2 lineages in the GISAID database, including genotypes arising during COVID-19 therapy. Globally, the...

Magnetic hypercrosslinked poly(styrene-co-divinylbenzene) microspheres (mgt.HPS1-NH2 and mgt.HPS2-NH2) containing different contents of amino groups were prepared and characterized in this study. The microspheres were used for the capture of uncompacted and compacted bacterial and calf thymus DNAs in the presence of different PEG 6000 and NaCl conc...

The genus Rosa comprises more than 100 woody species characterized by intensive hybridization, introgression, and an overall complex evolutionary history. Besides many diploid species (2n = 2x = 14) polyploids ranging from 3x to 10x are frequently found. Here we analyzed 5S ribosomal DNA in 19 species covering two subgenera and the major sections w...

The essential components of splicing are the splicing factors accumulated in nuclear speckles; thus, we studied how DNA damaging agents and A-type lamin depletion affect the properties of these regions, positive on the SC-35 protein. We observed that inhibitor of PARP (poly (ADP-ribose) polymerase), and more pronouncedly inhibitors of RNA polymeras...

Repeated sequences and polyploidy play a central role in plant genome dynamics. Here, we analyze the evolutionary dynamics of repeats in tetraploid and hexaploid Spartina species that diverged during the last 10 million years within the Chloridoideae, one of the poorest investigated grass lineages. From high-throughput genome sequencing, we annotat...

Given the 2,400-fold range of genome sizes (0.06-148.9 Gbp (gigabase pair)) of seed plants (angiosperms and gymno-sperms) with a broadly similar gene content (amounting to approximately 0.03 Gbp), the repeat-sequence content of the genome might be expected to increase with genome size, resulting in the largest genomes consisting almost entirely of...

Background and Aims Three out of four RNA components of ribosomes are encoded by 45S rDNA loci, whose transcripts are processed into 18S, 5.8S and 26S ribosomal RNAs. The loci are organized as long head-to-tail tandem arrays of nearly identical units spanning over several megabases of sequence. Due to this peculiar structure, the number of rRNA gen...

Nucleolar dominance (ND) consists of the reversible silencing of 35/45S rDNA loci inherited from one of the ancestors of an allopolyploid. The molecular mechanisms by which one ancestral rDNA set is selected for silencing remain unclear. We applied a combination of molecular (Southern blot hybridisation, RT‐CAPS), genomic (analysis of variants) and...

Sex determination and sex chromosomes have been extensively studied due to their importance in evolutionary biology. Species of dioecious plants, which may have sex chromosomes, offer us unique insights into the history of this phenomenon across the Tree of Life. Here, we present Sex‐chrom: a database on plant sex chromosomes (www.sexchrom.csic.es)...

Cellular senescence, induced by genotoxic or replication stress, is accompanied by defects in nuclear morphology and nuclear membrane-heterochromatin disruption. In this work, we analyzed cytological and molecular changes in the linker of nucleoskeleton and cytoskeleton (LINC) complex proteins in senescence triggered by γ-irradiation. We used human...

Background: The world pandemy caused by SARS-CoV-2 spreading has raised considerable interest about its evolutionary origin and genome structure. Here we analysed mutation patterns in 13 human SARS-COV-2 isolates and a closely related RaTG13 isolated from Rhinolophus affinis bat. We also evaluated the CpG dinucleotide contents in SARS-COV-2 and oth...

Large variations in genome size are observed in angiosperms as a result of whole-genome duplications and the balance between amplification and deletion of repetitive DNA, together explaining the observed variation in plant genome size. In the genus Nicotiana, there are 42 cytogenetically diploid species that have been classified into eight sections...

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 tran...

IntroductionRibosomal DNA (rDNA) loci have been widely used for identification of allopolyploids and hybrids, although few of these studies employed high-throughput sequencing data. Here we use graph clustering implemented in the RepeatExplorer (RE) pipeline to analyze homoeologous 5S rDNA arrays at the genomic level searching for hybridogenic orig...

The DNA damage response is mediated by both DNA repair proteins and epigenetic markers. Here, we observe that N6-methyladenosine (m6A), a mark of the epitranscriptome, was common in RNAs accumulated at UV-damaged chromatin; however, inhibitors of RNA polymerases I and II did not affect the m6A RNA level at the irradiated genomic regions. After geno...

Large variations in genome size are observed in angiosperms as a result of whole-genome duplications and the balance between amplification and deletion of repetitive DNA, together explaining the observed variation in plant genome size. In the genus Nicotiana, there are 42 cytogenetically diploid species that have been classified into eight sections...

Introduction: In plants, the multicopy genes encoding ribosomal RNA (rDNA) typically exhibit heterochromatic features and high level of DNA methylation. Here, we explored rDNA methylation in early diverging land plants from Bryophyta (15 species, 14 families) and Marchantiophyta (4 species, 4 families). DNA methylation was investigated by methylati...

The present work aims to evaluate epigenetic changes during ethylene (ET) induced germination in soybean [Glycine max (L.) Merrill]. Our results demonstrated that ethephon (2-chloroethylphosphonic acid, an ET-releasing compound) primed seeds exhibited: (1) DNA hypo-methylation of representative candidate genes (viz. ERF1b and AS-α1) and (2) functio...

The most of all Rosa species within the section Caninae are pentaploids (2n=5x=35), known as dogroses with an asymmetrical meiosis. During meiosis only two sets of chromosomes form bivalents while other sets are transmitted as univalents through the macrogamete. Here we isolated two specific sequences (5S rDNA A and 5S rDNA B) derived from the 5S r...

The intergenic spacer (IGS) of rDNA is frequently built of long blocks of tandem repeats. To estimate the intragenomic variability of such knotty regions, we employed PacBio sequencing of the Cucurbita moschata genome, in which thousands of rDNA copies are distributed across a number of loci. The rRNA coding regions are highly conserved, indicating...

Introduction: Gnetophytes, comprising the genera Ephedra, Gnetum and Welwitschia, are an understudied, enigmatic lineage of gymnosperms with a controversial phylogenetic relationship to other seed plants. Here we examined the organization of ribosomal DNA (rDNA) across representative species. Methods: We applied high-throughput sequencing approa...

The present work investigated a comprehensive genome-wide landscape of DNA methylome and its relationship with transcriptome upon gibberellin A3 (GA3) foliar application under practical field conditions in solanaceae model, Nicotiana tabacum L. Methylated DNA Immunoprecipitation-Sequencing (MeDIP-Seq) analysis uncovered over 82% (18,456) of differe...

The genomic shock hypothesis suggests that allopolyploidy is associated with genome changes driven by transposable elements, as a response to imbalances between parental insertion loads. To explore this hypothesis, we compared three allotetraploids, Nicotiana arentsii , N. rustica and N. tabacum , which arose over comparable time frames from hybrid...

The abundance and chromosomal organization of two repetitive sequences called 12-13P and 18-24J were analyzed in 24 diploid and nine polyploid species of Chenopodium s.l. with special attention to Chenopodium s.s.. Both sequences were predominantly present in Chenopodium s.s species, however, differences in the amplification levels were observed am...

Anchoring of heterochromatin to the nuclear envelope appears to be an important process ensuring the spatial organization of the chromatin structure and genome function in eukaryotic nuclei. Proteins of the inner nuclear membrane (INM) mediating these interactions are able to recognize lamina-associated heterochromatin domains (termed LAD) and simu...

Dogroses represent an exceptional system for studying the effects of genome doubling and hybridization: their asymmetrical meiosis enables recombination in bi-parentally inherited chromosomes but prevents it in maternally inherited ones. We employed fluorescent in situ hybridization, genome skimming, amplicon sequencing of genomic and cDNA as well...

Unfortunately in page 116, second paragraph, the sentence that starts with “Other exceptions include…” was incorrectly published. The complete correct sentence is given below. Other exceptions include the recently discovered Cestrum-type (TTTTTTAGGG) (Peška et al. 2015) and Allium-type telomeres (CTCGGTTATGGG) (Fajkus et al. 2016).