Biology subjects

Dreissig, S.

Publications and source records attributed to Dreissig, S..

4 recordsLinked to original sources

bioRxiv2026

Sex without crossovers mimics clonal reproduction in the holocentric plant Rhynchospora tenuis

Meiotic recombination ensures accurate chromosome segregation and promotes genetic diversity by generating crossovers between homologous chromosomes1. While essential in most sexually reproducing organisms, recombination is variably regulated and can be absent in some lineages, a condition known as achiasmy2. However, obligate achiasmy in both sexes of a sexual species has not been previously documented. Here, we investigate the beak-sedge Rhynchospora tenuis, a holocentric plant with the lowest known chromosome number among flowering plants (n = 2) and inverted meiosis3. Using chromosome-scale genome assemblies from nine accessions, molecular cytogenetics, immunocytochemistry, high-throughput single-gamete sequencing and whole-genome sequencing of controlled crosses, we show that R. tenuis undergoes obligate, genome-wide achiasmy in both male and female meiosis. Despite normal early meiotic axis formation, synapsis fails, crossovers are not detected cytologically or genetically, and univalents persist at metaphase I. Extensive haplotype-specific accumulation of transposable elements (TEs) generates segregation distortion (e.g. meiotic drive), favouring the transmission of larger, TE-rich chromosomes. Remarkably, sexual reproduction is retained with fertilisation producing viable seeds only when translocation-compatible gametes meet, indicating strong post-meiotic selection that eliminates incompatible homozygous combinations. As a result, all surviving offspring are genetically identical to the maternal genotype, effectively restoring heterozygosity each generation and mimicking clonal reproduction. We propose that the combined effects of recombination loss, low chromosome number, holocentricity, inverted meiosis, and selective transmission of longer chromosomes enable faithful segregation and clonal-like inheritance despite sexual reproduction. These findings challenge the boundary between sex and clonality, revealing a unique evolutionary strategy linking genome architecture, recombination loss, and transmission bias.

evolutionary biology↗

bioRxiv2023

Broad-scale signatures of linked selection under divergent recombination landscapes and mating systems in natural populations of rye and barley

Understanding the interactions between patterns of recombination, mating systems, and signatures of natural selection is a central aim in evolutionary biology. Patterns of recombination shape the evolution of genomes by affecting the efficacy of selection. Within populations, genetic shuffling is achieved through meiotic recombination, random chromosome segregation, and the frequency of outbreeding. Recombination landscapes vary between species and populations, and are further influenced by mating systems. Here, we use populations of two related grass species, rye (Secale cereale) and barley (Hordeum vulgare ssp. spontaneum), that differ in their mating system, to analyse signatures of linked selection under divergent recombination landscapes. Rye (outbreeding) and barley (inbreeding) are members of the Poaceae and diverged approximately 15 M years ago. We estimated population recombination rates, analysed patterns of genetic diversity, identified signatures of linked selection, and quantified the fraction and functional class of genes affected by linked selection. In this comparison, we detected signatures of linked selection in low-recombining regions in both species. In inbreeding barley, the low-recombining fraction of the genome was more than 2-fold larger than in outbreeding rye. Furthermore, considering differences in gene density across the genome, approximately 1.5 times more genes were affected by linked selection in barley than in rye. In both species, genomic regions affected by linked selection harbour mostly genes involved in basic cellular processes. We provide empirical evidence for quantitative differences in recombination landscapes between closely related species of divergent mating systems, and discuss the consequences of linked selection and the efficacy of natural selection. Significance statementThe ability of natural selection to disentangle beneficial from deleterious mutations across the genome is shaped by patterns of recombination, yet our understanding of the magnitude of this interaction is incomplete. In our work, we show that patterns of recombination differ between related outbreeding and inbreeding grass species, and that the efficacy of selection differs between them. We provide empirical evidence for quantitative differences in recombination landscapes and patterns of selection.

evolutionary biology↗

bioRxiv2020

More filtering on SNP calling does not remove evidence of inter-nucleus recombination in dikaryotic arbuscular mycorrhizal fungi

We respond to a recent reanalysis of single nucleus sequence data from Chen et al. 2018 eLife, which indicated that evidence of inter-nuclear recombination in dikaryotic arbuscular mycorrhizal fungi decreases when heterozygous, duplicated sites being supported by less than 5 reads, are removed from the dataset. Here, we show that applying a more stringent methodology for filtering SNP calls that focuses exclusively on single copy and homozygous regions with at least 5 reads supporting a given SNP, still recovers several hundreds putative inter-nucleus recombination events within the same dataset. We also provide evidence for retaining SNPs supported by less than 5 reads for genotyping individual nuclei using the same dataset.

genomics↗

bioRxiv2020

Unequal contribution of two paralogous centromeric histones to function the cowpea centromere

The legume cowpea (Vigna unguiculata, 2n=2x=22) has significant tolerance to drought and heat stress. Here we analysed and manipulated cowpea centromere-specific histone H3 (CENH3) genes, aiming to establish a centromere-based doubled-haploid method for use in genetic improvement of this dryland crop in future. Cowpea encodes two functional CENH3 variants (CENH3.1 and CENH3.2) and two CENH3 pseudogenes. Phylogenetic analysis suggests that gene duplication of CENH3 occurred independently during the speciation of V. unguiculata and the related V. mungo without a genome duplication event. Both functional cowpea CENH3 variants are transcribed, and the corresponding proteins are intermingled in subdomains of different types of centromere sequences in a tissue-specific manner together with the outer kinetochore protein CENPC. CENH3.2 is removed from the generative cell of mature pollen, while CENH3.1 persists. Differences between both CENH3 paralogs are restricted to the N-terminus. The complete CRISPR/Cas9-based inactivation of CENH3.1 resulted in delayed vegetative growth and sterility, indicating that this variant is needed for plant development and reproduction. By contrast, CENH3.2 knockout individuals did not show obvious defects during vegetative and reproductive development, suggesting that the gene is an early stage of subfunctionalization or pseudogenization. One-sentence summaryThe two paralogous centromeric histones (CENH3) of cowpea contribute unequal to the function of the centromere.

genetics↗