Biology subjects

Nascimento, T.

Publications and source records attributed to Nascimento, T..

3 recordsLinked to original sources

bioRxiv2026

Haplotype-specific chromosome painting unveils recombination patterns in the holocentric species Rhynchospora breviuscula H.Pfeiff.

The genus Rhynchospora Vahl (beak-sedges) comprises approximately 381 accepted species with a worldwide distribution, all of which possess holocentric chromosomes, where centromeric activity is distributed almost along the entire chromosome. Despite the recent advances, the mechanisms governing the dynamics of meiotic recombination in holocentric plants remain poorly understood. Here, we developed haplotype-specific oligo-FISH probes for chromosomes 1, 2, and 3 based on a haplotype-phased genome assembly of Rhynchospora breviuscula (n = 5), enabling homolog-specific chromosome painting. Each probe set was labelled with a distinct fluorophore and hybridised in situ to metaphase chromosomes of the reference plant and seven F1 individuals derived from self-crossed reference plants. This approach allowed the unambiguous discrimination of homologous haplotypes and the indirect visualisation of crossover (CO) events in recombined chromosomes. We observed that recombination events were predominantly located in terminal chromosomal regions, consistent across individuals. These results corroborate previous findings from single-cell recombination mapping and provide independent cytological validation of the recombination landscape in this species. Our study establishes haplotype-specific chromosome painting as a robust tool for high-resolution mapping of meiotic recombination in holocentric plants across generations. Furthermore, these probes provided a foundation for future investigations into inverted meiosis, a mechanism characterized by an alternative pattern of chromosome segregation in holocentric species.

genetics↗

bioRxiv2026

Holocentromere diversity in Cyperaceae: contrasting repeat organisation in Mapanioideae and Cyperoideae

Centromeres ensure accurate chromosome segregation and are typically confined to a single, localised region in monocentric chromosomes. In contrast, holocentric chromosomes exhibit kinetochore activity distributed along the chromosome length. Although holocentricity is widespread in Cyperaceae, the composition and organisation of these centromeres, as well as their evolutionary diversification, remain poorly understood. Here, we investigated centromere organisation in representatives of the subfamilies Mapanioideae (Hypolytrum schraderianum Nees) and Cyperoideae (Cladium mariscus (L.) Pohl) by combining genome assemblies, repeatome characterisation (RepeatExplorer), fluorescence in situ hybridisation (FISH), and immunolocalisation. Comparative synteny analyses incorporating the genomes of Rhynchospora breviuscula (n = 5) and Carex littledalei (n = 29) identified conserved blocks, eventually expanding almost whole chromosomes of H. schraderianum (n = 30) and Cl. mariscus (n = 39), despite divergent chromosome numbers and deep evolutionary distances within Cyperaceae. Mobile elements showed very low abundances and were uniformly dispersed, with Ty1/Copia Angela being the most abundant in both species. In Cl. mariscus, holocentromeres showed an extended distribution of centromere- and kinetochore-associated proteins along the chromosomes, largely colocalised with two satellite DNA repeats that form dispersed clusters. In contrast, H. schraderianum also displayed kinetochore signals along chromatids, but the most abundant satellite DNA family was enriched in distal and interstitial chromosomal regions rather than interspersed along the chromatids. Together, these results reveal different genomic architectures underlying holocentric organisation in phylogenetically distinct Cyperaceae lineages, suggesting that holocentromeres in this family have diversified with variation in centromere organisation in regard to its association with repetitive DNA.

evolutionary biology↗

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↗