Understanding evolution through exceptions
Relevant discoveries rarely emerge from repeating what is already known. They often emerge from exceptions.
We investigate how living systems reorganise fundamental mechanisms of reproduction when their chromosomes do not follow the conventional architecture. The exception, for us, is not an error. It is evolutionary potential.
Chromosomes without a single centromere
In most textbook organisms, each chromosome has one centromere: a single site where spindle fibres attach during cell division. Meiosis as we know it, with its pairing, crossovers and two rounds of segregation, was worked out in these monocentric species.
Holocentric organisms break this rule. Their centromere activity is spread along the whole length of each chromosome. This creates a problem for meiosis that each holocentric lineage has had to solve, and they have solved it in different ways.
Our main models are beak-sedges of the genus Rhynchospora (Cyperaceae), complemented by other holocentric plants such as woodrushes (Luzula) and sundews (Drosera), and by their monocentric relatives for comparison.
Research lines
1. Evolution of holocentric chromosomes
How does a lineage move from one centromere per chromosome to many?
Holocentricity has evolved independently several times in plants and animals. We compare holocentric species with their closest monocentric relatives to reconstruct this transition and to understand how centromeres built on repetitive DNA arise, spread and turn over.
Keywords: holocentromeres, centromeric repeats, karyotype evolution, chromosome fusions and fissions.
2. Genome organisation
What does a genome look like when centromeres are everywhere?
Using chromosome-scale and haplotype-resolved genome assemblies, we study how centromere distribution shapes the layout of genes, repeats and chromatin along chromosomes, and how holocentric genomes tolerate large-scale rearrangements. This work showed that repeat-based holocentromeres influence genome architecture and karyotype evolution in Rhynchospora.
Keywords: genome assembly, pangenomics, repeatome, chromatin organisation.
3. Meiotic recombination and crossover patterning
What decides where crossovers form when there is no single centromere to avoid?
In monocentric species, crossovers are typically suppressed around the centromere. Holocentric plants let us separate the effect of the centromere from other features of the chromosome. We map recombination at high resolution, follow the meiotic machinery by immunolocalisation and super-resolution microscopy, and study chromosome pairing and synapsis to identify the primary drivers of crossover placement.
This line is the core of the ERC Starting Grant project HoloRECOMB.
Keywords: homologous recombination, crossover interference, synaptonemal complex, single-gamete sequencing.
4. Inverted meiosis and chromosome segregation
How do holocentric chromosomes segregate faithfully through two meiotic divisions?
Several holocentric plants invert the canonical order of meiosis: sister chromatids separate in the first division and homologues in the second. We study how cohesion, chromosome condensation and chiasmata are regulated to make this possible, comparing chiasmatic meiosis in Rhynchospora radicans with achiasmatic meiosis in Rhynchospora tenuis.
In R. tenuis, we found that meiosis proceeds without crossovers, producing sexual offspring that genetically resemble clones.
Keywords: inverted meiosis, sister chromatid cohesion, achiasmy, chromosome segregation.
5. Comparative biology of exceptional systems
What do unusual reproductive systems reveal about general principles?
Beyond sedges, we work with collaborators on other organisms whose meiosis departs from the textbook: dogroses with their asymmetric meiosis and bimodal centromeres, carnivorous plants, and asexual planarians. We also study evening primroses (Oenothera), where permanent translocation heterozygosity (PTH) preserves heterozygosity despite habitual self-pollination. Reciprocal translocations restrict chromosome pairing to homologous ends, producing meiotic rings of up to 14 chromosomes rather than separate bivalents. We also ask how meiosis accommodates polyploidy, as in the dogroses, and whether holocentric chromosomes change the scope for meiotic drive, the biased transmission of selfish chromosomal elements through asymmetric female meiosis. Each system tests how far our conclusions extend.
Keywords: comparative genomics, asexuality, polyploidy, meiotic drive.
How we work
Cytogenetics and imaging
Fluorescence in situ hybridisation, chromosome painting, immunolocalisation and super-resolution microscopy to see chromosomes and meiotic proteins directly.
Genomics
Long-read sequencing, haplotype-resolved assemblies and pangenomes to read genome structure across species and populations.
Recombination mapping
Single-gamete and population sequencing to locate crossovers at high resolution.
Molecular and cell biology
Functional analysis of the proteins behind pairing, synapsis, cohesion and segregation.
Research principles
Evidence precedes interpretation.
From observation to mechanism.
Exceptional systems reveal fundamental biology.
Funding
Our research is supported by the Max Planck Society, the European Research Council (ERC Starting Grant HoloRECOMB, awarded 2023), the German Research Foundation (DFG), the Human Frontier Science Program (HFSP), the German Academic Exchange Service (DAAD) and the Cluster of Excellence on Plant Sciences (CEPLAS).