Meiotic recombination dynamics in plants with repeat-based holocentromeres shed light on the primary drivers of crossover patterning

Abstract

Centromeres strongly affect (epi)genomic architecture and meiotic recombination dynamics influencing the overall distribution and frequency of crossovers. Here, we studied how recombination is regulated and distributed in the holocentric plant Rhynchospora breviuscula, a species lacking localised centromeres. Combining immunocytochemistry, chromatin analysis and high-throughput single-pollen sequencing, we discovered that crossover frequency is higher at ends related to centred chromosomal regions. Contrasting the diffused distribution of (epi)genetic features and hundreds of repeat-based centromeric units. Remarkably, we found that crossovers were abolished at core centromeric units but not at their vicinity indicating the absence of a centromere effect across repeat-based holocentromeres. We further show that telomere-led pairing and synapsis of homologous chromosomes appear to be the primary force determining the observed U-shaped recombination landscape. While centromere and (epi)genetic properties only affect crossover positioning locally. Our results suggest that the conserved U-shaped crossover distribution of eukaryotes is independent of chromosome compartmentalisation and centromere organisation.