How to evolve without centromeres: meiotic recombination dynamics in holocentric plants

Introduction

Centromeres strongly affect genomic architecture and meiotic recombination distribution and also play a key role in constraining karyotype evolution. The recombination landscape is also heavily influenced by chromosome number and structure (i.e., karyotypes), as at least one crossover per chromosome (and rarely more than three) occurs in most species, making chromosome number the primary driver of recombination frequency. In addition, centromeres inhibit recombination, and therefore crossovers tend to occur mostly at chromosome ends.

Holocentric Chromosomes

However, several unrelated eukaryotic lineages do not have centromeres, or at least, not conventional ones. Such is the case for plants with holocentric chromosomes, where hundreds of small centromere-like units are evenly distributed across the length of the chromosome. Notably, holocentricity has evolved repeatedly across the tree of life and at least four times during plant evolution.

Research Opportunities

Holocentric plant species offer a unique opportunity to study the plasticity of meiotic recombination control. These species have lost typical centromeres, making them ideal for investigating how the recombination landscape was reshaped after the transition to holocentricity. Moreover, holocentricity unleashes changes in the karyotype, offering the possibility to analyze the effects of chromosome breaks and fusions on recombination frequency and distribution.

Project Aims

The HoloRECOMB project aims are as follows:

1. Analyze how transitions to holocentricity affect meiotic recombination dynamics in different holocentric plant lineages.
2. Explore the effect of chromosome breaks and fusions on crossover number and distribution.
3. Examine whether the crossover regulation in holocentric plants acts in a similar manner as in monocentric ones.

Conclusion

Understanding how holocentricity affects recombination dynamics will provide insights into important mechanistic aspects of meiosis with potential practical applications for crossover regulation in centromeric regions.