First systematic analysis in plants of the interaction network formed by recombination initiation proteins: a renewed model

During sexual reproduction, mother cells of gametes are subjected to dramatic assaults since their genetic material cannot be transmitted correctly without enduring an exorbitant number of lesions (several hundred double-strand breaks (DSBs) per cell). The model plant Arabidopsis thaliana is one of the rare eukaryotes in which large-scale screens have been carried out, giving access to many, if not all, of the players in the break formation pathway. Mathilde Grelon's team (MeioMe), in collaboration with Peter Schlögelhofer's team from the University of Vienna, has seized this opportunity to perform a systematic analysis of the biochemical, genetic and cytogenetic interactions of the pathway players. The results obtained provide a better understanding of how DNA breaks are made without compromising the integrity of the gene pool.

The mechanisms of meiotic CBD formation and the regulations involved are still largely unknown, although it is now clear that the catalytic complex responsible (formed by the proteins SPO11-1, SPO11-2 and MTOPVIB) has strong similarities with certain topoisomerases 1 & 2. In order to understand how the association and activation of the catalytic complex of CBD formation is regulated, we studied the biochemical and genetic interactions existing not only between the CBD-forming proteins, but also between these proteins and other components of the meiotic cellular machinery (chromosome axis, DNA repair proteins etc...).

The results obtained showed that:
> The proteins inducing DNA breaks are organized into several subcomplexes.
> The MTOPVIB protein occupies a central position in the picture since it is required (i) for the assembly of the catalytic complex 2, (ii) to recruit the catalytic part of the complex to the chromosome axis and (iii) to establish a link between the core proteins and their regulators.
> Among the DSB proteins, PRD3 is likely to play a key regulatory role since it establishes a link between the DSB formation and the DSB repair proteins.
> Finally, our analyses revealed drastic evolutionary divergences for several of the studied proteins.

This work represents a new step towards the understanding of the meiotic recombination initiation mechanisms. It allows to discriminate the catalytic from the regulatory functions involved and to envisage an in vivo and in vitro reconstruction of the DSB formation activity.

The genetic map (sites and rates of crossover formation) is largely determined by the meiotic CBD map. Consequently, the detailed characterization of the mechanisms involved in the initiation of meiotic recombination (nature of the complex, regulation of the assembly of the complex and regulation of its activity) is an essential prerequisite for the development of strategies to modify recombination patterns.