Moss non-canonical BRCA2 is a major actor for homologous recombination and gene targeting

Genome stability is essential for plant development, reproduction, and adaptation. Homologous recombination (HR) preserves genome integrity by repairing DNA damage and shapes genetic diversity. Understanding the mechanisms of HR can improve gene targeting in plants, a valuable advance for precise genome engineering. The moss Physcomitrium patens displays an exceptionally high rate of HR compared with other plants. However, the underlying mechanisms had remained unknown. Although the protein BRCA2 is crucial for HR in plants and other eukaryotes, its presence had not previously been detected in moss.

Results
The MeioMe and DRAGON teams identified a unique BRCA2 orthologue in Physcomitrium patens using bioinformatic approaches and carried out its functional characterization. This protein is notable for lacking a DNA-binding domain (DBD), which is otherwise highly conserved within this protein family. The brca2Δ moss mutants generated in this study exhibit reduced growth and abnormal spore formation, indicating developmental defects and sterility. In addition, the absence of BRCA2 renders these plants hypersensitive to genotoxic agents and abolishes gene targeting. The teams also experimentally demonstrated interactions between moss BRCA2 and DNA, as well as with a key recombinase (RAD51). Together, these findings suggest that this non-canonical BRCA2 protein efficiently orchestrates HR in moss despite the absence of a conserved DBD.

Perspectives
These results demonstrate a conserved role for BRCA2 in plants while highlighting the functional diversity of its homologues across eukaryotes. The identification of this non-canonical BRCA2 protein will enable detailed analysis of the biochemical and structural mechanisms underlying its functions in HR, with the prospect of addressing the following questions: how does moss BRCA2 bind DNA in the absence of a DBD? How does this absence alter BRCA2 interactions in vivo in moss? How is BRCA2 recruited to sites of DNA damage?
Beyond advancing our understanding of a key HR protein, these findings open several avenues for improving gene targeting strategies in plants.


Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences in collaboration.