Homologous recombination

Homologous recombination plays two opposite roles, contributing to genomic diversity through the exchange of homologous chromosomal segments and contributing as well to genomic stability through the repair of DNA breaks. We have investigated the control of homologous recombination in plants and have developed new technologies for the precise engineering of plant genomes (Gene targeting). One factor that represses homologous recombination in plants is the divergence between the recombination partners. We showed that a single mismatch can cause a 3-4 fold drop-off in somatic recombination between repeats. Genetic divergence can also cause a reduction in the rate of meiotic recombination. We demonstrated that the mismatch repair MSH2 gene is responsible for this divergence-based repression of recombination in both somatic and meiotic tissues. This work opens the prospect to use mismatch repair mutants for transferring genes across related species.

The genome of plants, like that of other eukaryotes, is organized into chromatin, a compact structure that reduces the accessibility of DNA to machineries such as transcription, replication, DNA recombination and repair. Plant genes, which contain the characteristic ATPase/helicase motifs of the chromatin remodeling Swi2/Snf2 family of proteins, have been thoroughly studied, but their role in homologous recombination or DNA repair has received limited attention. We showed that plant chromatin remodeling genes can control DNA recombination and DNA damage repair and in some cases are involved in the maintenance of genetic and epigenetic processes. Recently, we showed that the chromatin remodeling yeast RAD54 gene can enhance the frequency of gene targeting in plants by 1-2 orders of magnitude. This work paves the way for precise genetic engineering in plants, a technology that is expected to have a profound effect on scientific research in plant genetics as well as on the development of GMOs with well defined genetic modifications that would be less prone to gene silencing, easier to regulate and more acceptable to the broad public. We are building a new generation of vectors for gene targeting and we are further dissecting the machinery that controls the homologous integration of genes in the genome.