Résumé
The rad50 gene of Saccharomyces cerevisiae plays a crucial role in meiotic recombination as well as DNA repair during vegetative growth. The RAD50 protein interacts with the product of the Mre11 and Xrs2 genes to form a three-protein complex involved in the repair of DNA-double strand breaks (DSB). Yeast mutants lacking this complex are X-ray sensitive, defective in illegitimate recombination (IR) and show a weak hyper-rec phenotype for homologous recombination (HR) in dividing somatic cells. Recently, the Arabidopsis thaliana rad50 homologue gene has been cloned and intrachromosomal HR experiments involving homozygous and heterozygous mutants for this gene have confirmed the hyper-rec phenotype. Based on the sequence of the S. cerevisiae and the A. thaliana RAD50 protein, we designed degenerate primers and PCR-amplified a 300bp 3' region of this gene in rice (Oryza sativa L., cv. Nipponbare). This probe was mapped near the centromeric region on the long arm of chromosome 2 by hybridisation on a BAC library. Southern and Northern experiments showed the gene to be single locus and to be differentially expressed throughout the rice plant. We are currently examining the effect of silencing of the rad50 gene both on the plant as a whole and on HR versus IR frequencies by RNAi or antisense approaches. The characterisation of this gene, of which a loss of expression is lethal in mammals, will first serve to improve our knowledge of its function in plants. Moreover, it will increase our understanding of the recombination process in a model crop species and could enable improvements in plant biotechnology such as gene targeting and replacement. (Texte intégral)