Résumé
The detection and analysis of DNA polymorphism's become an essential aim in plant breeding, particularly for early selection of difficult phenotyping traits. As part of our citrus rootstock breeding program for tolerance to salinity, we are currently working on the search and study of homologous genes of ionic transporter of model plants. Here are presented the results concerning the diversity of the NhxI gene coding potentially for an antiport Na+/H+ identified in grapefruit fruits. 42 accessions of the Corsican citrus germplasm depository have been analysed for Restriction Fragment Length Polymorphism's using EcoRI and EcoRV restriction enzyme and an amplified fragment (1500 bp) covering the 5' region of grapefruit Nhx1 gene as probe. A important diversity has been detected and the RFLP profiles are in agreement with a single gene segregation and the known evolution pattern of the accessions. To detect polymorphism inside the gene sequence, the DNA of eight genotypes was amplified with specific primers of NhxI gene. These PCR products have been cloned into the vector pGEM-T and sequenced. Sequence comparison shows that the Poncirus trifoliata, known as a sodium excluder, differs 48bp in an intronic sequence compared with all the different species of Citrus genus analyzed. The later ones known as sodium includer have very similar sequences. Studies by RTPCR and northern are going on to analyze a possible correlation between the NhxI gene expression and citrus tolerance to salinity. (Texte intégral)