Plant & Animal Genomes XIV Conference

January 14-18, 2006
Town & Country Convention Center
San Diego, CA

Analysis Of The Interaction Melon-Melon Necrotic Spot Virus Controlled By The Recessive Resistance Gene Nsv

Christina Nieto^{1, 2} , Monica Morales^{1, 3} , Gisella Orjeda¹ , Veronica Truniger² , Michel Caboche¹ , Catherine Dojimont⁴ , Jordi Garcia-MAS³ , Miguel Aranda² , Abdel Bendahmane¹

¹  INRA-URGV. 2, rue Gaston Crémieux CP 5708. 91057, Evry Cedex, France.

²  CEBAS-CSIC. Apdo. correos 164. 30100 Espinardo, Murcia, Spain.

³  IRTA, Carretera de Cabrils s/n. 08348 Cabrils, Barcelona, Spain.

⁴  INRA-UGAFL, BP 94 - 84143, Montfavet Cedex, France.

Viruses constitute an increasing problem in modern, intensive agriculture. One example is Melon necrotic spot virus (MNSV), an RNA virus endemic in cucurbit crops worldwide. To control virus infections, natural dominant and recessive resistance genes have been identified and introduced into crop species.
The melon gene nsv is the only known natural source of resistance against MNSV. To characterise nsv-mediated resistance, we cloned the nsv locus using a positional cloning strategy and gene candidate approach. This was carried out through the development of a high-resolution genetic map of melon followed by the construction of a BAC library and the identification of a BAC clone carrying the nsv locus. We showed that the nsv locus encodes for an allele of the eukaryotic translation initiation factor 4E (eIF4E). We also confirmed eIF4E function by transient expression and complementation assays.
The nsv gene confers protection against all widespread MNSV strains except the isolate MNSV-264. Chimeric mutants between MNSV-264 and MNSV-Ma5 (a non resistance-breaking isolate) were generated through the exchange of different portions of their genomes using full length infectious cDNA clones. Analysis of protoplasts of susceptible and resistant melon cultivars inoculated with these mutants showed that the MNSV avirulence determinant resides in the 3´-untranslated region of the MNSV genome. To our knowledge, this is the only example in which resistance mediated by eIF4E encounters a non-coding RNA as avirulence determinant.