Nicotiana Benthamiana Resistance to Non-adapted Melon Necrotic Spot Virus Results from an Incompatible Interaction Between Virus RNA and Translation Initiation Factor 4E

Nicotiana benthamiana has been described as non-host for Melon necrotic spot virus (MNSV). We investigated the basis of this resistance using the unique opportunity provided by strain MNSV-264, a recombinant virus that is able to overcome the resistance. Analysis of chimeric MNSV mutants showed that virulence in N. benthamiana is conferred by a 49 nucleotide section of the MNSV-264 3'-UTR, which acts in this host as a cap-independent translational enhancer (3'-CITE). Although the 3'-CITE of non-adapted MNSV-Mα5 is active in susceptible melon, it does not promote efficient translation in N. benthamiana, thus preventing expression of proteins required for virus replication. However, MNSV-Mα5 gains the ability to multiply in N. benthamiana cells if eIF4E from a susceptible melon variety (Cm-eIF4E-S) is supplied in trans. These data show that N. benthamiana resistance to MNSV-Mα5 results from incompatibility between the MNSV-Mα5 3'-CITE and N. benthamiana eIF4E in initiating efficient translation of the viral genome. Therefore, non-host resistance conferred by the inability of a host susceptibility factor to support viral multiplication may be a possible mechanism for this type of resistance to viruses.