The Capsicum L3 gene-mediated resistance against the tobamoviruses is elicited by the coat protein.

The L3 gene is responsible for the hypersensitive response in Capsicum plants against infection by tobamoviruses. The resistance conferred by this gene is one of the most effective so far described against tobamoviruses. Certain isolates of pepper mild mottle virus (PMMV) are the only tobamoviruses able to overcome the L3 resistance. Chimeric viral genomes between PMMV-S (to which L3 plants are hypersensitive) and PMMV-I (an L3 resistance-breaking isolate) led us to conclude that sequence variation within the coat protein gene of both isolates determines their different virulence in L3L3 plants. Furthermore, the results indicate that a single amino acid substitution, Asn to Met, at position 138 of the PMMV-I coat protein is sufficient to induce the hypersensitive response and localization of viral infection in C. chinense plants. Finally, the use of a mutant coding for a truncated coat protein (maintaining the Met138 coding sequence at the RNA level) demonstrates that a functional coat protein is required for elicitation of the L3 gene-mediated resistance.