THE CAPSICUM L(3) GENE-MEDIATED RESISTANCE AGAINST THE TOBAMOVIRUSES IS ELICITED BY THE COAT PROTEIN

The L(3) gene is responsible for the hypersensitive response in Capsic um plants against infection by tobamoviruses. The resistance conferred by this gene is one of the most effective so far described against to bamoviruses. Certain isolates of pepper mild mottle virus (PMMV) are t he only tobamoviruses able to overcome the L(3) resistance. Chimeric v iral genomes between PMMV-S (to which L(3) plants are hypersensitive) and PMMV-I (an L(3) resistance-breaking isolate) led us to conclude th at sequence variation within the coal protein gene of both isolates de termines their different virulence in L(3)L(3) plants. Furthermore, th e 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. chi nense plants. Finally, the use of a mutant coding for a truncated coat protein (maintaining the Met(138), coding sequence at the RNA level) demonstrates that a functional coat protein is required for elicitatio n of the L(3) gene-mediated resistance. (C) 1995 Academic Press, Inc.