RESEARCH ARTICLE A Disease Resistance Gene in Arabidopsis with Specificity for Two Different Pathogen Avirulence Genes

The RPSS and RPMl disease resistance loci of Arabidopsis confer resistance to Pseudomonas syringae strains that carry the avirulence genes avrB and avrRpm7, respectively. We have previously shown that RPS3 and RPMl are closely llnked genetically. Here, we show that RPSS and RPMl are in fact the same gene. We screened a mutagenized Arabldop-sls population wlth a R syringae strain carrying avrB and found 12 susceptible mutants. AI112 mutants were also susceptible to an lsogenic strain carrying avrRpml, indlcating a loss of both RPS3 and RPMl functions. No mutants were recovered that lost only RPS3 function. Genetic analysis of four lndependent mutants revealed that the lesions were in RPS3. Thus, a single gene in Arabidopsis confers resistance that is specific to two distinct pathogen avirulence genes-a gene-for-genes interaction. This observation suggests that the RPS3IRPMl gene product can bind multiple pathogen ligands, or alternatively, that lt does not function as a receptor