ARABIDOPSIS MUTATIONS AT THE RPS2 LOCUS RESULT IN LOSS OF RESISTANCE TO PSEUDOMONAS-SYRINGAE STRAINS EXPRESSING THE AVIRULENCE GENE AVRRPT2

We isolated and characterized two Arabidopsis thaliana mutants that fa il to mount a hypersensitive defense response (HR) when infiltrated wi th phytopathogenic Pseudomonas strains carrying the avirulence (avr) g ene avrRpt2 but still mount an HR when infiltrated with strains carryi ng other avr genes. One of these mutants was isolated using a method w e developed that enriches for Arabidopsis seedlings that survive vacuu m-infiltration with a bacterial strain carrying an avr gene. Genetic a nalysis showed that the phenotypes of both mutants resulted from mutat ions at a single locus, RPS2. In contrast to the wild type, both rps2 mutants failed to limit the growth of Pseudomonas strains carrying avr Rpt2. Heterozygous RPS2/rps2 plants displayed a phenotype intermediate between those of RPS2/RPS2 and rps2/rps2 homozygotes. These experimen ts show that the wild-type allele at the rps2 locus, RPS2, encodes a c omponent of a signal transduction pathway that responds to a signal ge nerated by avrRpt2 and that RPS2 is required for the elicitation of an HR. RPS2 was mapped near the restriction fragment length polymorphism marker PG11 on chromosome IV.