NDR1, A LOCUS OF ARABIDOPSIS-THALIANA THAT IS REQUIRED FOR DISEASE RESISTANCE TO BOTH A BACTERIAL AND A FUNGAL PATHOGEN

We have employed Arabidopsis thaliana as a model host plant to genetic ally dissect the molecular pathways leading to disease resistance, A. thaliana accession Col-O is susceptible to the bacterial pathogen Pseu domonas syringae pv, tomato strain DC3000 but resistant in a race-spec ific manner to DC3000 carrying any one of the cloned avirulence genes avrB, avrRpm1, avrRpt2, and avrPph3. Fast-neutron-mutagenized Col-O M( 2) seed was screened to identify mutants susceptible to DC3000(avrB). Disease assays and analysis of in planta bacterial growth identified o ne mutant, ndr1-1 (non-race-specific disease resistance), that was sus ceptible to DC3000 expressing any one of the four avirulence genes tes ted. Interestingly, a hypersensitive-like response was still induced b y several of the strains. The ndr1-1 mutation also rendered the plant susceptible to several avirulent isolates of the fungal pathogen Peron ospora parasitica. Genetic analysis of ndr1-1 demonstrated that the mu tation segregated as a single recessive locus, located on chromosome I II. Characterization of the ndr1-1 mutation suggests that a common ste p exists in pathways of resistance to two unrelated pathogens.