1.1.15
AN ARABIDOPSIS THALIANA MUTANT THAT IS SUSCEPTIBLE TO MULTIPLE BACTERIAL AND FUNGAL PATHOGENS

PM MERRITT, RF WARREN and RW INNES

Department of Biology, Indiana University, Bloomington, Indiana 47405, USA

Background and objectives
Plant disease resistance often occurs via a gene-for-gene interaction whereby a plant R gene and a corresponding pathogen avr gene are required for a resistance response. In our effort to dissect the disease-resistance pathway in Arabidopsis thaliana, we have isolated a variety of mutants that affect pathogen resistance.

Results and conclusions
The gene PBS2 (avrPphB susceptible) was identified in a screen for mutant plants that had lost resistance to Pseudomonas syringae pv. tomato race DC3000 (Pst DC3000) expressing the avr-gene avrPphB. Phenotypically, pbs2 mutants are susceptible to Pst DC3000 expressing avrPphB. In addition, pbs2 mutants display enhanced susceptibility to Pst DC3000 strains expressing avrRpm1, avrB, or avrRpt2. Interestingly, pbs2 mutants retain resistance to Pst DC3000 expressing avrRps4. Mutation of PBS2 also causes a loss of resistance to several strains of the fungal pathogen Peronospora parasitica. These data suggest that PBS2 functions as a common step in multiple R-gene-mediated resistance pathways, acting between pathogen recognition and defence response. Also, the retention of resistance to some pathogen strains in pbs2 mutant plants suggests there are other pathways leading to defence responses that are independent of PBS2. PCR-based mapping has located PBS2 to the north end of chromosome one, between the markers nga63 and NCC1. Analysis of 846 F2 mapping lines (pbs2 x WS) has identified four plants with recombination events between these two markers, giving a map distance of 0.26 cM. This region of chromosome one also includes several other disease-resistance genes, R-gene-like sequences and defence-related genes including RPS5, RFL1 and EDR1 [1]. We are continuing our efforts to clone PBS2 by further analysing the four recombinants with additional markers and pathogenicity tests.

References
1. Simonich MT, Innes RW, 1995. Molecular Plant-Microbe Interactions 8, 637-640.