Plants can recognize pathogens through the action of disease resistance (R) genes, which confer resistance to pathogens expressing unique corresponding avirulence (avr) genes. The molecular basis of this gene-for-gene specificity is unknown. The Arabidopsis thaliana RPM1 gene enables dual specificity to pathogens expressing either of two unrelated Pseudomonas syringae avr genes. Despite this function, RPM1 encodes a protein sharing molecular features with recently described single-specificity R genes. Surprisingly, RPM1 is lacking from naturally occurring, disease-susceptible Arabidopsis accessions.

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