IDENTIFICATION OF A DISEASE RESISTANCE LOCUS IN ARABIDOPSIS THAT IS FUNCTIONALLY HOMOLOGOUS TO THE RPG1 LOCUS OF SOYBEAN

A new disease resistance locus in Arabidopsis, RPS3, was identified using a previously cloned avirulence gene from a non-Arabidopsis pathogen. The avrB avirulence gene from the soybean pathogen Pseudomonas syringae pv. glycinea was transferred into a P. syringae pv. tomato strain that is virulent on Arabidopsis, and conversion to avirulence was assayed on Arabidopsis plants. The avrB gene had avirulence activity on most, but not all, Arabidopsis ecotypes. Of 53 ecotypes examined, 45 were resistant to a P. syringae pv. tomato strain carrying avrB, and eight were susceptible. The inheritance of this resistance was examined using crosses between the resistant ecotype Col-0 and the susceptible ecotype Bla-2. In F2 plants from this cross, the ratio of resistant: susceptible plants was approximately 3:1, indicating that resistance to P. syringae expressing avrB is determined by a single dominant locus in ecotype Col-0, which we have designated RPS3. Using RFLP analysis, RPS3 was mapped to chromosome 3, adjacent to markers M583 and G4523, and less-than-or-equal-to 1 cM from another disease resistance locus, RPM1. In soybean, resistance to P. syringae strains that carry avrB is controlled by the locus RPG1. Thus, RPG1 and RPS3 both confer avrB-specific disease resistance, suggesting that these genes may be homologs.