Interference between Two Specific Pathogen Recognition Events Mediated by Distinct Plant Disease Resistance Genes.

We demonstrate that the interaction of the avirulence gene avrRpt2 and the cognate resistance gene RPS2 interferes with the interaction of avrRpm1-RPM1 in Arabidopsis. Interference is mediated outside of the bacterial pathogen Pseudomonas syringae, presumably at the level of recognition of avr-dependent signals, yet does not require the wild-type RPS2 product. A numerical excess of P. syringae expressing avrRpm1 can overcome this interference in mixed inoculations. The interference of avrRpt2-RPS2 engagement with RPM1-dependent functions is mirrored by transcriptional activation of genes preferentially expressed during RPM1- or RPS2-mediated disease resistance reactions. This demonstration of interference between two plant disease resistance genes suggests that their products compete for a common element(s) in a signal transduction pathway leading to disease resistance.