Hypersensitive response suppression by type III effectors of plant pathogenic bacteria

The suppressor activity of four representative avirulence (avr) genes from the Pseudomonas syringae group against elicitors of a general hypersensitive response (HR) was examined in tobacco leaves inoculated with double transformants of Pseudomonas fluorescens containing both a cosmid plasmid (pHIR11) carrying the hrp gene cluster and a plasmid carrying each avr gene. The double transformants Pf (pHIR11) containing avrB, avrRps4, or avrPto failed to induce an HR, but that carrying avrRpt2 did induce an HR as Pf (pHIR11 + empty vector) did. Thus, some Avr proteins seem to have suppressor activity against a general HR and should promote aggressiveness of the pathogens.