Hydrogen peroxide is indispensable to Xanthomonas oryzae pv. oryzae-induced hypersensitive response and nonhost resistance in Nicotiana benthamiana

Nonhost resistance is a durable and broad-spectrum resistance in plants that are outside of the given pathogens' host range. Previously, we reported that the important pathogen Xanthomonas oryzae pv. oryzae (Xoo), which causes bacterial blight disease in rice, rapidly triggers the hypersensitive response (HR) and nonhost resistance in its nonhost plant Nicotiana benthamiana. In this study, we optimized the conditions, including the inoculum concentration, the leaf positions for inoculation and the plant post-inoculation growth temperature, to induce Xoo-triggered HR and nonhost resistance. We demonstrated that inoculating with a Xoo concentration of 1 x 10(8) cfu mL(-1) in fully expanded leaves of N. benthamiana plants resulted in the strongest induction of HR and nonhost resistance. Furthermore, we probed the role of hydrogen peroxide (H2O2) in Xoo-induced HR and nonhost resistance. An exogenous supply of H2O2 accelerated Xoo-induced HR, while the elimination of H2O2 by the application of a catalase blocked the HR-mediated suppression of bacterial growth in N. benthamiana. Moreover, a dagger hrpD6 and a dagger hrcU Xoo mutants, which are deficient in H2O2 production, did not show an induction of HR, while another Xoo mutant, a dagger hpa1, caused a strong H2O2 accumulation prior to its delayed HR induction. Collectively, our results reveal that H2O2 is indispensable to Xoo-induced HR and nonhost resistance in N. benthamiana.