ABSTRACTThe plant pathogenRalstonia solanacearum, which causes bacterial wilt disease, is exposed to reactive oxygen species (ROS) during tomato infection and expresses diverse oxidative stress response (OSR) genes during midstage disease on tomato. TheR. solanacearumgenome predicts that the bacterium produces multiple and redundant ROS-scavenging enzymes but only one known oxidative stress response regulator, OxyR. AnR. solanacearumoxyRmutant had no detectable catalase activity, did not grow in the presence of 250 μM hydrogen peroxide, and grew poorly in the oxidative environment of solid rich media. This phenotype was rescued by the addition of exogenous catalase, suggesting thatoxyRis essential for the hydrogen peroxide stress response. Unexpectedly, theoxyRmutant strain grew better than the wild type in the presence of the superoxide generator paraquat. Gene expression studies indicated thatkatE,kaG,ahpC1,grxC, andoxyRitself were each differentially expressed in theoxyRmutant background and in response to hydrogen peroxide, suggesting thatoxyRis necessary for hydrogen peroxide-inducible gene expression. Additional OSR genes were differentially regulated in response to hydrogen peroxide alone. The virulence of theoxyRmutant strain was significantly reduced in both tomato and tobacco host plants, demonstrating thatR. solanacearumis exposed to inhibitory concentrations of ROSin plantaand that OxyR-mediated responses to ROS during plant pathogenesis are important forR. solanacearumhost adaptation and virulence.
Oxidative stress response ofInonotus obliquusinduced by hydrogen peroxide
