Redox sensor QSOX1 regulates plant immunity by targeting GSNOR to modulate ROS generation.

Reactive oxygen signaling regulates numerous biological processes, including stress responses in plants. Redox sensors transduce reactive oxygen signals into cellular responses. We present biochemical evidence that a plant quiescin sulfhydryl oxidase homolog (QSOX1) is a redox sensor that negatively regulates immunity against a bacterial pathogen. The expression level of QSOX1 is inversely correlated with pathogen-induced ROS accumulation. QSOX1 both senses and regulates ROS levels through interaction with and redox-mediated regulation of S-nitrosoglutathione reductase that, consistent with previous findings, influences reactive nitrogen-mediated regulation of ROS generation. Collectively, our data indicate that QSOX1 is a redox sensor that negatively regulates plant immunity by linking reactive oxygen- and reactive nitrogen-signaling to limit ROS production.