Redox control of systemic acquired resistance

Changes in gene expression during systemic acquired resistance (SAR) require the phenolic signaling molecule salicylic acid (SA) and are modulated by the interaction between the NON EXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1) protein and members of the TGA family of transcription factors. In the past two years, the activities of NPR1 and of the TGA factors TGA1 and TGA4 have been shown to be modulated by SA-induced oxidoreduction (redox) modifications of key cysteine residues. Reduction of two conserved cysteines in NPR1 leads to its monomerization and nuclear localization, which is required for the activation of PATHOGENESIS-RELATED(PR) genes. Reduction of conserved cysteines in TGA1 and TGA4 enables their interaction with NPR1, which acts as a redox-sensitive cofactor in stimulating TGA1 DNA-binding activity. The identity of the redox mediators that are involved in regulating NPR1 and TGA factors is unknown. However, a novel thioredoxin interacts with the disease resistance protein Cf-9 and modulates Cf-9-dependent signaling. These results begin to provide a mechanistic understanding of how SAR is regulated by redox conditions.