Hydrogen peroxide positively regulates brassinosteroid signaling through oxidation of the BRASSINAZOLE-RESISTANT1 transcription factor.

Hydrogen peroxide (H2 O2 ) is an important signaling molecule in plant developmental processes and stress responses. However, whether H2 O2 -mediated signaling crosstalks with plant hormone signaling is largely unclear. Here, we show that H2 O2 induces the oxidation of the BRASSINAZOLE-RESISTANT1 (BZR1) transcription factor, which functions as a master regulator of brassinosteroid (BR) signaling. Oxidative modification enhances BZR1 transcriptional activity by promoting its interaction with key regulators in the auxin-signaling and light-signaling pathways, including AUXIN RESPONSE FACTOR6 (ARF6) and PHYTOCHROME INTERACTING FACTOR4 (PIF4). Genome-wide analysis shows that H2 O2 -dependent regulation of BZR1 activity plays a major role in modifying gene expression related to several BR-mediated biological processes. Furthermore, we show that the thioredoxin TRXh5 can interact with BZR1 and catalyzes its reduction. We conclude that reversible oxidation of BZR1 connects H2 O2 -mediated and thioredoxin-mediated redox signaling to BR signaling to regulate plant development.