Single <i>cis</i> ‐elements in brassinosteroid‐induced upregulated genes are insufficient to recruit both redox states of the <scp>BIL1</scp> / <scp>BZR1 DNA</scp> ‐binding domain

The plant-specific transcription factor BRZ-INSENSITIVE-LONG 1 (BIL1)/BRASSINAZOLE-RESISTANT 1 (BZR1) regulates the growth of Arabidopsis thaliana via brassinosteroid signaling, acting as both a gene repressor and activator. Its upregulation requires environmental cues mediated by PHYTOCHROME INTERACTING FACTOR 4 (PIF4), with oxidative modifications via H₂O₂ enhancing their interaction. However, the nature of the tripartite complex of cis-elements, BIL1/BZR1, and PIF4 under redox changes remains unclear. Here, we demonstrate that oxidation of the DNA-binding domain (DBD) of BIL1/BZR1 alters its DNA-binding ability. However, single cis-elements enriched in brassinosteroid-induced genes do not support binding of either redox form, nor does BIL1/BZR1 DBD heterodimerize with PIF4 DBD on these elements. These findings highlight the complexity of brassinosteroid transcriptional regulation beyond DNA-binding specificity and redox modifications.