Positive regulator of brassinosteroid (BR) signaling. Transcription factor that activates target gene expression by binding specifically to the DNA sequence 5'-CANNTG-3'(E box) through its N-terminal domain. Can bind individually to the promoter as a homodimer or synergistically as a heterodimer with BIM1, BIM2 or BIM3. The C-terminal domain is probably involved in transcriptional activation (PubMed:12007405, PubMed:15680330, PubMed:18467490, PubMed:19170933). Recruits the transcription elongation factor IWS1 to control BR-regulated gene expression (PubMed:20139304). Forms a trimeric complex with IWS1 and ASHH2/SDG8 to regulate BR-regulated gene expression (PubMed:24838002). Promotes quiescent center (QC) self-renewal by cell divisions in the primary root. Binds to the E-boxes of the BRAVO promoter to repress its expression (PubMed:24981610). Interacts with ASK7/BIN2 through its C-terminal domain and with the bHLH transcription factors BIM1, BIM2 and BIM3 through its C- and N-terminal domains. Interacts (via N-terminus) with REF6 and ELF6 (PubMed:12427989, PubMed:15680330, PubMed:18467490). Interacts with MYB30 (PubMed:19170933). Interacts with IWS1 (PubMed:20139304). Interacts with ASHH2/SDG8 (PubMed:24838002). Binds to MYB56 when dephosphorylated in the nucleus of quiescent center (QC) cells (PubMed:24981610). Binds to WRKY46, WRKY54 and WRKY70 to cooperatively regulate the expression of target genes (PubMed:28576847). Brassinosteroid treatment triggers nuclear accumulation. A number of isoforms are produced. According to EST sequences. Ubiquitously expressed in cotyledons, leaves, hypocotyls and roots. The central part (140-272) is important for interaction with MYB30. Phosphorylated by ASK7/BIN2. Phosphorylation increases protein degradation and/or interferes with the nuclear localization. Reduced brassinosteroid (BR)-mediated quiescent center (QC) cells division. Belongs to the BZR/LAT61 family. Truncated N-terminus.