Positive brassinosteroid-signaling protein. Mediates downstream brassinosteroid-regulated growth response and feedback inhibition of brassinosteroid biosynthetic genes. May act as transcriptional repressor by binding the brassinosteroid-response element (5'-CGTGCG-3') in the promoter of GRAS32 (AC Q9LWU9), another positive regulator of brassinosteroid signaling (By similarity). Interacts with GF14C. Brassinosteroid promotes nuclear localization and binding to GF14C is required for cytoplasmic retention and efficient inhibition of BZR1 when brassinosteroid levels are low. Dephosphorylation after treatment with epibrassinolide. Belongs to the BZR/LAT61 family.