Regulates the brassinosteroid (BR) signaling pathway that mediates cell elongation and organ morphogenesis (PubMed:19202280). (Microbial infection) Facilitates the development of the powdery mildew fungus E.cruciferarum. (Microbial infection) May prevent cell death upon A.alternata f.sp. lycopersici (AAL) toxin treatment. Expressed in seedlings, roots, leaves, inflorescences and flowers. Repressed by Brz, a triazole compound that acts as a brassinosteroid (BR)-specific inhibitor. Delayed development of the powdery mildew fungus E.cruciferarum. Increased cell death upon A.alternata f.sp. lycopersici (AAL) toxin treatment. Belongs to the BI1 family.