Brassinolide

Brassinolide is a plant growth-promoting steroid isolated from Brassica napus pollen and functions as the most active brassinosteroid in plant growth regulation[1][2]. Mechanistically, brassinolide acts through the plasma-membrane receptor BRI1, which binds brassinolide through its extracellular domain and initiates brassinosteroid signaling[3][4]. BRI1 associates with BAK1, and the BRI1/BAK1 receptor kinase pair activates downstream phosphorylation events that regulate BIN2, BZR1, and BES1 transcriptional control[5][6]. In plant models, this pathway supports cell elongation, development, stress responses, and experimental analysis of brassinosteroid-dependent phenotypes[6][7]. Compared with related receptor isoforms, BRL1 recognizes brassinolide through a conserved binding site, but subtle structural differences generate differential brassinolide recognition within the BRI1 receptor family[8]. For research applications, brassinolide serves as an active pathway agonist, whereas brassinazole provides a triazole-type brassinosteroid biosynthesis inhibitor for dissecting brassinosteroid function in plants[9].