From Squalene to Brassinolide: The Steroid Metabolic and Signaling Pathways across the Plant Kingdom

ABSTRACTThe plant steroid hormones, brassinosteroids (BRs), and their precursors, phytosterols, play major roles in plant growth, development, and stress tolerance. Here, we review the impressive progress made during recent years in elucidating the components of the sterol and BR metabolic and signaling pathways, and in understanding their mechanism of action in both model plants and crops, such as Arabidopsis and rice. We also discuss emerging insights into the regulations of these pathways, their interactions with other hormonal pathways and multiple environmental signals, and the putative nature of sterols as signaling molecules.SUMMARYThe plant steroid hormones, brassinosteroids, and their precursors, phytosterols, are essential for plant growth, reproduction, and response to various abiotic and biotic stresses. We review their biological activities and discuss recent advances in elucidating their metabolism, transport, and signaling pathways.