Annu. Rev. Plant Biol. 2003. 54:137–64 doi: 10.1146/annurev.arplant.54.031902.134921 Copyright c  2003 by Annual Reviews. All rights reserved BIOSYNTHESIS AND METABOLISM OF BRASSINOSTEROIDS Shozo Fujioka 1 and Takao Yokota 2 1 Plant Functions Lab/Plant Science Center, RIKEN (The Institute of Physical and Chemical Research), Wako-shi, Saitama 351-0198, Japan; email: sfujioka@postman.riken.go.jp 2 Department of Biosciences, Teikyo University, Utsunomiya 320-8551, Japan; email: yokota@nasu.bio.teikyo-u.ac.jp Key Words Arabidopsis thaliana, Catharanthus roseus, cytochrome P450, dwarfism, brassinosteroid-deficient mutant ■ Abstract Brassinosteroids (BRs) are steroid hormones that regulate the growth and development of plants. Detailed study of the biosynthesis of brassinolide, a C 28 BR, revealed that two parallel routes, the early and late C-6 oxidation pathways, are connected at multiple steps and also are linked to the early C-22 oxidation pathway. Thus, BR biosynthetic pathways are highly networked. Furthermore, the biosynthesis of C 27 BRs was shown to proceed in a similar way to that of C 28 BRs. Information on enzymes and genes involved in the BR biosynthesis, as well as their regulation, has been obtained using BR-deficient and BR-insensitive mutants. In addition, the biosyn- thesis of sterols, which were recently recognized not only as precursors of BRs and membrane constituents, but also as modulators of plant development, is discussed. Var- ious metabolic reactions of BRs including epimerization, oxidation, and conjugation are also summarized. CONTENTS INTRODUCTION ..................................................... 138 BIOSYNTHESIS OF BRs ............................................... 138 New Findings in Early and Late C-6 Oxidation Pathways .................... 139 Refined Pathway from Campesterol to Campestanol ........................ 141 Early C-22 Oxidation Branch in the BR Biosynthetic Pathway ................ 141 Biosynthesis of C 27 BRs .............................................. 141 Enzymes, Genes, and Related Mutants ................................... 141 Regulation of BR Biosynthesis ......................................... 145 BR Biosynthesis Inhibitors ............................................ 146 BIOSYNTHESIS OF STEROLS ......................................... 146 Biosynthetic Pathways of Sterols ....................................... 146 Enzymes, Genes, and Related Mutants ................................... 148 METABOLISM OF BRs ................................................ 150 Metabolic Reactions of BRs ........................................... 150 1040-2519/03/0601-0137$14.00 137 Annu. Rev. Plant Biol. 2003.54:137-164. Downloaded from arjournals.annualreviews.org by University of Illinois - Urbana Champaign on 04/03/08. For personal use only.