CYP72B1 inactivates brassinosteroid hormones: An intersection between photomorphogenesis and plant steroid signal transduction

• Published in: Plant physiology (Bethesda) Vol. 133; no. 4; pp. 1643 - 1653
• Main Authors: Turk, E.M, Fujioka, S, Seto, H, Shimada, Y, Takatsuto, S, Yoshida, S, Denzel, M.A, Torres, Q.I, Neff, M.M
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.12.2003; American Society of Plant Physiologists
• Subjects: 26-hydroxybrassinolide; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; bioaccumulation; biochemical pathways; Biological and medical sciences; Biosynthesis; brassinolide; Brassinosteroids; castasterone; Cell physiology; Cholestanols - antagonists & inhibitors; Cloning, Molecular; CYP72B1 protein; cytochrome P-450; Cytochrome P-450 Enzyme System - metabolism; far-red light; Focus Issue on Light Signaling; Fundamental and applied biological sciences. Psychology; gene expression regulation; gene overexpression; Hormones; hydroxylase; hydroxylation; Hypocotyls; light; messenger RNA; Molecular and cellular biology; molecular sequence data; Morphogenesis - physiology; nucleotide sequences; oxygenases; Phenotypes; photomorphogenesis; physiological transport; Plant Growth Regulators - antagonists & inhibitors; Plant growth. Development of the storage organs; Plant physiology and development; plant proteins; plant response; Plants; Promoter Regions, Genetic - genetics; protein content; Recombinant Proteins - metabolism; RNA; seedling growth; Seedlings; Signal transduction; Signal Transduction - physiology; Steroids; Sterols - metabolism; transgenic plants; Vegetative apparatus, growth and morphogenesis. Senescence; Yeasts; Growth; Plant juvenile growth stage; Structure function relationship; Morphogenesis; Arabidopsis thaliana; Signal transduction; Regulation(control); Cruciferae; Dicotyledones; Light; Angiospermae; Plant growth substance; Intraspecific comparison; Enzyme; Cytochrome P450; Interaction; Genetic variant; Lactone; Photomorphogenesis; Oxygenase; Brassinosteroid; Spermatophyta; Oxidoreductases; Phytohormone; Mutation; Experimental plant; Photoregulation
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.103.030882

Active brassinosteroids, such as brassinolide (BL) and castasterone, are growth promoting plant hormones. An Arabidopsis cytochrome P450 monooxygenase encoded by CYP72B1 has been implicated in brassinosteroid catabolism as well as photomorphogenesis. We expressed CYP72B1 in yeast, coupled with brassinosteroid feeding, and established the biochemical function to be the hydroxylation of BL and castasterone, to give 26-hydroxybrassinolide and 26-hydroxycastasterone, respectively. Brassinosteroid feeding experiments with wild-type Arabidopsis, a CYP72B1 null mutant, and a CYP72B1 overexpression line demonstrated that carbon 26 hydroxylation of active brassinosteroids is an endogenous function of CYP72B1. Seedling growth assays demonstrated that 26-hydroxybrassinolide is an inactive brassinosteroid. Genetic and physiological analysis of the hypocotyl response to exogenous BL and varying intensities of white and monochromatic light suggested that CYP72B1 modulates photomorphogenesis primarily through far-red light and to a lesser extent through blue- and red-light pathways. CYP72B1 transcript accumulation in dark-grown seedlings was organ specific and down-regulated after 1 h of illumination in dim white, red, and blue light, but not far-red light. CYP72B1 translational fusions with the beta-glucuronidase reporter gene demonstrated that protein levels increased in the hypocotyl elongation zone when shifted from the dark to far-red light, but not blue or red light. We propose a model in which Arabidopsis seedling development switches from dark-grown development (skotomorphogenesis) to light-grown development (photomorphogenesis) in part by rapid modulation of brassinosteroid sensitivity and levels. CYP72B1 provides an intersection between the light and brassinosteroid pathways mainly by far-red-light-dependent modulation of brassinosteroid levels.