Hormone Synthetic Pathways and Genes in Arabidopsis: Brassinosteroids


Brassinosteroids are polyhydroxylated steroids. The most active compound is Brassinolide (BL). Since the discovery of BL, more than 70 natural analogs, collectively called brassinosteroids (BRs), have been isolated and characterized. Exogenous application of BRs to plants at nanomolar to micromolar concentrations has a wide spectrum of physiological effects, including promotion of cell elongation and division, enhancement of tracheary element differentiation, retardation of abscission, enhancement of gravitropic-induced bending, promotion of ethylene biosynthesis, and enhancement of stress resistance. A number of BR-deficient mutants have been discovered in Arabidopsis, pea, and tomato. These mutants exhibit dwarfism when grown in either light or dark conditions. Many of these mutants also have dark-green leaves, reduced fertility, a prolonged lifespan, and abnormal skotomorphogenesis. They are synthesized from campesterol via the mevalonate pathway. The biosynthetic pathway was elucidated in cultured cells of Catharanthus roseus by Japanese researchers, and then confirmed in Arabidopsis mutants. The major biosynthesis pathway in Arabidopsis is shown here.

Pathway map of Brassinosteroid biosynthesis
[MS PowerPoint: 445KB]

Genes on the pathway

Gene name Locus name Description
BAS1/CYP734A1 At2g26710 brassinosteroid C-26 hydroxylase
SOB7/CHI2/CYP72C1 At1g17060 putative brassinosteroid hydroxylase
BR6ox1/CYP85A1 At5g38970 brassinosteroid C-6 oxidase
BR6ox2/CYP85A2 At3g30180 brassinosteroid C-6 oxidase
CPD/CYP90A1 At5g05690 putative brassinosteroid hydroxylase
DWF4/CYP90B1 At3g50660 steroid C-22 hydroxylase
ROT3/CYP90C1 At4g36380 brassinosteroid C-23 hydroxylase
CYP90D1 At3g13730 brassinosteroid C-23 hydroxylase
DET2 At2g38050 steroid-5-alpha-reductase
DWF1/DIM At3g19820 sterol C-24 reductase
STE1/DWF7 At3g02580 delta7 sterol C-5 desaturase
DWF5 At1g50430 sterol delta7 reductase
UGT73C5 At2g36800 brassinosteroid 23-O-glucosilase
RIKEN Plant Hormone Research Network - RIKEN Center for Sustainable Resource Science