C-23 hydroxylation by Arabidopsis CYP90C1 and CYP90D1 reveals a novel shortcut in brassinosteroid biosynthesis

Plant Cell. 2006 Nov;18(11):3275-88. doi: 10.1105/tpc.106.045443. Epub 2006 Nov 30.


Brassinosteroids (BRs) are biosynthesized from campesterol via several cytochrome P450 (P450)-catalyzed oxidative reactions. We report the functional characterization of two BR-biosynthetic P450s from Arabidopsis thaliana: CYP90C1/ROTUNDIFOLIA3 and CYP90D1. The cyp90c1 cyp90d1 double mutant exhibits the characteristic BR-deficient dwarf phenotype, although the individual mutants do not display this phenotype. These data suggest redundant roles for these P450s. In vitro biochemical assays using insect cell-expressed proteins revealed that both CYP90C1 and CYP90D1 catalyze C-23 hydroxylation of various 22-hydroxylated BRs with markedly different catalytic efficiencies. Both enzymes preferentially convert 3-epi-6-deoxocathasterone, (22S,24R)-22-hydroxy-5alpha-ergostan-3-one, and (22S,24R)-22-hydroxyergost-4-en-3-one to 23-hydroxylated products, whereas they are less active on 6-deoxocathasterone. Likewise, cyp90c1 cyp90d1 plants were deficient in 23-hydroxylated BRs, and in feeding experiments using exogenously supplied intermediates, only 23-hydroxylated BRs rescued the growth deficiency of the cyp90c1 cyp90d1 mutant. Thus, CYP90C1 and CYP90D1 are redundant BR C-23 hydroxylases. Moreover, their preferential substrates are present in the endogenous Arabidopsis BR pool. Based on these results, we propose C-23 hydroxylation shortcuts that bypass campestanol, 6-deoxocathasterone, and 6-deoxoteasterone and lead directly from (22S,24R)-22-hydroxy-5alpha-ergostan-3-one and 3-epi-6-deoxocathasterone to 3-dehydro-6-deoxoteasterone and 6-deoxotyphasterol.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arabidopsis / drug effects
  • Arabidopsis / enzymology*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Carbon / metabolism*
  • Catalysis / drug effects
  • Cotyledon / drug effects
  • Cotyledon / enzymology
  • Cytochrome P-450 Enzyme System / deficiency
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism*
  • Exons / genetics
  • Gas Chromatography-Mass Spectrometry
  • Gene Expression / drug effects
  • Gene Expression Regulation, Enzymologic / drug effects
  • Gene Expression Regulation, Plant / drug effects
  • Hydroxylation / drug effects
  • Hypocotyl / drug effects
  • Hypocotyl / enzymology
  • Insecta / cytology
  • Introns / genetics
  • Kinetics
  • Mutation / genetics
  • Phenotype
  • Phytosterols / analysis
  • Phytosterols / biosynthesis*
  • Phytosterols / chemistry
  • Phytosterols / pharmacology
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Substrate Specificity


  • Arabidopsis Proteins
  • Phytosterols
  • RNA, Messenger
  • Carbon
  • Cytochrome P-450 Enzyme System
  • cytochrome P-450 90D1, Arabidopsis
  • ROT3 protein, Arabidopsis