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Plant Cell Advance Online Publication
Published on November 30, 2006; 10.1105/tpc.106.045443

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Received June 29, 2006
Returned for revision October 19, 2006
Accepted November 2, 2006

C-23 Hydroxylation by Arabidopsis CYP90C1 and CYP90D1 Reveals a Novel Shortcut in Brassinosteroid Biosynthesis

Toshiyuki Ohnishi 1, Anna-Maria Szatmari 2, Bunta Watanabe 1, Satomi Fujita 1, Simona Bancos 2, Csaba Koncz 3, Marcel Lafos 3, Kyomi Shibata 4, Takao Yokota 4, Kanzo Sakata 1, Miklos Szekeres 2, and Masaharu Mizutani 1*

1 Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
2 Institute of Plant Biology, Biological Research Center of the Hungarian Academy of Sciences, H-6701 Szeged, Hungary
3 Max Planck-Institut für Züchtungsforschung, D-50829 Koeln, Germany
4 Department of Biosciences, Teikyo University, Utsunomiya, 320-8551, Japan

* To whom correspondence should be addressed. E-mail: mizutani{at}scl.kyoto-u.ac.jp.

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-5{alpha}-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-5{alpha}-ergostan-3-one and 3-epi-6-deoxocathasterone to 3-dehydro-6-deoxoteasterone and 6-deoxotyphasterol.




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