PT  - JOURNAL ARTICLE
AU  - Ohnishi, Toshiyuki
AU  - Szatmari, Anna-Maria
AU  - Watanabe, Bunta
AU  - Fujita, Satomi
AU  - Bancos, Simona
AU  - Koncz, Csaba
AU  - Lafos, Marcel
AU  - Shibata, Kyomi
AU  - Yokota, Takao
AU  - Sakata, Kanzo
AU  - Szekeres, Miklos
AU  - Mizutani, Masaharu
TI  - C-23 Hydroxylation by <em>Arabidopsis</em> CYP90C1 and CYP90D1 Reveals a Novel Shortcut in Brassinosteroid Biosynthesis
AID  - 10.1105/tpc.106.045443
DP  - 2006 Nov 01
TA  - The Plant Cell
PG  - 3275--3288
VI  - 18
IP  - 11
4099  - http://www.plantcell.org/content/18/11/3275.short
4100  - http://www.plantcell.org/content/18/11/3275.full
SO  - Plant Cell2006 Nov 01; 18
AB  - 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-5α-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-5α-ergostan-3-one and 3-epi-6-deoxocathasterone to 3-dehydro-6-deoxoteasterone and 6-deoxotyphasterol.