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KMID : 0368420050480020237
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Journal of Plant Biology
2005 Volume.48 No. 2 p.237 ~ p.244
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A double mutant for theCYP85A1 andCYP85A2 Genes ofArabidopsis exhibits a Brassinosteroid dwarf phenotype
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Kwon Mi
Fujioka Shozo
Jeon Ji-Hyun
Kim Ho-Bang
Takatsuto Suguru
Yoshida Shigeo
An Chung-Sun
Choe Sung-Hwa
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Abstract
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Brassinosteroid (BR)-6-oxidases mediate the bridge reactions that connect the late and early C-6 oxidation pathways by converting 6-deoxoBR to 6-oxoBRs. Two similar genes ofArabidopsis, CYP85A1 (At5g38970) andCYP85A2 (At3g30180), are proposed to encode BR-6-oxidases based on findings that heterologously expressed genes mediate BR-6-oxidation reactions in yeast. However, genetic evidence that both genes are critically involved in the BR-6-oxidation step inArabidopsis has been limited. Here, we show that a double mutant for the two genes displays dwarfism similar to that of typical BR biosynthesis-deficient mutants, suggesting that they are the major BR-6-oxidases inArabidopsis. Examination of endogenous BR levels and metabolism monitoring tests using this double mutant revealed a great reduction in the levels of 6-oxoBRs, e.g., TY and CS, due to a lack in the conversion reactions from 6-deoxoCS to CS, and from 6-deoxoTY to TY. Surprisingly, the double mutant accumulated a significant amount of 6-oxocampestanol, suggesting that the upstream C-6 oxidation of campestanol to 6-oxocampestanol is not catalyzed by the two BR-6-oxidases inArabidopsis, rather, by another enzyme yet to be discovered.
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KEYWORD
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brassinosteroid, BR-6-oxidase, C-6 oxidation, cell elongation, CYP85, cytochrome P450
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