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Kim, Gyung-Tae,Fujioka, Shozo,Kozuka, Toshiaki,Tax, Frans E.,Takatsuto, Suguru,Yoshida, Shigeo,Tsukaya, Hirokazu Blackwell Science Ltd 2005 The Plant journal Vol.41 No.5
<P>Summary</P><P>Brassinosteroids (BRs) are plant hormones that are essential for a wide range of developmental processes in plants. Many of the genes responsible for the early reactions in the biosynthesis of BRs have recently been identified. However, several genes for enzymes that catalyze late steps in the biosynthesis pathways of BRs remain to be identified, and only a few genes responsible for the reactions that produce bioactive BRs have been identified. We found that the <I>ROTUNDIFOLIA3</I> (<I>ROT3</I>) gene, encoding the enzyme CYP90C1, which was specifically involved in the regulation of leaf length in <I>Arabidopsis thaliana</I>, was required for the late steps in the BR biosynthesis pathway. ROT3 appears to be required for the conversion of typhasterol to castasterone, an activation step in the BR pathway. We also analyzed the gene most closely related to <I>ROT3</I>, <I>CYP90D1</I>, and found that double mutants for <I>ROT3</I> and <I>CYP90D1</I> had a severe dwarf phenotype, whereas <I>cyp90d1</I> single knockout mutants did not. BR profiling in these mutants revealed that CYP90D1 was also involved in BR biosynthesis pathways. <I>ROT3</I> and <I>CYP90D1</I> were expressed differentially in leaves of <I>A. thaliana</I>, and the mutants for these two genes differed in their defects in elongation of hypocotyls under light conditions. The expression of <I>CYP90D1</I> was strongly induced in leaf petioles in the dark. The results of the present study provide evidence that the two cytochrome P450s, CYP90C1 and CYP90D1, play distinct roles in organ-specific environmental regulation of the biosynthesis of BRs.</P>