Poster: Hormone synthesis & metabolism

Abs # 470: A rice dwarf mutant, dwarf11 (d11), has a defect in the gene encoding a novel cytochrome P450 involved in brassinosteroid biosynthesis, which regulates seed length

Presenter:	Tanabe, Sumiyo , s0293001@s.fpu.ac.jp
Authors	Tanabe, Sumiyo  (A)   Ashikari, Motoyuki  (B)   Fujioka, Shozo  (C)   Takatsuto, Suguru  (D)   Yoshida, Shigeo  (C)   Kitano, Hidemi  (B)   Yano, Masahiro  (E)   Yoshimura, Atsushi  (F)   Matsuoka, Makoto  (B)   Fujisawa, Yukiko  (A)   Kato, Hisaharu  (A)   Iwasaki, Yukimoto  (A)
Affiliations:	(A): Faculty of Bioscience, Fukui Prefectural University (B): Bioscience and Biotechnology Center, Nagoya University (C): Plant Functions Laboratory, RIKEN (D): Department of Chemistry, Joetsu University of Education (E): National Institute of Agrobiological Science (F): Graduate School of Bioresource and Bioenvironmental Science, Kyushu University

A rice dwarf mutant, d11 showed characteristic phenotypes such as were the erection of leaves and the shortening of the second internode in culm and the grain length. The length of seeds in d11 was shorter than that in wild-type (WT), whereas the width of d11 seeds was the same as that of WT seeds. To understand the mechanisms of the production of seeds in a given form, we tried to identify the mutated gene of d11, and isolated the D11 gene by the map-based cloning method. The gene encoded a novel cytochrome P450 (CYP724B1). BLAST-enabled database searches revealed that the deduced amino acid sequence showed high similarity to a previously reported CYP90B protein from Arabidopsis DWF4/CYP90B and rice OsDWF4L over almost the entire region. The finding suggests that the D11 gene may encode a novel cytochrome P450 concerned with BR biosynthesis in rice. The expression of rice OsDWARF and D2 genes, which encoded oxidases of C-6 and C-3 of BRs, respectively, were regulated in a feedback manner by a bioactive BR, brassinolide (BL). Similarly, the expression of D11 gene was negatively regulated by BL. The negative feedback of the D11-gene expression supports the proposition that the gene is involved in BR biosynthesis. Quantitative analyses of endogenous sterols and BRs in WT and mutant plants indicated that D11/CYP724B1 might catalyze the two conversion steps from 3-dehydro-6-deoxoteasterone to 6-deoxotyphasterol and from 3-dehydroteasterone to typhasterol in the BR biosynthesis, and that the mutant was deficient in active BRs. The results indicate that D11 is one of the enzymes that catalyze BR biosynthesis and that BRs play an important role in the normal development of rice seeds.