title: Loss-of-function of a rice brassinosteroid biosynthetic enzyme, C-6 oxidase, prevents the organized arrangement and polar elongation of cells in the leaves and stem.
abstract: Molecular genetic and physiological studies on brassinosteroid (BR)-related mutants of dicot plants have revealed that BRs play important roles in normal plant growth and development. However, little is known about the function of BR in monocots (grasses), except for the phenotypic analysis of a rice mutant partially insensitive to BR signaling. To investigate the function of BR in monocots, we identified and characterized BR-deficient mutants of rice, BR-deficient dwarf1 (brd1). The brd1 mutants showed a range of abnormalities in organ development and growth, the most striking of which were defects in the elongation of the stem and leaves. Light microscopic observations revealed that this abnormality was primarily owing to a failure in the organization and polar elongation of the leaf and stem cells. The accumulation profile of BR compounds in the brd1 mutants suggested that these plants may be deficient in the activity of BR C-6 oxidase. Therefore, we cloned a rice gene, OsDWARF, which has a high sequence similarity to the tomato C-6 oxidase gene, DWARF. Introduction of the wild-type OsDWARF gene into brd1 rescued the abnormal phenotype of the mutants. The OsDWARF gene was expressed at a low level in all of the examined tissues, with preferential expression in the leaf sheath, and the expression was negatively regulated by brassinolide treatment. On the basis of these findings, we discuss the biological function of BRs in rice plants.
authors.affiliation: BioScience Center, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Hong
authors.forename: Miyako
authors.initials: M
authors.lastname: Ueguchi-Tanaka
authors.forename: Sae
authors.initials: S
authors.lastname: Shimizu-Sato
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Inukai
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Yukihisa
authors.initials: Y
authors.lastname: Shimada
authors.forename: Suguru
authors.initials: S
authors.lastname: Takatsuto
authors.forename: Masakazu
authors.initials: M
authors.lastname: Agetsuma
authors.forename: Shigeo
authors.initials: S
authors.lastname: Yoshida
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Sakurako
authors.initials: S
authors.lastname: Uozu
authors.forename: Hidemi
authors.initials: H
authors.lastname: Kitano
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Ashikari
authors.forename: Makoto
authors.initials: M
authors.lastname: Matsuoka
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D060406:Brassinosteroids; D016764:Cell Polarity; D002777:Cholestanols / Q000494:pharmacology; D020869:Gene Expression Profiling; D017343:Genes, Plant / Q000235:genetics; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009154:Mutation; D012275:Oryza / Q000166:cytology* / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010641:Phenotype; D018515:Plant Leaves / Q000166:cytology* / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D018547:Plant Stems / Q000166:cytology* / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D013260:Steroids, Heterocyclic / Q000494:pharmacology
chemical_list: D060406:Brassinosteroids; D002777:Cholestanols; D013260:Steroids, Heterocyclic; D010088:Oxidoreductases; C023623:brassinolide