title: Involvement of C-22-hydroxylated brassinosteroids in auxin-induced lamina joint bending in rice.
abstract: The rice lamina joint is ideal material for investigating the activity of brassinosteroids (BRs) and auxin because of its high sensitivity to these compounds. Using a series of rice BR biosynthetic and receptor mutants, we conducted lamina joint tests to elucidate the mechanism of cross-talk between BR and auxin signaling in lamina joint bending. In BR biosynthetic mutants d2 and brd1, which are defective in C-23 hydroxylase and C-6 oxidase, respectively, the lamina joint response to auxin was significantly higher than that of wild-type plants. The other BR-biosynthetic mutants, brd2, osdwarf4 and d11, which are defective in C-22-hydroxylated BRs, showed less or no response to auxin. These results suggest that C-22-hydroxylated BRs are involved in auxin-induced lamina joint bending. The results were supported by the observation that inhibition of the hyper-response to auxin in d2 was reduced by treatment with brassinazole, which inhibits the function of DWARF4, the C-22 hydroxylase. In d61, which is defective in OsBRI1, a possible BR receptor in rice, the bending angle of the lamina joint in response to auxin and C-22-hydroxylated 6-deoxoBRs was nearly the same as that in wild-type plants. This implies that C-22-hydroxylated BRs function in auxin signaling independently of OsBRI1. From these observations, we propose that C-22-hydroxylated BRs participate in auxin signaling via a novel OsBRI1-independent signaling pathway.
authors: RIKEN Adavanced Science Institute, Wako, Saitama, Japan. iripple1103@gmail.com
authors: Ayako
authors: A
authors: Nakamura
authors: Shozo
authors: S
authors: Fujioka
authors: Suguru
authors: S
authors: Takatsuto
authors: Masafumi
authors: M
authors: Tsujimoto
authors: Hidemi
authors: H
authors: Kitano
authors: Shigeo
authors: S
authors: Yoshida
authors: Tadao
authors: T
authors: Asami
authors: Takeshi
authors: T
authors: Nakano
mesh_terms: D060406:Brassinosteroids; D049108:Cell Enlargement; D002777:Cholestanols / Q000494:pharmacology*; D007210:Indoleacetic Acids / Q000494:pharmacology*; D009154:Mutation; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D013260:Steroids, Heterocyclic / Q000494:pharmacology*
chemical_list: D060406:Brassinosteroids; D002777:Cholestanols; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D013260:Steroids, Heterocyclic; C519615:BRI1 protein, Oryza sativa; D017346:Protein Serine-Threonine Kinases; C023623:brassinolide