title: BAS1 and SOB7 act redundantly to modulate Arabidopsis photomorphogenesis via unique brassinosteroid inactivation mechanisms.
abstract: Active brassinosteroids (BRs), such as brassinolide (BL) and castasterone (CS), are growth-promoting plant hormones. An Arabidopsis cytochrome P450 monooxygenase (CYP734A1, formerly CYP72B1), encoded by the BAS1 gene, inactivates BRs and modulates photomorphogenesis. BAS1 was identified as the overexpressed gene responsible for a dominant, BR-deficient mutant, bas1-D. This mutant was isolated in an activation-tagged screen designed to identify redundant genes that might not be identified in classic loss-of-function screens. Here we report the isolation of a second activation-tagged mutant with a BR-deficient phenotype. The mutant phenotype is caused by the overexpression of SOB7 (CYP72C1), a homolog of BAS1. We generated single and double null-mutants of BAS1 and SOB7 to test the hypothesis that these two genes act redundantly to modulate photomorphogenesis. BAS1 and SOB7 act redundantly with respect to light promotion of cotyledon expansion, repression of hypocotyl elongation and flowering time in addition to other phenotypes not regulated by light. We also provide biochemical evidence to suggest that BAS1 and SOB7 act redundantly to reduce the level of active BRs, but have unique mechanisms. Overexpression of SOB7 results in a dramatic reduction in endogenous CS levels, and although single null-mutants of BAS1 and SOB7 have the same level of CS as the wild type, the double null-mutant has twice the amount. Application of BL to overexpression lines of BAS1 or SOB7 results in enhanced metabolism of BL, though only BAS1 overexpression lines confer enhanced conversion to 26-OHBL, suggesting that SOB7 and BAS1 convert BL and CS into unique products.
authors.affiliation: Department of Biology, Washington University, Campus Box 1137, One Brookings Drive, St Louis, MO 63130, USA.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Turk
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Hideharu
authors.initials: H
authors.lastname: Seto
authors.forename: Yukihisa
authors.initials: Y
authors.lastname: Shimada
authors.forename: Suguru
authors.initials: S
authors.lastname: Takatsuto
authors.forename: Shigeo
authors.initials: S
authors.lastname: Yoshida
authors.forename: Huachun
authors.initials: H
authors.lastname: Wang
authors.forename: Quetzal I
authors.initials: QI
authors.lastname: Torres
authors.forename: Jason M
authors.initials: JM
authors.lastname: Ward
authors.forename: Girish
authors.initials: G
authors.lastname: Murthy
authors.forename: Jingyu
authors.initials: J
authors.lastname: Zhang
authors.forename: John C
authors.initials: JC
authors.lastname: Walker
authors.forename: Michael M
authors.initials: MM
authors.lastname: Neff
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000378:metabolism / Q000502:physiology*; D060406:Brassinosteroids; D002777:Cholestanols; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D008027:Light; D008969:Molecular Sequence Data; D010544:Peroxidases / Q000502:physiology*; D054464:Peroxiredoxins; D010641:Phenotype; D016415:Sequence Alignment; D013260:Steroids, Heterocyclic
chemical_list: D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols; D013260:Steroids, Heterocyclic; C083545:castasterone; D003577:Cytochrome P-450 Enzyme System; C500888:CYP72C1 protein, Arabidopsis; D010544:Peroxidases; C108214:BAS1 protein, Arabidopsis; D054464:Peroxiredoxins; C023623:brassinolide