title: Auxin stimulates DWARF4 expression and brassinosteroid biosynthesis in Arabidopsis.
abstract: Brassinosteroids (BRs) are growth-promoting steroidal hormones. Despite the importance of BRs in plant biology, the signal that initiates BR biosynthesis remains unknown. Among the enzymes involved in BR biosynthesis in Arabidopsis (Arabidopsis thaliana), DWARF4 catalyzes the rate-determining step. Through both the histochemical analysis of DWF4pro:GUS plants and the direct measurement of endogenous BR content, we discovered that BR biosynthesis is stimulated by auxin. When DWF4pro:GUS was subjected to auxin dose-response tests and a time-course analysis, GUS activity started to increase at an auxin concentration of 10 nm, rising noticeably after 1 h of auxin treatment. In addition, the analysis of the DWF4pro:GUS line in BR- and auxin-mutant backgrounds revealed that the induction by auxin requires auxin-signaling pathways but not BRs, which implies that auxin signaling directly controls BR biosynthesis. Furthermore, chromatin immunoprecipitation assays confirmed that auxin inhibits the binding of the transcriptional repressor, BZR1, to the DWF4 promoter. A microarray analysis that was designed to examine the transcriptomes after treatment with auxin alone or auxin plus brassinazole (a BR biosynthetic inhibitor) revealed that genes previously characterized as being auxin responsive are not properly regulated when BR biosynthesis is disrupted by brassinazole. Therefore, our results support the idea that auxin regulates BR biosynthesis, and that auxin thus relies on synthesized BRs for some of its growth-promoting effects in Arabidopsis.
authors.affiliation: School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea.
authors.forename: Yuhee
authors.initials: Y
authors.lastname: Chung
authors.forename: Puna M
authors.initials: PM
authors.lastname: Maharjan
authors.forename: Oksun
authors.initials: O
authors.lastname: Lee
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Suyoun
authors.initials: S
authors.lastname: Jang
authors.forename: Bokyung
authors.initials: B
authors.lastname: Kim
authors.forename: Suguru
authors.initials: S
authors.lastname: Takatsuto
authors.forename: Masafumi
authors.initials: M
authors.lastname: Tsujimoto
authors.forename: Hobang
authors.initials: H
authors.lastname: Kim
authors.forename: Seoae
authors.initials: S
authors.lastname: Cho
authors.forename: Taesung
authors.initials: T
authors.lastname: Park
authors.forename: Hyunwoo
authors.initials: H
authors.lastname: Cho
authors.forename: Ildoo
authors.initials: I
authors.lastname: Hwang
authors.forename: Sunghwa
authors.initials: S
authors.lastname: Choe
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D046228:Microarray Analysis; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D013256:Steroids / Q000096:biosynthesis*
chemical_list: C111451:AT3G50660 protein, Arabidopsis; D029681:Arabidopsis Proteins; C454444:BZR1 protein, Arabidopsis; D004268:DNA-Binding Proteins; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D010937:Plant Growth Regulators; D013256:Steroids; D015084:2,4-Dichlorophenoxyacetic Acid; D003577:Cytochrome P-450 Enzyme System