title: ARF7 increases the endogenous contents of castasterone through suppression of BAS1 expression in Arabidopsis thaliana.
abstract: Homeostasis of brassinosteroids (BRs) maintained by the balance between their biosynthesis and inactivation is important to coordinate the diverse physiological and developmental responses of plants. Although BR signaling regulates the endogenous levels of BRs via negative feedback regulation, it remains largely unknown how the biosynthesis and inactivation of BR are triggered. BAS1 encodes CYP734A1, which inactivates the biologically active BRs via C-26 hydroxylation and is down-regulated by a BR-responsive transcription factor, BZR1. Here it is demonstrated that the expression of the BAS1 gene is regulated by auxin response factors (ARFs) in Arabidopsis thaliana. Two successive E-box motifs on the BAS1 promoter function as BZR1 binding sites and are essential for BR-regulated BAS1 expression. The expression of BAS1 is increased in the arf7 and arf7arf19 mutants. The endogenous level of bioactive BR, castasterone, is greatly decreased in those mutants. ARF7 can bind to the E-box motifs of the BAS1 promoter where BZR1 binds, suggesting that ARF7 and BZR1 mutually compete for the same cis-element of the BAS1 promoter. Additionally, ARF7 directly interacts with BZR1, which inhibits their DNA binding activities and regulation of BAS1 expression. In conclusion, auxin signaling via ARF7 directly modulates the expression of BAS1 by competition with BZR1, thereby increasing the level of castasterone and promoting growth and development in A. thaliana.
authors.affiliation: Department of Life Science, College of Natural Sciences, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Ji-Hyun
authors.initials: JH
authors.lastname: Youn
authors.affiliation: Department of Life Science, College of Natural Sciences, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Min Kyun
authors.initials: MK
authors.lastname: Kim
authors.affiliation: Department of Life Science, College of Natural Sciences, Hanyang University, Seoul 133-791, Republic of Korea.
authors.forename: Eun-Ji
authors.initials: EJ
authors.lastname: Kim
authors.affiliation: Department of Life Science, College of Natural Sciences, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Seung-Hyun
authors.initials: SH
authors.lastname: Son
authors.affiliation: Department of Life Science, College of Natural Sciences, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Lee
authors.affiliation: Department of Life Science, College of Natural Sciences, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Mun-Seok
authors.initials: MS
authors.lastname: Jang
authors.affiliation: Department of Life Science, College of Natural Sciences, Hanyang University, Seoul 133-791, Republic of Korea; Research Institute for Convergence of Basic Sciences, Hanyang University, Seoul 133-791, Republic of Korea. Electronic address: twgibio@hanyang.ac.kr.
authors.forename: Tae-Wuk
authors.initials: TW
authors.lastname: Kim
authors.affiliation: Department of Life Science, College of Natural Sciences, Chung-Ang University, Seoul 156-756, Republic of Korea. Electronic address: skkimbio@cau.ac.kr.
authors.forename: Seong-Ki
authors.initials: SK
authors.lastname: Kim
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000187:drug effects* / Q000378:metabolism*; D060406:Brassinosteroids / Q000378:metabolism; D002777:Cholestanols / Q000032:analysis*; D006706:Homeostasis; D007210:Indoleacetic Acids / Q000378:metabolism; D054464:Peroxiredoxins / Q000187:drug effects*; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C503425:ARF7 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols; D007210:Indoleacetic Acids; D014157:Transcription Factors; C083545:castasterone; C108214:BAS1 protein, Arabidopsis; D054464:Peroxiredoxins
keywords: Arabidopsis; BAS1; Brassicaceae; Brassinosteroid homeostasis; Castasterone; Hormonal crosstalk