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Auxin stimulates DWARF4 expression and brassinosteroid biosynthesis in Arabidopsis
Author(s) -
Chung Yuhee,
Maharjan Puna M.,
Lee Oksun,
Fujioka Shozo,
Jang Suyoun,
Kim Bokyung,
Takatsuto Suguru,
Tsujimoto Masafumi,
Kim Hobang,
Cho Seoae,
Park Taesung,
Cho Hyunwoo,
Hwang Ildoo,
Choe Sunghwa
Publication year - 2011
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2011.04513.x
Subject(s) - auxin , brassinosteroid , arabidopsis , arabidopsis thaliana , biology , mutant , plant hormone , biosynthesis , chromatin immunoprecipitation , repressor , microbiology and biotechnology , biochemistry , gene , gene expression , promoter
Summary 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 n m , 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.