Auxin stimulates <i>DWARF4</i> expression and brassinosteroid biosynthesis in Arabidopsis

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公開日
2011-04-04
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1111/j.1365-313x.2011.04513.x
公開者
Wiley

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<jats:title>Summary</jats:title><jats:p>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 (<jats:italic>Arabidopsis thaliana</jats:italic>), DWARF4 catalyzes the rate‐determining step. Through both the histochemical analysis of <jats:italic>DWF4pro:GUS</jats:italic> plants and the direct measurement of endogenous BR content, we discovered that BR biosynthesis is stimulated by auxin. When <jats:italic>DWF4pro:GUS</jats:italic> was subjected to auxin dose–response tests and a time‐course analysis, GUS activity started to increase at an auxin concentration of 10 n<jats:sc>m</jats:sc>, rising noticeably after 1 h of auxin treatment. In addition, the analysis of the <jats:italic>DWF4pro:GUS</jats:italic> 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 <jats:italic>DWF4</jats:italic> 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.</jats:p>

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