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CELL BIOLOGY AND SIGNAL TRANSDUCTION

AGF1, an AT-Hook Protein, Is Necessary for the Negative Feedback of AtGA3ox1 Encoding GA 3-Oxidase^1,[W]

Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113–0033, Japan (A.M., S.I.); and Department of Biological Science, Graduate School of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739–8526, Japan (A.M., T.F., Y.T.)

Negative feedback is a fundamental mechanism of organisms to maintain the internal environment within tolerable limits. Gibberellins (GAs) are essential regulators of many aspects of plant development, including seed germination, stem elongation, and flowering. GA biosynthesis is regulated by the feedback mechanism in plants. GA 3-oxidase (GA3ox) catalyzes the final step of the biosynthetic pathway to produce the physiologically active GAs. Here, we found that only the AtGA3ox1 among the AtGA3ox family of Arabidopsis (Arabidopsis thaliana) is under the regulation of GA-negative feedback. We have identified a cis-acting sequence responsible for the GA-negative feedback of AtGA3ox1 using transgenic plants. Furthermore, we have identified an AT-hook protein, AGF1 (for the AT-hook protein of GA feedback regulation), as a DNA-binding protein for the cis-acting sequence of GA-negative feedback. The mutation in the cis-acting sequence abolished both GA-negative feedback and AGF1 binding. In addition, constitutive expression of AGF1 affected GA-negative feedback in Arabidopsis. Our results suggest that AGF1 plays a role in the homeostasis of GAs through binding to the cis-acting sequence of the GA-negative feedback of AtGA3ox1.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instruction for Authors (www.plantphysiol.org) is: Yohsuke Takahashi (ytakahas{at}hiroshima-u.ac.jp).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.093542

^* Corresponding author; e-mail ytakahas{at}hiroshima-u.ac.jp; fax 81–824–24–7392.

Received November 23, 2006; accepted January 21, 2007; published February 2, 2007.

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