1. Bioscience and Biotechnology Center, Nagoya University, Nagoya 464-8601, Japan
2. Department of Applied Biological Chemistry, The University of Tokyo, Tokyo 113-8657, Japan
3. Department of Biochemistry, National Institute of Agrobiological Sciences, Tsukuba 305-8602, Japan
4. BioResources Center, Riken, Tsukuba 305-0074, Japan
5. Institute of Botany Academia, Sinica, Taipei 11529, Taiwan
6. Biotechnology Research Center, The University of Tokyo, Tokyo 113-8657, Japan
7. †Present address: Institute of Biotechnology, Central Taiwan University of Science and Technology, Taichung 406, Taiwan
8. *These authors contributed equally to this work

Correspondence to: Makoto Matsuoka¹ Correspondence and requests for materials should be addressed to M.M. (Email: makoto@nuagr1.agr.nagoya-u.ac.jp). Sequence data from this article have been deposited in the DDBJ/EMBL/GenBank databases under accession number AB211399.

Abstract

Gibberellins (GAs) are phytohormones that are essential for many developmental processes in plants. It has been postulated that plants have both membrane-bound and soluble GA receptors; however, no GA receptors have yet been identified. Here we report the isolation and characterization of a new GA-insensitive dwarf mutant of rice, gid1. The GID1 gene encodes an unknown protein with similarity to the hormone-sensitive lipases, and we observed preferential localization of a GID1–green fluorescent protein (GFP) signal in nuclei. Recombinant glutathione S-transferase (GST)–GID1 had a high affinity only for biologically active GAs, whereas mutated GST–GID1 corresponding to three gid1 alleles had no GA-binding affinity. The dissociation constant for GA₄ was estimated to be around 10^-7 M, enough to account for the GA dependency of shoot elongation. Moreover, GID1 bound to SLR1, a rice DELLA protein, in a GA-dependent manner in yeast cells. GID1 overexpression resulted in a GA-hypersensitive phenotype. Together, our results indicate that GID1 is a soluble receptor mediating GA signalling in rice.

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