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The Arabidopsis gai mutant allele confers a reduction in gibberellin (GA) responsiveness. Here we report the molecular cloning of GAI and a closely related gene GRS. The predicted GAI (wild-type) and gai (mutant) proteins differ only by the deletion of a 17-amino-acid segment from within the amino-terminal region. GAI and GRS contain nuclear localization signals, a region of homology to a putative transcription factor, and motifs characteristic of transcriptional coactivators. Genetic analysis indicates that GAI is a repressor of GA responses, that GA can release this repression, and that gai is a mutant repressor that is relatively resistant to the effects of GA. Mutations at SPY and GAR2 suppress the gai phenotype, indicating the involvement of GAI, SPY, and GAR2 in a signaling pathway that regulates GA responses negatively. The existence of this pathway suggests that GA modulates plant growth through derepression rather than through simple stimulation.


Journal article


Genes Dev

Publication Date





3194 - 3205


Alleles, Amino Acid Sequence, Arabidopsis, Arabidopsis Proteins, Base Sequence, Cloning, Molecular, Consensus Sequence, DNA, Plant, Genes, Plant, Gibberellins, Mixed Function Oxygenases, Molecular Sequence Data, Mutagenesis, Insertional, Nuclear Localization Signals, Open Reading Frames, Plant Growth Regulators, Plant Proteins, RNA, Plant, Sequence Homology, Amino Acid, Signal Transduction, Suppression, Genetic, Triazoles