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A Rice gid1 Suppressor Mutant Reveals That Gibberellin Is Not Always Required for Interaction between Its Receptor, GID1, and DELLA Proteins

Yamamoto, Yuko, Hirai, Takaaki, Yamamoto, Eiji, Kawamura, Mayuko, Sato, Tomomi, Kitano, Hidemi, Matsuoka, Makoto, Ueguchi-Tanaka, Miyako
The plant cell 2010 v.22 no.11 pp. 3589-3602
Arabidopsis thaliana, rice, Glycine max, Oryza sativa, amino acid substitution, hormone receptors, amino acids, mutants, Brassica napus, gibberellins, rice protein, protein-protein interactions, surface plasmon resonance
To investigate gibberellin (GA) signaling using the rice (Oryza sativa) GA receptor GIBBERELLIN-INSENSITIVE DWARF1 (GID1) mutant gid1-8, we isolated a suppressor mutant, Suppressor of gid1-1 (Sgd-1). Sgd-1 is an intragenic mutant containing the original gid1-8 mutation (L45F) and an additional amino acid substitution (P99S) in the loop region. GID1P⁹⁹S interacts with the rice DELLA protein SLENDER RICE1 (SLR1), even in the absence of GA. Substitution of the 99th Pro with other amino acids revealed that substitution with Ala (P99A) caused the highest level of GA-independent interaction. Physicochemical analysis using surface plasmon resonance revealed that GID1P⁹⁹A has smaller Ka (association) and Kd (dissociation) values for GA₄ than does wild-type GID1. This suggests that the GID1P⁹⁹A lid is at least partially closed, resulting in both GA-independent and GA-hypersensitive interactions with SLR1. One of the three Arabidopsis thaliana GID1s, At GID1b, can also interact with DELLA proteins in the absence of GA, so we investigated whether GA-independent interaction of At GID1b depends on a mechanism similar to that of rice GID1P⁹⁹A. Substitution of the loop region or a few amino acids of At GID1b with those of At GID1a diminished its GA-independent interaction with GAI while maintaining the GA-dependent interaction. Soybean (Glycine max) and Brassica napus also have GID1s similar to At GID1b, indicating that these unique GID1s occur in various dicots and may have important functions in these plants.