| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2005: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
Gibberellins (GAs) are a large family of tetracyclic, diterpenoid plant hormones that induce a wide range of plant growth responses including seed germination, stem elongation, leaf expansion, pollen maturation and induction of flowering. Recent works using GA insensitive and GA hypersensitive mutants revealed that GA response is occurred by the degradation of DELLA protein, a putative transcription regulator, in GA dependent manner. However, molecular mechanisms of GA perception have not been clarified yet.
Here we report isolation and characterization of a new GA-insensitive dwarf mutant of rice, gid1^1. The GID1 gene encodes an unknown protein with similarity to the hormone-sensitive lipases, and we observed preferential localization of the GID1-GFP signal in nuclei. Recombinant 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 GA_4 was estimated to be around 10^<-7> M, enough to account for the GA dependency on 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. Taken together, these results indicate that GID1 is a soluble receptor mediating GA signalling in rice.
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