Abstract
Recent molecular genetical studies have identified several regulators in GA signaling. Among them, DELLA protein has been considered as the most important regulator, which negatively functions in GA signaling and its degradation through ubiquitin/proteasome pathway releases GA responses. Recently, we isolated a GA insensitive dwarf mutant of rice, gid1. The GID1 encodes an unknown protein mainly localized in nuclei with similarity to hormone sensitive lipases (HSL). Recombinant GST-GID1 had a high affinity only for bioactive GAs, while mutated GST-GID1 corresponding three gid1 alleles, had no GA-binding affinity. The Kd value for GA4 was estimated to be around 10-7M, enough to account for the GA dependency on shoot elongation. Interestingly, GID1 bound to SLR1, a rice DELLA protein, in a GA dependent manner in yeast cells, and GID1 overexpression resulted in a GA-hypersensitive phenotype. Based on these results, we concluded that GID1 is a soluble receptor mediating GA signaling in rice.
