STUDY ON THE DEGRADATION OF THE REPRESSOR OF GA SIGNALING

赤霉素（GAs）是四环二萜类植物激素的大家族，其诱导广泛的植物生长反应，包括种子萌发、茎伸长、叶扩展、花粉成熟和开花诱导。最近的工作，利用GA不敏感和GA过敏突变体显示，GA反应发生的降解DELLA蛋白，一个假定的转录调节，在GA依赖的方式。然而，GA感知的分子机制尚未阐明，在这里，我们报道了一个新的GA不敏感的水稻矮秆突变体gid 1 ^1的分离和鉴定。GID 1基因编码一种未知的蛋白质，其与GFP敏感的脂肪酶相似，并且我们观察到GID 1-GFP信号优先定位于细胞核中。重组GST-GID 1仅对具有生物活性的GA具有高亲和力，而对应于三个gid 1等位基因的突变GST-GID 1没有GA结合亲和力。GA_4的解离常数估计约为10 μ <-7>M，足以解释GA对芽伸长的依赖性。此外，在酵母细胞中，GID 1以GA依赖性方式与水稻DELLA蛋白SLR 1结合。GID 1过表达导致GA超敏表型。综上所述，这些结果表明，GID 1是一个可溶性受体介导GA信号在水稻。

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.