Identification and characterization of Arabidopsis gibberellin receptors

Abstract

SummaryThree gibberellin (GA) receptor genes (AtGID1a, AtGID1b and AtGID1c), each an ortholog of the rice GA receptor gene (OsGID1), were cloned from Arabidopsis, and the characteristics of their recombinant proteins were examined. The GA-binding activities of the three recombinant proteins were confirmed by an in vitro assay. Biochemical analyses revealed similar ligand selectivity among the recombinants, and all recombinants showed higher affinity to GA 4 than to other GAs. AtGID1b was unique in its binding affinity to GA 4 and in its pH dependence when compared with the other two, by only showing binding in a narrow pH range (pH 6.4-7.5) with 10-fold higher affinity (apparent K d for GA 4 = 3 · 10 )8 M) than AtGID1a and AtGID1c. A two-hybrid yeast system only showed in vivo interaction in the presence of GA 4 between each AtGID1 and the Arabidopsis DELLA proteins (AtDELLAs), negative regulators of GA signaling. For this interaction with AtDELLAs, AtGID1b required only one-tenth of the amount of GA 4 that was necessary for interaction between the other AtGID1s and AtDELLAs, reflecting its lower K d value. AtDELLA boosted the GA-binding activity of AtGID1 in vitro, which suggests the formation of a complex between AtDELLA and AtGID1-GA that binds AtGID1 to GA more tightly. The expression of each AtGID1 clone in the rice gid1-1 mutant rescued the GA-insensitive dwarf phenotype. These results demonstrate that all three AtGID1s functioned as GA receptors in Arabidopsis.

Genetic Characterization and Functional Analysis of the GID1 Gibberellin Receptors inArabidopsis

“…It has previously been shown by semiquantitative RT-PCR that the three genes are expressed in flowers, siliques, stems, leaves, roots, and imbibed seeds at similar levels (Nakajima et al, 2006). However, analysis of the AtGenExpress expression atlas data set (Schmid et al, 2005;www.weigelworld.…”

“…However, it is not clear whether or how GA-GID1 and SLR1 interaction promotes binding of the GID2 F-box component of the SCF E3 Ub ligase to SLR1. In the Arabidopsis genome, there are three GID1 homologous genes that have been designated: GID1a, GID1b, and GID1c (Nakajima et al, 2006). There is strong evidence to suggest that the proteins they encode function as GA receptors.…”

“…Currently, there is no genetic evidence demonstrating a role for the Arabidopsis GID1 genes in GA signaling. However, the three genes display overlapping expression profiles, suggesting that they perform functionally redundant roles (Nakajima et al, 2006).…”

“…The molecular mechanisms by which bioactive GAs regulate plant growth and development are less understood, although recent genetic and biochemical studies have identified several key components in GA signaling Sun and Gubler, 2004). The study of GA response in the model plant Arabidopsis thaliana, although fruitful, has been complicated by the high level of functional redundancy within GA signaling components King et al, 2001;Strader et al, 2004;Nakajima et al, 2006). By contrast, several GA signaling components in rice (Oryza sativa) are encoded by single genes, making it a powerful system for studying this pathway.…”

“…This is emphasized by a recent study by Ueguchi-Tanaka et al (2005) in which they identified the elusive GA receptor in rice. The identity of the GA receptors provides an important opportunity to dissect the GA signaling cascade in Arabidopsis (Nakajima et al, 2006).…”