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The GID2 gene encoded a 639-base-pair open reading frame capable of producing apolypeptide of 212 amino acid residues. The deduced amino acid sequence of GID2 contained an F-box domain(Fig. 1).F-box domains are found in specific components of the multisubunit SCF E3 ubiquitin ligase complex.The F-box protein in the SCF complex functions as a receptor that selectively recuits target proteins into the complex to degrade those proteins through ubiquitination.
GID2 influences the rice height through regulating GA signaling. GA are essential regulators of diverse growth and developmental process in plants. A GA signal promotes the degradation of SLR1 by the post-translational modification to be targeted by GID2.GID2 is a component of the SCF complex through an inieraction with a rice ASK1 homolog,OsSkp15(Fig. 2).
Domain analysis of GID2
Comparison of the primary structure between GID2 and Arabidopsis ortholog protein, SLR1, revealed that these F-box proteins share three conserved domains, the F-box, GGF, and LSL domains. In addition to these domains, GID2 has a unique N-terminal region(VR1), which is not shared with SLY1. The dwarf phenotype of gid2 was not rescued by the introduction of contructs such as ΔF, ΔGGF, or ΔLSL; however, it was rescued by the intact GID2 and ΔVR1. This result demonstrates thar all the conversed domains pointed out earlier are essential for the function of GID2 unlike the N-terminal region of GID2, which is not shared with SLY1.
ExpressionThe GID2 gene is expressed at different levels in all organs, preferentially expressed in unopened flowers, shoot apices, and elongation stem, and at lower levels in the leaf blades, leaf sheaths, roots, and rachis. Expression of GID2 preferentially occurs in rice organs actively synthesizing GA(Fig. 4).
The gid2 is a rice GA-insensitive dwarf mutant. It is caused by the loss function of a putative F-box protein.The gid2 mutant shows a severe dwarf phenotype with wide leaf blades and dark green leaves(Fig.5). The gid2 mutants are dwarfed because they accumulate SLR1.The gid2 mutants exhibit reduced GA responses and don’t resume normal growth when treated with GA. In gid2, a repressor for GA signaling, SLR1, is highly accumulated in a phosphorylated form and GA increases its concentration in the wild type(Fig. 6)
The F-box domain in GID2 is well conserved in other F-box proteins, with the greatest similarity to Arabidopsis SLY1, which is a positive regulator of GA signaling(Fig. 8)..F-box proteins occur widely throughout the eukaryote kingdom, in organisms ranging from yeast to humans, and they function as receptors that recuit proteins as substrates for ubiquitin-mediated degradation in the 26S proteasome. The SCF-mediated signaling pathway is well conserved in yeast, mammals and higher plants. GA-dependent phosphorylation of SLR1 triggers the ubiquitin-mediated degradation in a manner similar to the SCF-mediated in yeast and animals.
The interaction between GIBBERELLIN INSENSITIVE DWARF1 (GID1) and the N-terminal DELLA/TVHYNP motif of SLR1 triggers F-box protein GID2-mediated SLR1 degradation.The stable interaction of GID1-SLR1 through the GRAS domain is essential for the recognition of SLR1 by GID2. When the DELLA/TVHYNP motif of SLR1 binds with GID1, it enables the GRAS domain of SLR1 to interact with GID1 and that the stable GID1-SLR1 complex is efficiently recognized by GID2. In the absence of GA, DELLA represses GA action. When GA is present, the GA-bound GID1 receptor interacts with the DELLA/TVHYNP motif of DELLA protein. This interaction triggers DELLA protein degradation through the SCF-GID2/SLY1 proteasome pathway, and GA action occurs The binding of the DELLA/ TVHYNP motif to GID1 is not sufficient for SLR1 to be efficiently recognized by GID2 and that a stable interaction between GID1 and SLR1 through the GRAS domain of SLR1 is also essential. The interaction between the GRAS domain and GID1 serves as the recognition signal for targeting of SLR1 by GID2.
IdentificationofSLR1RegionsImportant for Interaction with GID1 and GID2
The GRAS domain has been divided into several subdomains: LHRI, VHIID, LHRII, PFYRE, and SAW(Fig. 9) In DELLA proteins, the DELLA/TVHYNP motif and the GRAS domain are connected by the poly S/T/V domain, a domain that shows large sequence variation among DELLA proteins. Poly S/T/V and LHRI are not important for the interaction with GID1 or GID2. VHIID is important for the interaction with GID2. LHRII is also important for interaction with GID2 and may be partially involved in the stable interaction with GID1. In the case of the PFYRE and SAW subdomains, the overall trend of the mutant proteins is apparently different from that of the previous four subdomains, and there are two valleys of interaction with GID1 in each one. Exchanges of DRF490-2AAA or HYY497-9AAA in the PFYRE subdomain dramatically reduced the interaction with GID1 and nearly eliminated GID2 interaction. In the SAW subdomain, G576V abolished interaction with both GID1 and GID2, as previously observed.
Domain Analysis of GA Signaling Components and a Model of GID1-SLR1-GID2 Complex Formation
In GID2, the GGF and LSL domains are necessary for the interaction with SLR1, GID1 regions other than those involved in the GID1-SLR1 interaction are not necessary for the SLR1-GID2 interaction. In SLR1, the poly S/T/V and LHRI subdomains might not be involved in the interaction with either GID1 or GID2. VHIID and LHRII seem to be preferentially involved in the interaction with GID2 and might be the direct GID2 binding site. The C-terminal region of the VHIID subdomain (LQ361-2) is also involved in the interaction with GID1(Fig. 10).
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Labs working on this gene
1 BioScience Center, Nagoya University, Nagoya, Japan.
2 BioResources Center, Riken, Tsukuba, Japan.
3 Division of Molecular and Life Science, Pohang University of Science and Technology, Republic of Korea.
4 Graduate School of Bioagricultural Science, Nagoya University, Nagoya, Japan.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Sasaki A.;Itoh H.;Gomi K.;Ueguchi-Tanaka M.;Ishiyama K.;Kobayashi M. Jeong DH.;An G.;Kitano H.;Ashikari M.;Matsuoka M Accumulation of phosphorylated repressor for gibberellin signaling in an F-box mutant. Science, 2003, 299: 1896-1898.
- ↑ 2.0 2.1 2.2 Nicholas P. Harberd. Relieving DELLA Restraint . Science, 2003, 299(5614): 1853-1854.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Kenji Gomi;Akie Sasaki;Hironori Itoh;Miyako Ueguchi-Tanaka;Motoyuki Ashikari;Hidemi Kitano;Makoto Matsuoka. GID2, an F-box subunit of the SCF E3 complex, specifically interacts with phosphorylated SLR1 protein and regulates the gibberellin-dependent degradation of SLR1 in rice. The Plant Journal, 2004, 37(4): 626-634.
- ↑ 4.0 4.1 4.2 Ko Hirano, Kenji Asano, Hiroyuki Tsuji, Mayuko Kawamura, Hitoshi Mori, Hidemi Kitano, Miyako Ueguchi-Tanaka, and Makoto Matsuoka. Characterization of the Molecular Mechanism Underlying Gibberellin Perception Complex Formation in Rice. The Plant Cell, 2010( 22): 2680–2696.