Dual Lipid Modification of Arabidopsis G<i>γ</i>-Subunits Is Required for Efficient Plasma Membrane Targeting

Zeng, Qin; Wang, Xuejun; Running, Mark

doi:10.1104/pp.106.093583

Cited by 78 publications

(106 citation statements)

References 98 publications

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“…These observations suggest that the two G␤␥ dimers of Arabidopsis, G␤␥1 and G␤␥ 2 , have distinct functions in different subcellular compartments. Also consistent with this concept is the observation that G␥ 1 (agg1) and G␥ 2 (agg2) mutants share different subsets of the several phenotypes reported for G␤ (agb1) mutants (12,54).…”

Section: Discussionsupporting

confidence: 63%

“…When a constitutively active form of rice G␣ is expressed in a G␣-null background, the constitutively active subunit is predominantly found in the monomeric form (28). Because the Arabidopsis G␣ exhibits slow GTPase activity, most if not all of the Arabidopsis G␣ protein is proposed to be in its active GTP-bound form (54,63). We found that H 2 O 2 promotes dissociation of Arabidopsis G␣ from the ϳ700 kDa complex (Fig.…”

Section: Discussionmentioning

confidence: 73%

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Characterization of the Arabidopsis Heterotrimeric G Protein

Wang

Assmann

Fedoroff

2008

Journal of Biological Chemistry

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We have used fluorescence resonance energy transfer and coimmunoprecipitation to analyze the interactions among the ␣, ␤, and ␥1 subunits of the Arabidopsis heterotrimeric G protein.Using cyan and yellow fluorescent protein fusion constructs, we show that overexpressed G␥ 1 localizes to protoplast membranes, but G␤ exhibits membrane localization only when the G␥ 1 protein is co-overexpressed. Overexpressed G␣ shows membrane localization unaccompanied by overexpression of either G␤ or G␥ 1 . We detect fluorescence resonance energy transfer between G␤ and G␥ 1 in the absence of G␣ overexpression and between G␣ and G␥ 1 but only when all three subunits are co-overexpressed. Both G␣ and G␤ are associated with large macromolecular complexes of ϳ700 kDa in the plasma membrane. G␣ is present in both large complexes and as free G␣ in plasma membranes from wild type plants. In plants homozygous for a null allele of the G␤ gene, G␣ is associated with smaller complexes in the 200 -400-kDa range, indicating that its presence in the large complex depends on association with G␤␥. Activation of the G␣ subunit with guanosine 5-3-O-(thio)triphosphate (GTP␥S) results in partial dissociation of G␣ from the complex. Hydrogen peroxide (H 2 O 2 ) promotes extensive dissociation of the G␣ complex but does not interfere with binding of GTP␥S to purified recombinant G␣, suggesting that reactive oxygen species affect the stability of the large complex but not the activity of G␣ itself.The results of pharmacological and genetic studies have provided evidence that the plant heterotrimeric G protein is involved in the transmission of light (1) and hormone signals (2) as well as in the regulation of ion channels (3). Arabidopsis gpa1 mutant plants, which lack the G␣ protein, encoded by the GPA1 gene, exhibit reduced cell division during hypocotyl and leaf formation (4), whereas overexpression of GPA1 causes ectopic cell division, including meristem proliferation (5). Homozygous gpa1 mutant plants are less sensitive to abscisic acid inhibition of stomatal opening and guard cell inward K ϩ currents than wild type plants (6). By contrast, gpa1 mutant seeds exhibit hypersensitivity to abscisic acid in inhibition of germination and in root growth and seedling gene expression. In addition, gpa1 mutant plants are hyposensitive to gibberellic acid and brassinolide (7,8). Arabidopsis agb1-2 mutant plants, which lack the G␤ protein encoded by the AGB1 gene, show alterations in leaf, flower and fruit development, decreased hypocotyl cell division and hypersensitivity to D-glucose (9 -11). There are two G␥ subunit genes in Arabidopsis, AGG1 and AGG2, and mutant analysis indicates that each G␥ subunit participates in a subset of G␤-related developmental processes (12).Evidence is also accumulating that the heterotrimeric G protein mediates plant responses to bacterial and fungal pathogens and abiotic stress. Heterotrimeric G protein signaling to membrane-bound NADPH oxidase has been implicated in the development of disease resistance and in the apoptotic...

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Section: Discussionsupporting

confidence: 63%

Section: Discussionmentioning

confidence: 73%

Characterization of the Arabidopsis Heterotrimeric G Protein

Wang

Assmann

Fedoroff

2008

Journal of Biological Chemistry

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“…To elucidate if GFP-SlGGB1 is located at the plasma membrane or just in peripheral cytoplasm, we produced mesophyll protoplasts from transgenic Arabidopsis plants expressing GFP-SlGGB1 and transfected them with the Arabidopsis Gg subunit AGG2 fused to mCherry as a control. The plasma membrane localization of AGG2 was established previously (Adjobo-Hermans et al, 2006;Zeng et al, 2007). Both proteins were detected at the plasma membrane, although with a different pattern, as depicted by red and green colors (Fig.…”

Section: Gfp-slggb1 Localizes To the Plasma Membrane Cytoplasm And Thmentioning

confidence: 75%

“…Lack of the isoprenylation motif in canonical (type A) Gg subunits results in the failure of plasma membrane targeting (Kino et al, 2005;Adjobo-Hermans et al, 2006;Zeng et al, 2007). We showed that GFP-SlGGB1 localizes to the nucleus, the plasma membrane, and the cytoplasm (Fig.…”

Section: The Type B Gg Subunit Slggb1 Has a Unique Localization Patternmentioning

confidence: 86%

Type B Heterotrimeric G Protein γ-Subunit Regulates Auxin and ABA Signaling in Tomato

Subramaniam

Trusov²,

Encina³

et al. 2015

Plant Physiol.

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Heterotrimeric G proteins composed of a, b, and g subunits are central signal transducers mediating the cellular response to multiple stimuli in most eukaryotes. Gg subunits provide proper cellular localization and functional specificity to the heterotrimer complex. Plant Gg subunits, divided into three structurally distinct types, are more diverse than their animal counterparts. Type B Gg subunits, lacking a carboxyl-terminal isoprenylation motif, are found only in flowering plants. We present the functional characterization of type B Gg subunit (SlGGB1) in tomato (Solanum lycopersicum). We show that SlGGB1 is the most abundant Gg subunit in tomato and strongly interacts with the Gb subunit. Importantly, the green fluorescent proteinSlGGB1 fusion protein as well as the carboxyl-terminal yellow fluorescent protein-SlGGB1/amino-terminal yellow fluorescent protein-Gb heterodimer were localized in the plasma membrane, nucleus, and cytoplasm. RNA interference-mediated silencing of SlGGB1 resulted in smaller seeds, higher number of lateral roots, and pointy fruits. The silenced lines were hypersensitive to exogenous auxin, while levels of endogenous auxins were lower or similar to those of the wild type. SlGGB1-silenced plants also showed strong hyposensitivity to abscisic acid (ABA) during seed germination but not in other related assays. Transcriptome analysis of the transgenic seeds revealed abnormal expression of genes involved in ABA sensing, signaling, and response. We conclude that the type B Gg subunit SlGGB1 mediates auxin and ABA signaling in tomato.

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“…To rule out the possibility that a Pd-like enrichment of GPI-anchored mCitrine is an artifact of a stress response at the PM associated with agroinfiltration, we tested the localization of a non-GPI PM protein in our expression system. As a control, we chose previously reported ARABIDOPSIS HETEROTRIMERIC G-PROTEIN g-SUBUNIT2 (AGG2) that is a prenylated PM protein (Zeng et al, 2007). Expression of mCitrine fused to AGG2 (mCit-AGG2) resulted in a uniform PM accumulation with no enrichment at discrete regions (Fig.…”

Section: Gpi Modification Is Required For Subcellular Targeting Of Camentioning

confidence: 99%

Glycosylphosphatidylinositol (GPI) modification serves as a primary plasmodesmal targeting signal

2016

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Plasmodesmata (Pd) are membranous channels that serve as a major conduit for cell-to-cell communication in plants. The Pdassociated b-1,3-glucanase (BG_pap) and CALLOSE BINDING PROTEIN1 (PDCB1) were identified as key regulators of Pd conductivity. Both are predicted glycosylphosphatidylinositol-anchored proteins (GPI-APs) carrying a conserved GPI modification signal. However, the subcellular targeting mechanism of these proteins is unknown, particularly in the context of other GPI-APs not associated with Pd. Here, we conducted a comparative analysis of the subcellular targeting of the two Pd-resident and two unrelated non-Pd GPI-APs in Arabidopsis (Arabidopsis thaliana). We show that GPI modification is necessary and sufficient for delivering both BG_pap and PDCB1 to Pd. Moreover, the GPI modification signal from both Pd-and non-Pd GPI-APs is able to target a reporter protein to Pd, likely to plasma membrane microdomains enriched at Pd. As such, the GPI modification serves as a primary Pd sorting signal in plant cells. Interestingly, the ectodomain, a region that carries the functional domain in GPI-APs, in Pd-resident proteins further enhances Pd accumulation. However, in non-Pd GPI-APs, the ectodomain overrides the Pd targeting function of the GPI signal and determines a specific GPI-dependent non-Pd localization of these proteins at the plasma membrane and cell wall. Domainswap analysis showed that the non-Pd localization is also dominant over the Pd-enhancing function mediated by a Pd ectodomain. In conclusion, our results indicate that segregation between Pd-and non-Pd GPI-APs occurs prior to Pd targeting, providing, to our knowledge, the first evidence of the mechanism of GPI-AP sorting in plants.

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Dual Lipid Modification of Arabidopsis Gγ-Subunits Is Required for Efficient Plasma Membrane Targeting

Cited by 78 publications

References 98 publications

Characterization of the Arabidopsis Heterotrimeric G Protein

Characterization of the Arabidopsis Heterotrimeric G Protein

Type B Heterotrimeric G Protein γ-Subunit Regulates Auxin and ABA Signaling in Tomato

Glycosylphosphatidylinositol (GPI) modification serves as a primary plasmodesmal targeting signal

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