A constituent of the chloroplast import complex represents a new type of GTP‐binding protein

Seedorf, Matthias; Waegemann, Karin; Soll, Jürgen

doi:10.1046/j.1365-313x.1995.7030401.x

Cited by 191 publications

(230 citation statements)

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“…The core components of the Toc complex are called Toc159, Toc34, and Toc75, according to their molecular weights (Hirsch et al, 1994;Kessler et al, 1994;Perry and Keegstra, 1994;Schnell et al, 1994;Seedorf et al, 1995;Bölter et al, 1998). Toc159 and Toc34 are related GTPases that have been proposed to act as preprotein receptors.…”

Section: Introductionmentioning

confidence: 99%

The Arabidopsisppi1Mutant Is Specifically Defective in the Expression, Chloroplast Import, and Accumulation of Photosynthetic Proteins[W]

et al. 2003

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The import of nucleus-encoded proteins into chloroplasts is mediated by translocon complexes in the envelope membranes. A component of the translocon in the outer envelope membrane, Toc34, is encoded in Arabidopsis by two homologous genes, atTOC33 and atTOC34 . Whereas atTOC34 displays relatively uniform expression throughout development, atTOC33 is strongly upregulated in rapidly growing, photosynthetic tissues. To understand the reason for the existence of these two related genes, we characterized the atTOC33 knockout mutant ppi1 . Immunoblotting and proteomics revealed that components of the photosynthetic apparatus are deficient in ppi1 chloroplasts and that nonphotosynthetic chloroplast proteins are unchanged or enriched slightly. Furthermore, DNA array analysis of 3292 transcripts revealed that photosynthetic genes are moderately, but specifically, downregulated in ppi1 . Proteome differences in ppi1 could be correlated with protein import rates: ppi1 chloroplasts imported the ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit and 33-kD oxygen-evolving complex precursors at significantly reduced rates, but the import of a 50S ribosomal subunit precursor was largely unaffected. The ppi1 import defect occurred at the level of preprotein binding, which is consistent with a role for atToc33 during preprotein recognition. The data suggest that atToc33 is involved preferentially in the import of photosynthetic proteins and, by extension, that atToc34 is involved in the import of nonphotosynthetic chloroplast proteins.

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Section: Introductionmentioning

confidence: 99%

The Arabidopsisppi1Mutant Is Specifically Defective in the Expression, Chloroplast Import, and Accumulation of Photosynthetic Proteins[W]

et al. 2003

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“…In pea, the Toc-complex consists of three major components forming a stable complex Ma et al, 1996). Toc159 (the number indicates the molecular mass in kD) and Toc34 are surface exposed, GTP-binding integral membrane proteins (Hirsch et al, 1994;Kessler et al, 1994;Seedorf et al, 1995;Chen et al, 2000a). The two proteins share a highly conserved GTP-binding domain .…”

Section: Introductionmentioning

confidence: 99%

AtToc90, a New GTP-Binding Component of the Arabidopsis Chloroplast Protein Import Machinery

et al. 2004

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AtToc159 is a GTP-binding chloroplast protein import receptor. In vivo, atToc159 is required for massive accumulation of photosynthetic proteins during chloroplast biogenesis. Yet, in mutants lacking atToc159 photosynthetic proteins still accumulate, but at strongly reduced levels whereas non-photosynthetic proteins are imported normally: This suggests a role for the homologues of atToc159 (atToc132, -120 and -90). Here, we show that atToc90 supports accumulation of photosynthetic proteins in plastids, but is not required for import of several constitutive proteins. Part of atToc90 associates with the chloroplast surface in vivo and with the Toc-complex core components (atToc75 and atToc33) in vitro suggesting a function in chloroplast protein import similar to that of atToc159. As both proteins specifically contribute to the accumulation of photosynthetic proteins in chloroplasts they may be components of the same import pathway.

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“…The expression of atToc75 and atToc33 in roots was not affected by the cia2 mutation ( Figure 5A), which correlated with the absence of expression of CIA2 in roots ( Figure 4A). In pea chloroplasts, Toc75 and Toc34 have been shown to be tightly associated (Seedorf et al, 1995). In vitro imported atToc33 and atToc34 also were shown to be associated with Toc75 in spinach chloroplasts (Gutensohn et al, 2000).…”

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Leaf-Specific Upregulation of Chloroplast Translocon Genes by a CCT Motif-Containing Protein, CIA2

Sun¹,

Chen²,

Lin³

et al. 2001

The Plant Cell

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Chloroplasts are a major destination of protein traffic within leaf cells. Protein import into chloroplasts is mediated by a set of translocon complexes at the chloroplast envelope. Current data indicate that the expression of translocon genes is regulated in a tissue-specific manner, possibly to accommodate the higher import demand of chloroplasts in leaves and the lower demand of plastids in other tissues. We have designed a transgene-based positive screen to isolate mutants disrupted in protein import into plastids. The first locus we isolated, CIA2 , encodes a protein containing a motif conserved within the CCT family of transcription factors. Biochemical analysis indicates that CIA2 is responsible for specific upregulation of the translocon genes atToc33 and atToc75 in leaves. Identification of CIA2 provides new insights into the tissue-specific regulation of translocon gene expression. INTRODUCTIONMost proteins in chloroplasts are encoded by the nucleus and imported post-translationally into chloroplasts. Except for some outer envelope membrane proteins, nucleusencoded chloroplast proteins are synthesized as higher molecular weight precursors with N-terminal extensions called transit peptides. Transit peptides are necessary and sufficient for the import of precursor proteins into chloroplasts. Transport across the double membrane envelope is mediated by a set of translocon components located in the envelope. Several translocon components have been identified from pea chloroplasts by cross-linking or coimmunoprecipitating with importing precursor proteins (reviewed by Schleiff and Soll, 2000). They are collectively named Toc (for translocon at the outer envelope membrane of chloroplasts) and Tic (for translocon at the inner envelope membrane of chloroplasts) proteins (Schnell et al., 1997).Among the Toc components identified, Toc159 is proposed to function as the transit peptide receptor (Perry and Keegstra, 1994;Ma et al., 1996). A considerable amount of evidence indicates that Toc75 is the major component of the protein-translocating channel in the outer membrane (Hinnah et al., 1997;Reumann et al., 1999). The function of Toc34 is not clear. It has been shown to be tightly associated with Toc75 (Seedorf et al., 1995). Arabidopsis has two Toc34 orthologs, atToc34 and atToc33. These two proteins seem to have distinct but overlapping functions (Gutensohn et al., 2000).Techniques such as coimmunoprecipitation and crosslinking, when used to identify translocon components, usually identify abundant and stably associated components. Regulatory components that are present in minute amounts or only transiently, and upstream regulators present in different locations, usually are missed by these techniques.More recently, genetics has been used to study protein import into chloroplasts. Arabidopsis mutants have been found for two translocon components, atToc159 (Bauer et al., 2000) and atToc33 (Jarvis et al., 1998). These mutants confirmed that the translocon components identified by cell biology techniques functi...

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A constituent of the chloroplast import complex represents a new type of GTP‐binding protein

Cited by 191 publications

References 50 publications

The Arabidopsisppi1Mutant Is Specifically Defective in the Expression, Chloroplast Import, and Accumulation of Photosynthetic Proteins[W]

The Arabidopsisppi1Mutant Is Specifically Defective in the Expression, Chloroplast Import, and Accumulation of Photosynthetic Proteins[W]

AtToc90, a New GTP-Binding Component of the Arabidopsis Chloroplast Protein Import Machinery

Leaf-Specific Upregulation of Chloroplast Translocon Genes by a CCT Motif-Containing Protein, CIA2

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