A consensus nomenclature for the protein-import components of the chloroplast envelope

Schnell, Danny J.; Blobel, Günter; Keegstra, Kenneth; Kessler, Félix; Ko, Kenton; Soll, Jürgen

doi:10.1016/s0962-8924(97)01111-2

Cited by 126 publications

(69 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

Section: Introductionmentioning

confidence: 99%

“…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).…”

mentioning

confidence: 99%

See 1 more Smart Citation

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

Sun¹,

Chen²,

Lin³

et al. 2001

The Plant Cell

View full text Add to dashboard Cite

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...

show abstract

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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

Sun¹,

Chen²,

Lin³

et al. 2001

The Plant Cell

View full text Add to dashboard Cite

show abstract

“…The transit sequence is recognized by the chloroplast protein import machinery, which initiates import. It consists of translocon complexes at the outer (TOC) and inner membrane of the chloroplast (TIC) (3)(4)(5).…”

mentioning

confidence: 99%

The novel chloroplast outer membrane kinase KOC1 is a required component of the plastid protein import machinery

Zufferey

Montandon

Douet

et al. 2017

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

“…Transport of nuclear-encoded proteins across the double-membrane envelope is mediated by a translocon complex located at the outer and inner envelope membranes of chloroplasts (Inaba and Schnell, 2008;Jarvis, 2008). These translocon components are named Toc (translocon at the outer envelope membrane of chloroplasts) and Tic (translocon at the inner envelope membrane of chloroplasts) proteins (Schnell et al, 1997).…”

mentioning

confidence: 99%

CIA2 Coordinately Up-Regulates Protein Import and Synthesis in Leaf Chloroplasts

2009

View full text Add to dashboard Cite

Plastid biogenesis and maintenance depend on the coordinated assembly of proteins imported from the cytosol with proteins translated within plastids. Chloroplasts in leaf cells have a greater need for protein import and protein synthesis than plastids in other organs due to the large amount of proteins required for photosynthesis. We previously reported that the Arabidopsis (Arabidopsis thaliana) transcription factor CIA2 specifically up-regulates leaf expression of genes encoding protein translocons Toc33 and Toc75, which are essential for protein import into chloroplasts. Protein import efficiency was therefore reduced in cia2 mutant chloroplasts. To further understand the function of CIA2, gene expression profiles of the wild type and a cia2 mutant were compared by microarray analysis. Interestingly, in addition to genes encoding protein translocon components, other genes down-regulated in cia2 almost exclusively encode chloroplast ribosomal proteins. Isolated cia2 mutant chloroplasts showed reduced translation efficiency and steady-state accumulation of plastid-encoded proteins. When CIA2 was ectopically expressed in roots, expression of both the protein translocon and ribosomal protein genes increased. Further analyses in vivo revealed that CIA2 up-regulated these genes by binding directly to their promoter regions. We propose that CIA2 is an important factor responsible for fulfilling the higher protein demands of leaf chloroplasts by coordinately increasing both protein import and protein translation efficiencies.

show abstract

A consensus nomenclature for the protein-import components of the chloroplast envelope

Cited by 126 publications

References 11 publications

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

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

The novel chloroplast outer membrane kinase KOC1 is a required component of the plastid protein import machinery

CIA2 Coordinately Up-Regulates Protein Import and Synthesis in Leaf Chloroplasts

Contact Info

Product

Resources

About