A SecY Homologue Is Required for the Elaboration of the Chloroplast Thylakoid Membrane and for Normal Chloroplast Gene Expression

Roy, Laura M.; Barkan, Alice

doi:10.1083/jcb.141.2.385

Cited by 92 publications

(76 citation statements)

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“…The genes that encode plastid-localized SecY, SecA, and SecE that function in protein translocation events in the thylakoid membranes have been described previously (Voelker et al, 1997;Roy and Barkan, 1998), and the functions of the proteins have been biochemically characterized (Nakai et al, 1994;Yuan et al, 1994;Schuenemann et al, 1999). We have identified and characterized two additional loci in the Arabidopsis genome that encode plastid-localized homologs of SecY and SecA, designated as SCY2 and SECA2.…”

Section: Discussion Dual Sec Systems In Plastids Reflect An Ancient Dmentioning

confidence: 99%

“…In mature chloroplasts, SCY1 is localized strictly to the thylakoids and cannot be detected in the envelope membranes even with extended exposure of the immunoblots (Fincher et al, 2003). The phenotype of mutations in SCY1, SECA1, and SECE1 in maize (Voelker et al, 1997;Roy and Barkan, 1998;Williams-Carrier et al, 2010) is impairment in thylakoid biogenesis and, for SCY1, subsequent seedling lethality. Similarly, we show here that mutations in Arabidopsis SCY1, SECA1, and SECE1 yield chlorotic phenotypes.…”

Section: Scy1 and Scy2 Perform Different Functionsmentioning

confidence: 99%

“…SECA1 and SCY1 have been shown to function in thylakoid transport of lumenal and some membrane proteins through genetic (Voelker et al, 1997;Roy and Barkan, 1998) and biochemical (Nakai et al, 1994;Yuan et al, 1994;Mori et al, 1999;Schuenemann et al, 1999) investigations. Based on their characteristics in in vitro transport assays, they appear to operate very similarly to the E. coli Sec translocase.…”

Section: Scy1 and Scy2 Perform Different Functionsmentioning

confidence: 99%

“…The SecYEG translocon is reduced to a complex of SecY and SecE homologs in chloroplasts, and there are two YidC homologs, Alb3 and Alb4. Disruption of the SecY gene in maize (Zea mays) results in pale seedlings and an arrest of seedling growth (Roy and Barkan, 1998). Disruption of the maize SecE gene produces a less severe, pale-green seedling phenotype (Williams-Carrier et al, 2010).…”

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confidence: 99%

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Plastids Contain a Second Sec Translocase System with Essential Functions

et al. 2010

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Proteins that are synthesized on cytoplasmic ribosomes but function within plastids must be imported and then targeted to one of six plastid locations. Although multiple systems that target proteins to the thylakoid membranes or thylakoid lumen have been identified, a system that can direct the integration of inner envelope membrane proteins from the stroma has not been previously described. Genetics and localization studies were used to show that plastids contain two different Sec systems with distinct functions. Loss-of-function mutations in components of the previously described thylakoid-localized Sec system, designated as SCY1 (At2g18710), SECA1 (At4g01800), and SECE1 (At4g14870) in Arabidopsis (Arabidopsis thaliana), result in albino seedlings and sucrose-dependent heterotrophic growth. Loss-of-function mutations in components of the second Sec system, designated as SCY2 (At2g31530) and SECA2 (At1g21650) in Arabidopsis, result in arrest at the globular stage and embryo lethality. Promoter-swap experiments provided evidence that SCY1 and SCY2 are functionally nonredundant and perform different roles in the cell. Finally, chloroplast import and fractionation assays and immunogold localization of SCY2-green fluorescent protein fusion proteins in root tissues indicated that SCY2 is part of an envelope-localized Sec system. Our data suggest that SCY2 and SECA2 function in Sec-mediated integration and translocation processes at the inner envelope membrane.

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Section: Discussion Dual Sec Systems In Plastids Reflect An Ancient Dmentioning

confidence: 99%

Section: Scy1 and Scy2 Perform Different Functionsmentioning

confidence: 99%

Section: Scy1 and Scy2 Perform Different Functionsmentioning

confidence: 99%

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confidence: 99%

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Plastids Contain a Second Sec Translocase System with Essential Functions

et al. 2010

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“…They also provided valuable information on the physiology and regulation of chloroplast protein import. Furthermore, maize and Arabidopsis mutants defective in protein transport to the thylakoid also have been isolated (Voelker and Barkan, 1995; Voelker et al, 1997;Roy and Barkan, 1998;Amin et al, 1999;Moore et al, 2000). These mutants helped to further define the various pathways of transport to the thylakoid and even helped to uncover a new export pathway in Escherichia coli .…”

Section: Introductionmentioning

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

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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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Protein Targeting, Intracellular

Hartmann¹

2002

Encyclopedia of Molecular Biology

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A SecY Homologue Is Required for the Elaboration of the Chloroplast Thylakoid Membrane and for Normal Chloroplast Gene Expression

Cited by 92 publications

References 51 publications

Plastids Contain a Second Sec Translocase System with Essential Functions

Plastids Contain a Second Sec Translocase System with Essential Functions

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

Protein Targeting, Intracellular

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