Toc, Tic, Tat et al.: structure and function of protein transport machineries in chloroplasts

Gutensohn, Michael; Fan, Enguo; Frielingsdorf, Stefan; Hanner, Peter; Hou, Bo; Hust, Bianca; Klösgen, Ralf Bernd

doi:10.1016/j.jplph.2005.11.009

Cited by 75 publications

(79 citation statements)

References 140 publications

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“…Protein import into chloroplasts requires the interaction of protein complexes spanning the inner and outer chloroplast envelope membranes (13,14). Currently, our knowledge about the protein import machinery dwarfs our mechanistic insights into lipid import into the plastid.…”

Section: Discussionmentioning

confidence: 99%

A phosphatidic acid-binding protein of the chloroplast inner envelope membrane involved in lipid trafficking

Awai

Tamot

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

200

209

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The biogenesis of the photosynthetic thylakoid membranes inside plant chloroplasts requires enzymes at the plastid envelope and the endoplasmic reticulum (ER). Extensive lipid trafficking is required for thylakoid lipid biosynthesis. Here the trigalactosyldiacylglycerol2 (tgd2) mutant of Arabidopsis is described. To the extent tested, tgd2 showed a complex lipid phenotype identical to the previously described tgd1 mutant. The aberrant accumulation of oligogalactolipids and triacylglycerols and the reduction of molecular species of galactolipids derived from the ER are consistent with a disruption of the import of ER-derived lipids into the plastid. The TGD1 protein is a permease-like component of an ABC transporter located in the chloroplast inner envelope membrane. The TGD2 gene encodes a phosphatidic acid-binding protein with a predicted mycobacterial cell entry domain. It is tethered to the inner chloroplast envelope membrane facing the outer envelope membrane. Presumed bacterial orthologs of TGD1 and TGD2 in Gram-negative bacteria are typically organized in transcriptional units, suggesting their involvement in a common biological process. Expression of the tgd2-1 mutant cDNA caused a dominantnegative effect replicating the tgd2 mutant phenotype. This result is interpreted as the interference of the mutant protein with its native protein complex. It is proposed that TGD2 represents the substrate-binding or regulatory component of a phosphatidic acid͞lipid transport complex in the chloroplast inner envelope membrane.Arabidopsis ͉ membrane transporter ͉ glycerolipids ͉ ABC transporter ͉ substrate-binding protein A s plant leaves expand the demand on the lipid biosynthetic machinery is high because leaf cells contain one of the most extensive membrane systems found in nature, the photosynthetic thylakoid membrane of chloroplasts. The most abundant thylakoid lipids include nonphosphorous galactolipids. Galactolipid biosynthesis involves the formation of phosphatidic acid (PA) in the plastid and at the endoplasmic reticulum (ER) in many plants (1, 2), including Arabidopsis. Fatty acids derived from de novo synthesis in the plastid are assembled into PA in the plastid or at the ER. In Arabidopsis, diacylglycerols derived from the plastid pathway or the ER pathway are present in galactolipids in approximately equal proportion (3). The Arabidopsis lipid galactosyltransferases MGD1 and DGD1, which successively galactosylate diacylglycerol, are associated with the inner and the outer chloroplast envelope membranes, respectively (4). The topology of the galactolipid biosynthetic machinery and the involvement of the ER pathway require extensive subcellular lipid trafficking, most of which is mechanistically not understood.To date, two mutants of Arabidopsis have been described that affect lipid trafficking from the ER to the plastid. The act1(ats1) mutant is deficient in the plastidic glycerol 3-phopshate acyltransferase, and most of the galactolipids in this mutant are derived from the ER pathway (5). In contrast, gala...

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Section: Discussionmentioning

confidence: 99%

A phosphatidic acid-binding protein of the chloroplast inner envelope membrane involved in lipid trafficking

Awai

Tamot

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

200

209

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“…The latter are first translocated across the chloroplast envelope via the TOC/TIC system, and then subsequently engage one of four different pathways for thylakoid targeting (Figure 4) (Jarvis and Robinson, 2004;Gutensohn et al, 2006;Schünemann, 2007).…”

Section: Targeting To the Thylakoidsmentioning

confidence: 99%

Chloroplast Biogenesis: Control of Plastid Development, Protein Import, Division and Inheritance

Sakamoto

Miyagishima

Jarvis

2008

The Arabidopsis Book

142

129

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The chloroplast is a multi-copy cellular organelle that not only performs photosynthesis but also synthesizes amino acids, lipids and phytohormones. The plastid also responds to environmental stimuli such as gravitropism. Biogenesis of chloroplasts is initiated from proplastids in shoot meristems, and involves a series of important events. In the last decade, considerable progress has been made towards understanding various aspects of chloroplast biogenesis at the molecular level, via studies in model systems such as Arabidopsis. This review focuses on two important aspects of chloroplast biogenesis, synthesis/assembly and division/transmission. Chloroplasts originated through endosymbiosis from an ancestor of extant cyanobacteria, and thus contain their own genomes. DNA in chloroplasts is organized into complexes with proteins, and these are called nucleoids. The synthesis of chloroplast proteins is regulated at various steps. However, a majority of proteins are synthesized in the cytosol, and their proper import into chloroplast compartments is a prerequisite for chloroplast development. Fundamental aspects of plastid gene expression/regulation and chloroplast protein transport are described, together with recent proteome analyses of the organelle. Chloroplasts are not de novo synthesized, but instead are propagated from pre-existing plastids. In addition, plastids are transmitted from generation to generation with a unique mode of inheritance. Our current knowledge on the division machinery and the inheritance of plastids is described.

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“…Four Toc translocons, the two GTP-binding proteins Toc159 and Toc34 [4][5][6], the translocation channel Toc75 [7,8], and Toc64 [9], have been characterised so far. Several Tic proteins, Tic110, Tic62, Tic55, Tic40, Tic22 and Tic20, have also been identified [2,3].…”

Section: Introductionmentioning

confidence: 99%

Differential uptake of photosynthetic and non‐photosynthetic proteins by pea root plastids

Yan¹,

Khan²,

Hase³

et al. 2006

FEBS Letters

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The photosynthetic proteins RuBiSCO, ferredoxin I and ferredoxin NADP + -oxidoreductase (pFNR) were efficiently imported into isolated pea chloroplasts but not into pea root plastids. By contrast non-photosynthetic ferredoxin III and heterotrophic FNR (hFNR) were efficiently imported into both isolated chloroplasts and root plastids. Chimeric ferredoxin I/ III (transit peptide of ferredoxin I attached to the mature region of ferredoxin III) only imported into chloroplasts. Ferredoxin III/I (transit peptide of ferredoxin III attached to the mature region of ferredoxin I) imported into both chloroplasts and root plastids. This suggests that import depends on specific interactions between the transit peptide and the translocon apparatus.

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Toc, Tic, Tat et al.: structure and function of protein transport machineries in chloroplasts

Cited by 75 publications

References 140 publications

A phosphatidic acid-binding protein of the chloroplast inner envelope membrane involved in lipid trafficking

A phosphatidic acid-binding protein of the chloroplast inner envelope membrane involved in lipid trafficking

Chloroplast Biogenesis: Control of Plastid Development, Protein Import, Division and Inheritance

Differential uptake of photosynthetic and non‐photosynthetic proteins by pea root plastids

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