The Light Reactions: A Guide to Recent Acquisitions for the Picture Gallery

Merchant, Sabeeha; Sawaya, M.R.

doi:10.1105/tpc.105.030676

Cited by 80 publications

(58 citation statements)

References 63 publications

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“…However, at light intensities of Ͼ400 mol⅐m Ϫ2 ⅐s Ϫ1 , the NPQ of the mutant was significantly higher than that of the wild type. Further analysis revealed that the additional NPQ was not rapidly reversible, The plants shown in C were exposed to illumination (300 mol⅐m Ϫ2 ⅐s Ϫ1 ) for 2 days after 7 weeks of growth in low light (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35) mol⅐m Ϫ2 ⅐s Ϫ1 ). indicating that the increased NPQ is due to a larger component of photoinhibitory quenching in the mutant.…”

Section: Resultsmentioning

confidence: 99%

“…Because the structures of the photosynthetic membrane complexes of chloroplasts have been described in x-ray crystallography analyses (26,27), it becomes increasingly important to understand the mechanisms underlying their assembly and maintenance. To this end, it is essential to identify and understand the proteins that function in the assembly and maintenance of the supermolecular complexes that catalyze this energy conversion in nature.…”

Section: Resultsmentioning

confidence: 99%

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A chloroplast cyclophilin functions in the assembly and maintenance of photosystem II in Arabidopsis thaliana

Cho

et al. 2007

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

154

144

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Photosynthetic light reactions rely on the proper function of large protein complexes (including photosystems I and II) that reside in the thylakoid membrane. Although their composition, structure, and function are known, the repertoire of assembly and maintenance factors is still being determined. Here we show that an immunophilin of the cyclophilin type, CYP38, plays a critical role in the assembly and maintenance of photosystem II (PSII) supercomplexes (SCs) in Arabidopsis. Mutant plants with the CYP38 gene interrupted by T-DNA insertion showed stunted growth and were hypersensitive to high light. Leaf chlorophyll fluorescence analysis and thylakoid membrane composition indicated that cyp38 mutant plants had defects in PSII SCs. Sucrose supplementation enabled the rescue of the mutant phenotype under low-light conditions, but failed to mitigate hypersensitivity to high-light stress. Protein radiolabeling assays showed that, although individual thylakoid proteins were synthesized equally in mutant and wild type, the assembly of the PSII SC was impaired in the mutant. In addition, the D1 and D2 components of the mutant PSII had a short half-life under high-light stress. The results provide evidence that CYP38 is necessary for the assembly and stabilization of PSII.thylakoid lumen ͉ immunophilin ͉ photosynthesis ͉ protein folding ͉ chaperone T he light reactions and attendant evolution of oxygen in photosynthesis are carried out by four multisubunit protein complexes residing in the chloroplast thylakoid membranes: photosystems I (PSI) and II (PSII), cytochrome b 6 f complex, and CF O -CF 1 complex (1-3). For a complete understanding of the photosynthetic process, it is essential to understand the biogenesis and maintenance of the participating complexes. Earlier studies on thylakoid protein supercomplex (SC) assembly, especially PSII, concentrated on the role of stromal factors, such as the translation and import machinery (4), because only a limited number of proteins were known to reside in the thylakoid lumen. However, recent proteomic findings suggest a population of 80-100 proteins in that compartment (5-7). The immunophilin family is one of the predominant groups identified.Immunophilins were originally discovered in their capacity as cellular receptors for immunosuppressive drugs: cyclosporin A and FK506 (8, 9). The receptors for cyclosporin A and FK506, named cyclophilins (CYPs) and FK506-binding proteins (FKBPs), respectively, were collectively designated as immunophilins. A common feature of most immunophilins is the associated peptidyl-prolyl cis-trans isomerase activity that catalyzes the cis-trans conversion of X-Pro peptide bonds, a rate-limiting step in protein folding (8). These proteins are now known to occur widely in organisms ranging from bacteria and fungi to animals and plants. Studies in animal and plant systems have uncovered diverse functions of immunophilins, such as protein foldases, chaperones, and scaffolding facilitators. They also possibly have unknown catalytic capabilities (10, ...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

A chloroplast cyclophilin functions in the assembly and maintenance of photosystem II in Arabidopsis thaliana

Cho

et al. 2007

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

154

144

View full text Add to dashboard Cite

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“…5A). PSI contains 12 Fe atoms in three 4Fe-4S clusters bound by the PSAA, B, and C subunits (Merchant and Sawaya, 2005). Surprisingly, the PSAA subunit of PSI, which carries the FeSx cluster, appeared to be slightly increased in abundance after Fe depletion (Fig.…”

Section: Fe Deficiency Affects Photosynthetic Electron Transport Primmentioning

confidence: 93%

“…It is interesting that the two heme-containing and chloroplast-encoded subunits of the cytochrome-b 6 f complex, Cytf and Cytb 6 , also undergo transcriptional down-regulation. The dimeric cytochrome-b 6 f complex is reported to contain 12 Fe atoms, the same number as is present in PSI (Merchant and Sawaya, 2005). Apparently, under impending Fe deficiency, downregulation of the cytochrome-b 6 f complex is preferred over removal of PSI, for which the core subunits are chloroplast encoded and the transcripts have an abundance comparable to the cytochrome-b 6 f complex subunits.…”

Section: Fe Sparing In Chloroplasts Targets Abundant Fe Proteinsmentioning

confidence: 99%

A Program for Iron Economy during Deficiency Targets Specific Fe Proteins

et al. 2017

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“…Clearly, a full understanding of the function of the chloroplastbased photosynthetic machinery requires not only that the structure of individual complexes be known, a task which has largely been achieved (reviewed in Nelson and Ben-Shem, 2004;Merchant and Sawaya, 2005), but also a precise knowledge of the spatial organization of the thylakoid membranes that host these complexes. In this work, we used dual-axis electron microscope tomography to examine the architecture of the thylakoid membranes of higher-plant chloroplasts in three dimensions in rapidly frozen, freeze-substituted leaves.…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Organization of Higher-Plant Chloroplast Thylakoid Membranes Revealed by Electron Tomography

et al. 2005

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The light-harvesting and energy-transducing functions of the chloroplast are performed within an intricate lamellar system of membranes, called thylakoid membranes, which are differentiated into granum and stroma lamellar domains. Using dualaxis electron microscope tomography, we determined the three-dimensional organization of the chloroplast thylakoid membranes within cryo-immobilized, freeze-substituted lettuce (Lactuca sativa) leaves. We found that the grana are built of repeating units that consist of paired layers formed by bifurcations of stroma lamellar sheets, which fuse within the granum body. These units are rotated relative to each other around the axis of the granum cylinder. One of the layers that makes up the pair bends upwards at its edge and fuses with the layer above it, whereas the other layer bends in the opposite direction and merges with the layer below. As a result, each unit in the granum is directly connected to its neighbors as well as to the surrounding stroma lamellae. This highly connected morphology has important consequences for the formation and function of the thylakoid membranes as well as for their stacking/unstacking response to variations in light conditions.

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The Light Reactions: A Guide to Recent Acquisitions for the Picture Gallery

Cited by 80 publications

References 63 publications

A chloroplast cyclophilin functions in the assembly and maintenance of photosystem II in Arabidopsis thaliana

A chloroplast cyclophilin functions in the assembly and maintenance of photosystem II in Arabidopsis thaliana

A Program for Iron Economy during Deficiency Targets Specific Fe Proteins

Three-Dimensional Organization of Higher-Plant Chloroplast Thylakoid Membranes Revealed by Electron Tomography

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