<i>CHLAMYDOMONAS REINHARDTII</i> AS THE PHOTOSYNTHETIC YEAST

Rochaix, Jean‐David

doi:10.1146/annurev.ge.29.120195.001233

Cited by 237 publications

(115 citation statements)

References 23 publications

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“…PCC 6803, the green alga Chlamydomonas reinhardtii is also widely used to study PSII through genetic means. Because of its eukaryotic nature, Chlamydomonas is possibly a more appropriate model system with which to study photosynthesis in higher plants (15). Unlike cyanobacteria and higher plants, the psbEFJL operon is naturally disrupted in C. reinhardtii.…”

Section: Photosystem Two (Psii)mentioning

confidence: 99%

The Chloroplast-encoded α Subunit of Cytochromeb-559 Is Required for Assembly of the Photosystem Two Complex in both the Light and the Dark in Chlamydomonas reinhardtii

Morais

Barber

Nixon

1998

Journal of Biological Chemistry

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The role of cytochrome b-559 in the photosystem two (PSII) complex has been investigated through the construction of a psbE null mutant by transformation of the chloroplast genome of the green alga Chlamydomonas reinhardtii. No PSII activity could be detected in this mutant either in oxygen evolution assays or by analysis of variable chlorophyll fluorescence. Immunoblotting experiments showed that the absence of PSII activity in the mutant was due to the loss of the PSII complex in both light-grown and dark-grown cultures. In contrast, the photosystem one reaction center polypeptide, PsaA, was present at wild-type levels in the mutant. RNA gel blot assays confirmed that the transcript levels for the psbA, psbD, and psbF genes were unaffected by disruption of the psbE gene, suggesting a post-transcriptional effect on their expression. Pulse-labeling experiments showed that either synthesis of PSII subunits was impaired in the psbE null mutant or there was extremely rapid degradation of newly synthesized subunits. Interestingly, the PsbE and PsbF subunits accumulated to wild-type levels in a psbA deletion mutant of C. reinhardtii, FuD7, which fails to synthesize D1 and assemble PSII. Our results provide evidence for a role for cytochrome b-559 in the early steps of assembly of the PSII complex, possibly as a redox-controlled nucleation factor that determines the level of PSII within the thylakoid membrane. Photosystem two (PSII)1 is a multisubunit complex within the thylakoid membrane that catalyzes the light-induced oxidation of water to molecular oxygen as well as the reduction of plastoquinone to plastoquinol (1). At the heart of PSII is a the reaction center (RC) complex composed of the polypeptides D1, D2, PsbI, and a transmembrane b-type cytochrome termed cytochrome b-559 (2). As yet, the function of this cytochrome within PSII is unresolved, but it probably plays a role in protecting the PSII RC from photoinactivation, possibly by acting as a source of electrons to reduce long-lived chlorophyll cation species within the PSII RC (3), which unless reduced would oxidize nearby amino acids within the protein complex (4).The structure of Cyt b-559 is quite unusual, as it is thought to be a heterodimer of two subunits arranged in parallel orientations: the ␣ subunit encoded by psbE and the ␤ subunit encoded by psbF (5). The haem molecule is likely to be ligated by the single histidine residues within each subunit (6). Although an ␣␤ heterodimeric structure for Cyt b-559 is generally favored, recent work has demonstrated that the genetic fusion of the N terminus of the ␤ subunit to the C terminus of the ␣ subunit in Synechocystis 6803 leads to the assembly of a functional cytochrome b-559 (7). Because the ␣␤ heterodimer model requires that the N termini of the monotopic ␣ and ␤ subunits lie on the same side of the membrane, the fusion of PsbE and PsbF without loss of PSII activity has been interpreted in terms of an ␣ 2 /␤ 2 homodimeric structure for Cyt b-559 with one haem bound to ␣ 2 and one to ␤ 2 (7). If this...

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Section: Photosystem Two (Psii)mentioning

confidence: 99%

The Chloroplast-encoded α Subunit of Cytochromeb-559 Is Required for Assembly of the Photosystem Two Complex in both the Light and the Dark in Chlamydomonas reinhardtii

Morais

Barber

Nixon

1998

Journal of Biological Chemistry

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“…We have exploited the unicellular green alga Chlamydomonas reinhardtii to examine P starvation responses in a photosynthetic eukaryote (5-7). Many of the powerful genetic and molecular tools used to elucidate biological processes in S. cerevisiae also can be applied to C. reinhardtii (14,15). Furthermore, the identification of C. reinhardtii regulatory elements is likely to provide clues important for defining analogous elements in the angiosperm cDNA and genomic sequence databases.…”

mentioning

confidence: 99%

Psr1, a nuclear localized protein that regulates phosphorus metabolism in Chlamydomonas

Wykoff

Grossman

Weeks

et al. 1999

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

245

198

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Understanding the ways in which phosphorus metabolism is regulated in photosynthetic eukaryotes is critical for optimizing crop productivity and managing aquatic ecosystems in which phosphorus can be a major source of pollution. Here we describe a gene encoding a regulator of phosphorus metabolism, designated Psr1 (phosphorus starvation response), from a photosynthetic eukaryote. The Psr1 protein is critical for acclimation of the unicellular green alga Chlamydomonas reinhardtii to phosphorus starvation. The N-terminal half of Psr1 contains a region similar to myb DNA-binding domains and the C-terminal half possesses glutamine-rich sequences characteristic of transcriptional activators. The level of Psr1 increases at least 10-fold upon phosphate starvation, and immunocytochemical studies demonstrate that this protein is nuclear-localized under both nutrientreplete and phosphorus-starvation conditions. Finally, Psr1 and angiosperm proteins have domains that are similar, suggesting a possible role for Psr1 homologs in the control of phosphorus metabolism in vascular plants. With the identification of regulators such as Psr1 it may become possible to engineer photosynthetic organisms for more efficient utilization of phosphorus and to establish better practices for the management of agricultural lands and natural ecosystems. P hosphorus (P) is a major component of nucleic acids and phospholipids and is present in the biosphere as the oxidized anion, phosphate (P i ). P i is not easily accessible to most plants and microbes because it forms insoluble precipitates with common cations or is covalently bound to organic molecules (1-3). Crop yields are limited by P availability, and, consequently, P, in the form of P i , is an important component of commercial fertilizers. A considerable proportion of this ''supplementary'' P i is leached from agricultural fields and deposited into aquatic ecosystems, triggering rapid algal proliferation (algal blooms), which leads to eutrophication and fish kills (2). The sustainability of agricultural yields and quality of aquatic ecosystems would benefit from more efficient acquisition and utilization of P. Efficient P utilization by crop plants would decrease our dependence on rock P i reserves, the mining of which has serious economic and ecological consequences (3). Thus, a more complete understanding of P utilization in plants has significant implications with respect to both the environment and world agriculture.P limitation triggers a suite of ''starvation responses'' in most organisms. These responses can be divided into two categories, the P-specific responses and the general responses (4-6). The P-specific responses promote efficient mobilization and acquisition of P from extracellular and intracellular stores (e.g., synthesis and secretion of phosphatases with broad substrate specificity, accumulation of high affinity P i transporters) (5, 7). The general responses allow for long-term survival by coordinating the metabolism of the cell to nutrient availability and growth po...

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“…Also consistent with an unfolding/refolding model is the inhibition by glyphosate of the import of the precursor for 5-enolpyruvylshikimate-3-phosphate synthase in the presence of its substrate [12]. Not much attention has so far been paid to the protein import into chloroplasts of Chlamydomonas reinhardii, although this unicellular green alga is widely used as a model organism to investigate various cell biological problems of green plants [13]. This neglect is probably due to the tedious isolation procedure for chloroplasts and to the fact that precursor proteins from higher plants are not imported or not correctly processed by Chlamydomonas chloroplasts, and vice versa [14].…”

Section: Introductionmentioning

confidence: 63%

Import inhibition of poly(His) containing chloroplast precursor proteins by Ni²⁺ ions

Rothen¹,

Thiess²,

Schumann³

et al. 1996

FEBS Letters

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The precursor of the small subunit of ribulose-l,5-bisphosphate carboxylase (pSS) and a modified pSS containing a C-terminal hexahistidyl tail (pSS(His)6) were imported into isolated Chlamydomonas chloroplasts with comparable efficiency. In the presence of Ni 2+ ions the import of pSS(His)6 was inhibited and the precursor bound to the envelope remained protease sensitive, while import of pSS was not affected. Addition of an excess of L-histidine suppressed the inhibition demonstrating that the hexahistidyl-Ni 2+ complex was responsible for import inhibition. Inhibition could be observed between about 0.5 and l0 mM Ni ~+, depending on the total protein content in the assay. Import incompetent Ni2+-precursor complexes can be used to study early events in chloroplast protein import.

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CHLAMYDOMONAS REINHARDTII AS THE PHOTOSYNTHETIC YEAST

Cited by 237 publications

References 23 publications

The Chloroplast-encoded α Subunit of Cytochromeb-559 Is Required for Assembly of the Photosystem Two Complex in both the Light and the Dark in Chlamydomonas reinhardtii

The Chloroplast-encoded α Subunit of Cytochromeb-559 Is Required for Assembly of the Photosystem Two Complex in both the Light and the Dark in Chlamydomonas reinhardtii

Psr1, a nuclear localized protein that regulates phosphorus metabolism in Chlamydomonas

Import inhibition of poly(His) containing chloroplast precursor proteins by Ni²⁺ ions

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CHLAMYDOMONAS REINHARDTII AS THE PHOTOSYNTHETIC YEAST

Cited by 237 publications

References 23 publications

The Chloroplast-encoded α Subunit of Cytochromeb-559 Is Required for Assembly of the Photosystem Two Complex in both the Light and the Dark in Chlamydomonas reinhardtii

The Chloroplast-encoded α Subunit of Cytochromeb-559 Is Required for Assembly of the Photosystem Two Complex in both the Light and the Dark in Chlamydomonas reinhardtii

Psr1, a nuclear localized protein that regulates phosphorus metabolism in Chlamydomonas

Import inhibition of poly(His) containing chloroplast precursor proteins by Ni2+ ions

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Import inhibition of poly(His) containing chloroplast precursor proteins by Ni²⁺ ions