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Scientific Reports Oct 2017In oxygenic photosynthesis the initial photochemical processes are carried out by photosystem I (PSI) and II (PSII). Although subunit composition varies between...
In oxygenic photosynthesis the initial photochemical processes are carried out by photosystem I (PSI) and II (PSII). Although subunit composition varies between cyanobacterial and plastid photosystems, the core structures of PSI and PSII are conserved throughout photosynthetic eukaryotes. So far, the photosynthetic complexes have been characterised in only a small number of organisms. We performed in silico and biochemical studies to explore the organization and evolution of the photosynthetic apparatus in the chromerids Chromera velia and Vitrella brassicaformis, autotrophic relatives of apicomplexans. We catalogued the presence and location of genes coding for conserved subunits of the photosystems as well as cytochrome bf and ATP synthase in chromerids and other phototrophs and performed a phylogenetic analysis. We then characterised the photosynthetic complexes of Chromera and Vitrella using 2D gels combined with mass-spectrometry and further analysed the purified Chromera PSI. Our data suggest that the photosynthetic apparatus of chromerids underwent unique structural changes. Both photosystems (as well as cytochrome bf and ATP synthase) lost several canonical subunits, while PSI gained one superoxide dismutase (Vitrella) or two superoxide dismutases and several unknown proteins (Chromera) as new regular subunits. We discuss these results in light of the extraordinarily efficient photosynthetic processes described in Chromera.
Topics: Alveolata; Evolution, Molecular; Gene Deletion; Mass Spectrometry; Photosynthesis; Photosystem I Protein Complex; Phylogeny; Superoxide Dismutase; Thylakoids
PubMed: 29038514
DOI: 10.1038/s41598-017-13575-x -
Physiologia Plantarum Jan 2022The Lycophyte Selaginella martensii efficiently acclimates to diverse light environments, from deep shade to full sunlight. The plant does not modulate the abundance of...
The Lycophyte Selaginella martensii efficiently acclimates to diverse light environments, from deep shade to full sunlight. The plant does not modulate the abundance of the Light Harvesting Complex II, mostly found as a free trimer, and does not alter the maximum capacity of thermal dissipation (NPQ). Nevertheless, the photoprotection is expected to be modulatable upon long-term light acclimation to preserve the photosystems (PSII, PSI). The effects of long-term light acclimation on PSII photoprotection were investigated using the chlorophyll fluorometric method known as "photochemical quenching measured in the dark" (qP ). Singularly high-qP values at relatively low irradiance suggest a heterogeneous antenna system (PSII antenna uncoupling). The extent of antenna uncoupling largely depends on the light regime, reaching the highest value in sun-acclimated plants. In parallel, the photoprotective NPQ (pNPQ) increased from deep-shade to high-light grown plants. It is proposed that the differences in the long-term modulation in the photoprotective capacity are proportional to the amount of uncoupled LHCII. In deep-shade plants, the inconsistency between invariable maximum NPQ and lower pNPQ is attributed to the thermal dissipation occurring in the PSII core.
Topics: Arabidopsis; Chlorophyll; Light; Light-Harvesting Protein Complexes; Photosynthesis; Photosystem II Protein Complex; Selaginellaceae
PubMed: 34811759
DOI: 10.1111/ppl.13604 -
Frontiers in Plant Science 2022Iron is a cofactor of photosystems and electron carriers in the photosynthetic electron transport chain. Low concentrations of dissolved iron are, therefore, the...
Iron is a cofactor of photosystems and electron carriers in the photosynthetic electron transport chain. Low concentrations of dissolved iron are, therefore, the predominant factor that limits the growth of phototrophs in large parts of the open sea like the Southern Ocean and the North Pacific, resulting in "high nutrient-low chlorophyll" (HNLC) areas. Diatoms are among the most abundant microalgae in HNLC zones. Besides efficient iron uptake mechanisms, efficient photoprotection might be one of the key traits enabling them to outcompete other algae in HNLC regions. In diatoms, Lhcx proteins play a crucial role in one of the main photoprotective mechanisms, the energy-dependent fluorescence quenching (qE). The expression of Lhcx proteins is strongly influenced by various environmental triggers. We show that Lhcx2 responds specifically and in a very sensitive manner to iron limitation in the diatom on the same timescale as the known iron-regulated genes and By comparing Lhcx2 knockout lines with wild type cells, we reveal that a strongly increased qE under iron limitation is based on the upregulation of Lhcx2. Other observed iron acclimation phenotypes in include a massively reduced chlorophyll content/cell, a changed ratio of light harvesting and photoprotective pigments per chlorophyll , a decreased amount of photosystem II and photosystem I cores, an increased functional photosystem II absorption cross section, and decoupled antenna complexes. HO formation at photosystem I induced by high light is lowered in iron-limited cells, while the amount of total reactive oxygen species is rather increased. Our data indicate a possible reduction in singlet oxygen by Lhcx2-based qE, while the other iron acclimation phenotype parameters monitored are not affected by the amount of Lhcx2 and qE.
PubMed: 35371185
DOI: 10.3389/fpls.2022.841058 -
BMC Biology Dec 2022Despite a global prevalence of photosynthetic organisms in the ocean's mesophotic zone (30-200+ m depth), the mechanisms that enable photosynthesis to proceed in this...
BACKGROUND
Despite a global prevalence of photosynthetic organisms in the ocean's mesophotic zone (30-200+ m depth), the mechanisms that enable photosynthesis to proceed in this low light environment are poorly defined. Red coralline algae are the deepest known marine benthic macroalgae - here we investigated the light harvesting mechanism and mesophotic acclimatory response of the red coralline alga Lithothamnion glaciale.
RESULTS
Following initial absorption by phycourobilin and phycoerythrobilin in phycoerythrin, energy was transferred from the phycobilisome to photosystems I and II within 120 ps. This enabled delivery of 94% of excitations to reaction centres. Low light intensity, and to a lesser extent a mesophotic spectrum, caused significant acclimatory change in chromophores and biliproteins, including a 10% increase in phycoerythrin light harvesting capacity and a 20% reduction in chlorophyll-a concentration and photon requirements for photosystems I and II. The rate of energy transfer remained consistent across experimental treatments, indicating an acclimatory response that maintains energy transfer.
CONCLUSIONS
Our results demonstrate that responsive light harvesting by phycobilisomes and photosystem functional acclimation are key to red algal success in the mesophotic zone.
Topics: Phycoerythrin; Phycobilisomes; Photosynthesis; Light; Rhodophyta; Photosystem I Protein Complex
PubMed: 36575464
DOI: 10.1186/s12915-022-01480-3 -
The Biochemical Journal Jun 2021Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel...
Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel mechanistic insights into binding and electron transfer between PSI and Pc. Structural data at 2.74 Å resolution reveals strong hydrophobic interactions in the plant PSI-Pc ternary complex, leading to exclusion of water molecules from PsaA-PsaB/Pc interface once the PSI-Pc complex forms. Upon oxidation of Pc, a slight tilt of bound oxidized Pc allows water molecules to accommodate the space between Pc and PSI to drive Pc dissociation. Such a scenario is consistent with the six times larger dissociation constant of oxidized as compared with reduced Pc and mechanistically explains how this molecular machine optimized electron transfer for fast turnover.
Topics: Binding Sites; Chlamydomonas reinhardtii; Electron Transport; Hydrophobic and Hydrophilic Interactions; Kinetics; Models, Molecular; Oxidation-Reduction; Photosystem I Protein Complex; Plastocyanin; Protein Binding; Protein Conformation
PubMed: 34085703
DOI: 10.1042/BCJ20210267 -
Plant, Cell & Environment Sep 2021Vascular plants use carotenoids and chlorophylls a and b to harvest solar energy in the visible region (400-700 nm), but they make little use of the far-red (FR)...
Vascular plants use carotenoids and chlorophylls a and b to harvest solar energy in the visible region (400-700 nm), but they make little use of the far-red (FR) light. Instead, some cyanobacteria have developed the ability to use FR light by redesigning their photosynthetic apparatus and synthesizing red-shifted chlorophylls. Implementing this strategy in plants is considered promising to increase crop yield. To prepare for this, a characterization of the FR light-induced changes in plants is necessary. Here, we explore the behaviour of Arabidopsis thaliana upon exposure to FR light by following the changes in morphology, physiology and composition of the photosynthetic complexes. We found that after FR-light treatment, the ratio between the photosystems and their antenna size drastically readjust in an attempt to rebalance the energy input to support electron transfer. Despite a large increase in PSBS accumulation, these adjustments result in strong photoinhibition when FR-adapted plants are exposed to light again. Crucially, FR light-induced changes in the photosynthetic membrane are not the result of senescence, but are a response to the excitation imbalance between the photosystems. This indicates that an increase in the FR absorption by the photosystems should be sufficient for boosting photosynthetic activity in FR light.
Topics: Adaptation, Physiological; Arabidopsis; Chlorophyll; Fluorescence; Light; Light-Harvesting Protein Complexes; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Plant Leaves; Thylakoids
PubMed: 33599977
DOI: 10.1111/pce.14032 -
Nature Communications Jun 2018In oxygenic photosynthesis, light energy is converted into redox energy by two photosystems (PSI and PSII). PSI forms one of the largest multiprotein complexes in...
In oxygenic photosynthesis, light energy is converted into redox energy by two photosystems (PSI and PSII). PSI forms one of the largest multiprotein complexes in thylakoid membranes consisting of a core complex, peripheral light-harvesting complexes (LHCIs) and cofactors. Although the high-resolution structure of the PSI-LHCI complex has been determined, the assembly process remains unclear due to the rapid nature of the assembly process. Here we show that two conserved chloroplast-encoded auxiliary factors, Ycf3 and Ycf4, form modules that mediate PSI assembly. The first module consists of the tetratricopeptide repeat protein Ycf3 and its interacting partner, Y3IP1, and mainly facilitates the assembly of reaction center subunits. The second module consists of oligomeric Ycf4 and facilitates the integration of peripheral PSI subunits and LHCIs into the PSI reaction center subcomplex. We reveal that these two modules are major mediators of the PSI-LHCI assembly process.
Topics: Chlamydomonas reinhardtii; Light-Harvesting Protein Complexes; Photosynthesis; Photosystem I Protein Complex; Plants, Genetically Modified; Protozoan Proteins; Spectrum Analysis; Thylakoids
PubMed: 29934511
DOI: 10.1038/s41467-018-04823-3 -
Plant, Cell & Environment Jul 2012A generalized model for electron (e(-) ) transport limited C(4) photosynthesis of NAD-malic enzyme and NADP-malic enzyme subtypes is presented. The model is used to... (Review)
Review
A generalized model for electron (e(-) ) transport limited C(4) photosynthesis of NAD-malic enzyme and NADP-malic enzyme subtypes is presented. The model is used to review the thylakoid stoichiometries in vivo under strictly limiting light conditions, using published data on photosynthetic quantum yield and on photochemical efficiencies of photosystems (PS). Model review showed that cyclic e(-) transport (CET), rather than direct O(2) photoreduction, most likely contributed significantly to the production of extra ATP required for the C(4) cycle. Estimated CET, and non-cyclic e(-) transport supporting processes like nitrogen reduction, accounted for ca. 45 and 7% of total photosystem I (PSI) e(-) fluxes, respectively. The factor for excitation partitioning to photosystem II (PSII) was ca. 0.4. Further model analysis, in terms of the balanced NADPH: ATP ratio required for metabolism, indicated that: (1) the Q-cycle is obligatory; (2) the proton: ATP ratio is 4; and (3) the efficiency of proton pumping per e(-) transferred through the cytochrome b(6) /f complex is the same for CET and non-cyclic pathways. The analysis also gave an approach to theoretically assess CO(2) leakiness from bundle-sheath cells, and projected a leakiness of 0.07-0.16. Compared with C(3) photosynthesis, the most striking C(4) stoichiometry is its high fraction of CET.
Topics: Adenosine Triphosphate; Electron Transport; Light; Malate Dehydrogenase; Models, Biological; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Plant Leaves
PubMed: 22321164
DOI: 10.1111/j.1365-3040.2012.02490.x -
Plant, Cell & Environment Oct 2022Photosynthetic light reactions require strict regulation under dynamic environmental conditions. Still, depending on environmental constraints, photoinhibition of...
Photosynthetic light reactions require strict regulation under dynamic environmental conditions. Still, depending on environmental constraints, photoinhibition of Photosystem (PSII) or PSI occurs frequently. Repair of photodamaged PSI, in sharp contrast to that of PSII, is extremely slow and leads to a functional imbalance between the photosystems. Slow PSI recovery prompted us to take advantage of the PSI-specific photoinhibition treatment and investigate whether the imbalance between functional PSII and PSI leads to acclimation of photosynthesis to PSI-limited conditions, either by short-term or long-term acclimation mechanisms as tested immediately after the photoinhibition treatment or after 24 h recovery in growth conditions, respectively. Short-term acclimation mechanisms were induced directly upon inhibition, including thylakoid protein phosphorylation that redirects excitation energy to PSI as well as changes in the feedback regulation of photosynthesis, which relaxed photosynthetic control and excitation energy quenching. Longer-term acclimation comprised reprogramming of the stromal redox system and an increase in ATP synthase and Cytochrome b f abundance. Acclimation to PSI-limited conditions restored the CO assimilation capacity of plants without major PSI repair. Response to PSI inhibition demonstrates that plants efficiently acclimate to changes occurring in the photosynthetic apparatus, which is likely a crucial component in plant acclimation to adverse environmental conditions.
Topics: Acclimatization; Electron Transport; Light; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Plants; Thylakoids
PubMed: 35916195
DOI: 10.1111/pce.14400 -
Biochimica Et Biophysica Acta.... Dec 2019Thylakoids are the place of the light-photosynthetic reactions. To gain maximal efficiency, these reactions are conditional to proper pigment-pigment and protein-protein...
Thylakoids are the place of the light-photosynthetic reactions. To gain maximal efficiency, these reactions are conditional to proper pigment-pigment and protein-protein interactions. In higher plants thylakoids, the interactions lead to a lateral asymmetry in localization of protein complexes (i.e. granal/stromal thylakoids) that have been defined as a domain-like structures characteristic by different biochemical composition and function (Albertsson P-Å. 2001,Trends Plant Science 6: 349-354). We explored this complex organization of thylakoid pigment-proteins at single cell level in the cyanobacterium Synechocystis sp. PCC 6803. Our 3D confocal images captured heterogeneous distribution of all main photosynthetic pigment-protein complexes (PPCs), Photosystem I (fluorescently tagged by YFP), Photosystem II and Phycobilisomes. The acquired images depicted cyanobacterial thylakoid membrane as a stable, mosaic-like structure formed by microdomains (MDs). These microcompartments are of sub-micrometer in sizes (~0.5-1.5 μm), typical by particular PPCs ratios and importantly without full segregation of observed complexes. The most prevailing MD is represented by MD with high Photosystem I content which allows also partial separation of Photosystems like in higher plants thylakoids. We assume that MDs stability (in minutes) provides optimal conditions for efficient excitation/electron transfer. The cyanobacterial MDs thus define thylakoid membrane organization as a system controlled by co-localization of three main PPCs leading to formation of thylakoid membrane mosaic. This organization might represent evolutional and functional precursor for the granal/stromal spatial heterogeneity in photosystems that is typical for higher plant thylakoids.
Topics: Bacterial Proteins; Imaging, Three-Dimensional; Membrane Microdomains; Microscopy, Confocal; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Phycobilisomes; Synechocystis; Thylakoids
PubMed: 31344362
DOI: 10.1016/j.bbabio.2019.07.008