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Biochimica Et Biophysica Acta.... May 2021Cytochrome bf (cytbf) lies at the heart of the light-dependent reactions of oxygenic photosynthesis, where it serves as a link between photosystem II (PSII) and... (Review)
Review
Cytochrome bf (cytbf) lies at the heart of the light-dependent reactions of oxygenic photosynthesis, where it serves as a link between photosystem II (PSII) and photosystem I (PSI) through the oxidation and reduction of the electron carriers plastoquinol (PQH) and plastocyanin (Pc). A mechanism of electron bifurcation, known as the Q-cycle, couples electron transfer to the generation of a transmembrane proton gradient for ATP synthesis. Cytbf catalyses the rate-limiting step in linear electron transfer (LET), is pivotal for cyclic electron transfer (CET) and plays a key role as a redox-sensing hub involved in the regulation of light-harvesting, electron transfer and photosynthetic gene expression. Together, these characteristics make cytbf a judicious target for genetic manipulation to enhance photosynthetic yield, a strategy which already shows promise. In this review we will outline the structure and function of cytbf with a particular focus on new insights provided by the recent high-resolution map of the complex from Spinach.
Topics: Cell Respiration; Cytochrome b6f Complex; Electron Transport; Electrons; Photosynthesis
PubMed: 33460588
DOI: 10.1016/j.bbabio.2021.148380 -
International Journal of Molecular... Jan 2022MicroRNA408 () is an ancient and highly conserved miRNA, which is involved in the regulation of plant growth, development and stress response. However, previous research... (Review)
Review
MicroRNA408 () is an ancient and highly conserved miRNA, which is involved in the regulation of plant growth, development and stress response. However, previous research results on the evolution and functional roles of and its targets are relatively scattered, and there is a lack of a systematic comparison and comprehensive summary of the detailed evolutionary pathways and regulatory mechanisms of and its targets in plants. Here, we analyzed the evolutionary pathway of in plants, and summarized the functions of and its targets in regulating plant growth and development and plant responses to various abiotic and biotic stresses. The evolutionary analysis shows that is an ancient and highly conserved microRNA, which is widely distributed in different plants. regulates the growth and development of different plants by down-regulating its targets, encoding blue copper (Cu) proteins, and by transporting Cu to plastocyanin (PC), which affects photosynthesis and ultimately promotes grain yield. In addition, improves tolerance to stress by down-regulating target genes and enhancing cellular antioxidants, thereby increasing the antioxidant capacity of plants. This review expands and promotes an in-depth understanding of the evolutionary and regulatory roles of and its targets in plants.
Topics: Biological Evolution; Gene Expression Regulation, Plant; MicroRNAs; Multigene Family; Organ Specificity; Plant Development; Plant Physiological Phenomena; RNA, Messenger; RNA, Plant; Stress, Physiological
PubMed: 35008962
DOI: 10.3390/ijms23010530 -
Frontiers in Plant Science 2019Unicellular cyanobacteria are thought to be the evolutionary ancestors of plant chloroplasts and are widely used both for chemical production and as model organisms in... (Review)
Review
Unicellular cyanobacteria are thought to be the evolutionary ancestors of plant chloroplasts and are widely used both for chemical production and as model organisms in studies of photosynthesis. Although most research focused on increasing reducing power (that is, NADPH) as target of metabolic engineering, the physiological roles of NAD(P)(H) in cyanobacteria poorly understood. In cyanobacteria such as the model species sp. PCC 6803, most metabolic pathways share a single compartment. This complex metabolism raises the question of how cyanobacteria control the amounts of the redox pairs NADH/NAD and NADPH/NADP in the cyanobacterial metabolic pathways. For example, photosynthetic and respiratory electron transport chains share several redox components in the thylakoid lumen, including plastoquinone, cytochrome (cyt ), and the redox carriers plastocyanin and cytochrome . In the case of photosynthesis, NADP acts as an important electron mediator on the acceptor-side of photosystem I (PSI) in the linear electron chain as well as in the plant chloroplast. Meanwhile, in respiration, most electrons derived from NADPH and NADH are transferred by NAD(P)H dehydrogenases. Therefore, it is expected that employs unique NAD(P)(H) -pool control mechanisms to regulate the mixed metabolic systems involved in photosynthesis and respiration. This review article summarizes the current state of knowledge of NAD(P)(H) metabolism in . In particular, we focus on the physiological function in of NAD kinase, the enzyme that phosphorylates NAD to NADP.
PubMed: 31316540
DOI: 10.3389/fpls.2019.00847 -
Biochimica Et Biophysica Acta.... Nov 2020Plastocyanin and cytochrome c, abundant proteins in photosynthesis, are readouts for cellular copper status in Chlamydomonas and other algae. Their accumulation is... (Review)
Review
Plastocyanin and cytochrome c, abundant proteins in photosynthesis, are readouts for cellular copper status in Chlamydomonas and other algae. Their accumulation is controlled by a transcription factor copper response regulator (CRR1). The replacement of copper-containing plastocyanin with heme-containing cytochrome c spares copper and permits preferential copper (re)-allocation to cytochrome oxidase. Under copper-replete situations, the quota depends on abundance of various cuproproteins and is tightly regulated, except under zinc-deficiency where acidocalcisomes over-accumulate Cu(I). CRR1 has a transcriptional activation domain, a Zn-dependent DNA binding SBP-domain with a nuclear localization signal, and a C-terminal Cys-rich region that represses the zinc regulon. CRR1 activates >60 genes in Chlamydomonas through GTAC-containing CuREs; transcriptome differences are recapitulated in the proteome. The differentially-expressed genes encode assimilatory copper transporters of the CTR/SLC31 family including a novel soluble molecule, redox enzymes in the tetrapyrrole pathway that promote chlorophyll biosynthesis and photosystem 1 accumulation, and other oxygen-dependent enzymes, which may influence thylakoid membrane lipids, specifically polyunsaturated galactolipids and γ-tocopherol. CRR1 also down-regulates 2 proteins in Chlamydomonas: for plastocyanin, by activation of proteolysis, while for the di‑iron subunit of the cyclase in chlorophyll biosynthesis, through activation of an upstream promoter that generates a poorly-translated 5' extended transcript containing multiple short ORFs that inhibit translation. The functions of many CRR1-target genes are unknown, and the copper protein inventory in Chlamydomonas includes several whose functions are unexplored. The comprehensive picture of cuproproteins and copper homeostasis in this system is well-suited for reverse genetic analyses of these under-investigated components in copper biology.
Topics: Chlamydomonas; Copper; Cytochromes c6; Dihydrodipicolinate Reductase; Electron Transport Complex IV; Gene Expression Regulation, Plant; Homeostasis; Photosynthesis; Plastocyanin; Transcriptome
PubMed: 32800924
DOI: 10.1016/j.bbamcr.2020.118822 -
Frontiers in Plant Science 2022In this study, the differences in chlorophyll fluorescence transient (OJIP) and modulated 820 nm reflection (MR) of cucumber leaves were probed to demonstrate an insight...
In this study, the differences in chlorophyll fluorescence transient (OJIP) and modulated 820 nm reflection (MR) of cucumber leaves were probed to demonstrate an insight into the precise influence of melatonin (MT) on cucumber photosystems under low temperature stress. We pre-treated cucumber seedlings with different levels of MT (0, 25, 50, 100, 200, and 400 μmol · L) before imposing low temperature stress (10 °C/6 °C). The results indicated that moderate concentrations of MT had a positive effect on the growth of low temperature-stressed cucumber seedlings. Under low temperature stress conditions, 100 μmol · L (MT 100) improved the performance of the active photosystem II (PSII) reaction centers (PIabs), the oxygen evolving complex activity (OEC centers) and electron transport between PSII and PSI, mainly by decreasing the L-band, K-band, and G-band, but showed differences with different duration of low temperature stress. In addition, these indicators related to quantum yield and energy flux of PSII regulated by MT indicated that MT (MT 100) effectively protected the electron transport and energy distribution in the photosystem. According to the results of ≥ 1 and MR signals, MT also affected PSI activity. MT 100 decreased the minimal value of MR/MR and the oxidation rate of plastocyanin (PC) and PSI reaction center (P700) ( ), while increased △MR/MR and deoxidation rates of PC and P ( ). The loss of the slow phase of MT 200 and MT 400-treated plants in the MR kinetics was due to the complete prevention of electron movement from PSII to re-reduce the PC and P700 . These results suggest that appropriate MT concentration (100 μmol · L) can improve the photosynthetic performance of PS II and electron transport from primary quinone electron acceptor (Q) to secondary quinone electron acceptor (Q), promote the balance of energy distribution, strengthen the connectivity of PSI and PSII, improve the electron flow of PSII Q to PC and P from reaching PSI by regulating multiple sites of electron transport chain in photosynthesis, and increase the pool size and reduction rates of PSI in low temperature-stressed cucumber plants, All these modifications by MT 100 treatment promoted the photosynthetic electron transfer smoothly, and further restored the cucumber plant growth under low temperature stress. Therefore, we conclude that spraying MT at an appropriate concentration is beneficial for protecting the photosynthetic electron transport chain, while spraying high concentrations of MT has a negative effect on regulating the low temperature tolerance in cucumber.
PubMed: 36407604
DOI: 10.3389/fpls.2022.1029854 -
Nature Plants Oct 2022Photosystem I (PSI) enables photo-electron transfer and regulates photosynthesis in the bioenergetic membranes of cyanobacteria and chloroplasts. Being a multi-subunit...
Photosystem I (PSI) enables photo-electron transfer and regulates photosynthesis in the bioenergetic membranes of cyanobacteria and chloroplasts. Being a multi-subunit complex, its macromolecular organization affects the dynamics of photosynthetic membranes. Here we reveal a chloroplast PSI from the green alga Chlamydomonas reinhardtii that is organized as a homodimer, comprising 40 protein subunits with 118 transmembrane helices that provide scaffold for 568 pigments. Cryogenic electron microscopy identified that the absence of PsaH and Lhca2 gives rise to a head-to-head relative orientation of the PSI-light-harvesting complex I monomers in a way that is essentially different from the oligomer formation in cyanobacteria. The light-harvesting protein Lhca9 is the key element for mediating this dimerization. The interface between the monomers is lacking PsaH and thus partially overlaps with the surface area that would bind one of the light-harvesting complex II complexes in state transitions. We also define the most accurate available PSI-light-harvesting complex I model at 2.3 Å resolution, including a flexibly bound electron donor plastocyanin, and assign correct identities and orientations to all the pigments, as well as 621 water molecules that affect energy transfer pathways.
Topics: Photosystem I Protein Complex; Plastocyanin; Light-Harvesting Protein Complexes; Protein Subunits; Cyanobacteria; Water; Photosystem II Protein Complex
PubMed: 36229605
DOI: 10.1038/s41477-022-01253-4 -
Chemical Reviews Feb 2021This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome and (Cyt/) membranous multisubunit homodimeric... (Review)
Review
This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome and (Cyt/) membranous multisubunit homodimeric complexes. These remarkable molecular machines catalyze electron transfer from membranous quinones to water-soluble electron carriers (such as cytochromes or plastocyanin), coupling electron flow to proton translocation across the energy-transducing membrane and contributing to the generation of a transmembrane electrochemical potential gradient, which powers cellular metabolism in the majority of living organisms. Cyts/ share many similarities but also have significant differences. While decades of research have provided extensive knowledge on these enzymes, several important aspects of their molecular mechanisms remain to be elucidated. We summarize a broad range of structural, mechanistic, and physiological aspects required for function of Cyt/, combining textbook fundamentals with new intriguing concepts that have emerged from more recent studies. The discussion covers but is not limited to (i) mechanisms of energy-conserving bifurcation of electron pathway and energy-wasting superoxide generation at the quinol oxidation site, (ii) the mechanism by which semiquinone is stabilized at the quinone reduction site, (iii) interactions with substrates and specific inhibitors, (iv) intermonomer electron transfer and the role of a dimeric complex, and (v) higher levels of organization and regulation that involve Cyts/. In addressing these topics, we point out existing uncertainties and controversies, which, as suggested, will drive further research in this field.
Topics: Animals; Catalysis; Cytochrome b6f Complex; Electron Transport Complex III; Humans; Membranes; Molecular Dynamics Simulation; Photosynthesis; Protein Conformation; Respiration; Rhodobacter capsulatus; Thermodynamics
PubMed: 33464892
DOI: 10.1021/acs.chemrev.0c00712 -
Biochimica Et Biophysica Acta.... Sep 2021Many cyanobacteria species can use both plastocyanin and cytochrome c as lumenal electron carriers to shuttle electrons from the cytochrome bf to either photosystem I or...
Many cyanobacteria species can use both plastocyanin and cytochrome c as lumenal electron carriers to shuttle electrons from the cytochrome bf to either photosystem I or the respiratory cytochrome c oxidase. In Synechocystis sp. PCC6803 placed in darkness, about 60% of the active PSI centres are bound to a reduced electron donor which is responsible for the fast re-reduction of Pin vivo after a single charge separation. Here, we show that both cytochrome c and plastocyanin can bind to PSI in the dark and participate to the fast phase of P reduction, but the fraction of pre-bound PSI is smaller in the case of cytochrome c than with plastocyanin. Because of the inter-connection of respiration and photosynthesis in cyanobacteria, the inhibition of the cytochrome c oxidase results in the over-reduction of the photosynthetic electron transfer chain in the dark that translates into a lag in the kinetics of P oxidation at the onset of light. We show that this is true both with plastocyanin and cytochrome c, indicating that the partitioning of electron transport between respiration and photosynthesis is regulated in the same way independently of which of the two lumenal electron carriers is present, although the mechanisms of such regulation are yet to be understood.
Topics: Chlorophyll; Cyanobacteria; Cytochromes c6; Electron Transport; Electron Transport Complex IV; Kinetics; Oxidation-Reduction; Photosynthesis; Photosystem I Protein Complex; Plastocyanin; Synechocystis; Thylakoids
PubMed: 34004195
DOI: 10.1016/j.bbabio.2021.148449 -
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 -
International Journal of Molecular... May 2024Photosynthesis, as the primary source of energy for all life forms, plays a crucial role in maintaining the global balance of energy, entropy, and enthalpy in living... (Review)
Review
Photosynthesis, as the primary source of energy for all life forms, plays a crucial role in maintaining the global balance of energy, entropy, and enthalpy in living organisms. Among its various building blocks, photosystem I (PSI) is responsible for light-driven electron transfer, crucial for generating cellular reducing power. PSI acts as a light-driven plastocyanin-ferredoxin oxidoreductase and is situated in the thylakoid membranes of cyanobacteria and the chloroplasts of eukaryotic photosynthetic organisms. Comprehending the structure and function of the photosynthetic machinery is essential for understanding its mode of action. New insights are offered into the structure and function of PSI and its associated light-harvesting proteins, with a specific focus on the remarkable structural conservation of the core complex and high plasticity of the peripheral light-harvesting complexes.
Topics: Photosystem I Protein Complex; Photosynthesis; Light-Harvesting Protein Complexes; Cyanobacteria; Models, Molecular; Electron Transport
PubMed: 38791114
DOI: 10.3390/ijms25105073