scholarly journals Overexpression of plastid terminal oxidase in Synechocystis sp. PCC 6803 alters cellular redox state

2017 ◽  
Vol 372 (1730) ◽  
pp. 20160379 ◽  
Author(s):  
Kathleen Feilke ◽  
Ghada Ajlani ◽  
Anja Krieger-Liszkay
Keyword(s):  
Higher Plants ◽  
Photosynthetic Apparatus ◽  
Oxygenic Photosynthesis ◽  
Terminal Oxidase ◽  
Cellular Redox ◽  
Excess Electrons ◽  
Plastid Terminal Oxidase ◽  
Absorption Measurements ◽  
Pcc 6803

Cyanobacteria are the most ancient organisms performing oxygenic photosynthesis, and they are the ancestors of plant plastids. All plastids contain the plastid terminal oxidase (PTOX), while only certain cyanobacteria contain PTOX. Many putative functions have been discussed for PTOX in higher plants including a photoprotective role during abiotic stresses like high light, salinity and extreme temperatures. Since PTOX oxidizes PQH 2 and reduces oxygen to water, it is thought to protect against photo-oxidative damage by removing excess electrons from the plastoquinone (PQ) pool. To investigate the role of PTOX we overexpressed rice PTOX fused to the maltose-binding protein (MBP-OsPTOX) in Synechocystis sp. PCC 6803, a model cyanobacterium that does not encode PTOX. The fusion was highly expressed and OsPTOX was active, as shown by chlorophyll fluorescence and P 700 absorption measurements. The presence of PTOX led to a highly oxidized state of the NAD(P)H/NAD(P) + pool, as detected by NAD(P)H fluorescence. Moreover, in the PTOX overexpressor the electron transport capacity of PSI relative to PSII was higher, indicating an alteration of the photosystem I (PSI) to photosystem II (PSII) stoichiometry. We suggest that PTOX controls the expression of responsive genes of the photosynthetic apparatus in a different way from the PQ/PQH 2 ratio. This article is part of the themed issue ‘Enhancing photosynthesis in crop plants: targets for improvement’.

Auxiliary functions in photosynthesis: the role of the FtsH protease

2001 ◽  
Vol 29 (4) ◽  
pp. 455-459 ◽  
Author(s):  
S. Bailey ◽  
P. Silva ◽  
P. Nixon ◽  
C. Mullineaux ◽  
C. Robinson ◽  
...  
Keyword(s):  
Molecular Chaperones ◽  
Protein Targeting ◽  
Photosynthetic Apparatus ◽  
Oxygenic Photosynthesis ◽  
Turnover Rates ◽  
Dynamic Nature ◽  
Auxiliary Functions ◽  
Zinc Metalloprotease ◽  
Ftsh Protease

Oxygenic photosynthesis can be described effectively by using two long-standing models: the Z-scheme and the chemiosmotic hypothesis. However, these models do not reveal the dynamic nature of the thylakoid membrane and the four major complexes that it binds. The composition of the photosynthetic apparatus is continually changing in response to a range of environmental stimuli. In addition, many photosynthetic components have some of the highest turnover rates in Nature. Changes in composition and turnover of photosynthetic components require the degradation of existing and damaged polypeptides and the resynthesis and co-ordinated assembly of new polypeptides and their associated cofactors. This is achieved by several auxiliary functions, including proteolysis, protein targeting and the action of molecular chaperones. Some of the components involved in these functions, such as translocons, chaperones and proteases, have been identified but many of the auxiliary functions of photosynthesis remain uncharacterized. Among the proteases known to be associated with the thylakoids is the zinc metalloprotease FtsH, which might also act as a chaperone. Here we provide an overview of the thylakoid FtsH protease and discuss its role in the maintenance and assembly of the photosynthetic apparatus.

scholarly journals Photosynthetic apparatus of purple bacteria

2002 ◽  
Vol 35 (1) ◽  
pp. 1-62 ◽  
Author(s):  
Xiche Hu ◽  
Thorsten Ritz ◽  
Ana Damjanović ◽  
Felix Autenrieth ◽  
Klaus Schulten
Keyword(s):  
Photosynthetic Bacteria ◽  
Higher Plants ◽  
Purple Bacteria ◽  
Photosynthetic Apparatus ◽  
Excitation Transfer ◽  
Oxygenic Photosynthesis ◽  
Photosynthetic Reaction Centers ◽  
Primary Charge Separation ◽  
Photosynthetic Membrane ◽  
Light Harvesting Complexes

1. Introduction 22. Structure of the bacterial PSU 52.1 Organization of the bacterial PSU 52.2 The crystal structure of the RC 92.3 The crystal structures of LH-II 112.4 Bacteriochlorophyll pairs in LH-II and the RC 132.5 Models of LH-I and the LH-I-RC complex 152.6 Model for the PSU 173. Excitation transfer in the PSU 183.1 Electronic excitations of BChls 22 3.1.1 Individual BChls 22 3.1.2 Rings of BChls 22 3.1.2.1 Exciton states 22 3.1.3 Effective Hamiltonian 24 3.1.4 Optical properties 25 3.1.5 The effect of disorder 263.2 Theory of excitation transfer 29 3.2.1 General theory 29 3.2.2 Mechanisms of excitation transfer 32 3.2.3 Approximation for long-range transfer 34 3.2.4 Transfer to exciton states 353.3 Rates for transfer processes in the PSU 37 3.3.1 Car→BChl transfer 37 3.3.1.1 Mechanism of Car→BChl transfer 39 3.3.1.2 Pathways of Car→BChl transfer 40 3.3.2 Efficiency of Car→BChl transfer 40 3.3.3 B800-B850 transfer 44 3.3.4 LH-II→LH-II transfer 44 3.3.5 LH-II→LH-I transfer 45 3.3.6 LH-I→RC transfer 45 3.3.7 Excitation migration in the PSU 46 3.3.8 Genetic basis of PSU assembly 494. Concluding remarks 535. Acknowledgments 556. References 55Life as we know it today exists largely because of photosynthesis, the process through which light energy is converted into chemical energy by plants, algae, and photosynthetic bacteria (Priestley, 1772; Barnes, 1893; Wurmser, 1925; Van Niel, 1941; Clayton & Sistrom, 1978; Blankenship et al. 1995; Ort & Yocum, 1996). Historically, photosynthetic organisms are grouped into two classes. When photosynthesis is carried out in the presence of air it is called oxygenic photosynthesis (Ort & Yocum, 1996). Otherwise, it is anoxygenic (Blankenship et al. 1995). Higher plants, algae and cyanobacteria perform oxygenic photosynthesis, which involves reduction of carbon dioxide to carbohydrate and oxidation of water to produce molecular oxygen. Some photosynthetic bacteria, such as purple bacteria, carry out anoxygenic photosynthesis that involves oxidation of molecules other than water. In spite of these differences, the general principles of energy transduction are the same in anoxygenic and oxygenic photosynthesis (Van Niel, 1931, 1941; Stanier, 1961; Wraight, 1982; Gest, 1993). The primary processes of photosynthesis involve absorption of photons by light-harvesting complexes (LHs), transfer of excitation energy from LHs to the photosynthetic reaction centers (RCs), and the primary charge separation across the photosynthetic membrane (Sauer, 1975; Knox, 1977; Fleming & van Grondelle, 1994; van Grondelle et al. 1994). In this article, we will focus on the anoxygenic photosynthetic process in purple bacteria, since its photosynthetic system is the most studied and best characterized during the past 50 years.

scholarly journals Cytochrome cM downscales photosynthesis under photomixotrophy in Synechocystis sp. PCC 6803

2019 ◽  
Author(s):  
Daniel Solymosi ◽  
Dorota Muth-Pawlak ◽  
Lauri Nikkanen ◽  
Duncan Fitzpatrick ◽  
Ravendran Vasudevan ◽  
...  
Keyword(s):  
Photosynthetic Apparatus ◽  
Wild Type ◽  
Gene Encoding ◽  
Transport Chain ◽  
Similar Phenotype ◽  
Photosynthetic Microorganisms ◽  
Photosynthesis And Respiration ◽  
Pcc 6803

AbstractPhotomixotrophy is a metabolic state, which enables photosynthetic microorganisms to simultaneously perform photosynthesis and metabolism of imported organic carbon substrates. This process is complicated in cyanobacteria, since many, including Synechocystis sp. PCC 6803, conduct photosynthesis and respiration in an interlinked thylakoid membrane electron transport chain. Under photomixotrophy, the cell must therefore tightly regulate electron fluxes from photosynthetic and respiratory complexes. In this study, we show via characterization of photosynthetic apparatus and the proteome, that photomixotrophic growth results in a gradual reduction of the plastoquinone pool in wild-type Synechocystis, which fully downscales photosynthesis over three days of growth. This process is circumvented by deleting the gene encoding cytochrome cM (CytM), a cryptic c-type heme protein widespread in cyanobacteria. ΔCytM maintained active photosynthesis over the three day period, demonstrated by high photosynthetic O2 and CO2 fluxes and effective yields of Photosystem II and Photosystem I. Overall, this resulted in a higher growth rate than wild-type, which was maintained by accumulation of proteins involved in phosphate and metal uptake, and cofactor biosynthetic enzymes. While the exact role of CytM has not been determined, a mutant deficient in the thylakoid-localised respiratory terminal oxidases and CytM (ΔCox/Cyd/CytM) displayed a similar phenotype under photomixotrophy to ΔCytM, demonstrating that CytM is not transferring electrons to these complexes, which has previously been suggested. In summary, the obtained data suggests that CytM may have a regulatory role in photomixotrophy by reducing the photosynthetic capacity of cells.One sentence summaryThe cryptic, highly conserved cytochrome cM completely blocks photosynthesis in Synechocystis under three days of photomixotrophy, possibly by suppressing CO2 assimilation.

scholarly journals Dual Role of the Plastid Terminal Oxidase in Tomato

2007 ◽  
Vol 145 (3) ◽  
pp. 691-702 ◽  
Author(s):  
Maryam Shahbazi ◽  
Matthias Gilbert ◽  
Anne-Marie Labouré ◽  
Marcel Kuntz
Keyword(s):  
Dual Role ◽  
Terminal Oxidase ◽  
Plastid Terminal Oxidase

scholarly journals Computational Analysis of Alternative Photosynthetic Electron Flows Linked With Oxidative Stress

2021 ◽  
Vol 12 ◽  
Author(s):  
Nima P. Saadat ◽  
Tim Nies ◽  
Marvin van Aalst ◽  
Brandon Hank ◽  
Büsra Demirtas ◽  
...  
Keyword(s):  
Energy Demand ◽  
Computational Analysis ◽  
Adverse Reactions ◽  
Mechanistic Model ◽  
Photosynthetic Apparatus ◽  
Environmental Perturbations ◽  
C3 Photosynthesis ◽  
Ros Formation ◽  
Plastid Terminal Oxidase

During photosynthesis, organisms respond to their energy demand and ensure the supply of energy and redox equivalents that sustain metabolism. Hence, the photosynthetic apparatus can, and in fact should, be treated as an integrated supply-demand system. Any imbalance in the energy produced and consumed can lead to adverse reactions, such as the production of reactive oxygen species (ROS). Reaction centres of both photosystems are known sites of ROS production. Here, we investigate in particular the central role of Photosystem I (PSI) in this tightly regulated system. Using a computational approach we have expanded a previously published mechanistic model of C3 photosynthesis by including ROS producing and scavenging reactions around PSI. These include two water to water reactions mediated by Plastid terminal oxidase (PTOX) and Mehler and the ascorbate-glutathione (ASC-GSH) cycle, as a main non-enzymatic antioxidant. We have used this model to predict flux distributions through alternative electron pathways under various environmental stress conditions by systematically varying light intensity and enzymatic activity of key reactions. In particular, we studied the link between ROS formation and activation of pathways around PSI as potential scavenging mechanisms. This work shines light on the role of alternative electron pathways in photosynthetic acclimation and investigates the effect of environmental perturbations on PSI activity in the context of metabolic productivity.

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