scholarly journals Revealing the architecture of the photosynthetic apparatus in the diatom Thalassiosira pseudonana

2021 ◽  
Author(s):  
Rameez Arshad ◽  
Claudio Calvaruso ◽  
Egbert J Boekema ◽  
Claudia Büchel ◽  
Roman Kouřil
Keyword(s):  
Carbon Fixation ◽  
Light Harvesting ◽  
Electron Tomography ◽  
Three Dimensional ◽  
Photosynthetic Apparatus ◽  
Volume Averaging ◽  
Adaptation Strategy ◽  
Thalassiosira Pseudonana ◽  
Diatom Species ◽  
Light Harvesting Complexes

Abstract Diatoms are a large group of marine algae that are responsible for about one-quarter of global carbon fixation. Light-harvesting complexes of diatoms are formed by the fucoxanthin chlorophyll a/c proteins and their overall organization around core complexes of photosystem (PS) I and II is unique in the plant kingdom. Using cryo-electron tomography, we have elucidated the structural organization of PSII and PSI supercomplexes and their spatial segregation in the thylakoid membrane of the model diatom species Thalassiosira pseudonana. Three-dimensional sub-volume averaging revealed that the PSII supercomplex of Thalassiosira pseudonana incorporates a trimeric form of light-harvesting antenna, which differs from the tetrameric antenna observed previously in another diatom, Chaetoceros gracilis. Surprisingly, the organization of the PSI supercomplex is conserved in both diatom species. These results strongly suggest that different diatom classes have various architectures of PSII as an adaptation strategy, whilst a convergent evolution occurred concerning PSI and the overall plastid structure.

Macroorganisation and flexibility of thylakoid membranes

2019 ◽  
Vol 476 (20) ◽  
pp. 2981-3018 ◽  
Author(s):  
Petar H. Lambrev ◽  
Parveen Akhtar
Keyword(s):  
Light Harvesting ◽  
Current Knowledge ◽  
Three Dimensional ◽  
Photosynthetic Apparatus ◽  
Dynamic Responses ◽  
State Transitions ◽  
Photochemical Quenching ◽  
Light Harvesting Complex ◽  
Complex Ii ◽  
Light Harvesting Complex Ii

Abstract The light reactions of photosynthesis are hosted and regulated by the chloroplast thylakoid membrane (TM) — the central structural component of the photosynthetic apparatus of plants and algae. The two-dimensional and three-dimensional arrangement of the lipid–protein assemblies, aka macroorganisation, and its dynamic responses to the fluctuating physiological environment, aka flexibility, are the subject of this review. An emphasis is given on the information obtainable by spectroscopic approaches, especially circular dichroism (CD). We briefly summarise the current knowledge of the composition and three-dimensional architecture of the granal TMs in plants and the supramolecular organisation of Photosystem II and light-harvesting complex II therein. We next acquaint the non-specialist reader with the fundamentals of CD spectroscopy, recent advances such as anisotropic CD, and applications for studying the structure and macroorganisation of photosynthetic complexes and membranes. Special attention is given to the structural and functional flexibility of light-harvesting complex II in vitro as revealed by CD and fluorescence spectroscopy. We give an account of the dynamic changes in membrane macroorganisation associated with the light-adaptation of the photosynthetic apparatus and the regulation of the excitation energy flow by state transitions and non-photochemical quenching.

Overexpression of Thalassiosira pseudonana violaxanthin de-epoxidase-like 2 (VDL2) increases fucoxanthin while stoichiometrically reducing diadinoxanthin cycle pigment abundance

2020 ◽  
Author(s):  
Olga Gaidarenko ◽  
Dylan W. Mills ◽  
Maria Vernet ◽  
Mark Hildebrand
Keyword(s):  
Light Harvesting ◽  
Photosynthetic Pigment ◽  
Carotenoid Biosynthesis ◽  
Thalassiosira Pseudonana ◽  
Physiological Data ◽  
Biosynthesis Pathway ◽  
Chloroplast Targeting ◽  
Light Harvesting Complexes ◽  
Carotenoid Biosynthesis Pathway ◽  
Transcriptomic Responses

ABSTRACTDespite the ubiquity and ecological importance of diatoms, much remains to be understood about their physiology and metabolism, including their carotenoid biosynthesis pathway. Early carotenoid biosynthesis steps are well-conserved, while the identity of the enzymes that catalyze the later steps and their order remain unclear. Those steps lead to the biosynthesis of the final pathway products: the main accessory light-harvesting pigment fucoxanthin (Fx) and the main photoprotective pigment pool comprised of diadinoxanthin (Ddx) and its reversibly de-epoxidized form diatoxanthin (Dtx). We used sequence comparison to known carotenoid biosynthesis enzymes to identify novel candidates in the diatom Thalassiosira pseudonana. Microarray and RNA-seq data was used to select candidates with transcriptomic responses similar to known carotenoid biosynthesis genes and to create full-length gene models, and we focused on those that encode proteins predicted to be chloroplast-localized. We identified a violaxanthin de-epoxidase-like gene (Thaps3_11707, VDL2) that when overexpressed results in increased Fx abundance while stoichiometrically reducing Ddx+Dtx. Based on transcriptomics, we hypothesize that Thaps3_10233 may also contribute to Fx biosynthesis, in addition to VDL2. Separately using antisense RNA to target VDL2, VDL1, and both LUT1-like copies (hypothesized to catalyze an earlier step in the pathway) simultaneously, reduced the overall cellular photosynthetic pigment content, including chlorophylls, suggesting destabilization of light-harvesting complexes by Fx deficiency. Based on transcriptomic and physiological data, we hypothesize that the two predicted T. pseudonana zeaxanthin epoxidases have distinct functions and that different copies of phytoene synthase and phytoene desaturase may serve to initiate carotenoid biosynthesis in response to different cellular needs. Finally, nine carotene cis/trans isomerase (CRTISO) candidates identified based on sequence identity to known CRTISO proteins were narrowed to two most likely to be part of the T. pseudonana carotenoid biosynthesis pathway based on transcriptomic responses and predicted chloroplast targeting.

scholarly journals Native architecture of the Chlamydomonas chloroplast revealed by in situ cryo-electron tomography

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Benjamin D Engel ◽  
Miroslava Schaffer ◽  
Luis Kuhn Cuellar ◽  
Elizabeth Villa ◽  
Jürgen M Plitzko ◽  
...  
Keyword(s):  
Focused Ion Beam ◽  
Carbon Fixation ◽  
Nearest Neighbor ◽  
Electron Tomography ◽  
Close Association ◽  
Ion Beam ◽  
Three Dimensional ◽  
Chloroplast Envelope ◽  
Cryo Electron Tomography ◽  
Subtomogram Averaging

Chloroplast function is orchestrated by the organelle's intricate architecture. By combining cryo-focused ion beam milling of vitreous Chlamydomonas cells with cryo-electron tomography, we acquired three-dimensional structures of the chloroplast in its native state within the cell. Chloroplast envelope inner membrane invaginations were frequently found in close association with thylakoid tips, and the tips of multiple thylakoid stacks converged at dynamic sites on the chloroplast envelope, implicating lipid transport in thylakoid biogenesis. Subtomogram averaging and nearest neighbor analysis revealed that RuBisCO complexes were hexagonally packed within the pyrenoid, with ∼15 nm between their centers. Thylakoid stacks and the pyrenoid were connected by cylindrical pyrenoid tubules, physically bridging the sites of light-dependent photosynthesis and light-independent carbon fixation. Multiple parallel minitubules were bundled within each pyrenoid tubule, possibly serving as conduits for the targeted one-dimensional diffusion of small molecules such as ATP and sugars between the chloroplast stroma and the pyrenoid matrix.

scholarly journals Divergence of photosynthetic strategies amongst marine diatoms

PLoS ONE ◽  
2020 ◽  
Vol 15 (12) ◽  
pp. e0244252
Author(s):  
Nerissa L. Fisher ◽  
Douglas A. Campbell ◽  
David J. Hughes ◽  
Unnikrishnan Kuzhiumparambil ◽  
Kimberly H. Halsey ◽  
...  
Keyword(s):  
Light Harvesting ◽  
Light Exposure ◽  
High Growth ◽  
Nonphotochemical Quenching ◽  
Thalassiosira Pseudonana ◽  
Marine Phytoplankton ◽  
Diatom Species ◽  
Light Regimes ◽  
Intermediate Response ◽  
Excitation Pressure

Marine phytoplankton, and in particular diatoms, are responsible for almost half of all primary production on Earth. Diatom species thrive from polar to tropical waters and across light environments that are highly complex to relatively benign, and so have evolved highly divergent strategies for regulating light capture and utilization. It is increasingly well established that diatoms have achieved such successful ecosystem dominance by regulating excitation energy available for generating photosynthetic energy via highly flexible light harvesting strategies. However, how different light harvesting strategies and downstream pathways for oxygen production and consumption interact to balance excitation pressure remains unknown. We therefore examined the responses of three diatom taxa adapted to inherently different light climates (estuarine Thalassioisira weissflogii, coastal Thalassiosira pseudonana and oceanic Thalassiosira oceanica) during transient shifts from a moderate to high growth irradiance (85 to 1200 μmol photons m-2 s-1). Transient high light exposure caused T. weissflogii to rapidly downregulate PSII with substantial nonphotochemical quenching, protecting PSII from inactivation or damage, and obviating the need for induction of O2 consuming (light-dependent respiration, LDR) pathways. In contrast, T. oceanica retained high excitation pressure on PSII, but with little change in RCII photochemical turnover, thereby requiring moderate repair activity and greater reliance on LDR. T. pseudonana exhibited an intermediate response compared to the other two diatom species, exhibiting some downregulation and inactivation of PSII, but high repair of PSII and induction of reversible PSII nonphotochemical quenching, with some LDR. Together, these data demonstrate a range of strategies for balancing light harvesting and utilization across diatom species, which reflect their adaptation to sustain photosynthesis under environments with inherently different light regimes.

Influence of thylakoid membrane lipids on the structure of aggregated light-harvesting complexes of the diatom Thalassiosira pseudonana and the green alga Mantoniella squamata

2017 ◽  
Vol 160 (3) ◽  
pp. 339-358 ◽  
Author(s):  
Susann Schaller-Laudel ◽  
Dariusz Latowski ◽  
Małgorzata Jemioła-Rzemińska ◽  
Kazimierz Strzałka ◽  
Sebastian Daum ◽  
...  
Keyword(s):  
Green Alga ◽  
Thylakoid Membrane ◽  
Light Harvesting ◽  
Membrane Lipids ◽  
Thalassiosira Pseudonana ◽  
Light Harvesting Complexes ◽  
Mantoniella Squamata

scholarly journals Photosynthetic Light-Harvesting (Antenna) Complexes—Structures and Functions

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3378
Author(s):  
Heiko Lokstein ◽  
Gernot Renger ◽  
Jan Götze
Keyword(s):  
Cross Sections ◽  
Light Harvesting ◽  
Photosynthetic Apparatus ◽  
Structural Diversity ◽  
Reaction Centers ◽  
Photosynthetic Membrane ◽  
Light Harvesting Complexes ◽  
Tentative Explanation ◽  
Light Harvesting Antenna ◽  
Photosynthetic Antenna

Chlorophylls and bacteriochlorophylls, together with carotenoids, serve, noncovalently bound to specific apoproteins, as principal light-harvesting and energy-transforming pigments in photosynthetic organisms. In recent years, enormous progress has been achieved in the elucidation of structures and functions of light-harvesting (antenna) complexes, photosynthetic reaction centers and even entire photosystems. It is becoming increasingly clear that light-harvesting complexes not only serve to enlarge the absorption cross sections of the respective reaction centers but are vitally important in short- and long-term adaptation of the photosynthetic apparatus and regulation of the energy-transforming processes in response to external and internal conditions. Thus, the wide variety of structural diversity in photosynthetic antenna “designs” becomes conceivable. It is, however, common for LHCs to form trimeric (or multiples thereof) structures. We propose a simple, tentative explanation of the trimer issue, based on the 2D world created by photosynthetic membrane systems.

scholarly journals Dichotomous disorder model for single light-harvesting complexes

2019 ◽  
Vol 58 (4) ◽  
Author(s):  
Danielis Rutkauskas
Keyword(s):  
Light Harvesting ◽  
Purple Bacteria ◽  
Photosynthetic Apparatus ◽  
Theoretical Research ◽  
Spectral Signature ◽  
Reaction Centre ◽  
Excitation Energies ◽  
Light Harvesting Complexes ◽  
Protein Scaffold ◽  
Migration Pathways

Photosynthetic organisms conserve the captured energy of solar radiation into stable chemical forms. To do so, they have evolved specialized systems of pigment–protein complexes consisting of light-harvesting antennas and reaction centres. Photosynthetic antennas contain remarkably dense arrangements of light-absorbing pigments held by the protein scaffold, and their function is to absorb light and funnel the excitation energy to the reaction centre. Decades of experimental and theoretical research resulted in a detailed understanding of the energy migration pathways within the photosynthetic apparatus. The key parameters determining the excitation relaxation and transfer are inter-pigment coupling and energetic disorder or non-equality of excitation energies at equivalent pigment sites due to the interaction with the disordered protein scaffold. Circularly symmetric light-harvesting antennas from purple bacteria present a beautiful example of the interplay between these parameters. The spectral signature of this interplay could be observed with the single-molecule fluorescence microscopy techniques. The results of these measurements were interpreted with an intuitively clear dichotomous model of disorder of pigment site energies.

scholarly journals Fluctuating antenna model: Applications and prospects

2019 ◽  
Vol 58 (4) ◽  
Author(s):  
Gediminas Trinkūnas ◽  
Jevgenij Chmeliov
Keyword(s):  
Three Dimensional ◽  
Photosynthetic Apparatus ◽  
Reaction Centre ◽  
Light Harvesting Complexes ◽  
Short And Long Term ◽  
Reduced Dimension ◽  
Isolated Systems ◽  
Antenna Model

Recently, we proposed a simple conceptual fluctuating antenna model (FAM), describing excitation diffusion and trapping in a continuous medium, where variations of the excitation transfer pathways are taken into account by the introduced fractional space dimension. Since then, this model has been successfully applied to simulate multi-exponential excitation quenching kinetics in a series of plant photosynthetic systems, purified from the thylakoid membranes, without invoking a radical pair state in the reaction centre. Here, we overview this model and its parameters obtained for various systems, and extend the area of its applications to several pigment–protein supercomplexes containing the photosystem I (PSI). We show that while the diffusion in the PSI core is virtually three-dimensional, the PSI core aggregates interconnected with other light-harvesting complexes (LHCI and/or LHCII) are characterized by a substantially reduced dimension, which indicates a smaller number of energy transfer links from LHCI to the PSI core. We also suggest that in vivo both PSI and PSII antennae are substantially larger than those observed in the isolated systems: PSII antenna contains in total about 6 LHCII trimers while PSI is aggregated with at least one LHCII trimer. The obtained results show that FAM can be a very useful tool to follow photosynthetic apparatus transformations during short- and long-term adaptation to varying light, monitored by kinetic fluorescence spectroscopy.

Practical electron tomography

1995 ◽  
Vol 53 ◽  
pp. 742-743
Author(s):  
C.L. Woodcock
Keyword(s):  
Electron Tomography ◽  
Tomographic Reconstruction ◽  
Three Dimensional ◽  
3D Shape ◽  
Computational Resources ◽  
Shape Of Particles

Despite the potential of the technique, electron tomography has yet to be widely used by biologists. This is in part related to the rather daunting list of equipment and expertise that are required. Thanks to continuing advances in theory and instrumentation, tomography is now more feasible for the non-specialist. One barrier that has essentially disappeared is the expense of computational resources. In view of this progress, it is time to give more attention to practical issues that need to be considered when embarking on a tomographic project. The following recommendations and comments are derived from experience gained during two long-term collaborative projects.Tomographic reconstruction results in a three dimensional description of an individual EM specimen, most commonly a section, and is therefore applicable to problems in which ultrastructural details within the thickness of the specimen are obscured in single micrographs. Information that can be recovered using tomography includes the 3D shape of particles, and the arrangement and dispostion of overlapping fibrous and membranous structures.

Three-Dimensional reconstruction of isolated centrosomes by automated electron tomography

1994 ◽  
Vol 52 ◽  
pp. 310-311
Author(s):  
M.B. Braunfeld ◽  
M. Moritz ◽  
B.M. Alberts ◽  
J.W. Sedat ◽  
D.A. Agard
Keyword(s):  
Electron Tomography ◽  
Three Dimensional ◽  
Vital Role ◽  
Complex Nature ◽  
Animal Cells ◽  
Microtubule Organizing Center ◽  
Nucleation Sites ◽  
Dimensional Reconstruction ◽  
Organizing Center ◽  
Resolution Model

In animal cells, the centrosome functions as the primary microtubule organizing center (MTOC). As such the centrosome plays a vital role in determining a cell's shape, migration, and perhaps most importantly, its division. Despite the obvious importance of this organelle little is known about centrosomal regulation, duplication, or how it nucleates microtubules. Furthermore, no high resolution model for centrosomal structure exists.We have used automated electron tomography, and reconstruction techniques in an attempt to better understand the complex nature of the centrosome. Additionally we hope to identify nucleation sites for microtubule growth.Centrosomes were isolated from early Drosophila embryos. Briefly, after large organelles and debris from homogenized embryos were pelleted, the resulting supernatant was separated on a sucrose velocity gradient. Fractions were collected and assayed for centrosome-mediated microtubule -nucleating activity by incubating with fluorescently-labeled tubulin subunits. The resulting microtubule asters were then spun onto coverslips and viewed by fluorescence microscopy.

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