- I am a plant and environmental biologist studying molecular mechanisms which allowed photosynthetic organsms to conqu... moreI am a plant and environmental biologist studying molecular mechanisms which allowed photosynthetic organsms to conquer land and optimize primary productivity in different environments with particular focus in light harvesting and light use efficiency. Applied aspects of our work include improving crop photosynthetic efficiency and resistance to abiotic stresses. Complementary research focuses on biofuel production to minimize CO2 release in athmosphere and air pollution.edit
SummaryIn natural ecosystems, plants compete for space, nutrients and light. The optically dense canopies limit the penetration of photosynthetically active radiation and light often becomes a growth‐limiting factor for the understory.... more
SummaryIn natural ecosystems, plants compete for space, nutrients and light. The optically dense canopies limit the penetration of photosynthetically active radiation and light often becomes a growth‐limiting factor for the understory. The reduced availability of photons in the lower leaf layers is also a major constraint for yield potential in canopies of crop monocultures. Traditionally, crop breeding has selected traits related to plant architecture and nutrient assimilation rather than light use efficiency. Leaf optical density is primarily determined by tissue morphology and by the foliar concentration of photosynthetic pigments (chlorophylls and carotenoids). Most pigment molecules are bound to light‐harvesting antenna proteins in the chloroplast thylakoid membranes, where they serve photon capture and excitation energy transfer toward reaction centers of photosystems. Engineering the abundance and composition of antenna proteins has been suggested as a strategy to improve lig...
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Abstract Photosynthetic microalgae hold great potential as light-driven heterologous protein expression hosts. In particular, the algal chloroplast is an ideal sub-cellular site for the compartmentalized synthesis and accumulation of... more
Abstract Photosynthetic microalgae hold great potential as light-driven heterologous protein expression hosts. In particular, the algal chloroplast is an ideal sub-cellular site for the compartmentalized synthesis and accumulation of high-value recombinant proteins. However, full integration of transplastomic algal biotechnology in the large-scale production of biocatalysts still suffers from major bottlenecks, such as genetic instability and pest contamination. To enhance the reliability of plastid-based algal expression platforms we developed a self-reinforcing genetic system in Chlamydomonas reinhardtii. We transformed the plastome with a bifunctional transgene encoding an in vivo cleavable fusion polypeptide composed of a hyperthermophilic cellulase and the phosphite dehydrogenase PTXD. The dual use of phosphite as a low-cost, environmentally friendly selective agent and fertilizer afforded axenic algal cultivation via mixotrophic metabolism and efficient expression of the hydrolytic enzyme. This study provides an example of chloroplast genetic engineering in which biosafety is integrated in the sustainable management of microalgal monocultures to produce enzymes with industrial applications.
Research Interests: Biochemistry, Enzymology, Molecular Biology, Photosynthesis, Biotechnology, and 15 moreBiorefinery, Biology, Molecular Genetics, Microalgae, Plant Molecular Biology, Protein Engineering, Biocatalysis, Alternative Fuels, Phosphorus, Chloroplast Transformation, Chlamydomonas, Circular Economy, Chloroplast, Heterologous Expression, and Chlamydomonas Reinhardtii
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ABSTRACT Definition of the SubjectAlgae are oxygenic photoautotrophs, offering a very high level of biodiversity and thus suitable for different practical applications. Today, they are mainly cultivated for human/animal food or to extract... more
ABSTRACT Definition of the SubjectAlgae are oxygenic photoautotrophs, offering a very high level of biodiversity and thus suitable for different practical applications. Today, they are mainly cultivated for human/animal food or to extract high-value chemicals and pharmaceuticals. However, their exploitation could be extended. Algae are attractive as high yield biomass producers, because of the short life cycle, the ability to grow up to very high cell densities, and the easy large-scale cultivation that does not compete with other demands such as those of conventional crops agriculture. Algae can be a resource of renewable, sustainable biofuels. In addition, they can be transformed into “cell factories” to produce recombinant proteins of interest for pharmaceutical companies.IntroductionAlgae are described as “lower” plants that never have true stems, roots, and leaves, and grow photoautotrophically by performing oxygenic photos ...
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We demonstrate an ultrabroadband two-dimensional electronic spectrometer that maps energy flow across the visible range. This apparatus enables observation of previously unexplored carotenoid-mediated light-harvesting dynamics in plants,... more
We demonstrate an ultrabroadband two-dimensional electronic spectrometer that maps energy flow across the visible range. This apparatus enables observation of previously unexplored carotenoid-mediated light-harvesting dynamics in plants, including identification of a debated carotenoid dark state.
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This book introduces the basic physical, chemical, and biological principles underlying the first steps in photosynthesis: light absorption, excitation energy transfer, and charge separation. In Part 1, we introduce pigments and their... more
This book introduces the basic physical, chemical, and biological principles underlying the first steps in photosynthesis: light absorption, excitation energy transfer, and charge separation. In Part 1, we introduce pigments and their spectroscopic/ redox properties. In Part 2, pigment-proteins as they occur in various natural systems (plants, algae, photosynthetic bacteria) are described, including the regulation of light harvesting. Part 3 deals with the physics underlying light harvesting: energy transfer and electron transport. Part 4 introduces basic and advanced spectroscopic methods, including data analysis. In Part 5, we discuss artificial and natural photosynthetic systems, how they are assembled, and what the energy transfer properties are
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Green plants prevent photodamage under high light conditions by dissipating excess energy as heat. Conformational changes of the photosynthetic antenna complexes activate dissipation by leveraging the sensitivity of the photophysics of... more
Green plants prevent photodamage under high light conditions by dissipating excess energy as heat. Conformational changes of the photosynthetic antenna complexes activate dissipation by leveraging the sensitivity of the photophysics of the chlorophyll and carotenoids to their surrounding protein. However, the mechanisms and site of dissipation are still debated, largely due to two challenges. First, experiments have been performed in detergent, which can induce non-native conformations, or in vivo, where contributions from the multiple complexes cannot be disentangled and are further obfuscated by laser-induced artifacts. Second, because of the ultrafast timescales and large energy gaps involved, measurements lacked the temporal or spectral requirements. Here, we overcome both challenges by applying ultrabroadband two-dimensional electronic spectroscopy to the principal antenna complex, light-harvesting complex II, in a near-native membrane. The spectra show that the membrane enhanc...
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Green plants prevent photodamage under high light conditions by dissipating excess energy as heat. Conformational changes of the photosynthetic antenna complexes activate dissipation by leveraging the sensitivity of the photophysics of... more
Green plants prevent photodamage under high light conditions by dissipating excess energy as heat. Conformational changes of the photosynthetic antenna complexes activate dissipation by leveraging the sensitivity of the photophysics of the chlorophyll and carotenoids to their surrounding protein. However, the mechanisms and site of dissipation are still debated, largely due to two challenges. First, because of the ultrafast timescales and large energy gaps involved, measurements lacked the temporal or spectral requirements. Second, experiments have been performed in detergent, which can induce non-native conformations, or in vivo, where contributions from the multiple complexes cannot be disentangled and are further obfuscated by laser-induced artifacts. Here, we overcome both challenges by applying ultrabroadband two-dimensional electronic spectroscopy to the principal antenna complex, light-harvesting complex II, in a near-native membrane. The membrane enhances two dissipative pat...
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Significance Protein flexibility is essential for the robustness of biological systems, yet the dynamics underlying this flexibility are difficult to observe, because they are small, fast, and stochastic. Photoprotection in plants is... more
Significance Protein flexibility is essential for the robustness of biological systems, yet the dynamics underlying this flexibility are difficult to observe, because they are small, fast, and stochastic. Photoprotection in plants is critical for robust growth under highly variable sunlight, but the complexity of photosynthetic proteins means that identifying conformational states and dynamics responsible is challenging. Here, we develop a method using the correlation function of the fluorescence lifetime to characterize multiple dynamical processes in single proteins. By applying this method to the protein Light-Harvesting Complex Stress Related 1 (LHCSR1), we identify two local protein motions that control quenching of excess sunlight, which is a photoprotective effect. Our analytical approach enables a structure-based understanding of the photoprotective mechanisms in green plants.
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We utilise ultrabroadband two-dimensional electronic spectroscopy to map out pathways of energy flow in LHCII across the entire visible region. In addition to the well-established, low-lying chlorophyll Qy bands, our results reveal... more
We utilise ultrabroadband two-dimensional electronic spectroscopy to map out pathways of energy flow in LHCII across the entire visible region. In addition to the well-established, low-lying chlorophyll Qy bands, our results reveal additional pathways of energy relaxation on the higher-lying excited states involving the S2 energy levels of carotenoids, including ultrafast carotenoid-to-chlorophyll energy transfer on 90-150 fs timescales.
Research Interests: Physics and Spectroscopy
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Marine diatoms are prominent phytoplankton organisms, optimally performing photosynthesis in extremely variable environments. Diatoms possess a strong ability to dissipate excess absorbed energy as heat via non-photochemical quenching... more
Marine diatoms are prominent phytoplankton organisms, optimally performing photosynthesis in extremely variable environments. Diatoms possess a strong ability to dissipate excess absorbed energy as heat via non-photochemical quenching (NPQ). This process relies on changes in carotenoid pigment composition (xanthophyll cycle) and on specific members of the light-harvesting complex (LHC) family specialized in photoprotection (LHCX), which potentially act as NPQ effectors. However, the link between light stress, NPQ, and the existence of different LHCX isoforms is not understood in these organisms. Using picosecond fluorescence analysis, we observed two types of NPQ in the pennate diatom Phaeodactylum tricornutum, depending on light conditions. Short exposure of low-light acclimated cells to high light triggers the onset of energy quenching close to the core of Photosystem II, while prolonged light stress activates NPQ in the antenna. Biochemical analysis indicates a link between the c...
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Plants harvest photons for photosynthesis using light-harvesting complexes (LHCs)-an array of chlorophyll proteins that can reversibly switch from harvesting to energy-dissipation mode to prevent over-excitation and damage of the... more
Plants harvest photons for photosynthesis using light-harvesting complexes (LHCs)-an array of chlorophyll proteins that can reversibly switch from harvesting to energy-dissipation mode to prevent over-excitation and damage of the photosynthetic apparatus. In unicellular algae and lower plants this process requires the LHCSR proteins which senses over-acidification of the lumen trough protonatable residues exposed to the thylakoid lumen to activate quenching reactions. Further activation is provided by replacement of the violaxanthin ligand with its de-epoxidized product, zeaxanthin, also induced by excess light. We have produced the ppLHCSR1 protein from Physcomitrella patens by over-expression in tobacco and purified it in either its violaxanthin- or the zeaxanthin-binding form with the aim of analyzing their spectroscopic properties at either neutral or acidic pH. Using femtosecond spectroscopy, we demonstrated that the energy dissipation is achieved by two distinct quenching mechanism which are both activated by low pH. The first is present in both ppLHCSR1-Vio and ppLHCSR1-Zea and is characterized by 30-40ps time constant. The spectrum of the quenching product is reminiscent of a carotenoid radical cation, suggesting that the pH-induced quenching mechanism is likely electron transfer from the carotenoid to the excited Chl a. In addition, a second quenching channel populating the S1 state of carotenoid via energy transfer from Chl is found exclusively in the ppLHCSR1-Zea at pH5. These results provide proof of principle that more than one quenching mechanism may operate in the LHC superfamily and also help understanding the photoprotective role of LHCSR proteins and the evolution of LHC antennae.
Research Interests: Chemistry, Kinetics, Photochemistry, Photosynthesis, Tobacco, and 14 moreCarotenoids, Medicine, Biological Sciences, Chlorophyll, Physical sciences, Electron Transport, Spectrum analysis, Energy Transfer, Photoprotection, Protein Binding, Hydrogen-Ion Concentration, Femtosecond Spectroscopy, Biochemistry and cell biology, and Non-photochemical quenching
Light Harvesting Complex II (LHCII) serves a central role in light harvesting for oxygenic photosynthesis, and is arguably the most important photosynthetic antenna complex. In this work, we present two-dimensional electronic-vibrational... more
Light Harvesting Complex II (LHCII) serves a central role in light harvesting for oxygenic photosynthesis, and is arguably the most important photosynthetic antenna complex. In this work, we present two-dimensional electronic-vibrational (2DEV) spectra of LHCII isolated from spinach, demonstrating the possibility of using this technique to track the transfer of electronic excitation energy between specific pigments within the complex. We assign the spectral bands via comparison with the 2DEV spectra of the isolated chromophores, chlorophyll a and b, and present evidence that excitation energy between the pigments of the complex are observed in these spectra. Finally, we analyze the essential components of the 2DEV spectra using singular value decomposition, which makes it possible to reveal the relaxation pathways within this complex.
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In oxygenic photosynthesis, light harvesting is regulated to safely dissipate excess energy and prevent the formation of harmful photoproducts. Regulation is known to be necessary for fitness, but the molecular mechanisms are not... more
In oxygenic photosynthesis, light harvesting is regulated to safely dissipate excess energy and prevent the formation of harmful photoproducts. Regulation is known to be necessary for fitness, but the molecular mechanisms are not understood. One challenge has been that ensemble experiments average over active and dissipative behaviours, preventing identification of distinct states. Here, we use single-molecule spectroscopy to uncover the photoprotective states and dynamics of the light-harvesting complex stress-related 1 (LHCSR1) protein, which is responsible for dissipation in green algae and moss. We discover the existence of two dissipative states. We find that one of these states is activated by pH and the other by carotenoid composition, and that distinct protein dynamics regulate these states. Together, these two states enable the organism to respond to two types of intermittency in solar intensity-step changes (clouds and shadows) and ramp changes (sunrise), respectively. Our...
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Background The light-harvesting antennae of photosystem (PS) I and PSII are pigment-protein complexes responsible of the initial steps of sunlight conversion into chemical energy. In natural environments plants are constantly confronted... more
Background The light-harvesting antennae of photosystem (PS) I and PSII are pigment-protein complexes responsible of the initial steps of sunlight conversion into chemical energy. In natural environments plants are constantly confronted with the variability of the photosynthetically active light spectrum. PSII and PSI operate in series but have different optimal excitation wavelengths. The prompt adjustment of light absorption by photosystems is thus crucial to ensure efficient electron flow needed to sustain downstream carbon fixing reactions. Fast structural rearrangements equilibrate the partition of excitation pressure between PSII and PSI following the enrichment in the red (PSII-favoring) or far-red (PSI-favoring) spectra. Redox imbalances trigger state transitions (ST), a photoacclimation mechanism which involves the reversible phosphorylation/dephosphorylation of light harvesting complex II (LHCII) proteins by the antagonistic activities of the State Transition 7 (STN7) kina...
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The reduction of greenhouse gases (GHGs) emission by replacing fossil energy stocks with carbon–neutral fuels is a major topic of the political and scientific debate on environmental sustainability. Such shift in energy sources is... more
The reduction of greenhouse gases (GHGs) emission by replacing fossil energy stocks with carbon–neutral fuels is a major topic of the political and scientific debate on environmental sustainability. Such shift in energy sources is expected to curtail the accumulation rate of atmospheric CO2, which is a strong infrared absorber and thus contributes to the global warming effect. Although such change would produce desirable outputs, the consequences of a drastic decrease in atmospheric CO2 (the substrate of photosynthesis) should be carefully considered in the light of its potential impact on ecosystems stability and agricultural productivity. Indeed, plants regulate CO2 uptake and water loss through the same anatomical structure: the leaf stomata. A reduced CO2 availability is thus expected to enhance transpiration rate in plants decreasing their water use efficiency and imposing an increased water demand for both agricultural and wild ecosystems. We suggest that this largely underest...
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Photosynthetic microbes are gaining increasing attention as heterologous hosts for the light-driven, low-cost production of high-value recombinant proteins. Recent advances in the manipulation of unicellular algal genomes offer the... more
Photosynthetic microbes are gaining increasing attention as heterologous hosts for the light-driven, low-cost production of high-value recombinant proteins. Recent advances in the manipulation of unicellular algal genomes offer the opportunity to establish engineered strains as safe and viable alternatives to conventional heterotrophic expression systems, including for their use in the feed, food, and biopharmaceutical industries. Due to the relatively small size of their genomes, algal chloroplasts are excellent targets for synthetic biology approaches, and are convenient subcellular sites for the compartmentalized accumulation and storage of products. Different classes of recombinant proteins, including enzymes and peptides with therapeutical applications, have been successfully expressed in the plastid of the model organism Chlamydomonas reinhardtii, and of a few other species, highlighting the emerging potential of transplastomic algal biotechnology. In this review, we provide a...
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Photosynthesis uses sunlight to convert water and carbon dioxide into biomass and oxygen. When in excess, light can be dangerous for the photosynthetic apparatus because it can cause photo-oxidative damage and decreases the efficiency of... more
Photosynthesis uses sunlight to convert water and carbon dioxide into biomass and oxygen. When in excess, light can be dangerous for the photosynthetic apparatus because it can cause photo-oxidative damage and decreases the efficiency of photosynthesis because of photoinhibition. Plants have evolved many photoprotective mechanisms in order to face reactive oxygen species production and thus avoid photoinhibition. These mechanisms include quenching of singlet and triplet excited states of chlorophyll, synthesis of antioxidant molecules and enzymes and repair processes for damaged photosystem II and photosystem I reaction centers. This review focuses on the mechanisms involved in photoprotection of chloroplasts through dissipation of energy absorbed in excess.
Research Interests: Chemistry, Photochemistry, Photosynthesis, Medicine, Antioxidants, and 13 moreChlorophyll, Chlorophyll Fluorescence, Light, Plants, ROS, Singlet Oxygen, Photoprotection, Photosystem II, Chloroplast, Photoinhibition, Biochemistry and cell biology, Non-photochemical quenching, and Medical biochemistry and metabolomics
Carotenoids represent the first line of defence of photosystems against singlet oxygen (1O2) toxicity, because of their capacity to quench the chlorophyll triplet state (3Chl) through a physical mechanism based on the transfer of triplet... more
Carotenoids represent the first line of defence of photosystems against singlet oxygen (1O2) toxicity, because of their capacity to quench the chlorophyll triplet state (3Chl) through a physical mechanism based on the transfer of triplet excitation (triplet–triplet energy transfer, TTET). In previous works, we showed that the antenna LHCII is characterised by a robust photoprotective mechanism, able to adapt to the removal of individual chlorophylls while maintaining a remarkable capacity for 3Chl quenching. In this work, we investigated the effects on this quenching induced in LHCII by the replacement of the lutein bound at the L1 site with violaxanthin and zeaxanthin. We studied LHCII isolated from the Arabidopsis thaliana mutants lut2—in which lutein is replaced by violaxanthin—and lut2 npq2, in which all xanthophylls are replaced constitutively by zeaxanthin. We characterised the photophysics of these systems via optically detected magnetic resonance (ODMR) and time-resolved ele...
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SummaryLand plant chloroplasts differ from algal ones for their thylakoid membranes being organized in grana: piles of vesicles paired by their stromal surface, forming domains including Photosystem (PS) II and its antenna while excluding... more
SummaryLand plant chloroplasts differ from algal ones for their thylakoid membranes being organized in grana: piles of vesicles paired by their stromal surface, forming domains including Photosystem (PS) II and its antenna while excluding PS I and ATPase to stroma membranes, connecting grana stacks. The molecular basis of grana stacking remain unclear. We obtained genotypes lacking the trimeric antenna complex (Lhcb1-2-3), the monomeric Lhcb4-5-6, or both. Full deletion caused loss of grana, while either monomers or trimers support 50% stacking. The expression of Lhcb5 alone restored stacking at 50%, while Lhcb2 alone produced huge grana which broke down upon light exposure. Cyclic electron transport was maintained in the lack of stacking, while excitation energy balance between photosystems and the repair efficiency of damaged Photosystem II were affected. We conclude that grana evolved for need of regulating energy balance between photosystems under terrestrial canopy involving ra...
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Xanthophylls are coloured isoprenoid metabolites synthesized in many organisms with a variety of functions from the attraction of animals for impollination to absorption of light energy for photosynthesis to photoprotection against... more
Xanthophylls are coloured isoprenoid metabolites synthesized in many organisms with a variety of functions from the attraction of animals for impollination to absorption of light energy for photosynthesis to photoprotection against photooxidative stress. The finding by Proctor and co-workers makes a new addition to the last type of functions by showing that zeaxanthin is instrumental in coordinating chlorophyll biosynthesis with the insertion of pigment-binding proteins into the photosynthetic membrane by glueing the protein components catalyzing these functions into a supercomplex and regulating its activity.
Research Interests: Medicine and Biochemical
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Photosynthetic organisms prevent oxidative stress from light energy absorbed in excess through several photoprotective mechanisms. A major component is thermal dissipation of chlorophyll singlet excited states and is called... more
Photosynthetic organisms prevent oxidative stress from light energy absorbed in excess through several photoprotective mechanisms. A major component is thermal dissipation of chlorophyll singlet excited states and is called nonphotochemical quenching (NPQ). NPQ is catalyzed in green algae by protein subunits called LHCSRs (Light Harvesting Complex Stress Related), homologous to the Light Harvesting Complexes (LHC), constituting the antenna system of both photosystem I (PSI) and PSII. We investigated the role of LHCSR1 and LHCSR3 in NPQ activation to verify whether these proteins are involved in thermal dissipation of PSI excitation energy, in addition to their well-known effect on PSII. To this aim, we measured the fluorescence emitted at 77 K by whole cells in a quenched or unquenched state, using green fluorescence protein as the internal standard. We show that NPQ activation by high light treatment in Chlamydomonas reinhardtii leads to energy quenching in both PSI and PSII antenn...
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Energy-dependent quenching of chlorophyll fluorescence (qE) reflects the action of a powerful mechanism of protection from photoinhibition in which the low pH in the chloroplast lumen induces dissipation of excess excitation energy.... more
Energy-dependent quenching of chlorophyll fluorescence (qE) reflects the action of a powerful mechanism of protection from photoinhibition in which the low pH in the chloroplast lumen induces dissipation of excess excitation energy. Dicyclohexylcarbodumide (DCCD), a protein-modifying agent, is a powerful inhibitor of qE and has been shown to react with acidic residues, in a hydrophobic environment, involved in proton translocation. The CP29 subunit of photosystem II has been proposed to be the site of qE quenching and shown to bind DCCD. We have hypothesised, on the basis of the CP29 protein sequence and of the structure of light-harvesting complex II protein, that glutamic acid 166 is the DCCD binding site. In this study, we have produced recombinant proteins either with wildtype sequence or carrying a mutation on the 166 position. We show that the mutant protein does not bind DCCD. This identifies E166 as the site whose protonation may lead to a conformational change triggering qE.
Research Interests: Chemistry, Photosynthesis, Medicine, Chlorophyll, Chlorophyll Fluorescence, and 15 morePage, Molecular cloning, Protein Sequence Analysis, Amino Acid Sequence, Photosystem II, Recombinant Protein, Polyacrylamide Gel Electrophoresis, Recombinant Proteins, Binding Site, Conformational Change, Glutamic Acid, Biochemistry and cell biology, Apoproteins, Molecular Sequence Data, and binding sites
Oxygenic photoautotrophs require mechanisms for rapidly matching the level of chlorophyll excited states from light harvesting with the rate of electron transport from water to carbon dioxide. These photoprotective reactions prevent... more
Oxygenic photoautotrophs require mechanisms for rapidly matching the level of chlorophyll excited states from light harvesting with the rate of electron transport from water to carbon dioxide. These photoprotective reactions prevent formation of reactive excited states and photoinhibition. The fastest response to excess illumination is the so-called non-photochemical quenching which, in higher plants, requires the luminal pH sensor PsbS and other yet unidentified components of the photosystem II antenna. Both trimeric light-harvesting complex II (LHCII) and monomeric LHC proteins have been indicated as site(s) of the heat-dissipative reactions. Different mechanisms have been proposed: energy transfer to a lutein quencher in trimers, formation of a zeaxanthin radical cation in monomers. Here, we report on the construction of a mutant lacking all monomeric LHC proteins but retaining LHCII trimers. Its non-photochemical quenching induction rate was substantially slower with respect to ...
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Light-harvesting complexes (LHCs) are major constituents of the antenna systems in higher plant photosystems. Four Lhca subunits are tightly bound to the photosystem I (PSI) core complex, forming its outer antenna moiety called LHCI. The... more
Light-harvesting complexes (LHCs) are major constituents of the antenna systems in higher plant photosystems. Four Lhca subunits are tightly bound to the photosystem I (PSI) core complex, forming its outer antenna moiety called LHCI. The Arabidopsis thaliana mutant ΔLhca lacks all Lhca1-4 subunits and compensates for its decreased antenna size by binding LHCII trimers, the main constituent of the photosystem II antenna system, to PSI. In this work we have investigated the effect of LHCI/LHCII substitution by comparing the light harvesting and excitation energy transfer efficiency properties of PSI complexes isolated from ΔLhca mutants and from the wild type, as well as the consequences for plant growth. We show that the excitation energy transfer efficiency was not compromised by the substitution of LHCI with LHCII but a significant reduction in the absorption cross-section was observed. The absence of LHCI subunits in PSI thus significantly limits light harvesting, even on LHCII bi...
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Light Harvesting Complex Stress Related 3 (LHCSR3) is the protein essential for photoprotective excess energy dissipation (non-photochemical quenching, NPQ) in the model green alga Chlamydomonas reinhardtii. Activation of NPQ requires low... more
Light Harvesting Complex Stress Related 3 (LHCSR3) is the protein essential for photoprotective excess energy dissipation (non-photochemical quenching, NPQ) in the model green alga Chlamydomonas reinhardtii. Activation of NPQ requires low pH in the thylakoid lumen, which is induced in excess light conditions and sensed by lumen-exposed acidic residues. In this work we have used site-specific mutagenesis in vivo and in vitro for identification of the residues in LHCSR3 that are responsible for sensing lumen pH. Lumen-exposed protonatable residues, aspartate and glutamate, were mutated to asparagine and glutamine, respectively. By expression in a mutant lacking all LHCSR isoforms, residues D117, E221 and E224 were shown to be essential for LHCSR3-dependent NPQ induction in C. reinhardtii. Analysis of recombinant proteins carrying the same mutations refolded in vitro with pigments showed that the capacity of responding to low pH by decreasing the fluorescence lifetime, present in the w...
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Microalgae represent a carbon-neutral source of bulk biomass, for extraction of high-value compounds and production of renewable fuels. Due to their high metabolic activity and reproduction rates, species of the genus Chlorella are highly... more
Microalgae represent a carbon-neutral source of bulk biomass, for extraction of high-value compounds and production of renewable fuels. Due to their high metabolic activity and reproduction rates, species of the genus Chlorella are highly productive when cultivated in photobioreactors. However, wild-type strains show biological limitations making algal bioproducts expensive compared to those extracted from other feedstocks. Such constraints include inhomogeneous light distribution due to high optical density of the culture, and photoinhibition of the surface-exposed cells. Thus, the domestication of algal strains for industry makes it increasingly important to select traits aimed at enhancing light-use efficiency while withstanding excess light stress. Carotenoids have a crucial role in protecting against photooxidative damage and, thus, represent a promising target for algal domestication. We applied chemical mutagenesis to Chlorella vulgaris and selected for enhanced tolerance to ...