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Tomoko Shinomura - One of the best experts on this subject based on the ideXlab platform.

  • Suppression of the phytoene synthase gene (EgcrtB) alters carotenoid content and intracellular structure of Euglena gracilis
    BMC Plant Biology, 2017
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Mika Soshino, Noriko Nagata, Tomoko Shinomura
    Abstract:

    Background Photosynthetic organisms utilize carotenoids for photoprotection as well as light harvesting. Our previous study revealed that high-intensity light increases the expression of the gene for phytoene synthase (Eg crtB ) in Euglena gracilis (a unicellular phytoflagellate), the encoded enzyme catalyzes the first committed step of the carotenoid biosynthesis pathway. To examine carotenoid synthesis of E. gracilis in response to light stress, we analyzed carotenoid species and content in cells grown under various light intensities. In addition, we investigated the effect of suppressing Eg crtB with RNA interference (RNAi) on growth and carotenoid content. Results After cultivation for 7 days under continuous light at 920 μmol m^−2 s^−1, β-carotene, Diadinoxanthin (Ddx), and diatoxanthin (Dtx) content in cells was significantly increased compared with standard light intensity (55 μmol m^−2 s^−1). The high-intensity light (920 μmol m^−2 s^−1) increased the pool size of Diadinoxanthin cycle pigments (i.e., Ddx + Dtx) by 1.2-fold and the Dtx/Ddx ratio from 0.05 (control) to 0.09. In contrast, the higher-intensity light treatment caused a 58% decrease in chlorophyll ( a  +  b ) content and diminished the number of thylakoid membranes in chloroplasts by approximately half compared with control cells, suggesting that the high-intensity light-induced accumulation of carotenoids is associated with an increase in both the number and size of lipid globules in chloroplasts and the cytoplasm. Transient suppression of Eg crtB in this alga by RNAi resulted in significant decreases in cell number, chlorophyll, and total major carotenoid content by 82, 82 and 86%, respectively, relative to non-electroporated cells. Furthermore, suppression of Eg crtB decreased the number of chloroplasts and thylakoid membranes and increased the Dtx/Ddx ratio by 1.6-fold under continuous illumination even at the standard light intensity, indicating that blocking carotenoid synthesis increased the susceptibility of cells to light stress. Conclusions Our results indicate that suppression of Eg crtB causes a significant decrease in carotenoid and chlorophyll content in E. gracilis accompanied by changes in intracellular structures, suggesting that Dtx (de-epoxidized form of Diadinoxanthin cycle pigments) contributes to photoprotection of this alga during the long-term acclimation to light-induced stress.

  • Suppression of the phytoene synthase gene (EgcrtB) alters carotenoid content and intracellular structure of Euglena gracilis.
    BMC plant biology, 2017
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Mika Soshino, Noriko Nagata, Tomoko Shinomura
    Abstract:

    Photosynthetic organisms utilize carotenoids for photoprotection as well as light harvesting. Our previous study revealed that high-intensity light increases the expression of the gene for phytoene synthase (EgcrtB) in Euglena gracilis (a unicellular phytoflagellate), the encoded enzyme catalyzes the first committed step of the carotenoid biosynthesis pathway. To examine carotenoid synthesis of E. gracilis in response to light stress, we analyzed carotenoid species and content in cells grown under various light intensities. In addition, we investigated the effect of suppressing EgcrtB with RNA interference (RNAi) on growth and carotenoid content. After cultivation for 7 days under continuous light at 920 μmol m−2 s−1, β-carotene, Diadinoxanthin (Ddx), and diatoxanthin (Dtx) content in cells was significantly increased compared with standard light intensity (55 μmol m−2 s−1). The high-intensity light (920 μmol m−2 s−1) increased the pool size of Diadinoxanthin cycle pigments (i.e., Ddx + Dtx) by 1.2-fold and the Dtx/Ddx ratio from 0.05 (control) to 0.09. In contrast, the higher-intensity light treatment caused a 58% decrease in chlorophyll (a + b) content and diminished the number of thylakoid membranes in chloroplasts by approximately half compared with control cells, suggesting that the high-intensity light-induced accumulation of carotenoids is associated with an increase in both the number and size of lipid globules in chloroplasts and the cytoplasm. Transient suppression of EgcrtB in this alga by RNAi resulted in significant decreases in cell number, chlorophyll, and total major carotenoid content by 82, 82 and 86%, respectively, relative to non-electroporated cells. Furthermore, suppression of EgcrtB decreased the number of chloroplasts and thylakoid membranes and increased the Dtx/Ddx ratio by 1.6-fold under continuous illumination even at the standard light intensity, indicating that blocking carotenoid synthesis increased the susceptibility of cells to light stress. Our results indicate that suppression of EgcrtB causes a significant decrease in carotenoid and chlorophyll content in E. gracilis accompanied by changes in intracellular structures, suggesting that Dtx (de-epoxidized form of Diadinoxanthin cycle pigments) contributes to photoprotection of this alga during the long-term acclimation to light-induced stress.

  • Additional file 2: Figure S2. of Suppression of the phytoene synthase gene (EgcrtB) alters carotenoid content and intracellular structure of Euglena gracilis
    2017
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Mika Soshino, Noriko Nagata, Tomoko Shinomura
    Abstract:

    Effects of suppressing EgcrtB on carotenoid composition of E. gracilis cells. (A–C) HPLC chromatogram (445 nm) of extracts from E. gracilis cells treated without electroporation or EgcrtB-dsRNA (non-electroporated) (A), or cells treated with (C) or without EgcrtB-dsRNA (B). (Insets) Same chromatograms with an expanded y axis. mAU, milli-absorbance units. 1, neoxanthin; 2, Diadinoxanthin; 3, all trans-diatoxanthin; 4–6, cis-diatoxanthin; 7, chlorophyll b; 8, chlorophyll a; 9, β-carotene (PDF 69 kb

  • Additional file 1: Figure S1. of Suppression of the phytoene synthase gene (EgcrtB) alters carotenoid content and intracellular structure of Euglena gracilis
    2017
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Mika Soshino, Noriko Nagata, Tomoko Shinomura
    Abstract:

    Effects of light intensity on carotenoid composition of E. gracilis cells. (A–E) HPLC chromatogram (445 nm) of extracts from E. gracilis grown under illumination at 27 (A), 55 (B), 240 (C), 460 (D), or 920 μmol m−2 s−1 (E) for 7 days. (Insets) Same chromatograms with an expanded y axis. mAU, milli-absorbance units. 1, neoxanthin; 2, Diadinoxanthin; 3, all trans-diatoxanthin; 4–6, cis-diatoxanthin; 7, chlorophyll b; 8, chlorophyll a; 9, β-carotene (PDF 96 kb

  • identification and functional analysis of the geranylgeranyl pyrophosphate synthase gene crte and phytoene synthase gene crtb for carotenoid biosynthesis in euglena gracilis
    BMC Plant Biology, 2016
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Senji Takahashi, Tomoko Shinomura
    Abstract:

    Background Euglena gracilis, a unicellular phytoflagellate within Euglenida, has attracted much attention as a potential feedstock for renewable energy production. In outdoor open-pond cultivation for biofuel production, excess direct sunlight can inhibit photosynthesis in this alga and decrease its productivity. Carotenoids play important roles in light harvesting during photosynthesis and offer photoprotection for certain non-photosynthetic and photosynthetic organisms including cyanobacteria, algae, and higher plants. Although, Euglenida contains β-carotene and xanthophylls (such as zeaxanthin, diatoxanthin, Diadinoxanthin and 9′-cis neoxanthin), the pathway of carotenoid biosynthesis has not been elucidated.

Reimund Goss - One of the best experts on this subject based on the ideXlab platform.

  • Lipid Dependence of Xanthophyll Cycling in Higher Plants and Algae.
    Frontiers in plant science, 2020
    Co-Authors: Reimund Goss, Dariusz Latowski
    Abstract:

    The xanthophyll cycles of higher plants and algae represent an important photoprotection mechanism. Two main xanthophyll cycles are known, the violaxanthin cycle of higher plants, green and brown algae and the Diadinoxanthin cycle of Bacillariophyceae, Xanthophyceae, Haptophyceae, and Dinophyceae. The forward reaction of the xanthophyll cycles consists of the enzymatic de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin or Diadinoxanthin to diatoxanthin during periods of high light illumination. It is catalyzed by the enzymes violaxanthin or Diadinoxanthin de-epoxidase. During low light or darkness the back reaction of the cycle, which is catalyzed by the enzymes zeaxanthin or diatoxanthin epoxidase, restores the epoxidized xanthophylls by a re-introduction of the epoxy groups. The de-epoxidation reaction takes place in the lipid phase of the thylakoid membrane and thus, depends on the nature, three dimensional structure and function of the thylakoid lipids. As the xanthophyll cycle pigments are usually associated with the photosynthetic light-harvesting proteins, structural re-arrangements of the proteins and changes in the protein-lipid interactions play an additional role for the operation of the xanthophyll cycles. In the present review we give an introduction to the lipid and fatty acid composition of thylakoid membranes of higher plants and algae. We introduce the readers to the reaction sequences, enzymes and function of the different xanthophyll cycles. The main focus of the review lies on the lipid dependence of xanthophyll cycling. We summarize the current knowledge about the role of lipids in the solubilization of xanthophyll cycle pigments. We address the importance of the three-dimensional lipid structures for the enzymatic xanthophyll conversion, with a special focus on non-bilayer lipid phases which are formed by the main thylakoid membrane lipid monogalactosyldiacylglycerol. We additionally describe how lipids and light-harvesting complexes interact in the thylakoid membrane and how these interactions can affect the structure of the thylakoids. In a dedicated chapter we offer a short overview of current membrane models, including the concept of membrane domains. We then use these concepts to present a model of the operative xanthophyll cycle as a transient thylakoid membrane domain which is formed during high light illumination of plants or algal cells.

  • Effect of Lipids on Violaxanthin and Diadinoxanthin De-Epoxidation
    Advanced Topics in Science and Technology in China, 2013
    Co-Authors: Dariusz Latowski, Reimund Goss, Susann Schaller, Joanna Grzyb, Kazimierz Strzałka
    Abstract:

    Violaxanthin (Vx) and Diadinoxanthin (Ddx) de-epoxidation are light dependent steps in one of the most important photoprotecting processes called respectively violaxanthin and Diadinoxanthin cycle. Violaxanthin cycle operates in vascular plants and many groups of algae while Diadinoxanthin cycle is present in diatoms. In this study the influence of lipids on de-epoxidation of Vx and Ddx was investigated. In particular, the dependence between conversion of Vx into antheraxanthin and zeaxanthin as well as Ddx to diatoxanthin and the molecular dynamics of hydrophobic fraction of aggregates formed by inverted micelles, which are necessary for de-epoxidation, was studied. Thickness of the hydrophobic fraction of the aggregates, size of the inverted micelles, suggested by mathematical description of these structures and solubility of Vx and Ddx in various kind of lipids were the other tested parameters. Obtained results show that the rate of de-epoxidation is strongly dependent on physical/chemical properties of lipids. The key role for violaxanthin or Diadinoxanthin de-epoxidase activation play non-bilayer lipids and the parameters of inverted micelles created by them, such as thickness, diameter and molecular dynamics of their hydrophobic core.

  • Violaxanthin and Diadinoxanthin de-epoxidation in various model lipid systems.
    Acta biochimica Polonica, 2012
    Co-Authors: Dariusz Latowski, Reimund Goss, Monika Bojko, Kazimierz Strzałka
    Abstract:

    The xanthophyll cycle is an important photoprotective process functioning in plants. One of its forms, the violaxanthin (Vx) cycle, involves interconversion between: Vx, antheraxanthin (Ax) and zeaxanthin (Zx). Another kind of the xanthophyll cycle is the Diadinoxanthin (Ddx) cycle in which interconversion between Ddx and diatoxanthin (Dtx) occurs. In this study an information on molecular mechanism and regulation of these two types of the xanthophyll cycle is presented. The influence of lipids on the de-epoxidation of the xanthophyll cycle pigments was investigated, with special focus put on the significance of physical properties of the aggregates formed by inverted lipid micelles, which are necessary for activity of the xanthophyll cycle enzymes. In particular, thickness of the hydrophobic fraction of the aggregates, size of the inverted micelles, suggested by mathematical description of the structures and solubility of Vx and Ddx in various kind of lipids were studied. Obtained results show that the rate of de-epoxidation is strongly dependent on the physicochemical properties of the lipids used. The key role for enzyme activation play non-bilayer lipids and the parameters of inverted micelles such as thickness, fluidity of hydrophobic core and their diameter. The presented results show that MGDG and other non-lamellar lipids like different forms of phosphatidylethanolamine are necessary for the Vx and Ddx de-epoxidation because they provide the three-dimensional structures, which are needed for the binding of de-epoxidases and for the accessibility of Vx and Ddx to these enzymes.

  • Evidence for the Existence of One Antenna-Associated, Lipid-Dissolved and Two Protein-Bound Pools of Diadinoxanthin Cycle Pigments in Diatoms
    Plant physiology, 2010
    Co-Authors: Bernard Lepetit, Christian Wilhelm, Daniela Volke, Matthias Gilbert, Reimund Goss
    Abstract:

    We studied the localization of Diadinoxanthin cycle pigments in the diatoms Cyclotella meneghiniana and Phaeodactylum tricornutum. Isolation of pigment protein complexes revealed that the majority of high-light-synthesized Diadinoxanthin and diatoxanthin is associated with the fucoxanthin chlorophyll protein (FCP) complexes. The characterization of intact cells, thylakoid membranes, and pigment protein complexes by absorption and low-temperature fluorescence spectroscopy showed that the FCPs contain certain amounts of protein-bound Diadinoxanthin cycle pigments, which are not significantly different in high-light and low-light cultures. The largest part of high-light-formed Diadinoxanthin cycle pigments, however, is not bound to antenna apoproteins but located in a lipid shield around the FCPs, which is copurified with the complexes. This lipid shield is primarily composed of the thylakoid membrane lipid monogalactosyldiacylglycerol. We also show that the photosystem I (PSI) fraction contains a tightly connected FCP complex that is enriched in protein-bound Diadinoxanthin cycle pigments. The peripheral FCP and the FCP associated with PSI are composed of different apoproteins. Tandem mass spectrometry analysis revealed that the peripheral FCP is composed mainly of the light-harvesting complex protein Lhcf and also significant amounts of Lhcr. The PSI fraction, on the other hand, shows an enrichment of Lhcr proteins, which are thus responsible for the Diadinoxanthin cycle pigment binding. The existence of lipid-dissolved and protein-bound Diadinoxanthin cycle pigments in the peripheral antenna and in PSI is discussed with respect to different specific functions of the xanthophylls.

  • regulation and function of xanthophyll cycle dependent photoprotection in algae
    Photosynthesis Research, 2010
    Co-Authors: Reimund Goss, Torsten Jakob
    Abstract:

    The xanthophyll cycle represents one of the important photoprotection mechanisms in plant cells. In the present review, we summarize current knowledge about the violaxanthin cycle of vascular plants, green and brown algae, and the Diadinoxanthin cycle of the algal classes Bacillariophyceae, Xanthophyceae, Haptophyceae, and Dinophyceae. We address the biochemistry of the xanthophyll cycle enzymes with a special focus on protein structure, co-substrate requirements and regulation of enzyme activity. We present recent ideas regarding the structural basis of xanthophyll cycle-dependent photoprotection, including different models for the mechanism of non-photochemical quenching of chlorophyll a fluorescence. In a dedicated chapter, we also describe the unique violaxanthin antheraxanthin cycle of the Prasinophyceae, together with its implication for the mechanism of xanthophyll cycle-dependent heat dissipation. The interaction between the Diadinoxanthin cycle and alternative electron flow pathways in the chloroplasts of diatoms is an additional topic of this review, and in the last chapter we cover aspects of the importance of xanthophyll cycle-dependent photoprotection for different algal species in their natural environments.

Christian Wilhelm - One of the best experts on this subject based on the ideXlab platform.

  • Evidence for the Existence of One Antenna-Associated, Lipid-Dissolved and Two Protein-Bound Pools of Diadinoxanthin Cycle Pigments in Diatoms
    Plant physiology, 2010
    Co-Authors: Bernard Lepetit, Christian Wilhelm, Daniela Volke, Matthias Gilbert, Reimund Goss
    Abstract:

    We studied the localization of Diadinoxanthin cycle pigments in the diatoms Cyclotella meneghiniana and Phaeodactylum tricornutum. Isolation of pigment protein complexes revealed that the majority of high-light-synthesized Diadinoxanthin and diatoxanthin is associated with the fucoxanthin chlorophyll protein (FCP) complexes. The characterization of intact cells, thylakoid membranes, and pigment protein complexes by absorption and low-temperature fluorescence spectroscopy showed that the FCPs contain certain amounts of protein-bound Diadinoxanthin cycle pigments, which are not significantly different in high-light and low-light cultures. The largest part of high-light-formed Diadinoxanthin cycle pigments, however, is not bound to antenna apoproteins but located in a lipid shield around the FCPs, which is copurified with the complexes. This lipid shield is primarily composed of the thylakoid membrane lipid monogalactosyldiacylglycerol. We also show that the photosystem I (PSI) fraction contains a tightly connected FCP complex that is enriched in protein-bound Diadinoxanthin cycle pigments. The peripheral FCP and the FCP associated with PSI are composed of different apoproteins. Tandem mass spectrometry analysis revealed that the peripheral FCP is composed mainly of the light-harvesting complex protein Lhcf and also significant amounts of Lhcr. The PSI fraction, on the other hand, shows an enrichment of Lhcr proteins, which are thus responsible for the Diadinoxanthin cycle pigment binding. The existence of lipid-dissolved and protein-bound Diadinoxanthin cycle pigments in the peripheral antenna and in PSI is discussed with respect to different specific functions of the xanthophylls.

  • The lipid dependence of Diadinoxanthin de-epoxidation presents new evidence for a macrodomain organization of the diatom thylakoid membrane
    Journal of plant physiology, 2009
    Co-Authors: Reimund Goss, Bernard Lepetit, Jana Nerlich, Susann Schaller, Astrid Vieler, Christian Wilhelm
    Abstract:

    The present study shows that thylakoid membranes of the diatom Cyclotella meneghiniana contain much higher amounts of negatively charged lipids than higher plant or green algal thylakoids. Based on these findings, we examined the influence of SQDG on the de-epoxidation reaction of the Diadinoxanthin cycle and compared it with results from the second negatively charged thylakoid lipid PG. SQDG and PG exhibited a lower capacity for the solubilization of the hydrophobic xanthophyll cycle pigment Diadinoxanthin than the main membrane lipid MGDG. Although complete pigment solubilization took place at higher concentrations of the negatively charged lipids, SQDG and PG strongly suppressed the de-epoxidation of Diadinoxanthin in artificial membrane systems. In in vitro assays employing the isolated Diadinoxanthin cycle enzyme Diadinoxanthin de-epoxidase, no or only a very weak de-epoxidation reaction was observed in the presence of SQDG or PG, respectively. In binary mixtures of the inverted hexagonal phase forming lipid MGDG with the negatively charged bilayer lipids, comparable suppression took place. This is in contrast to binary mixtures of MGDG with the neutral bilayer lipids DGDG and PC, where rapid and efficient de-epoxidation was observed. In complex lipid mixtures resembling the lipid composition of the native diatom thylakoid membrane, we again found strong suppression of Diadinoxanthin de-epoxidation due to the presence of SQDG or PG. We conclude that, in the native thylakoids of diatoms, a strict separation of the MGDG and SQDG domains must occur; otherwise, the rapid Diadinoxanthin de-epoxidation observed in intact cells upon illumination would not be possible.

  • the regulation of xanthophyll cycle activity and of non photochemical fluorescence quenching by two alternative electron flows in the diatoms phaeodactylum tricornutum and cyclotella meneghiniana
    Biochimica et Biophysica Acta, 2009
    Co-Authors: Irina Grouneva, Torsten Jakob, Christian Wilhelm, Reimund Goss
    Abstract:

    Intact cells of diatoms are characterized by a rapid diatoxanthin epoxidation during low light periods following high light illumination while epoxidation is severely restricted in phases of complete darkness. The present study shows that rapid diatoxanthin epoxidation is dependent on the availability of the cofactor of diatoxanthin epoxidase, NADPH, which cannot be generated in darkness due to the inactivity of PSI. In the diatom Phaeodactylum tricornutum, NADPH production during low light is dependent on PSII activity, and addition of DCMU consequently abolishes diatoxanthin epoxidation. In contrast to P. tricornutum, DCMU does not affect diatoxanthin epoxidation in Cyclotella meneghiniana, which shows the same rapid epoxidation in low light both in the absence or presence of DCMU. Measurements of the reduction state of the PQ pool and PSI activity indicate that, in the presence of DCMU, NADPH production in C. meneghiniana occurs via alternative electron transport, which includes electron donation from the chloroplast stroma to the PQ pool and, in a second step, from PQ to PSI. Similar electron flow to PQ is also observed during high light illumination of DCMU-treated P. tricornutum cells. In contrast to C. meneghiniana, the electrons are not directed to PSI, but most likely to a plastoquinone oxidase. This chlororespiratory electron transport leads to the establishment of an uncoupler-sensitive proton gradient in the presence of DCMU, which induces Diadinoxanthin de-epoxidation and NPQ. In C. meneghiniana, electron flow to the plastoquinone oxidase is restricted, and consequently, Diadinoxanthin de-epoxidation and NPQ is not observed after addition of DCMU.

  • A New Multicomponent NPQ Mechanism in the Diatom Cyclotella meneghiniana
    Plant and Cell Physiology, 2008
    Co-Authors: Irina Grouneva, Torsten Jakob, Christian Wilhelm, Reimund Goss
    Abstract:

    In the present study we report that in the diatom Cyclotella meneghiniana the diatoxanthin-dependent non-photochemical quenching of chlorophyll fluorescence (NPQ) is heterogeneous and consists of three different components. (i) A transient NPQ component that generates immediately upon illumination, depends on the transthylakoid proton gradient as well as on the light intensity, and is modulated by the initial diatoxanthin content of the cells. It is located in the antenna complexes of C. meneghiniana and is comparable with the transient NPQ observed in vascular plants. (ii) A steady-state NPQ component is observed during later stages of the high-light illumination and depends on the diatoxanthin content formed by the light-activated Diadinoxanthin cycle. (iii) A fast relaxing NPQ component is seen upon a transition of high-light-illuminated cells to complete darkness. This component relaxes within a time frame of tens of seconds and its extent is correlated with the amount of diatoxanthin formed during the phase of actinic illumination. It cannot be observed in dithiothreitol-treated cells where the de-epoxidation of Diadinoxanthin to diatoxanthin is suppressed. The fast relaxing component can be interpreted as a relaxation of part of the steady-state NPQ. The different diatoxanthin-dependent components are characterized by different quenching efficiencies of diatoxanthin. Diatoxanthin involved in the transient NPQ exhibits a 2-fold higher quenching efficiency compared with diatoxanthin participating in the steady-state NPQ. It is proposed that the different quenching efficiencies of diatoxanthin are caused by the existence of different diatoxanthin pools within the antenna system of C. meneghiniana.

  • Xanthophyll synthesis in diatoms: quantification of putative intermediates and comparison of pigment conversion kinetics with rate constants derived from a model.
    Planta, 2001
    Co-Authors: Martin Lohr, Christian Wilhelm
    Abstract:

    Recently, we reported the presence of the violaxanthin-antheraxanthin-zeaxanthin cycle in diatoms, and showed that violaxanthin is the putative precursor of both Diadinoxanthin and fucoxanthin in the diatom Phaeodactylum tricornutum Bohlin (M. Lohr and C. Wilhelm, 1999, Proc. Natl. Acad. Sci. USA 96: 8784–8789). In the present study, two possible intermediates in the synthesis of violaxanthin from β-carotene were identified in P. tricornutum, namely β-cryptoxanthin and β-cryptoxanthin epoxide. In low light, the latter pigment prevails, but in high light β-cryptoxanthin accumulates, probably as the result of an increased activity of the xantophyll-cycle de-epoxidase. The apparent kinetics of several xanthophyll conversion steps were determined for P. tricornutum and Cyclotella meneghiniana Kutzing. The experimentally determined conversion rates were used to evaluate the hypothetical pathway of xanthophyll synthesis in diatoms. For this purpose a mathematical model was developed which allows the calculation of theoretical rates of pigment conversion for microalgae under steady-state growth conditions. A comparison between measured and calculated conversion rates agreed well with the proposal of a sequential synthesis of fucoxanthin via violaxanthin and Diadinoxanthin. The postulation of zeaxanthin as an obligatory intermediate in the synthesis of violaxanthin, however, resulted in large discrepancies between the measured and calculated rates of its epoxidation. Instead of zeaxanthin, β-cryptoxanthin epoxide may be involved in the biosynthesis of violaxanthin in diatoms.

Johann Lavaud - One of the best experts on this subject based on the ideXlab platform.

  • Diversity in Xanthophyll Cycle Pigments Content and Related Nonphotochemical Quenching (NPQ) Among Microalgae: Implications for Growth Strategy and Ecology.
    Journal of phycology, 2020
    Co-Authors: Thomas Lacour, Marcel Babin, Johann Lavaud
    Abstract:

    Xanthophyll cycle‐related non‐photochemical quenching, which is present in most photoautotrophs, allows dissipating excess light energy. Xanthophyll cycle‐related NPQ depends principally on xanthophyll cycle pigments composition and their effective involvement in non‐photochemical quenching. Xanthophyll cycle‐related NPQ is tightly controlled by environmental conditions in a species/strain specific manner. These features are especially relevant in microalgae living in a complex and highly variable environment. The goal of this study was to perform a comparative assessment of non‐photochemical quenching ecophysiologies across microalgal taxa in order to underline specific involvement of non‐photochemical quenching in growth adaptations and strategies. We used both published results and data acquired in our laboratory to understand the relationships between growth conditions (irradiance, temperature and nutrient availability), xanthophyll cycle composition and xanthophyll cycle pigments quenching efficiency in microalgae from various taxa. We found that in Diadinoxanthin‐containing species, the xanthophyll cycle pigment pool is controlled by energy pressure in all species. At any given energy pressure, however, the diatoxanthin content is higher in diatoms than in other Diadinoxanthin‐containing species. XC pigments quenching efficiency is species‐specific and decreases with acclimation to higher irradiances. We found a clear link between the natural light environment of species/ecotypes and quenching efficiency amplitude. The presence of diatoxanthin or zeaxanthin at steady state in all species examined at moderate and high irradiances suggests that cells maintain a light‐harvesting capacity in excess to cope with potential decrease in light intensity.

  • Diversity in xanthophyll cycle pigments content and related non-photochemical quenching (NPQ) among microalgae: implications for growth strategy and ecology
    Journal of Phycology, 2019
    Co-Authors: Thomas Lacour, Marcel Babin, Johann Lavaud
    Abstract:

    Xanthophyll cycle‐related non‐photochemical quenching, which is present in most photoautotrophs, allows dissipating excess light energy. Xanthophyll cycle‐related NPQ depends principally on xanthophyll cycle pigments composition and their effective involvement in non‐photochemical quenching. Xanthophyll cycle‐related NPQ is tightly controlled by environmental conditions in a species/strain specific manner. These features are especially relevant in microalgae living in a complex and highly variable environment. The goal of this study was to perform a comparative assessment of non‐photochemical quenching ecophysiologies across microalgal taxa in order to underline specific involvement of non‐photochemical quenching in growth adaptations and strategies. We used both published results and data acquired in our laboratory to understand the relationships between growth conditions (irradiance, temperature and nutrient availability), xanthophyll cycle composition and xanthophyll cycle pigments quenching efficiency in microalgae from various taxa. We found that in Diadinoxanthin‐containing species, the xanthophyll cycle pigment pool is controlled by energy pressure in all species. At any given energy pressure, however, the diatoxanthin content is higher in diatoms than in other Diadinoxanthin‐containing species. XC pigments quenching efficiency is species‐specific and decreases with acclimation to higher irradiances. We found a clear link between the natural light environment of species/ecotypes and quenching efficiency amplitude. The presence of diatoxanthin or zeaxanthin at steady state in all species examined at moderate and high irradiances suggests that cells maintain a light‐harvesting capacity in excess to cope with potential decrease in light intensity.

  • The light-harvesting antenna of the diatom Phaeodactylum tricornutum: Evidence for a Diadinoxanthin binding sub-complex
    FEBS Journal, 2005
    Co-Authors: Gérard Guglielmi, Johann Lavaud, Bernard Rousseau, Anne-lise Etienne, Jean Houmard, Alexander V. Ruban
    Abstract:

    Diatoms differ from higher plants by their antenna system, in terms of both polypeptide and pigment contents. A rapid isolation procedure was designed for the membrane-intrinsic light harvesting complexes (LHC) of the diatom Phaeodactylum tricornutum to establish whether different LHC subcomplexes exist, as well to determine an uneven distribution between them of pigments and polypeptides. Two distinct fractions were separated that contain functional oligomeric complexes. The major and more stable complex (≈ 75% of total polypeptides) carries most of the chlorophyll a, and almost only one type of carotenoid, fucoxanthin. The minor complex, carrying ≈ 10–15% of the total antenna chlorophyll and only a little chlorophyll c, is highly enriched in Diadinoxanthin, the main xanthophyll cycle carotenoid. The two complexes also differ in their polypeptide composition, suggesting specialized functions within the antenna. The Diadinoxanthin-enriched complex could be where the de-epoxidation of Diadinoxanthin into diatoxanthin mostly occurs.

  • The light-harvesting antenna of the diatom Phaeodactylum tricornutum. Evidence for a Diadinoxanthin-binding subcomplex.
    The FEBS journal, 2005
    Co-Authors: Gérard Guglielmi, Johann Lavaud, Bernard Rousseau, Anne-lise Etienne, Jean Houmard, Alexander V. Ruban
    Abstract:

    Diatoms differ from higher plants by their antenna system, in terms of both polypeptide and pigment contents. A rapid isolation procedure was designed for the membrane-intrinsic light harvesting complexes (LHC) of the diatom Phaeodactylum tricornutum to establish whether different LHC subcomplexes exist, as well to determine an uneven distribution between them of pigments and polypeptides. Two distinct fractions were separated that contain functional oligomeric complexes. The major and more stable complex (≈ 75% of total polypeptides) carries most of the chlorophyll a, and almost only one type of carotenoid, fucoxanthin. The minor complex, carrying ≈ 10–15% of the total antenna chlorophyll and only a little chlorophyll c, is highly enriched in Diadinoxanthin, the main xanthophyll cycle carotenoid. The two complexes also differ in their polypeptide composition, suggesting specialized functions within the antenna. The Diadinoxanthin-enriched complex could be where the de-epoxidation of Diadinoxanthin into diatoxanthin mostly occurs.

  • In diatoms, a transthylakoid proton gradient alone is not sufficient to induce a non-photochemical fluorescence quenching.
    FEBS Letters, 2002
    Co-Authors: Johann Lavaud, Bernard Rousseau, Anne-lise Etienne
    Abstract:

    Non-photochemical fluorescence quenching (NPQ) in diatoms is associated with a xanthophyll cycle involving Diadinoxanthin (DD) and its de-epoxidized form, diatoxanthin (DT). In higher plants, an obligatory role of de-epoxidized xanthophylls in NPQ remains controversial and the presence of a transthylakoid proton gradient (ΔpH) alone may induce NPQ. We used inhibitors to alter the amplitude of ΔpH and/or DD de-epoxidation, and coupled NPQ. No ΔpH-dependent quenching was detected in the absence of DT. In diatoms, both ΔpH and DT are required for NPQ. The binding of DT to protonated antenna sites could be obligatory for energy dissipation.

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  • Carotenoid accumulation in the eyespot apparatus required for phototaxis is independent of chloroplast development in Euglena gracilis
    Plant science : an international journal of experimental plant biology, 2020
    Co-Authors: Shun Tamaki, Shota Kato, Takahiro Ishikawa, Takashi Maoka, Yuri Tanno, Kazunari Ozasa, Mayumi Wakazaki, Mayuko Sato, Kiminori Toyooka, Mizuo Maeda
    Abstract:

    Abstract Euglena gracilis exhibits photomovements in response to various light stimuli, such as phototactic and photophobic responses. Our recent study revealed that carotenoids in the eyespot apparatus are required for triggering phototaxis in this alga. However, the role of chloroplasts in eyespot formation is not understood. Here, we isolated carotenoid-less (cl) strains of E. gracilis from cells silenced gene expression of phytoene synthase (EgcrtB). Unlike WT, the culture colors of cl1, cl3, and the non-photosynthetic mutant SM-ZK were orange, while that of cl4 was white. Electron microscope observations showed that SM-ZK, cl1, and cl3 had no developed chloroplast and formed a normal eyespot apparatus, similar to that of WT, but this was not the case for cl4. Carotenoids detected in WT were Diadinoxanthin, neoxanthin, and β-carotene. However, the most abundant species of SM-ZK, cl1, and cl3 was zeaxanthin, and there was no Diadinoxanthin or neoxanthin. Photomovement analysis showed that SM-ZK, cl1, and cl3 exhibited negative phototactic and photophobic responses, similar to those of WT, whereas cl4 lacked negative phototaxis. Taken together, the formation of the eyespot apparatus required for phototaxis is independent of chloroplast development in E. gracilis, suggesting that this property is different from other photosynthetic flagellates.

  • Suppression of the phytoene synthase gene (EgcrtB) alters carotenoid content and intracellular structure of Euglena gracilis
    BMC Plant Biology, 2017
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Mika Soshino, Noriko Nagata, Tomoko Shinomura
    Abstract:

    Background Photosynthetic organisms utilize carotenoids for photoprotection as well as light harvesting. Our previous study revealed that high-intensity light increases the expression of the gene for phytoene synthase (Eg crtB ) in Euglena gracilis (a unicellular phytoflagellate), the encoded enzyme catalyzes the first committed step of the carotenoid biosynthesis pathway. To examine carotenoid synthesis of E. gracilis in response to light stress, we analyzed carotenoid species and content in cells grown under various light intensities. In addition, we investigated the effect of suppressing Eg crtB with RNA interference (RNAi) on growth and carotenoid content. Results After cultivation for 7 days under continuous light at 920 μmol m^−2 s^−1, β-carotene, Diadinoxanthin (Ddx), and diatoxanthin (Dtx) content in cells was significantly increased compared with standard light intensity (55 μmol m^−2 s^−1). The high-intensity light (920 μmol m^−2 s^−1) increased the pool size of Diadinoxanthin cycle pigments (i.e., Ddx + Dtx) by 1.2-fold and the Dtx/Ddx ratio from 0.05 (control) to 0.09. In contrast, the higher-intensity light treatment caused a 58% decrease in chlorophyll ( a  +  b ) content and diminished the number of thylakoid membranes in chloroplasts by approximately half compared with control cells, suggesting that the high-intensity light-induced accumulation of carotenoids is associated with an increase in both the number and size of lipid globules in chloroplasts and the cytoplasm. Transient suppression of Eg crtB in this alga by RNAi resulted in significant decreases in cell number, chlorophyll, and total major carotenoid content by 82, 82 and 86%, respectively, relative to non-electroporated cells. Furthermore, suppression of Eg crtB decreased the number of chloroplasts and thylakoid membranes and increased the Dtx/Ddx ratio by 1.6-fold under continuous illumination even at the standard light intensity, indicating that blocking carotenoid synthesis increased the susceptibility of cells to light stress. Conclusions Our results indicate that suppression of Eg crtB causes a significant decrease in carotenoid and chlorophyll content in E. gracilis accompanied by changes in intracellular structures, suggesting that Dtx (de-epoxidized form of Diadinoxanthin cycle pigments) contributes to photoprotection of this alga during the long-term acclimation to light-induced stress.

  • Suppression of the phytoene synthase gene (EgcrtB) alters carotenoid content and intracellular structure of Euglena gracilis.
    BMC plant biology, 2017
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Mika Soshino, Noriko Nagata, Tomoko Shinomura
    Abstract:

    Photosynthetic organisms utilize carotenoids for photoprotection as well as light harvesting. Our previous study revealed that high-intensity light increases the expression of the gene for phytoene synthase (EgcrtB) in Euglena gracilis (a unicellular phytoflagellate), the encoded enzyme catalyzes the first committed step of the carotenoid biosynthesis pathway. To examine carotenoid synthesis of E. gracilis in response to light stress, we analyzed carotenoid species and content in cells grown under various light intensities. In addition, we investigated the effect of suppressing EgcrtB with RNA interference (RNAi) on growth and carotenoid content. After cultivation for 7 days under continuous light at 920 μmol m−2 s−1, β-carotene, Diadinoxanthin (Ddx), and diatoxanthin (Dtx) content in cells was significantly increased compared with standard light intensity (55 μmol m−2 s−1). The high-intensity light (920 μmol m−2 s−1) increased the pool size of Diadinoxanthin cycle pigments (i.e., Ddx + Dtx) by 1.2-fold and the Dtx/Ddx ratio from 0.05 (control) to 0.09. In contrast, the higher-intensity light treatment caused a 58% decrease in chlorophyll (a + b) content and diminished the number of thylakoid membranes in chloroplasts by approximately half compared with control cells, suggesting that the high-intensity light-induced accumulation of carotenoids is associated with an increase in both the number and size of lipid globules in chloroplasts and the cytoplasm. Transient suppression of EgcrtB in this alga by RNAi resulted in significant decreases in cell number, chlorophyll, and total major carotenoid content by 82, 82 and 86%, respectively, relative to non-electroporated cells. Furthermore, suppression of EgcrtB decreased the number of chloroplasts and thylakoid membranes and increased the Dtx/Ddx ratio by 1.6-fold under continuous illumination even at the standard light intensity, indicating that blocking carotenoid synthesis increased the susceptibility of cells to light stress. Our results indicate that suppression of EgcrtB causes a significant decrease in carotenoid and chlorophyll content in E. gracilis accompanied by changes in intracellular structures, suggesting that Dtx (de-epoxidized form of Diadinoxanthin cycle pigments) contributes to photoprotection of this alga during the long-term acclimation to light-induced stress.

  • Additional file 2: Figure S2. of Suppression of the phytoene synthase gene (EgcrtB) alters carotenoid content and intracellular structure of Euglena gracilis
    2017
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Mika Soshino, Noriko Nagata, Tomoko Shinomura
    Abstract:

    Effects of suppressing EgcrtB on carotenoid composition of E. gracilis cells. (A–C) HPLC chromatogram (445 nm) of extracts from E. gracilis cells treated without electroporation or EgcrtB-dsRNA (non-electroporated) (A), or cells treated with (C) or without EgcrtB-dsRNA (B). (Insets) Same chromatograms with an expanded y axis. mAU, milli-absorbance units. 1, neoxanthin; 2, Diadinoxanthin; 3, all trans-diatoxanthin; 4–6, cis-diatoxanthin; 7, chlorophyll b; 8, chlorophyll a; 9, β-carotene (PDF 69 kb

  • Additional file 1: Figure S1. of Suppression of the phytoene synthase gene (EgcrtB) alters carotenoid content and intracellular structure of Euglena gracilis
    2017
    Co-Authors: Shota Kato, Shinichi Takaichi, Takahiro Ishikawa, Masashi Asahina, Mika Soshino, Noriko Nagata, Tomoko Shinomura
    Abstract:

    Effects of light intensity on carotenoid composition of E. gracilis cells. (A–E) HPLC chromatogram (445 nm) of extracts from E. gracilis grown under illumination at 27 (A), 55 (B), 240 (C), 460 (D), or 920 μmol m−2 s−1 (E) for 7 days. (Insets) Same chromatograms with an expanded y axis. mAU, milli-absorbance units. 1, neoxanthin; 2, Diadinoxanthin; 3, all trans-diatoxanthin; 4–6, cis-diatoxanthin; 7, chlorophyll b; 8, chlorophyll a; 9, β-carotene (PDF 96 kb