| 1. |
- Bailleul, Benjamin, et al.
(author)
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Energetic coupling between plastids and mitochondria drives CO2 assimilation in diatoms.
- 2015
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 524:7565, s. 366-9
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Journal article (peer-reviewed)abstract
- Diatoms are one of the most ecologically successful classes of photosynthetic marine eukaryotes in the contemporary oceans. Over the past 30 million years, they have helped to moderate Earth's climate by absorbing carbon dioxide from the atmosphere, sequestering it via the biological carbon pump and ultimately burying organic carbon in the lithosphere. The proportion of planetary primary production by diatoms in the modern oceans is roughly equivalent to that of terrestrial rainforests. In photosynthesis, the efficient conversion of carbon dioxide into organic matter requires a tight control of the ATP/NADPH ratio which, in other photosynthetic organisms, relies principally on a range of plastid-localized ATP generating processes. Here we show that diatoms regulate ATP/NADPH through extensive energetic exchanges between plastids and mitochondria. This interaction comprises the re-routing of reducing power generated in the plastid towards mitochondria and the import of mitochondrial ATP into the plastid, and is mandatory for optimized carbon fixation and growth. We propose that the process may have contributed to the ecological success of diatoms in the ocean.
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| 2. |
- Bo, Davide Dal, et al.
(author)
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Consequences of Mixotrophy on Cell Energetic Metabolism in Microchloropsis gaditana Revealed by Genetic Engineering and Metabolic Approaches
- 2021
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In: Frontiers in Plant Science. - : Frontiers Media S.A.. - 1664-462X. ; 12
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Journal article (peer-reviewed)abstract
- Algae belonging to the Microchloropsis genus are promising organisms for biotech purposes, being able to accumulate large amounts of lipid reserves. These organisms adapt to different trophic conditions, thriving in strict photoautotrophic conditions, as well as in the concomitant presence of light plus reduced external carbon as energy sources (mixotrophy). In this work, we investigated the mixotrophic responses of Microchloropsis gaditana (formerly Nannochloropsis gaditana). Using the Biolog growth test, in which cells are loaded into multiwell plates coated with different organic compounds, we could not find a suitable substrate for Microchloropsis mixotrophy. By contrast, addition of the Lysogeny broth (LB) to the inorganic growth medium had a benefit on growth, enhancing respiratory activity at the expense of photosynthetic performances. To further dissect the role of respiration in Microchloropsis mixotrophy, we focused on the mitochondrial alternative oxidase (AOX), a protein involved in energy management in other algae prospering in mixotrophy. Knocking-out the AOX1 gene by transcription activator-like effector nuclease (TALE-N) led to the loss of capacity to implement growth upon addition of LB supporting the hypothesis that the effect of this medium was related to a provision of reduced carbon. We conclude that mixotrophic growth in Microchloropsis is dominated by respiratory rather than by photosynthetic energetic metabolism and discuss the possible reasons for this behavior in relationship with fatty acid breakdown via β-oxidation in this oleaginous alga.
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| 3. |
- Boudière, Laurence, et al.
(author)
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Glycerolipids in photosynthesis : composition, synthesis and trafficking.
- 2014
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In: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1837:4, s. 470-80
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Journal article (peer-reviewed)abstract
- Glycerolipids constituting the matrix of photosynthetic membranes, from cyanobacteria to chloroplasts of eukaryotic cells, comprise monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and phosphatidylglycerol. This review covers our current knowledge on the structural and functional features of these lipids in various cellular models, from prokaryotes to eukaryotes. Their relative proportions in thylakoid membranes result from highly regulated and compartmentalized metabolic pathways, with a cooperation, in the case of eukaryotes, of non-plastidic compartments. This review also focuses on the role of each of these thylakoid glycerolipids in stabilizing protein complexes of the photosynthetic machinery, which might be one of the reasons for their fascinating conservation in the course of evolution. This article is part of a Special Issue entitled: Dynamic and ultrastructure of bioenergetic membranes and their components.
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| 4. |
- Ezzedine, Jade A., et al.
(author)
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Adaptive traits of cysts of the snow alga Sanguina nivaloides unveiled by 3D subcellular imaging
- 2023
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In: Nature Communications. - 2041-1723. ; 14:1
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Journal article (peer-reviewed)abstract
- Sanguina nivaloides is the main alga forming red snowfields in high mountains and Polar Regions. It is non-cultivable. Analysis of environmental samples by X-ray tomography, focused-ion-beam scanning-electron-microscopy, physicochemical and physiological characterization reveal adaptive traits accounting for algal capacity to reside in snow. Cysts populate liquid water at the periphery of ice, are photosynthetically active, can survive for months, and are sensitive to freezing. They harbor a wrinkled plasma membrane expanding the interface with environment. Ionomic analysis supports a cell efflux of K+, and assimilation of phosphorus. Glycerolipidomic analysis confirms a phosphate limitation. The chloroplast contains thylakoids oriented in all directions, fixes carbon in a central pyrenoid and produces starch in peripheral protuberances. Analysis of cells kept in the dark shows that starch is a short-term carbon storage. The biogenesis of cytosolic droplets shows that they are loaded with triacylglycerol and carotenoids for long-term carbon storage and protection against oxidative stress.
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| 5. |
- Flori, Serena, et al.
(author)
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Plastid thylakoid architecture optimizes photosynthesis in diatoms
- 2017
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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 8:1
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Journal article (peer-reviewed)abstract
- Photosynthesis is a unique process that allows independent colonization of the land by plants and of the oceans by phytoplankton. Although the photosynthesis process is well understood in plants, we are still unlocking the mechanisms evolved by phytoplankton to achieve extremely efficient photosynthesis. Here, we combine biochemical, structural and in vivo physiological studies to unravel the structure of the plastid in diatoms, prominent marine eukaryotes. Biochemical and immunolocalization analyses reveal segregation of photosynthetic complexes in the loosely stacked thylakoid membranes typical of diatoms. Separation of photosystems within subdomains minimizes their physical contacts, as required for improved light utilization. Chloroplast 3D reconstruction and in vivo spectroscopy show that these subdomains are interconnected, ensuring fast equilibration of electron carriers for efficient optimum photosynthesis. Thus, diatoms and plants have converged towards a similar functional distribution of the photosystems although via different thylakoid architectures, which likely evolved independently in the land and the ocean.
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| 6. |
- Petroutsos, Dimitris, et al.
(author)
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Evolution of galactoglycerolipid biosynthetic pathways--from cyanobacteria to primary plastids and from primary to secondary plastids.
- 2014
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In: Progress in lipid research. - : Elsevier BV. - 0163-7827 .- 1873-2194. ; 54, s. 68-85
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Journal article (peer-reviewed)abstract
- Photosynthetic membranes have a unique lipid composition that has been remarkably well conserved from cyanobacteria to chloroplasts. These membranes are characterized by a very high content in galactoglycerolipids, i.e., mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively). Galactoglycerolipids make up the bulk of the lipid matrix in which photosynthetic complexes are embedded. They are also known to fulfill specific functions, such as stabilizing photosystems, being a source of polyunsaturated fatty acids for various purposes and, in some eukaryotes, being exported to other subcellular compartments. The conservation of MGDG and DGDG suggests that selection pressures might have conserved the enzymes involved in their biosynthesis, but this does not appear to be the case. Important evolutionary transitions comprise primary endosymbiosis (from a symbiotic cyanobacterium to a primary chloroplast) and secondary endosymbiosis (from a symbiotic unicellular algal eukaryote to a secondary plastid). In this review, we compare biosynthetic pathways based on available molecular and biochemical data, highlighting enzymatic reactions that have been conserved and others that have diverged or been lost, as well as the emergence of parallel and alternative biosynthetic systems originating from other metabolic pathways. Questions for future research are highlighted.
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