Plastid thylakoid architecture optimizes photosynthesis in diatoms

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.ISSN:2041-172

Cytoklepty in the plankton: A host strategy to optimize the bioenergetic machinery of endosymbiotic algae

Endosymbioses have shaped the evolutionary trajectory of life and remain ecologically important. Investigating oceanic photosymbioses can illuminate how algal endosymbionts are energetically exploited by their heterotrophic hosts and inform on putative initial steps of plastid acquisition in eukaryotes. By combining three-dimensional subcellular imaging with photophysiology, carbon flux imaging, and transcriptomics, we show that cell division of endosymbionts (Phaeocystis) is blocked within hosts (Acantharia) and that their cellular architecture and bioenergetic machinery are radically altered. Transcriptional evidence indicates that a nutrient-independent mechanism prevents symbiont cell division and decouples nuclear and plastid division. As endosymbiont plastids proliferate, the volume of the photosynthetic machinery volume increases 100-fold in correlation with the expansion of a reticular mitochondrial network in close proximity to plastids. Photosynthetic efficiency tends to increase with cell size, and photon propagation modeling indicates that the networked mitochondrial architecture enhances light capture. This is accompanied by 150-fold higher carbon uptake and up-regulation of genes involved in photosynthesis and carbon fixation, which, in conjunction with a ca.15-fold size increase of pyrenoids demonstrates enhanced primary production in symbiosis. Mass spectrometry imaging revealed major carbon allocation to plastids and transfer to the host cell. As in most photosymbioses, microalgae are contained within a host phagosome (symbiosome), but here, the phagosome invaginates into enlarged microalgal cells, perhaps to optimize metabolic exchange. This observation adds evidence that the algal metamorphosis is irreversible. Hosts, therefore, trigger and benefit from major bioenergetic remodeling of symbiotic microalgae with potential consequences for the oceanic carbon cycle. Unlike other photosymbioses, this interaction represents a so-called cytoklepty, which is a putative initial step toward plastid acquisition

GeneFarm, structural and functional annotation of Arabidopsis gene and protein families by a network of experts

Genomic projects heavily depend on genome annotations and are limited by the current deficiencies in the published predictions of gene structure and function. It follows that, improved annotation will allow better data mining of genomes, and more secure planning and design of experiments. The purpose of the GeneFarm project is to obtain homogeneous, reliable, documented and traceable annotations for Arabidopsis nuclear genes and gene products, and to enter them into an added-value database. This re-annotation project is being performed exhaustively on every member of each gene family. Performing a family-wide annotation makes the task easier and more efficient than a gene-by-gene approach since many features obtained for one gene can be extrapolated to some or all the other genes of a family. A complete annotation procedure based on the most efficient prediction tools available is being used by 16 partner laboratories, each contributing annotated families from its field of expertise. A database, named GeneFarm, and an associated user-friendly interface to query the annotations have been developed. More than 3000 genes distributed over 300 families have been annotated and are available at http://genoplante-info.infobiogen.fr/Genefarm/. Furthermore, collaboration with the Swiss Institute of Bioinformatics is underway to integrate the GeneFarm data into the protein knowledgebase Swiss-Pro

GeneFarm, structural and functional annotation of Arabidopsis gene and protein families by a network of experts

Genomic projects heavily depend on genome annotations and are limited by the current deficiencies in the published predictions of gene structure and function. It follows that, improved annotation will allow better data mining of genomes, and more secure planning and design of experiments. The purpose of the GeneFarm project is to obtain homogeneous, reliable, documented and traceable annotations for Arabidopsis nuclear genes and gene products, and to enter them into an added-value database. This re-annotation project is being performed exhaustively on every member of each gene family. Performing a family-wide annotation makes the task easier and more efficient than a gene-by-gene approach since many features obtained for one gene can be extrapolated to some or all the other genes of a family. A complete annotation procedure based on the most efficient prediction tools available is being used by 16 partner laboratories, each contributing annotated families from its field of expertise. A database, named GeneFarm, and an associated user-friendly interface to query the annotations have been developed. More than 3000 genes distributed over 300 families have been annotated and are available at http://genoplante-info.infobiogen.fr/Genefarm/. Furthermore, collaboration with the Swiss Institute of Bioinformatics is underway to integrate the GeneFarm data into the protein knowledgebase Swiss-Prot

Origin, Evolution and Division of Plastids

International audienceAll living eukaryotic cells with mitochondria, and plastids if any, within their cytoplasm, are the result of two billion years of evolution. These organelles are the result of two distinct endosymbioses. The increase in oxygen in the atmosphere supports the origin for mitochondria about 2.2 billion years ago, an origin probably due to a single invasion of a host cell by an alpha-proteobacterium-like organism. Plastids originated between 1.6 and 0.6 billion years ago as a result of a symbiotic association between a cyanobacterium and a mitochondriate eukaryote. This endosymbiotic event generated the green, red and blue algal lineages, which subsequently spread their chloroplasts when the new photosynthetic eukaryotes were, in their turn, engulfed by nonphotosynthetic eukaryotes (between, 1.2 and 0.55 billion years ago) generating more algal divisions. These symbiotic events would have been in vain if the continuity of the newly acquired organelles had not been maintained. Since the first observations of chloroplast in the mid nineteenth century, progress made in microscopy techniques, during the first half of the twentieth century, demonstrated without ambiguity that this continuity is the result of division of pre-existing chloroplasts. Moreover, thanks to the completion of sequencing projects and the use of classical and reverse genetic approaches, it was then possible to show that the chloroplast division machinery is an evolutionary hybrid, which has retained the activity of several prokaryotically-derived proteins together with components that have evolved from proteins present in the eukaryotic ancestor

Le microscope pour décrypter l’architecture du vivant

National audienc

Détermination des fonctions des protéines Ftsz dans la division et la biogenèse des plastes de plantes supérieures par la caractérisation des mutants FtsZ d'Arabidopsis thaliana

Chloroplast division in plant cells uses proteins from both the prokaryotic and eukaryotic ancestors. The prokaryotic derived proteins include FtsZ, the progenitor oftubulin. When bacteria only use one FtsZ protein to divide, chloroplasts in higher plants use two distinct FtsZ proteins: FtsZI and FtsZ2. The characterization of FtsZ Arabidopsis thaliana mutants shows that plant FtsZ proteins in addition to be involved in plastid division have gained new functions in plant development during evolution. The observation that association of plastid FtsZ with thylakoid membranes is developmentally regulated suggests a function of FtsZ proteins during leaf development in chloroplast biogenesis. The number and size of starch granules in mutants together with FtsZ expression during the proplastid-amyloplast transition suggest a function in starch granules metabolism.La division des chloroplastes des cellules végétales fait intervenir des protéines d'origine procaryotique et eucaryotique. Panni les protéines d'origine procaryotique on trouve la protéine FtsZ, l'ancêtre de la tubuline. Alors que les bactéries n'utilisent qu'une protéine FtsZ pour se diviser, les chloroplastes de plantes supérieures possèdent deux familles de protéines FtsZ : FtsZI et FtsZ2. La caractérisation des mutants FtsZ d'Arabidopsis thaliana montre que les protéines FtsZ en plus d'être impliquées dans la division des plastes ont acquis de nouvelles fonctions au cours de l'évolution. La localisation des protéines FtsZ avec les thylacoïdes au cours du développement suggère un rôle des protéines FtsZ dans la biogenèse des chloroplastes au cours du développement des feuilles. Le nombre et la taille des grains d'amidon dans les mutants d'Arabidopsis, ainsi que l'expression des protéines FtsZ au cours de la transition proplastes-amyloplastes dans les cellules BY2 de tabac, suggèrent une fonction de ces protéines dans le métabolisme du grain d'amidon.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF