The Phaeodactylum genome reveals the evolutionary history of diatom genomes
2008, Bowler, Chris, Allen, Andrew E., Badger, Jonathan H., Grimwood, Jane, Jabbari, Kamel, Kuo, Alan, Maheswari, Uma, Martens, Cindy, Maumus, Florian, Otillar, Robert P., Rayko, Edda, Salamov, Asaf, Vandepoele, Klaas, Beszteri, Bank, Gruber, Ansgar, Heijde, Marc, Katinka, Michael, Mock, Thomas, Valentin, Klaus, Verret, Fréderic, Berges, John A., Brownlee, Colin, Cadoret, Jean-Paul, Chiovitti, Anthony, Choi, Chang Jae, Coesel, Sacha, De Martino, Alessandra, Detter, John Chris, Durkin, Colleen, Falciatore, Angela, Fournet, Jérome, Haruta, Miyoshi, Huysman, Marie J. J., Jenkins, Bethany D., Jiroutova, Katerina, Jorgensen, Richard E., Joubert, Yolaine, Kaplan, Aaron, Kröger, Nils, Kroth, Peter G., La Roche, Julie, Lindquist, Erica, Lommer, Markus, Martin Jézéquel, Véronique, Lopez, Pascal J., Lucas, Susan, Mangogna, Manuela, McGinnis, Karen, Medlin, Linda K., Montsant, Anton, Oudot Le Secq, Marie-Pierre, Napoli, Carolyn, Obornik, Miroslav, Schnitzler Parker, Micaela, Petit, Jean-Louis, Porcel, Betina M., Poulsen, Nicole, Robison, Matthew, Rychlewski, Leszek, Rynearson, Tatiana A., Schmutz, Jeremy, Shapiro, Harris, Siaut, Magali, Stanley, Michele S., Sussman, Michael R., Taylor, Alison R., Vardi, Assaf, Dassow, Peter von, Vyverman, Wim, Willis, Anusuya, Wyrwicz, Lucjan S., Rokhsar, Daniel S., Weissenbach, Jean, Armbrust, E. Virginia, Green, Beverley R., Van de Peer, Yves, Grigoriev, Igor V.
Diatoms are photosynthetic secondary endosymbionts found throughout marine and freshwater environments, and are believed to be responsible for around one-fifth of the primary productivity on Earth. The genome sequence of the marine centric diatom Thalassiosira pseudonana was recently reported, revealing a wealth of information about diatom biology. Here we report the complete genome sequence of the pennate diatom Phaeodactylum tricornutum and compare it with that of T. pseudonana to clarify evolutionary origins, functional significance and ubiquity of these features throughout diatoms. In spite of the fact that the pennate and centric lineages have only been diverging for 90 million years, their genome structures are dramatically different and a substantial fraction of genes (40%) are not shared by these representatives of the two lineages. Analysis of molecular divergence compared with yeasts and metazoans reveals rapid rates of gene diversification in diatoms. Contributing factors include selective gene family expansions, differential losses and gains of genes and introns, and differential mobilization of transposable elements. Most significantly, we document the presence of hundreds of genes from bacteria. More than 300 of these gene transfers are found in both diatoms, attesting to their ancient origins, and many are likely to provide novel possibilities for metabolite management and for perception of environmental signals. These findings go a long way towards explaining the incredible diversity and success of the diatoms in contemporary oceans.
A Model for Carbohydrate Metabolism in the Diatom Phaeodactylum tricornutum Deduced from Comparative Whole Genome Analysis
2008, Kroth, Peter G., Chiovitti, Anthony, Gruber, Ansgar, Martin-Jezequel, Veronique, Mock, Thomas, Schnitzler Parker, Micaela, Stanley, Michele S., Kaplan, Aaron, Caron, Lise, Weber, Till, Maheswari, Uma, Armbrust, Elisabeth Virginia, Bowler, Chris, Kroymann, Juergen
Diatoms are unicellular algae responsible for approximately 20% of global carbon fixation. Their evolution by secondary endocytobiosis resulted in a complex cellular structure and metabolism compared to algae with primary plastids.
The whole genome sequence of the diatom Phaeodactylum tricornutum has recently been completed. We identified and annotated genes for enzymes involved in carbohydrate pathways based on extensive EST support and comparison to the whole genome sequence of a second diatom, Thalassiosira pseudonana. Protein localization to mitochondria was predicted based on identified similarities to mitochondrial localization motifs in other eukaryotes, whereas protein localization to plastids was based on the presence of signal peptide motifs in combination with plastid localization motifs previously shown to be required in diatoms. We identified genes potentially involved in a C4-like photosynthesis in P. tricornutum and, on the basis of sequence-based putative localization of relevant proteins, discuss possible differences in carbon concentrating mechanisms and CO2 fixation between the two diatoms. We also identified genes encoding enzymes involved in photorespiration with one interesting exception: glycerate kinase was not found in either P. tricornutum or T. pseudonana. Various Calvin cycle enzymes were found in up to five different isoforms, distributed between plastids, mitochondria and the cytosol. Diatoms store energy either as lipids or as chrysolaminaran (a β-1,3-glucan) outside of the plastids. We identified various β-glucanases and large membrane-bound glucan synthases. Interestingly most of the glucanases appear to contain C-terminal anchor domains that may attach the enzymes to membranes.
Here we present a detailed synthesis of carbohydrate metabolism in diatoms based on the genome sequences of Thalassiosira pseudonana and Phaeodactylum tricornutum. This model provides novel insights into acquisition of dissolved inorganic carbon and primary metabolic pathways of carbon in two different diatoms, which is of significance for an improved understanding of global carbon cycles.