title: Intracellular distribution of the reductive and oxidative pentose phosphate pathways in two diatoms.
abstract: Diatoms contribute a large proportion to the worldwide primary production and are particularly effective in fixing carbon dioxide. Possibly because diatom plastids originate from a secondary endocytobiosis, their cellular structure is more complex and metabolic pathways are rearranged within diatom cells compared to cells containing primary plastids. We annotated genes encoding isozymes of the reductive and oxidative pentose phosphate pathways in the genomes of the centric diatom Thalassiosira pseudonana and the pennate diatom Phaeodactylum tricornutum and bioinformatically inferred their intracellular distribution. Prediction results were confirmed by fusion of selected presequences to Green Fluorescent Protein and expression of these constructs in P. tricornutum. Calvin cycle enzymes for the carbon fixation and reduction of 3-phosphoglycerate are present in single isoforms, while we found multiple isoenzymes involved in the regeneration of ribulose-1,5-bisphosphate. We only identified one cytosolic sedoheptulose-1,7-bisphosphatase in both investigated diatoms. The oxidative pentose phosphate pathway seems to be restricted to the cytosol in diatoms, since we did not find stromal glucose-6-phosphate dehydrogenase and 6-phosphogluconolactone dehydrogenase isoforms. However, the two species apparently possess a plastidic phosphogluconolactonase. A 6-phosphogluconolactone dehydrogenase is apparently plastid associated in P. tricornutum and might be active in the periplastidic compartment, suggesting that this compartment might be involved in metabolic processes in diatoms.
authors.affiliation: Pflanzliche Okophysiologie, Universität Konstanz, Konstanz, Germany. ansgar.gruber@uni-konstanz.de
authors.forename: Ansgar
authors.initials: A
authors.lastname: Gruber
authors.forename: Till
authors.initials: T
authors.lastname: Weber
authors.forename: Carolina Río
authors.initials: CR
authors.lastname: Bártulos
authors.forename: Sascha
authors.initials: S
authors.lastname: Vugrinec
authors.forename: Peter G
authors.initials: PG
authors.lastname: Kroth
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D002245:Carbon Dioxide / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D017377:Diatoms / Q000201:enzymology* / Q000235:genetics; D016678:Genome; D005988:Glyceric Acids / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010427:Pentose Phosphate Pathway; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis; D010802:Phylogeny; D018087:Plastids / Q000201:enzymology; D012274:Ribulosephosphates / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D005988:Glyceric Acids; D007527:Isoenzymes; D012274:Ribulosephosphates; D002245:Carbon Dioxide; C001933:ribulose-1,5 diphosphate; C005156:3-phosphoglycerate; D010088:Oxidoreductases; D010744:Phosphoric Monoester Hydrolases; C022627:sedoheptulose-bisphosphatase