title: Clarification of Photorespiratory Processes and the Role of Malic Enzyme in Diatoms.
abstract: Evidence suggests that diatom photorespiratory metabolism is distinct from other photosynthetic eukaryotes in that there may be at least two routes for the metabolism of the photorespiratory metabolite glycolate. One occurs primarily in the mitochondria and is similar to the C2 photorespiratory pathway, and the other processes glycolate through the peroxisomal glyoxylate cycle. Genomic analysis has identified the presence of key genes required for glycolate oxidation, the glyoxylate cycle, and malate metabolism, however, predictions of intracellular localization can be ambiguous and require verification. This knowledge gap leads to uncertainties surrounding how these individual pathways operate, either together or independently, to process photorespiratory intermediates under different environmental conditions. Here, we combine in silico sequence analysis, in vivo protein localization techniques and gene expression patterns to investigate key enzymes potentially involved in photorespiratory metabolism in the model diatom Thalassiosira pseudonana. We demonstrate the peroxisomal localization of isocitrate lyase and the mitochondrial localization of malic enzyme and a glycolate oxidase. Based on these analyses, we propose an updated model for photorespiratory metabolism in T. pseudonana, as well as a mechanism by which C2 photorespiratory metabolism and its associated pathways may operate during silicon starvation and growth arrest.
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, U.S.A.
authors.forename: Aubrey
authors.initials: A
authors.lastname: Davis
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, U.S.A.
authors.forename: Raffaela
authors.initials: R
authors.lastname: Abbriano
authors.affiliation: Integrative Oceanography Division, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, U.S.A.; J. Craig Venter Institute, La Jolla, CA, U.S.A.
authors.forename: Sarah R
authors.initials: SR
authors.lastname: Smith
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, U.S.A.. Electronic address: mhildebrand@ucsd.edu.
authors.forename: Mark
authors.initials: M
authors.lastname: Hildebrand
mesh_terms: D020418:Algal Proteins / Q000235:genetics; D017377:Diatoms / Q000201:enzymology / Q000378:metabolism*; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D010084:Oxidation-Reduction; D010788:Photosynthesis; D010802:Phylogeny
chemical_list: D020418:Algal Proteins; D008291:Malate Dehydrogenase; C030574:malate dehydrogenase (decarboxylating)
keywords: Diatom; Thalassiosira pseudonana.; glyoxylate cycle; malic enzyme; photorespiration