title: SLC4 family transporters in a marine diatom directly pump bicarbonate from seawater.
abstract: Photosynthesis in marine diatoms is a vital fraction of global primary production empowered by CO(2)-concentrating mechanisms. Acquisition of HCO(3)(-) from seawater is a critical primary step of the CO(2)-concentrating mechanism, allowing marine photoautotrophic eukaryotes to overcome CO(2) limitation in alkaline high-salinity water. However, little is known about molecular mechanisms governing this process. Here, we show the importance of a plasma membrane-type HCO(3)(-) transporter for CO(2) acquisition in a marine diatom. Ten putative solute carrier (SLC) family HCO(3)(-) transporter genes were found in the genome of the marine pennate diatom Phaeodactylum tricornutum. Homologs also exist in marine centric species, Thalassiosira pseudonana, suggesting a general occurrence of SLC transporters in marine diatoms. Seven genes were found to encode putative mammalian-type SLC4 family transporters in P. tricornutum, and three of seven genes were specifically transcribed under low CO(2) conditions. One of these gene products, PtSLC4-2, was localized at the plasmalemma and significantly stimulated both dissolved inorganic carbon (DIC) uptake and photosynthesis in P. tricornutum. DIC uptake by PtSLC4-2 was efficiently inhibited by an anion-exchanger inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, in a concentration-dependent manner and highly dependent on Na(+) ions at concentrations over 100 mM. These results show that DIC influx into marine diatoms is directly driven at the plasmalemma by a specific HCO(3)(-) transporter with a significant halophilic nature.
authors.affiliation: Research Centre for Environmental Bioscience, Department of Bioscience, School of Science and Technology,  Kwansei Gakuin University, Sanda, Hyogo 669-1337,  Japan.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Nakajima
authors.forename: Atsuko
authors.initials: A
authors.lastname: Tanaka
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Matsuda
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000595:Amino Acid Sequence; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D017377:Diatoms / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D008954:Models, Biological; D008969:Molecular Sequence Data; D010788:Photosynthesis / Q000187:drug effects; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012623:Seawater / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D001639:Bicarbonates; D026901:Membrane Transport Proteins; D020033:Protein Isoforms; D002245:Carbon Dioxide; D002244:Carbon; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid