title: The carbonic anhydrase CAH1 is an essential component of the carbon-concentrating mechanism inNannochloropsis oceanica.
abstract: Aquatic photosynthetic organisms cope with low environmental CO2concentrations through the action of carbon-concentrating mechanisms (CCMs). Known eukaryotic CCMs consist of inorganic carbon transporters and carbonic anhydrases (and other supporting components) that culminate in elevated [CO2] inside a chloroplastic Rubisco-containing structure called a pyrenoid. We set out to determine the molecular mechanisms underlying the CCM in the emerging model photosynthetic stramenopile,Nannochloropsis oceanica, a unicellular picoplanktonic alga that lacks a pyrenoid. We characterizedCARBONIC ANHYDRASE 1(CAH1) as an essential component of the CCM inN. oceanicaCCMP1779. We generated insertions in this gene by directed homologous recombination and found that thecah1mutant has severe defects in growth and photosynthesis at ambient CO2We identified CAH1 as an α-type carbonic anhydrase, providing a biochemical role in CCM function. CAH1 was found to localize to the lumen of the epiplastid endoplasmic reticulum, with its expression regulated by the external inorganic carbon concentration at both the transcript and protein levels. Taken together, these findings show thatCAH1is an indispensable component of what may be a simple but effective and dynamic CCM inN. oceanica.
authors.affiliation: Howard Hughes Medical Institute, University of California, Berkeley, CA 94720.|Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720.
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Gee
authors.affiliation: Howard Hughes Medical Institute, University of California, Berkeley, CA 94720; niyogi@berkeley.edu.|Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720.|Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Krishna K
authors.identifier: 0000-0001-7229-2071
authors.initials: KK
authors.lastname: Niyogi
mesh_terms: D020418:Algal Proteins / Q000378:metabolism; D000595:Amino Acid Sequence; D059001:Aquatic Organisms; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010788:Photosynthesis / Q000502:physiology; D058009:Stramenopiles / Q000502:physiology*
chemical_list: D020418:Algal Proteins; D002245:Carbon Dioxide; D002244:Carbon; D002256:Carbonic Anhydrases
keywords: algae; carbon-concentrating mechanism; carbonic anhydrase; heterokont; photosynthesis