FIRST INDUCED PLASTID GENOME MUTATIONS IN AN ALGA WITH SECONDARY PLASTIDS: psbA MUTATIONS IN THE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) REVEAL CONSEQUENCES ON THE REGULATION OF PHOTOSYNTHESIS

Authors

  • Arne C. Materna,

    1. Group of Plant Ecophysiology, Biology Department, Mailbox M611, University of Konstanz, Universitätsstraße 10, 78457 Konstanz, Germany
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    • Present address: Alm Laboratory, Civil and Environmental Engineering, Massachusetts Institute of Technology (MIT), 77 Massachusetts Ave., 48-208, Cambridge, MA 02139, USA.

    • These authors contributed equally to this work.

  • Sabine Sturm,

    1. Group of Plant Ecophysiology, Biology Department, Mailbox M611, University of Konstanz, Universitätsstraße 10, 78457 Konstanz, Germany
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    • These authors contributed equally to this work.

  • Peter G. Kroth,

    1. Group of Plant Ecophysiology, Biology Department, Mailbox M611, University of Konstanz, Universitätsstraße 10, 78457 Konstanz, Germany
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  • Johann Lavaud

    1. Group of Plant Ecophysiology, Biology Department, Mailbox M611, University of Konstanz, Universitätsstraße 10, 78457 Konstanz, Germany
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    • Author for correspondence: e-mail johann.lavaud@univ-lr.fr.

    • Present address: UMR CNRS 6250 ‘LIENSs’, Institute for Coastal and Environmental Research, University of La Rochelle, 2 rue Olympe de Gouges, 17042 La Rochelle Cedex, France.


  • Received 27 June 2008. Accepted 16 March 2009.

Abstract

Diatoms play a crucial role in the biochemistry and ecology of most aquatic ecosystems, especially because of their high photosynthetic productivity. They often have to cope with a fluctuating light climate and a punctuated exposure to excess light, which can be harmful for photosynthesis. To gain insight into the regulation of photosynthesis in diatoms, we generated and studied mutants of the diatom Phaeodactylum tricornutum Bohlin carrying functionally altered versions of the plastidic psbA gene encoding the D1 protein of the PSII reaction center (PSII RC). All analyzed mutants feature an amino acid substitution in the vicinity of the QB-binding pocket of D1. We characterized the photosynthetic capacity of the mutants in comparison to wildtype cells, focusing on the way they regulate their photochemistry as a function of light intensity. The results show that the mutations resulted in constitutive changes of PSII electron transport rates. The extent of the impairment varies between mutants depending on the proximity of the mutation to the QB-binding pocket and/or to the nonheme iron within the PSII RC. The effects of the mutations described here for P. tricornutum are similar to effects in cyanobacteria and green microalgae, emphasizing the conservation of the D1 protein structure among photosynthetic organisms of different evolutionary origins.

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