The functions of several small subunits of the large photosynthetic multiprotein complex PSI (Photosystem I) are not yet understood. To elucidate the function of the small plastome-encoded PsaJ subunit, we have produced knockout mutants by chloroplast transformation in tobacco (Nicotiana tabacum). PsaJ binds two chlorophyll-a molecules and is localized at the periphery of PSI, close to both the Lhca2- and Lhca3-docking sites and the plastocyanin-binding site. Tobacco psaJ-knockout lines do not display a visible phenotype. Despite a 25% reduction in the content of redox-active PSI, neither growth rate nor assimilation capacity are altered in the mutants. In vivo, redox equilibration of plastocyanin and PSI is as efficient as in the wild-type, indicating that PsaJ is not required for fast plastocyanin oxidation. However, PsaJ is involved in PSI excitation: altered 77 K chlorophyll-a fluorescence emission spectra and reduced accumulation of Lhca3 indicate that antenna binding and exciton transfer to the PSI reaction centre are impaired in ΔpsaJ mutants. Under limiting light intensities, growth of ΔpsaJ plants is retarded and the electron-transport chain is far more reduced than in the wild-type, indicating that PSI excitation might limit electron flux at sub-saturating light intensities. In addition to defining in vivo functions of PsaJ, our data may also have implications for the interpretation of the crystal structure of PSI.
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Research Article|
March 26 2007
The plastome-encoded PsaJ subunit is required for efficient Photosystem I excitation, but not for plastocyanin oxidation in tobacco
Mark A. Schöttler;
Mark A. Schöttler
1
1Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany
1To whom correspondence should be addressed (email schoettler@mpimp-golm.mpg.de).
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Claudia Flügel;
Claudia Flügel
1Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany
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Wolfram Thiele;
Wolfram Thiele
1Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany
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Sandra Stegemann;
Sandra Stegemann
1Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany
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Ralph Bock
Ralph Bock
1Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany
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Biochem J (2007) 403 (2): 251–260.
Article history
Received:
October 18 2006
Revision Received:
December 19 2006
Accepted:
January 09 2007
Accepted Manuscript online:
January 09 2007
Citation
Mark A. Schöttler, Claudia Flügel, Wolfram Thiele, Sandra Stegemann, Ralph Bock; The plastome-encoded PsaJ subunit is required for efficient Photosystem I excitation, but not for plastocyanin oxidation in tobacco. Biochem J 15 April 2007; 403 (2): 251–260. doi: https://doi.org/10.1042/BJ20061573
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