The plastid-encoded PsaI subunit stabilizes photosystem I during leaf senescence in tobacco.
PsaI is the only subunit of PSI whose precise physiological function has not yet been elucidated in higher plants. While PsaI is involved in PSI trimerization in cyanobacteria, trimerization was lost during the evolution of the eukaryotic PSI, and the entire PsaI side of PSI underwent major structural remodelling to allow for binding of light harvesting complex II antenna proteins during state transitions. Here, we have generated a tobacco (Nicotiana tabacum) knockout mutant of the plastid-encoded psaI gene. We show that PsaI is not required for the redox reactions of PSI. Neither plastocyanin oxidation nor the processes at the PSI acceptor side are impaired in the mutant, and both linear and cyclic electron flux rates are unaltered. The PSI antenna cross section is unaffected, state transitions function normally, and binding of other PSI subunits to the reaction centre is not compromised. Under a wide range of growth conditions, the mutants are phenotypically and physiologically indistinguishable from wild-type tobacco. However, in response to high-light and chilling stress, and especially during leaf senescence, PSI content is reduced in the mutants, indicating that the I-subunit plays a role in stabilizing PSI complexes.
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Mark Aurel
MA
Schöttler
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Wolfram
W
Thiele
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Karolina
K
Belkius
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Sonja Verena
SV
Bergner
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Claudia
C
Flügel
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Gal
G
Wittenberg
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Shreya
S
Agrawal
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Sandra
S
Stegemann
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Stephanie
S
Ruf
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Ralph
R
Bock
D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018087:Plastids / Q000378:metabolism; D010970:Plastocyanin / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism
D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D010970:Plastocyanin
Chloroplast transformation; PsaI; heat stress; leaf senescence; light acclimation; photosynthesis; photosystem I; plastocyanin; tobacco.