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Photodamage of iron–sulphur clusters in photosystem I induces non-photochemical energy dissipation


Photosystem I (PSI) uses light energy and electrons supplied by photosystem II (PSII) to reduce NADP+ to NADPH. PSI is very tolerant of excess light but extremely sensitive to excess electrons from PSII. It has been assumed that PSI is protected from photoinhibition by strict control of the intersystem electron transfer chain (ETC). Here we demonstrate that the iron–sulphur (FeS) clusters of PSI are more sensitive to high light stress than previously anticipated, but PSI with damaged FeS clusters still functions as a non-photochemical photoprotective energy quencher (PSI-NPQ). Upon photoinhibition of PSI, the highly reduced ETC further triggers thylakoid phosphorylation-based mechanisms that increase energy flow towards PSI. It is concluded that the sensitivity of FeS clusters provides an additional photoprotective mechanism that is able to downregulate PSII, based on PSI quenching and protein phosphorylation.

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Figure 1: Redox kinetics of PSI when shifting the WT and pgr5 plants from growth light to high light for indicated time periods.
Figure 2: Room temperature EPR spectra from thylakoid membranes from WT and the pgr5 mutant.
Figure 3: Reduction of the FA and FB centres of PSI in the thylakoid membrane at 16 K.
Figure 4: Fluorescence emission spectra from WT and the pgr5 plants.
Figure 5: Gaussian decomposition of low temperature fluorescence emission spectra at 0 min and 120 min high-light-treated thylakoids of WT and pgr5.
Figure 6: Schematic representation of the regulatory functions of PSI in the presence (WT plants) and absence (pgr5 mutant) of ΔpH-dependent control mechanisms.


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Research was financially supported by the Academy of Finland Center of Excellence project (271832), a post-doctoral research grant to M.T. (260094) and an Academy Professor research grant to E.-M.A. (273870). S.S. and F.M. thankfully acknowledge the Swedish Research Council, the Swedish Energy Agency and the Knut and Alice Wallenberg Foundation. The PsaD antibody is a kind gift from H. Vibe Scheller, and the pgr5 mutant and the gl1 wild-type control were kindly provided by T. Shikanai.

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A.T., M.T., M.S., A.J. and E.-M.A. designed the study; A.T. and F.M. performed the research; A.T., F.M. and M.G. contributed analytical tools; A.T., M.T., S.S., F.M. and E.-M.A. analysed the data; A.T., F.M., M.T., M.S. and E.-M.A. wrote the paper.

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Correspondence to Mikko Tikkanen or Eva-Mari Aro.

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Tiwari, A., Mamedov, F., Grieco, M. et al. Photodamage of iron–sulphur clusters in photosystem I induces non-photochemical energy dissipation. Nature Plants 2, 16035 (2016).

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