title: Photodamage of iron-sulphur clusters in photosystem I induces non-photochemical energy dissipation.
abstract: 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.
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Arjun
authors.initials: A
authors.lastname: Tiwari
authors.affiliation: Molecular Biomimetics, Department of Chemistry-Ångström Laboratory, Uppsala University, Box 523, SE-75120 Uppsala, Sweden.
authors.forename: Fikret
authors.initials: F
authors.lastname: Mamedov
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Michele
authors.initials: M
authors.lastname: Grieco
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Marjaana
authors.initials: M
authors.lastname: Suorsa
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Anjana
authors.initials: A
authors.lastname: Jajoo
authors.affiliation: Molecular Biomimetics, Department of Chemistry-Ångström Laboratory, Uppsala University, Box 523, SE-75120 Uppsala, Sweden.
authors.forename: Stenbjörn
authors.initials: S
authors.lastname: Styring
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Tikkanen
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
mesh_terms: D017360:Arabidopsis / Q000378:metabolism / Q000528:radiation effects*; D007501:Iron / Q000378:metabolism*; D008027:Light; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D013312:Stress, Physiological; D013455:Sulfur / Q000378:metabolism*
chemical_list: D045331:Photosystem I Protein Complex; D013455:Sulfur; D007501:Iron