title: A type II NAD(P)H dehydrogenase mediates light-independent plastoquinone reduction in the chloroplast of Chlamydomonas.
abstract: In photosynthetic eukaryotes, nonphotochemical plastoquinone (PQ) reduction is important for the regulation of photosynthetic electron flow. In green microalgae where this process has been demonstrated, the chloroplastic enzyme that catalyses nonphotochemical PQ reduction has not been identified yet. Here, we show by an RNA interference (RNAi) approach that the NDA2 gene, belonging to a type II NAD(P)H dehydrogenases family in the green microalga Chlamydomonas reinhardtii, encodes a chloroplastic dehydrogenase that functions to reduce PQ nonphotochemically in this alga. Using a specific antibody, we show that the Nda2 protein is localized in chloroplasts of wild-type cells and is absent in two Nda2-RNAi cell lines. In both mutant cell lines, nonphotochemical PQ reduction is severely affected, as indicated by altered chlorophyll fluorescence transients after saturating illumination. Compared with wild type, change in light excitation distribution between photosystems ('state transition') upon inhibition of mitochondrial electron transport is strongly impaired in transformed cells because of inefficient PQ reduction. Furthermore, the amount of hydrogen produced by Nda2-RNAi cells under sulfur deprivation is substantially decreased compared with wild type, which supports previous assumptions that endogenous substrates serve as source of electrons for hydrogen formation. These results demonstrate the importance of Nda2 for nonphotochemical PQ reduction and associated processes in C. reinhardtii.
authors.affiliation: Laboratorie of Plant Biochemistry and Photobiology, Department of Life Sciences, Institute of Plant Biology, B22, University of Liège, 27 Boulevard du Rectorat, 4000-Liège, Belgium.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Jans
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Mignolet
authors.forename: Pierre-Alain
authors.initials: PA
authors.lastname: Houyoux
authors.forename: Pierre
authors.initials: P
authors.lastname: Cardol
authors.forename: Bart
authors.initials: B
authors.lastname: Ghysels
authors.forename: Stéphan
authors.initials: S
authors.lastname: Cuiné
authors.forename: Laurent
authors.initials: L
authors.lastname: Cournac
authors.forename: Gilles
authors.initials: G
authors.lastname: Peltier
authors.forename: Claire
authors.initials: C
authors.lastname: Remacle
authors.forename: Fabrice
authors.initials: F
authors.lastname: Franck
mesh_terms: D000818:Animals; D002696:Chlamydomonas / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D004579:Electron Transport; D006859:Hydrogen; D008027:Light; D009252:NADPH Dehydrogenase / Q000502:physiology*; D010084:Oxidation-Reduction / Q000528:radiation effects; D010971:Plastoquinone / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology
chemical_list: D034741:RNA, Small Interfering; D006859:Hydrogen; D009252:NADPH Dehydrogenase; D010971:Plastoquinone