title: The plastid terminal oxidase: its elusive function points to multiple contributions to plastid physiology.
abstract: Plastids have retained from their cyanobacterial ancestor a fragment of the respiratory electron chain comprising an NADPH dehydrogenase and a diiron oxidase, which sustain the so-called chlororespiration pathway. Despite its very low turnover rates compared with photosynthetic electron flow, knocking out the plastid terminal oxidase (PTOX) in plants or microalgae leads to severe phenotypes that encompass developmental and growth defects together with increased photosensitivity. On the basis of a phylogenetic and structural analysis of the enzyme, we discuss its physiological contribution to chloroplast metabolism, with an emphasis on its critical function in setting the redox poise of the chloroplast stroma in darkness. The emerging picture of PTOX is that of an enzyme at the crossroads of a variety of metabolic processes, such as, among others, the regulation of cyclic electron transfer and carotenoid biosynthesis, which have in common their dependence on the redox state of the plastoquinone pool, set largely by the activity of PTOX in darkness.
authors.affiliation: Laboratoire de Physiologie Membranaire et Moléculaire du Chloroplaste, UMR 7141, Centre National de la Recherche Scientifique-Université Pierre et Marie Curie;
authors.forename: Wojciech J
authors.initials: WJ
authors.lastname: Nawrocki
authors.forename: Nicolas J
authors.initials: NJ
authors.lastname: Tourasse
authors.forename: Antoine
authors.initials: A
authors.lastname: Taly
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rappaport
authors.forename: Francis-André
authors.initials: FA
authors.lastname: Wollman
mesh_terms: D002736:Chloroplasts / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D004579:Electron Transport; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010788:Photosynthesis; D010802:Phylogeny; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D010088:Oxidoreductases
keywords: PTOX; carotenoid biosynthesis; chloroplast; chlororespiration; electron transfer; redox poise; retrograde signaling; structural model