title: Ultrastructure of the Periplastidial Compartment of the Diatom Phaeodactylum tricornutum.
abstract: Diatoms contain a secondary plastid that derives from a red algal symbiont. This organelle is limited by four membranes. The two outermost membranes are the chloroplast endoplasmic reticulum membrane (cERM), which is continuous with the host outer nuclear envelope, and the periplastidial membrane (PPM). The two innermost membranes correspond to the outer and inner envelope membranes (oEM and iEM) of the symbiont's chloroplast. Between the PPM and oEM lies a minimized symbiont cytoplasm, the periplastidial compartment (PPC). In Phaeodactylum tricornutum, PPC-resident proteins are localized in "blob-like-structures", which remain associated with plastids after cell disruption. We analyzed disrupted Phaeodactylum cells by focused ion beam scanning electron microscopy, revealing the presence of a vesicular network (VN) in the PPC, at a location consistent with blob-like structures. Presence of a VN in the PPC was confirmed in intact cells. Additionally, direct membrane contacts were observed between the PPM and nuclear inner envelope membrane at the level of the chloroplast-nucleus isthmus. This study provides insights into the PPC ultrastructure and opens perspectives on the function of this residual cytoplasm of red algal origin.
authors.affiliation: Laboratoire de Physiologie Cellulaire et Végétale, Unité Mixte de Recherche 5168 CNRS - CEA - INRA - Université Grenoble Alpes, Institut de Recherche en Sciences et Technologies pour le Vivant, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cédex 9, France.
authors.forename: Serena
authors.initials: S
authors.lastname: Flori
authors.affiliation: Laboratoire d'Etudes des Matériaux par Microscopie Avancée, Institut Nanosciences et Cryogénie, Service de Physique des matériaux et Microstructures, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cédex 9, France.
authors.forename: Pierre-Henri
authors.initials: PH
authors.lastname: Jouneau
authors.affiliation: Laboratoire de Physiologie Cellulaire et Végétale, Unité Mixte de Recherche 5168 CNRS - CEA - INRA - Université Grenoble Alpes, Institut de Recherche en Sciences et Technologies pour le Vivant, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cédex 9, France.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Finazzi
authors.affiliation: Laboratoire de Physiologie Cellulaire et Végétale, Unité Mixte de Recherche 5168 CNRS - CEA - INRA - Université Grenoble Alpes, Institut de Recherche en Sciences et Technologies pour le Vivant, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cédex 9, France. Electronic address: eric.marechal@cea.fr.
authors.forename: Eric
authors.initials: E
authors.lastname: Maréchal
authors.affiliation: Laboratoire de Physiologie Cellulaire et Végétale, Unité Mixte de Recherche 5168 CNRS - CEA - INRA - Université Grenoble Alpes, Institut de Recherche en Sciences et Technologies pour le Vivant, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cédex 9, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Falconet
mesh_terms: D003593:Cytoplasm / Q000648:ultrastructure; D017377:Diatoms / Q000648:ultrastructure*; D007425:Intracellular Membranes / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D018087:Plastids / Q000648:ultrastructure; D022161:Transport Vesicles / Q000648:ultrastructure
keywords: Phaeodactylum; SELMA.; diatoms; periplastidial compartment; secondary endosymbiosis; secondary plastids