title: High light acclimation in the secondary plastids containing diatom Phaeodactylum tricornutum is triggered by the redox state of the plastoquinone pool.
abstract: In diatoms, the process of energy-dependent chlorophyll fluorescence quenching (qE) has an important role in photoprotection. Three components are essential for qE: (1) the light-dependent generation of a transthylakoidal proton gradient; (2) the deepoxidation of the xanthophyll diadinoxanthin (Dd) into diatoxanthin (Dt); and (3) specific nucleus-encoded antenna proteins, called Light Harvesting Complex Protein X (LHCX). We used the model diatom Phaeodactylum tricornutum to investigate the concerted light acclimation response of the qE key components LHCX, proton gradient, and xanthophyll cycle pigments (Dd+Dt) and to identify the intracellular light-responsive trigger. At high-light exposure, the up-regulation of three of the LHCX genes and the de novo synthesis of Dd+Dt led to a pronounced rise of qE. By inhibiting either the conversion of Dd to Dt or the translation of LHCX genes, qE amplification was abolished and the diatom cells suffered from stronger photoinhibition. Artificial modification of the redox state of the plastoquinone (PQ) pool via 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone resulted in a disturbance of Dd+Dt synthesis in an opposite way. Moreover, we could increase the transcription of two of the four LHCX genes under low-light conditions by reducing the PQ pool using 5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone. Altogether, our results underline the central role of the redox state of the PQ pool in the light acclimation of diatoms. Additionally, they emphasize strong evidence for the existence of a plastid-to-nucleus retrograde signaling mechanism in an organism with plastids that derived from secondary endosymbiosis.
authors.affiliation: Littoral Environnement et Sociétés, Unité Mixte de Recherche 7266, Centre National de la Recherche Scientifique-University of La Rochelle, Institute for Coastal and Environmental Research, 17000 La Rochelle, France. bernard.lepetit@univ-lr.fr
authors.forename: Bernard
authors.initials: B
authors.lastname: Lepetit
authors.forename: Sabine
authors.initials: S
authors.lastname: Sturm
authors.forename: Alessandra
authors.initials: A
authors.lastname: Rogato
authors.forename: Ansgar
authors.initials: A
authors.lastname: Gruber
authors.forename: Matthias
authors.initials: M
authors.lastname: Sachse
authors.forename: Angela
authors.initials: A
authors.lastname: Falciatore
authors.forename: Peter G
authors.initials: PG
authors.lastname: Kroth
authors.forename: Johann
authors.initials: J
authors.lastname: Lavaud
mesh_terms: D000064:Acclimatization / Q000187:drug effects / Q000528:radiation effects*; D016227:Benzoquinones / Q000494:pharmacology; D015153:Blotting, Western; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D017377:Diatoms / Q000235:genetics / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D004237:Diuron / Q000494:pharmacology; D005453:Fluorescence; D015870:Gene Expression / Q000187:drug effects / Q000528:radiation effects; D006540:Herbicides / Q000494:pharmacology; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects / Q000528:radiation effects; D018087:Plastids / Q000235:genetics / Q000378:metabolism*; D010971:Plastoquinone / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D006540:Herbicides; D045342:Light-Harvesting Protein Complexes; D020033:Protein Isoforms; D011500:Protein Synthesis Inhibitors; D024341:Xanthophylls; D002734:Chlorophyll; D003513:Cycloheximide; D004237:Diuron; D010971:Plastoquinone; D004229:Dithiothreitol