TY - JOUR T1 - High Light Acclimation in the Secondary Plastids Containing Diatom <em>Phaeodactylum tricornutum</em> is Triggered by the Redox State of the Plastoquinone Pool JF - Plant Physiology JO - Plant Physiol. SP - 853 LP - 865 DO - 10.1104/pp.112.207811 VL - 161 IS - 2 AU - Lepetit, Bernard AU - Sturm, Sabine AU - Rogato, Alessandra AU - Gruber, Ansgar AU - Sachse, Matthias AU - Falciatore, Angela AU - Kroth, Peter G. AU - Lavaud, Johann Y1 - 2013/02/01 UR - http://www.plantphysiol.org/content/161/2/853.abstract N2 - 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.GlossaryDddiadinoxanthinDtdiatoxanthinDd+Dtdiadinoxanthin + diatoxanthinqEenergy-dependent chlorophyll fluorescence quenchingPQplastoquinoneDCMU3-(3,4-dichlorophenyl)-1,1-dimethylureaDBMIB5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinoneROSreactive oxygen speciesNPQnonphotochemical fluorescence quenchingΔpHtransthylakoidal proton gradientLLlow lightmHLmedium low lightHLhigh lightChl achlorophyll aFxfucoxanthinFv/Fmmaximum photochemical efficiency of PSII in the dark-adapted stateCHXcycloheximideDTTdithiothreitolQBsecondary electron-accepting plastoquinone of PSIIQAprimary electron-accepting plastoquinone of PSIILL100light intensity of 100 µmol photons m−2 s−1VDEviolaxanthin deepoxidaseVDLviolaxanthin deepoxidase-like enzymesVDRviolaxanthin deepoxidase-related enzymecDNAcomplementary DNAFv/Fmeffective PSII quantum yield ER -