Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Selective mRNA sequestration by OLIGOURIDYLATE BINDING PROTEIN 1 contributes to translational control during hypoxia in Arabidopsis

ABSTRACT: Low oxygen stress dynamically regulates the translation of cellular mRNAs as a means of energy conservation in seedlings of Arabidopsis thaliana. Most of the highly hypoxia-induced mRNAs are recruited to polysomes and actively translated, whereas other cellular mRNAs become translationally inactive and are either targeted for stabilization or degradation. Here we identify the involvement of OLIGOURIDYLATE BINDING PROTEIN 1 (UBP1), a triple RNA Recognition Motif protein, in dynamic and reversible aggregation of translationally repressed mRNAs during hypoxia. Mutation or downregulation of UBP1C interferes with seedling establishment and reduces survival of low oxygen stress. By use of messenger ribonucleoprotein immunopurification, we show that UBP1C constitutively binds a subpopulation of mRNAs characterized by U-rich 3M-bM-^@M-^Y-untranslated regions under normoxic conditions. During hypoxia, UBP1C association with non-U-rich mRNAs is enhanced concomitant with its aggregation into microscopically visible cytoplasmic foci, referred to as UBP1 stress granules (SGs). This UBP1C-mRNA association occurs as global levels of protein synthesis decline. Upon reoxygenation, rapid UBP1 SG disaggregation coincides with the return of the stabilized mRNAs to polysomes. The mRNAs that are highly induced and translated during hypoxia largely circumvent UBP1C sequestration. Thus, UBP1 is established as a component of dynamically assembled cytoplasmic mRNPs that sequester mRNAs that are poorly translated during a transient low energy stress. Immunoprecipated RNA associated with Arabidopsis UBP1C (IP) was compared with total cellular RNA from light (L), mock dark (D), 2 h hypoxia, and 2 h hypoxia + 20 min reoxygenation treated samples with duplicate hybridizations to the Affymetrix ATH1 Genechip array.

ORGANISM(S): Arabidopsis thaliana

SUBMITTER: Reed Sorenson

PROVIDER: E-GEOD-49411 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Intermittent hypoxia is a common stressor in estuarine and coastal habitats due to the diurnal and tidal cycles of oxygen availability. Oxygen deficiency results in energy stress by limiting aerobic ATP production, while reoxygenation may lead to oxidative injury due to the excessive production of reactive oxygen species (ROS) in mitochondria. Mitochondria are a key intracellular target of hypoxia-reoxygenation (H/R) stress due to their central role in ATP production, ROS generation and stress signaling. Marine intertidal bivalves such as the Pacific oyster Crassostrea gigas are adapted to frequent H/R cycles in the intertidal zone and maintain mitochondrial integrity and aerobic function despite frequent oxygen fluctuations. To gain insight into the molecular responses of mitochondria of the hypoxia-tolerant Pacific oyster to H/R stress, we studied changes in oxidative phosphorylation (OXPHOS) capacity, proton leak and activity of the electron transport system enzymes (ETS) in gill mitochondria of C. gigas. We furthermore investigated shifts in mitochondrial proteome and phosphoproteome after 24 h of hypoxia and 1 h of post-hypoxic recovery. Oyster mitochondria maintained normal ETS and OXPHOS capacity during H/R stress, despite a slight but significant decline in cytochrome c oxidase (Complex IV) activity after reoxygenation. Fifty total proteins and 36 phosphoproteins were differentially abundant in mitochondria of H/R exposed oysters compared with the controls. Rearrangements of the mitochondrial (phospho)proteome during H/R stress involved upregulation of mitochondrial ETS (most notably Complexes I and IV) and iron-binding proteins (frataxin and ferrochelatase) as well as suppression of the metabolic pathways that channel electrons to ubiquinone, possibly as a mechanism to limit ROS production due to the iron overload and reverse flow of electrons through ETS. H/R stress also led to upregulation of a mitophagic activator serine/threonine protein phosphatase PGAM5 and dephosphorylation of metalloendopeptidase OMA1 indicating stimulation of mitochondrial quality control mechanisms during reoxygenation. Changes in the overall abundance and phosphorylation levels of several key proteins involved in the mitochondrial protein homeostasis (including subunits of the mitochondrial ribosome, mitochondrial inner membrane translocase and elongation factor G) are consistent with the suppression of the protein synthesis during hypoxia, likely as an energy-saving mechanism. Overall, our study indicates that shifts in the mitochondrial (phospho-)proteome play an important role in responses of oysters to H/R stress and might complement adaptations of anaerobic metabolism and metabolic rate depression in ensuring hypoxic survival and rapid recovery in this hypoxia-tolerant intertidal species.

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Selective mRNA sequestration by OLIGOURIDYLATE BINDING PROTEIN 1 contributes to translational control during hypoxia in Arabidopsis

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