Browsing by Subject "ALTERNATIVE OXIDASE"

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  • Pascual, Jesus; Rahikainen, Moona; Angeleri, Martina; Alegre, Sara; Gossens, Richard; Shapiguzov, Alexey; Heinonen, Arttu; Trotta, Andrea; Durian, Guido; Winter, Zsofia; Sinkkonen, Jari; Kangasjarvi, Jaakko; Whelan, James; Kangasjärvi, Saijaliisa (2021)
    Mitochondria are tightly embedded within metabolic and regulatory networks that optimize plant performance in response to environmental challenges. The best-known mitochondrial retrograde signaling pathway involves stress-induced activation of the transcription factor NAC DOMAIN CONTAINING PROTEIN 17 (ANAC017), which initiates protective responses to stress-induced mitochondrial dysfunction in Arabidopsis (Arabidopsis thaliana). Posttranslational control of the elicited responses, however, remains poorly understood. Previous studies linked protein phosphatase 2A subunit PP2A-B'gamma, a key negative regulator of stress responses, with reversible phosphorylation of ACONITASE 3 (ACO3). Here we report on ACO3 and its phosphorylation at Ser91 as key components of stress regulation that are induced by mitochondrial dysfunction. Targeted mass spectrometry-based proteomics revealed that the abundance and phosphorylation of ACO3 increased under stress, which required signaling through ANAC017. Phosphomimetic mutation at ACO3-Ser91 and accumulation of ACO3(S91D)-YFP promoted the expression of genes related to mitochondrial dysfunction. Furthermore, ACO3 contributed to plant tolerance against ultraviolet B (UV-B) or antimycin A-induced mitochondrial dysfunction. These findings demonstrate that ACO3 is both a target and mediator of mitochondrial dysfunction signaling, and critical for achieving stress tolerance in Arabidopsis leaves.
  • Syrjänen, Leo; Valanne, Susanna; Kuuslahti, Marianne; Tuomela, Tea; Sriram, Ashwin; Sanz, Alberto; Jacobs, Howard T.; Rämet, Mika; Parkkila, Seppo (2015)
    Background: Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous enzymes that catalyze the reversible hydration reaction of carbon dioxide. CAs are present as six structurally divergent enzyme families: alpha, beta, gamma, delta, zeta and eta. beta-CAs have a wide distribution across different species including invertebrates. Previously, we showed that Drosophila melanogaster beta-CA is a highly active mitochondrial enzyme. In this study, we investigated the function of Drosophila beta-CA by silencing the expression of the beta-CA gene using UAS/GAL4-based RNA interference (RNAi) in Drosophila in vivo. Results: Crossing beta-CA RNAi lines over ubiquitous Actin driver flies did not produce any viable progeny, indicating that beta-CA expression is required for fly development. RNAi silencing of beta-CA ubiquitously in adult flies did not affect their survival rate or function of mitochondrial electron transport chain. Importantly, beta-CA RNAi led to impaired reproduction. All beta-CA knockdown females were sterile, and produced few or no eggs. Whole ovaries of knockdown females looked normal but upon cadherin staining, there was an apparent functional defect in migration of border cells, which are considered essential for normal fertilization. Conclusions: These results indicate that although Drosophila beta-CA is dispensable for survival of adult flies, it is essential for female fertility.
  • Shapiguzov, Alexey; Nikkanen, Lauri; Fitzpatrick, Duncan; Vainonen, Julia P.; Gossens, Richard; Alseekh, Saleh; Aarabi, Fayezeh; Tiwari, Arjun; Blokhina, Olga; Panzarova, Klara; Benedikty, Zuzana; Tyystjärvi, Esa; Fernie, Alisdair R.; Trtilek, Martin; Aro, Eva-Mari; Rintamäki, Eevi; Kangasjarvi, Jaakko (2020)
    The Arabidopsis mutant rcd1 is tolerant to methyl viologen (MV). MV enhances the Mehler reaction, i.e. electron transfer from Photosystem I (PSI) to O-2, generating reactive oxygen species (ROS) in the chloroplast. To study the MV tolerance of rcd1, we first addressed chloroplast thiol redox enzymes potentially implicated in ROS scavenging. NADPH-thioredoxin oxidoreductase type C (NTRC) was more reduced in rcd1. NTRC contributed to the photosynthetic and metabolic phenotypes of rcd1, but did not determine its MV tolerance. We next tested rcd1 for alterations in the Mehler reaction. In rcd1, but not in the wild type, the PSI-to-MV electron transfer was abolished by hypoxic atmosphere. A characteristic feature of rcd1 is constitutive expression of mitochondrial dysfunction stimulon (MDS) genes that affect mitochondrial respiration. Similarly to rcd1, in other MDS-overexpressing plants hypoxia also inhibited the PSI-to-MV electron transfer. One possible explanation is that the MDS gene products may affect the Mehler reaction by altering the availability of O-2. In green tissues, this putative effect is masked by photosynthetic O-2 evolution. However, O-2 evolution was rapidly suppressed in MV-treated plants. Transcriptomic meta-analysis indicated that MDS gene expression is linked to hypoxic response not only under MV, but also in standard growth conditions. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.
  • Dhandapani, Praveen K.; Begines-Moreno, Isabel M.; Brea-Calvo, Gloria; Gärtner, Ulrich; Graeber, Thomas G.; Javier Sanchez, Gerardo; Morty, Rory E.; Schönig, Kai; ten Hoeve, Johanna; Wietelmann, Astrid; Braun, Thomas; Jacobs, Howard T.; Szibor, Marten (2019)
    Constitutive expression of the chemokine Mcp1 in mouse cardiomyocytes creates a model of inflammatory cardiomyopathy, with death from heart failure at age 7-8 months. A critical pathogenic role has previously been proposed for induced oxidative stress, involving NADPH oxidase activation. To test this idea, we exposed the mice to elevated oxygen levels. Against expectation, this prevented, rather than accelerated, the ultrastructural and functional signs of heart failure. This result suggests that the immune signaling initiated by Mcp1 leads instead to the inhibition of cellular oxygen usage, for which mitochondrial respiration is an obvious target. To address this hypothesis, we combined the Mcp1 model with xenotopic expression of the alternative oxidase (AOX), which provides a sink for electrons blocked from passage to oxygen via respiratory complexes III and IV. Ubiquitous AOX expression provided only a minor delay to cardiac functional deterioration and did not prevent the induction of markers of cardiac and metabolic remodeling considered a hallmark of the model. Moreover, cardiomyocyte-specific AOX expression resulted in exacerbation of Mcp1-induced heart failure, and failed to rescue a second cardiomyopathy model directly involving loss of cIV. Our findings imply that mitochondria! involvement in the pathology of inflammatory cardiomyopathy is multifaceted and complex.
  • Marshall, John D.; Laudon, Hjalmar; Makela, Annikki; Peichl, Matthias; Hasselquist, Niles; Nasholm, Torgny (2021)
    Forests pass water and carbon through while converting portions to streamflow, soil organic matter, wood production, and other ecosystem services. The efficiencies of these transfers are but poorly quantified. New theory and new instruments have made it possible to use stable isotope composition to provide this quantification of efficiencies wherever there is a measurable difference between the branches of a branchpoint. We present a linked conceptual model that relies on isotopes of hydrogen, carbon, and oxygen to describe these branchpoints along the pathway from precipitation to soil and biomass carbon sequestration and illustrate how it can be tested and generalized. Plain Language Summary The way a forest works can be described in terms of carbon and water budgets, which describe the ways that carbon and water flow through the forest. The paths of such flows are frequently branched and the branches are often different in their stable isotope composition. This means that stable isotopes can be used to describe the branching events. We present isotopic methods of quantifying several such events, then link them in a chain that begins with the evaporation of water and ends with biomass production.
  • George, Jack; Tuomela, Tea; Kemppainen, Esko; Nurminen, Antti; Braun, Samuel; Yalgin, Cagri; Jacobs, Howard T. (2019)
    ABSTRACTThe Drosophila bang-sensitive mutant tko25t, manifesting a global deficiency in oxidative phosphorylation due to a mitochondrial protein synthesis defect, exhibits a pronounced delay in larval development. We previously identified a number of metabolic abnormalities in tko25t larvae, including elevated pyruvate and lactate, and found the larval gut to be a crucial tissue for the regulation of larval growth in the mutant. Here we established that expression of wild-type tko in any of several other tissues of tko25t also partially alleviates developmental delay. The effects appeared to be additive, whilst knockdown of tko in a variety of specific tissues phenocopied tko25t, producing developmental delay and bang-sensitivity. These findings imply the existence of a systemic signal regulating growth in response to mitochondrial dysfunction. Drugs and RNAi-targeted on pyruvate metabolism interacted with tko25t in ways that implicated pyruvate or one of its metabolic derivatives in playing a central role in generating such a signal. RNA-seq revealed that dietary pyruvate-induced changes in transcript representation were mostly non-coherent with those produced by tko25t or high-sugar, consistent with the idea that growth regulation operates primarily at the translational and/or metabolic level.
  • Kemppainen, Esko; George, Jack; Garipler, Görkem; Tuomela, Tea; Kiviranta, Essi; Soga, Tomoyoshi; Dunn, Cory D.; Jacobs, Howard T. (2016)
    The Drosophila mutant tko(25t) exhibits a deficiency ofmitochondrial protein synthesis, leading to a global insufficiency of respiration and oxidative phosphorylation. This entrains an organismal phenotype of developmental delay and sensitivity to seizures induced bymechanical stress. We found that the mutant phenotype is exacerbated in a dose-dependent fashion by high dietary sugar levels. tko(25t) larvae were found to exhibit severe metabolic abnormalities that were further accentuated by high-sugar diet. These include elevated pyruvate and lactate, decreased ATP and NADPH. Dietary pyruvate or lactate supplementation phenocopied the effects of high sugar. Based on tissue-specific rescue, the crucial tissue in which this metabolic crisis initiates is the gut. It is accompanied by down-regulation of the apparatus of cytosolic protein synthesis and secretion at both the RNA and post-translational levels, including a novel regulation of S6 kinase at the protein level.
  • Rashid, Fatimah Azzahra Ahmad; Crisp, Peter A.; Zhang, You; Berkowitz, Oliver; Pogson, Barry J.; Day, David A.; Masle, Josette; Dewar, Roderick; Whelan, James; Atkin, Owen K.; Scafaro, Andrew P. (2020)
    To further our understanding of how sustained changes in temperature affect the carbon economy of rice (Oryza sativa), hydroponically grown plants of the IR64 cultivar were developed at 30°C/25°C (day/night) before being shifted to 25/20°C or 40/35°C. Leaf messenger RNA and protein abundance, sugar and starch concentrations, and gas‐exchange and elongation rates were measured on preexisting leaves (PE) already developed at 30/25°C or leaves newly developed (ND) subsequent to temperature transfer. Following a shift in growth temperature, there was a transient adjustment in metabolic gene transcript abundance of PE leaves before homoeostasis was reached within 24 hr, aligning with Rdark (leaf dark respiratory CO2 release) and An (net CO2 assimilation) changes. With longer exposure, the central respiratory protein cytochrome c oxidase (COX) declined in abundance at 40/35°C. In contrast to Rdark, An was maintained across the three growth temperatures in ND leaves. Soluble sugars did not differ significantly with growth temperature, and growth was fastest with extended exposure at 40/35°C. The results highlight that acclimation of photosynthesis and respiration is asynchronous in rice, with heat‐acclimated plants exhibiting a striking ability to maintain net carbon gain and growth when exposed to heat‐wave temperatures, even while reducing investment in energy‐conserving respiratory pathways.
  • Szibor, Marten; Schreckenberg, Rolf; Gizatullina, Zemfira; Dufour, Eric; Wiesnet, Marion; Dhandapani, Praveen K.; Debska-Vielhaber, Grazyna; Heidler, Juliana; Wittig, Ilka; Nyman, Tuula A.; Gärtner, Ulrich; Hall, Andrew R.; Pell, Victoria; Viscomi, Carlo; Krieg, Thomas; Murphy, Michael P.; Braun, Thomas; Gellerich, Frank N.; Schlüter, Klaus-Dieter; Jacobs, Howard T. (2020)
    Abstract Cardiac ischaemia-reperfusion (I/R) injury has been attributed to stress signals arising from an impaired mitochondrial electron transport chain (ETC), which include redox imbalance, metabolic stalling and excessive production of reactive oxygen species (ROS). The alternative oxidase (AOX) is a respiratory enzyme, absent in mammals, that accepts electrons from a reduced quinone pool to reduce oxygen to water, thereby restoring electron flux when impaired and, in the process, blunting ROS production. Hence, AOX represents a natural rescue mechanism from respiratory stress. This study aimed to determine how respiratory restoration through xenotopically expressed AOX affects the re-perfused post-ischaemic mouse heart. As expected, AOX supports ETC function and attenuates the ROS load in post-anoxic heart mitochondria. However, post-ischaemic cardiac remodelling over 3 and 9 weeks was not improved. AOX blunted transcript levels of factors known to be up-regulated upon I/R such as the atrial natriuretic peptide (Anp) whilst expression of pro-fibrotic and pro-apoptotic transcripts were increased. Ex vivo analysis revealed contractile failure at nine but not 3 weeks after ischaemia whilst label-free quantitative proteomics identified an increase in proteins promoting adverse extracellular matrix remodelling. Together, this indicates an essential role for ETC-derived signals during cardiac adaptive remodelling and identified ROS as a possible effector.
  • Gonzalez de Cozar, Jose M.; Gerards, Mike; Teeri, Eveliina; George, Jack; Dufour, Eric; Jacobs, Howard T.; Joers, Priit (2019)
    Mitochondrial DNA (mtDNA) replication uses a simple core machinery similar to those of bacterial viruses and plasmids, but its components are challenging to unravel. Here, we found that, as in mammals, the single Drosophila gene for RNase H1 (rnh1) has alternative translational start sites, resulting in two polypeptides, targeted to either mitochondria or the nucleus. RNAi-mediated rnh1 knockdown did not influence growth or viability of S2 cells, but compromised mtDNA integrity and copy number. rnh1 knockdown in intact flies also produced a phenotype of impaired mitochondrial function, characterized by respiratory chain deficiency, locomotor dysfunction, and decreased lifespan. Its overexpression in S2 cells resulted in cell lethality after 5-9 days, attributable to the nuclearly localized isoform. rnh1 knockdown and overexpression produced opposite effects on mtDNA replication intermediates. The most pronounced effects were seen in genome regions beyond the major replication pauses where the replication fork needs to progress through a gene cluster that is transcribed in the opposite direction. RNase H1 deficiency led to an accumulation of replication intermediates in these zones, abundant mtDNA molecules joined by four-way junctions, and species consistent with fork regression from the origin. These findings indicate replication stalling due to the presence of unprocessed RNA/DNA heteroduplexes, potentially leading to the degradation of collapsed forks or to replication restart by a mechanism involving strand invasion. Both mitochondrial RNA and DNA syntheses were affected by rnh1 knockdown, suggesting that RNase H1 also plays a role in integrating or coregulating these processes in Drosophila mitochondria.
  • Brosche, Mikael; Blomster, Tiina; Salojärvi, Jarkko; Cui, Fuqiang; Sipari, Nina; Leppälä, Johanna; Lamminmäki, Airi; Tomai, Gloria; Narayanasamy, Shaman; Reddy, Ramesha A.; Keinänen, Markku Juhani; Overmyer, Kirk; Kangasjärvi, Jaakko (2014)