1
|
Mancera-Martínez E, Dong Y, Makarian J, Srour O, Thiébeauld O, Jamsheer M, Chicher J, Hammann P, Schepetilnikov M, Ryabova LA. Phosphorylation of a reinitiation supporting protein, RISP, determines its function in translation reinitiation. Nucleic Acids Res 2021; 49:6908-6924. [PMID: 34133725 PMCID: PMC8266674 DOI: 10.1093/nar/gkab501] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 05/14/2021] [Accepted: 06/14/2021] [Indexed: 12/12/2022] Open
Abstract
Reinitiation supporting protein, RISP, interacts with 60S (60S ribosomal subunit) and eIF3 (eukaryotic initiation factor 3) in plants. TOR (target-of-rapamycin) mediates RISP phosphorylation at residue Ser267, favoring its binding to eL24 (60S ribosomal protein L24). In a viral context, RISP, when phosphorylated, binds the CaMV transactivator/ viroplasmin, TAV, to assist in an exceptional mechanism of reinitiation after long ORF translation. Moreover, we show here that RISP interacts with eIF2 via eIF2β and TOR downstream target 40S ribosomal protein eS6. A RISP phosphorylation knockout, RISP-S267A, binds preferentially eIF2β, and both form a ternary complex with eIF3a in vitro. Accordingly, transient overexpression in plant protoplasts of RISP-S267A, but not a RISP phosphorylation mimic, RISP-S267D, favors translation initiation. In contrast, RISP-S267D preferentially binds eS6, and, when bound to the C-terminus of eS6, can capture 60S in a highly specific manner in vitro, suggesting that it mediates 60S loading during reinitiation. Indeed, eS6-deficient plants are highly resistant to CaMV due to their reduced reinitiation capacity. Strikingly, an eS6 phosphomimic, when stably expressed in eS6-deficient plants, can fully restore the reinitiation deficiency of these plants in cellular and viral contexts. These results suggest that RISP function in translation (re)initiation is regulated by phosphorylation at Ser267.
Collapse
Affiliation(s)
- Eder Mancera-Martínez
- Institut de biologie de moléculaire des plantes UPR2357 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Yihan Dong
- Institut de biologie de moléculaire des plantes UPR2357 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Joelle Makarian
- Institut de biologie de moléculaire des plantes UPR2357 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Ola Srour
- Institut de biologie de moléculaire des plantes UPR2357 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Odon Thiébeauld
- Institut de biologie de moléculaire des plantes UPR2357 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Muhammed Jamsheer
- Institut de biologie de moléculaire des plantes UPR2357 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Johana Chicher
- Plateforme protéomique Strasbourg Esplanade FRC1589 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Philippe Hammann
- Plateforme protéomique Strasbourg Esplanade FRC1589 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Mikhail Schepetilnikov
- Institut de biologie de moléculaire des plantes UPR2357 du CNRS, Université de Strasbourg, Strasbourg, France
| | - Lyubov A Ryabova
- Institut de biologie de moléculaire des plantes UPR2357 du CNRS, Université de Strasbourg, Strasbourg, France
| |
Collapse
|
2
|
Obomighie I, Lapenas K, Murphy BE, Bowles AMC, Bechtold U, Prischi F. The Role of Ribosomal Protein S6 Kinases in Plant Homeostasis. Front Mol Biosci 2021; 8:636560. [PMID: 33778006 PMCID: PMC7988200 DOI: 10.3389/fmolb.2021.636560] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Accepted: 01/11/2021] [Indexed: 01/11/2023] Open
Abstract
The p70 ribosomal S6 kinase (S6K) family is a group of highly conserved kinases in eukaryotes that regulates cell growth, cell proliferation, and stress response via modulating protein synthesis and ribosomal biogenesis. S6Ks are downstream effectors of the Target of Rapamycin (TOR) pathway, which connects nutrient and energy signaling to growth and homeostasis, under normal and stress conditions. The plant S6K family includes two isoforms, S6K1 and S6K2, which, despite their high level of sequence similarity, have distinct functions and regulation mechanisms. Significant advances on the characterization of human S6Ks have occurred in the past few years, while studies on plant S6Ks are scarce. In this article, we review expression and activation of the two S6K isoforms in plants and we discuss their roles in mediating responses to stresses and developmental cues.
Collapse
Affiliation(s)
| | - Kestutis Lapenas
- School of Life Sciences, University of Essex, Colchester, United Kingdom
| | - Billy E Murphy
- School of Life Sciences, University of Essex, Colchester, United Kingdom
| | | | - Ulrike Bechtold
- School of Life Sciences, University of Essex, Colchester, United Kingdom
| | - Filippo Prischi
- School of Life Sciences, University of Essex, Colchester, United Kingdom
| |
Collapse
|
3
|
Zhigailov AV, Stanbekova GE, Beisenov DK, Nizkorodova AS, Polimbetova NS, Iskakov BK. Constructing the constitutively active ribosomal protein S6 kinase 2 from Arabidopsis thaliana (AtRPS6K2) and testing its activity in vitro. Vavilovskii Zhurnal Genet Selektsii 2021; 24:233-238. [PMID: 33659803 PMCID: PMC7904244 DOI: 10.18699/vj20.39-o] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Ribosomal protein S6 (RPS6) is the only phosphorylatable protein of the eukaryotic 40S ribosomal subunit. Ribosomes with phosphorylated RPS6 can selectively translate 5'TOP-(5'-terminal oligopyrimidine)-containing mRNAs that encode most proteins of the translation apparatus. The study of translational control of 5'TOP-mRNAs, which are preferentially translated when RPS6 is phosphorylated and cease to be translated when RPS6 is de-phosphorylated, is particularly important. In Arabidopsis thaliana, AtRPS6 is phosphorylated by kinase AtRPS6K2, which should in turn be phosphorylated by upper level kinases (AtPDK1 - at serine (S) 296, AtTOR - at threonine (T) 455 and S437) for full activation. We have cloned AtRPS6K2 cDNA gene and carried out in vitro mutagenesis replacing codons encoding S296, S437 and T455 by triplets of phosphomimetic glutamic acid (E). After the expression of both natural and mutated cDNAs in Escherichia coli cells, two recombinant proteins were isolated: native AtRPS6K2 and presumably constitutively active AtRPS6K2(S296E, S437E, T455E). The activity of these variants was tested in vitro. Both kinases could phosphorylate wheat (Triticum aestivum L.) TaRPS6 as part of 40S ribosomal subunits isolated from wheat embryos, though the non-mutated variant had less activity than phosphomimetic one. The ability of recombinant non-mutated kinase to phosphorylate TaRPS6 can be explained by its phosphorylation by bacterial kinases during the expression and isolation steps. The phosphomimetically mutated AtRPS6K2(S296E, S437E, T455E) can serve as a tool to investigate preferential translation of 5'TOP-mRNAs in wheat germ cell-free system, in which most of 40S ribosomal subunits have phosphorylated TaRPS6. Besides, such an approach has a biotechnological application in producing genetically modified plants with increased biomass and productivity through stimulation of cell growth and division.
Collapse
Affiliation(s)
- A V Zhigailov
- M.A. Aitkhozhin Institute of Molecular Biology and Biochemistry, Almaty, Kazakhstan
| | - G E Stanbekova
- M.A. Aitkhozhin Institute of Molecular Biology and Biochemistry, Almaty, Kazakhstan
| | - D K Beisenov
- M.A. Aitkhozhin Institute of Molecular Biology and Biochemistry, Almaty, Kazakhstan Institute of Plant Biology and Biotechnology, Almaty, Kazakhstan
| | - A S Nizkorodova
- M.A. Aitkhozhin Institute of Molecular Biology and Biochemistry, Almaty, Kazakhstan
| | - N S Polimbetova
- M.A. Aitkhozhin Institute of Molecular Biology and Biochemistry, Almaty, Kazakhstan
| | - B K Iskakov
- M.A. Aitkhozhin Institute of Molecular Biology and Biochemistry, Almaty, Kazakhstan Institute of Plant Biology and Biotechnology, Almaty, Kazakhstan
| |
Collapse
|
4
|
Upadhyaya S, Agrawal S, Gorakshakar A, Rao BJ. TOR kinase activity in Chlamydomonas reinhardtii is modulated by cellular metabolic states. FEBS Lett 2020; 594:3122-3141. [PMID: 32677084 DOI: 10.1002/1873-3468.13888] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Revised: 11/28/2019] [Accepted: 11/28/2019] [Indexed: 12/25/2022]
Abstract
Target of rapamycin (TOR) kinase is a sensor and a central integrator of internal and external metabolic cues. However, in algae and in higher plants, the components of TOR kinase signaling are yet to be characterized. Here, we establish an assay system to study TOR kinase activity in Chlamydomonas reinhardtii using the phosphorylation status of its putative downstream target, CrS6K. Using this assay, we probe the modulation of cellular TOR kinase activity under various physiological states such as photoautotrophy, heterotrophy, mixotrophy, and nitrogen (N) starvation. Importantly, we uncover that excess acetate in the medium leads to high cellular reactive oxygen species levels, triggering autophagy and a concomitant drop in TOR kinase activity in a dose-dependent manner, thus leading to a N-starvation-like cellular phenotype, even when nitrogen is present.
Collapse
Affiliation(s)
- Shivani Upadhyaya
- Department of Biological Sciences, Tata Institute of Fundamental Research (TIFR), Mumbai, India
| | - Shreya Agrawal
- Max Planck Institute of Molecular Plant Physiology, Potsdam, Germany
| | - Anmol Gorakshakar
- School of Biosciences and Technology, VIT University, Vellore, India
| | | |
Collapse
|
5
|
Mizoi J, Kanazawa N, Kidokoro S, Takahashi F, Qin F, Morimoto K, Shinozaki K, Yamaguchi-Shinozaki K. Heat-induced inhibition of phosphorylation of the stress-protective transcription factor DREB2A promotes thermotolerance of Arabidopsis thaliana. J Biol Chem 2018; 294:902-917. [PMID: 30487287 DOI: 10.1074/jbc.ra118.002662] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 11/13/2018] [Indexed: 12/19/2022] Open
Abstract
Plants have evolved complex systems to rapidly respond to severe stress conditions, such as heat, cold, and dehydration. Dehydration-responsive element-binding protein 2A (DREB2A) is a key transcriptional activator that induces many heat- and drought-responsive genes, increases tolerance to both heat and drought stress, and suppresses plant growth in Arabidopsis thaliana. DREB2A expression is induced by stress, but stabilization of the DREB2A protein in response to stress is essential for activating the expression of downstream stress-inducible genes. Under nonstress growth conditions, an integral negative regulatory domain (NRD) destabilizes DREB2A, but the mechanism by which DREB2A is stabilized in response to stress remains unclear. Here, based on bioinformatics, mutational, MS, and biochemical analyses, we report that Ser/Thr residues in the NRD are phosphorylated under nonstress growth conditions and that their phosphorylation decreases in response to heat. Furthermore, we found that this phosphorylation is likely mediated by casein kinase 1 and is essential for the NRD-dependent, proteasomal degradation of DREB2A under nonstress conditions. These observations suggest that inhibition of NRD phosphorylation stabilizes and activates DREB2A in response to heat stress to enhance plant thermotolerance. Our study reveals the molecular basis for the coordination of stress tolerance and plant growth through stress-dependent transcriptional regulation, which may allow the plants to rapidly respond to fluctuating environmental conditions.
Collapse
Affiliation(s)
- Junya Mizoi
- From the Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Natsumi Kanazawa
- From the Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Satoshi Kidokoro
- From the Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Fuminori Takahashi
- Gene Discovery Research Group, RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan, and
| | - Feng Qin
- the Biological Resources and Postharvest Division, Japan International Research Center for Agricultural Sciences, Tsukuba, Ibaraki 305-8686, Japan
| | - Kyoko Morimoto
- From the Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Kazuo Shinozaki
- Gene Discovery Research Group, RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan, and
| | - Kazuko Yamaguchi-Shinozaki
- From the Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan,
| |
Collapse
|
6
|
Yaguchi M, Kozaki A. Plant S6 kinases do not require hydrophobic motif phosphorylation for activity in yeast lacking Ypk3. FEBS Lett 2018; 592:610-620. [PMID: 29355926 DOI: 10.1002/1873-3468.12980] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2017] [Revised: 12/25/2017] [Accepted: 01/15/2018] [Indexed: 11/09/2022]
Abstract
The ribosomal protein S6 kinases (S6K) are among the major substrates and crucial effectors of the target of rapamycin (TOR) kinase, which is an evolutionarily conserved regulator of cell growth and proliferation. Recent research indicates that yeast Ypk3 is an ortholog of mammalian S6Ks. Here, we find that plant S6Ks restore ribosomal protein S6 phosphorylation in a rapamycin-sensitive manner in yeast cells lacking Ypk3. However, phosphorylation of a hydrophobic motif, which is mediated through TOR signaling and essential for mammalian S6K activity, is not detected in plant S6Ks. Furthermore, deletion of the N-terminal region of rice S6Ks shows phosphorylation of the hydrophobic motif and reduced rapamycin sensitivity. Our findings suggest a mechanism of plant S6K activation distinct from that of mammalian S6Ks.
Collapse
Affiliation(s)
| | - Akiko Kozaki
- Department of Biology, Shizuoka University, Japan
| |
Collapse
|
7
|
Schepetilnikov M, Ryabova LA. Recent Discoveries on the Role of TOR (Target of Rapamycin) Signaling in Translation in Plants. PLANT PHYSIOLOGY 2018; 176:1095-1105. [PMID: 29122989 PMCID: PMC5813564 DOI: 10.1104/pp.17.01243] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Accepted: 11/09/2017] [Indexed: 05/18/2023]
Abstract
TOR signaling regulates plant translation via a specific translation initiation mechanism: reinitiation.
Collapse
Affiliation(s)
- Mikhail Schepetilnikov
- Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, UPR 2357, Université de Strasbourg, 67084 Strasbourg, France
| | - Lyubov A Ryabova
- Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, UPR 2357, Université de Strasbourg, 67084 Strasbourg, France
| |
Collapse
|
8
|
Abstract
This chapter describes a method of plant cytosolic ribosomes isolation typically used for further proteomic studies. Detailed description procedures including plant material disruption, various centrifugation steps, sucrose cushion centrifugation, and quality control of preparation are provided.
Collapse
|
9
|
Linn J, Ren M, Berkowitz O, Ding W, van der Merwe MJ, Whelan J, Jost R. Root Cell-Specific Regulators of Phosphate-Dependent Growth. PLANT PHYSIOLOGY 2017; 174:1969-1989. [PMID: 28465462 PMCID: PMC5490885 DOI: 10.1104/pp.16.01698] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 05/01/2017] [Indexed: 05/07/2023]
Abstract
Cellular specialization in abiotic stress responses is an important regulatory feature driving plant acclimation. Our in silico approach of iterative coexpression, interaction, and enrichment analyses predicted root cell-specific regulators of phosphate starvation response networks in Arabidopsis (Arabidopsis thaliana). This included three uncharacterized genes termed Phosphate starvation-induced gene interacting Root Cell Enriched (PRCE1, PRCE2, and PRCE3). Root cell-specific enrichment of 12 candidates was confirmed in promoter-GFP lines. T-DNA insertion lines of 11 genes showed changes in phosphate status and growth responses to phosphate availability compared with the wild type. Some mutants (cbl1, cipk2, prce3, and wdd1) displayed strong biomass gain irrespective of phosphate supply, while others (cipk14, mfs1, prce1, prce2, and s6k2) were able to sustain growth under low phosphate supply better than the wild type. Notably, root or shoot phosphate accumulation did not strictly correlate with organ growth. Mutant response patterns markedly differed from those of master regulators of phosphate homeostasis, PHOSPHATE STARVATION RESPONSE1 (PHR1) and PHOSPHATE2 (PHO2), demonstrating that negative growth responses in the latter can be overcome when cell-specific regulators are targeted. RNA sequencing analysis highlighted the transcriptomic plasticity in these mutants and revealed PHR1-dependent and -independent regulatory circuits with gene coexpression profiles that were highly correlated to the quantified physiological traits. The results demonstrate how in silico prediction of cell-specific, stress-responsive genes uncovers key regulators and how their manipulation can have positive impacts on plant growth under abiotic stress.
Collapse
Affiliation(s)
- Joshua Linn
- Department of Animal, Plant, and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, VIC 3083, Australia
| | - Meiyan Ren
- Department of Animal, Plant, and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, VIC 3083, Australia
| | - Oliver Berkowitz
- Department of Animal, Plant, and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, VIC 3083, Australia
| | - Wona Ding
- College of Science and Technology, Ningbo University, Ningbo, 315211 Zhejiang Province, People's Republic of China
| | - Margaretha J van der Merwe
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Perth, Western Australia, WA 6009, Australia
| | - James Whelan
- Department of Animal, Plant, and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, VIC 3083, Australia
| | - Ricarda Jost
- Department of Animal, Plant, and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, VIC 3083, Australia
| |
Collapse
|
10
|
Dobrenel T, Caldana C, Hanson J, Robaglia C, Vincentz M, Veit B, Meyer C. TOR Signaling and Nutrient Sensing. ANNUAL REVIEW OF PLANT BIOLOGY 2016; 67:261-85. [PMID: 26905651 DOI: 10.1146/annurev-arplant-043014-114648] [Citation(s) in RCA: 243] [Impact Index Per Article: 30.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
All living organisms rely on nutrients to sustain cell metabolism and energy production, which in turn need to be adjusted based on available resources. The evolutionarily conserved target of rapamycin (TOR) protein kinase is a central regulatory hub that connects environmental information about the quantity and quality of nutrients to developmental and metabolic processes in order to maintain cellular homeostasis. TOR is activated by both nitrogen and carbon metabolites and promotes energy-consuming processes such as cell division, mRNA translation, and anabolism in times of abundance while repressing nutrient remobilization through autophagy. In animals and yeasts, TOR acts antagonistically to the starvation-induced AMP-activated kinase (AMPK)/sucrose nonfermenting 1 (Snf1) kinase, called Snf1-related kinase 1 (SnRK1) in plants. This review summarizes the immense knowledge on the relationship between TOR signaling and nutrients in nonphotosynthetic organisms and presents recent findings in plants that illuminate the crucial role of this pathway in conveying nutrient-derived signals and regulating many aspects of metabolism and growth.
Collapse
Affiliation(s)
- Thomas Dobrenel
- Institut Jean-Pierre Bourgin, UMR 1318 INRA AgroParisTech, ERL CNRS 3559, Saclay Plant Sciences, Versailles 78026, France;
- Umeå Plant Science Center, Department of Plant Physiology, Umeå University, Umeå 90187, Sweden
| | - Camila Caldana
- Molecular Physiology of Plant Biomass Production Group, Max Planck Partner Group, Brazilian Bioethanol Science and Technology Laboratory, CEP 13083-100 Campinas, São Paulo, Brazil
| | - Johannes Hanson
- Umeå Plant Science Center, Department of Plant Physiology, Umeå University, Umeå 90187, Sweden
| | - Christophe Robaglia
- Laboratoire de Génétique et Biophysique des Plantes, UMR 7265, DSV, IBEB, SBVME, CEA, CNRS, Aix Marseille Université, Faculté des Sciences de Luminy, Marseille 13009, France
| | - Michel Vincentz
- Laboratório de Genética de Plantas, Centro de Biologia Molecular e Engenharia Genética, Universidade Estadual de Campinas, CEP 13083-875 Campinas, São Paulo, Brazil
| | - Bruce Veit
- Forage Improvement, AgResearch, Institute of Fundamental Sciences, Massey University, Palmerston North 4442, New Zealand
| | - Christian Meyer
- Institut Jean-Pierre Bourgin, UMR 1318 INRA AgroParisTech, ERL CNRS 3559, Saclay Plant Sciences, Versailles 78026, France;
| |
Collapse
|
11
|
Dobrenel T, Mancera-Martínez E, Forzani C, Azzopardi M, Davanture M, Moreau M, Schepetilnikov M, Chicher J, Langella O, Zivy M, Robaglia C, Ryabova LA, Hanson J, Meyer C. The Arabidopsis TOR Kinase Specifically Regulates the Expression of Nuclear Genes Coding for Plastidic Ribosomal Proteins and the Phosphorylation of the Cytosolic Ribosomal Protein S6. FRONTIERS IN PLANT SCIENCE 2016; 7:1611. [PMID: 27877176 PMCID: PMC5100631 DOI: 10.3389/fpls.2016.01611] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 10/12/2016] [Indexed: 05/05/2023]
Abstract
Protein translation is an energy consuming process that has to be fine-tuned at both the cell and organism levels to match the availability of resources. The target of rapamycin kinase (TOR) is a key regulator of a large range of biological processes in response to environmental cues. In this study, we have investigated the effects of TOR inactivation on the expression and regulation of Arabidopsis ribosomal proteins at different levels of analysis, namely from transcriptomic to phosphoproteomic. TOR inactivation resulted in a coordinated down-regulation of the transcription and translation of nuclear-encoded mRNAs coding for plastidic ribosomal proteins, which could explain the chlorotic phenotype of the TOR silenced plants. We have identified in the 5' untranslated regions (UTRs) of this set of genes a conserved sequence related to the 5' terminal oligopyrimidine motif, which is known to confer translational regulation by the TOR kinase in other eukaryotes. Furthermore, the phosphoproteomic analysis of the ribosomal fraction following TOR inactivation revealed a lower phosphorylation of the conserved Ser240 residue in the C-terminal region of the 40S ribosomal protein S6 (RPS6). These results were confirmed by Western blot analysis using an antibody that specifically recognizes phosphorylated Ser240 in RPS6. Finally, this antibody was used to follow TOR activity in plants. Our results thus uncover a multi-level regulation of plant ribosomal genes and proteins by the TOR kinase.
Collapse
Affiliation(s)
- Thomas Dobrenel
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
- Université Paris-Sud–Université Paris-SaclayOrsay, France
- Umeå Plant Science Center, Department of Plant Physiology, Umeå UniversityUmeå, Sweden
| | - Eder Mancera-Martínez
- Institut de Biologie Moléculaire des Plantes, UPR 2357 CNRS, Université de StrasbourgStrasbourg, France
| | - Céline Forzani
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
| | - Marianne Azzopardi
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
| | | | - Manon Moreau
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
- Laboratoire de Génétique et Biophysique des Plantes, UMR 7265, DSV, IBEB, SBVME, CEA, CNRS, Aix-Marseille Université, Faculté des Sciences de LuminyMarseille, France
| | - Mikhail Schepetilnikov
- Institut de Biologie Moléculaire des Plantes, UPR 2357 CNRS, Université de StrasbourgStrasbourg, France
| | - Johana Chicher
- Plateforme Protéomique Strasbourg-Esplanade, CNRS FRC1589, Institut de Biologie Moléculaire et CellulaireStrasbourg, France
| | | | - Michel Zivy
- Plateforme PAPPSO, UMR GQE-Le MoulonGif sur Yvette, France
| | - Christophe Robaglia
- Laboratoire de Génétique et Biophysique des Plantes, UMR 7265, DSV, IBEB, SBVME, CEA, CNRS, Aix-Marseille Université, Faculté des Sciences de LuminyMarseille, France
| | - Lyubov A. Ryabova
- Institut de Biologie Moléculaire des Plantes, UPR 2357 CNRS, Université de StrasbourgStrasbourg, France
| | - Johannes Hanson
- Umeå Plant Science Center, Department of Plant Physiology, Umeå UniversityUmeå, Sweden
| | - Christian Meyer
- Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-SaclayVersailles, France
- *Correspondence: Christian Meyer,
| |
Collapse
|
12
|
Abstract
Although the eukaryotic TOR (target of rapamycin) kinase signalling pathway has emerged as a key player for integrating nutrient-, energy- and stress-related cues with growth and metabolic outputs, relatively little is known of how this ancient regulatory mechanism has been adapted in higher plants. Drawing comparisons with the substantial knowledge base around TOR kinase signalling in fungal and animal systems, functional aspects of this pathway in plants are reviewed. Both conserved and divergent elements are discussed in relation to unique aspects associated with an autotrophic mode of nutrition and adaptive strategies for multicellular development exhibited by plants.
Collapse
|
13
|
Spatial Regulation of Root Growth: Placing the Plant TOR Pathway in a Developmental Perspective. Int J Mol Sci 2015; 16:19671-97. [PMID: 26295391 PMCID: PMC4581319 DOI: 10.3390/ijms160819671] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2015] [Revised: 07/11/2015] [Accepted: 08/11/2015] [Indexed: 12/30/2022] Open
Abstract
Plant cells contain specialized structures, such as a cell wall and a large vacuole, which play a major role in cell growth. Roots follow an organized pattern of development, making them the organs of choice for studying the spatio-temporal regulation of cell proliferation and growth in plants. During root growth, cells originate from the initials surrounding the quiescent center, proliferate in the division zone of the meristem, and then increase in length in the elongation zone, reaching their final size and differentiation stage in the mature zone. Phytohormones, especially auxins and cytokinins, control the dynamic balance between cell division and differentiation and therefore organ size. Plant growth is also regulated by metabolites and nutrients, such as the sugars produced by photosynthesis or nitrate assimilated from the soil. Recent literature has shown that the conserved eukaryotic TOR (target of rapamycin) kinase pathway plays an important role in orchestrating plant growth. We will summarize how the regulation of cell proliferation and cell expansion by phytohormones are at the heart of root growth and then discuss recent data indicating that the TOR pathway integrates hormonal and nutritive signals to orchestrate root growth.
Collapse
|
14
|
Ribosomal Protein S6 Phosphorylation: Four Decades of Research. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 320:41-73. [PMID: 26614871 DOI: 10.1016/bs.ircmb.2015.07.006] [Citation(s) in RCA: 182] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The phosphorylation of ribosomal protein S6 (rpS6) has been described for the first time about four decades ago. Since then, numerous studies have shown that this modification occurs in response to a wide variety of stimuli on five evolutionarily conserved serine residues. However, despite a large body of information on the respective kinases and the signal transduction pathways, the physiological role of rpS6 phosphorylation remained obscure until genetic manipulations were applied in both yeast and mammals in an attempt to block this modification. Thus, studies based on both mice and cultured cells subjected to disruption of the genes encoding rpS6 and the respective kinases, as well as the substitution of the phosphorylatable serine residues in rpS6, have laid the ground for the elucidation of the multiple roles of this protein and its posttranslational modification. This review focuses primarily on newly identified kinases that phosphorylate rpS6, pathways that transduce various signals into rpS6 phosphorylation, and the recently established physiological functions of this modification. It should be noted, however, that despite the significant progress made in the last decade, the molecular mechanism(s) underlying the diverse effects of rpS6 phosphorylation on cellular and organismal physiology are still poorly understood.
Collapse
|
15
|
Lehti-Shiu MD, Shiu SH. Diversity, classification and function of the plant protein kinase superfamily. Philos Trans R Soc Lond B Biol Sci 2012; 367:2619-39. [PMID: 22889912 DOI: 10.1098/rstb.2012.0003] [Citation(s) in RCA: 202] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Eukaryotic protein kinases belong to a large superfamily with hundreds to thousands of copies and are components of essentially all cellular functions. The goals of this study are to classify protein kinases from 25 plant species and to assess their evolutionary history in conjunction with consideration of their molecular functions. The protein kinase superfamily has expanded in the flowering plant lineage, in part through recent duplications. As a result, the flowering plant protein kinase repertoire, or kinome, is in general significantly larger than other eukaryotes, ranging in size from 600 to 2500 members. This large variation in kinome size is mainly due to the expansion and contraction of a few families, particularly the receptor-like kinase/Pelle family. A number of protein kinases reside in highly conserved, low copy number families and often play broadly conserved regulatory roles in metabolism and cell division, although functions of plant homologues have often diverged from their metazoan counterparts. Members of expanded plant kinase families often have roles in plant-specific processes and some may have contributed to adaptive evolution. Nonetheless, non-adaptive explanations, such as kinase duplicate subfunctionalization and insufficient time for pseudogenization, may also contribute to the large number of seemingly functional protein kinases in plants.
Collapse
Affiliation(s)
- Melissa D Lehti-Shiu
- Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA
| | | |
Collapse
|
16
|
Ren M, Venglat P, Qiu S, Feng L, Cao Y, Wang E, Xiang D, Wang J, Alexander D, Chalivendra S, Logan D, Mattoo A, Selvaraj G, Datla R. Target of rapamycin signaling regulates metabolism, growth, and life span in Arabidopsis. THE PLANT CELL 2012; 24:4850-74. [PMID: 23275579 PMCID: PMC3556962 DOI: 10.1105/tpc.112.107144] [Citation(s) in RCA: 183] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Target of Rapamycin (TOR) is a major nutrition and energy sensor that regulates growth and life span in yeast and animals. In plants, growth and life span are intertwined not only with nutrient acquisition from the soil and nutrition generation via photosynthesis but also with their unique modes of development and differentiation. How TOR functions in these processes has not yet been determined. To gain further insights, rapamycin-sensitive transgenic Arabidopsis thaliana lines (BP12) expressing yeast FK506 Binding Protein12 were developed. Inhibition of TOR in BP12 plants by rapamycin resulted in slower overall root, leaf, and shoot growth and development leading to poor nutrient uptake and light energy utilization. Experimental limitation of nutrient availability and light energy supply in wild-type Arabidopsis produced phenotypes observed with TOR knockdown plants, indicating a link between TOR signaling and nutrition/light energy status. Genetic and physiological studies together with RNA sequencing and metabolite analysis of TOR-suppressed lines revealed that TOR regulates development and life span in Arabidopsis by restructuring cell growth, carbon and nitrogen metabolism, gene expression, and rRNA and protein synthesis. Gain- and loss-of-function Ribosomal Protein S6 (RPS6) mutants additionally show that TOR function involves RPS6-mediated nutrition and light-dependent growth and life span in Arabidopsis.
Collapse
Affiliation(s)
- Maozhi Ren
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | - Prakash Venglat
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | - Shuqing Qiu
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | - Li Feng
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | - Yongguo Cao
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | - Edwin Wang
- Computational Chemistry and Bioinformatics Group, Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec H4P 2R2, Canada
| | - Daoquan Xiang
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | - Jinghe Wang
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | | | | | - David Logan
- Université d’Angers, Institut de Recherche en Horticulture et Semences, SFR 4207 QUASAV, LUNAM Université, Angers cedex 1, France
| | - Autar Mattoo
- Sustainable Agricultural Systems Laboratory, U.S. Department of Agriculture–Agricultural Research Service, Beltsville Agricultural Research Center, Beltsville, Maryland 20705-2350
| | - Gopalan Selvaraj
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | - Raju Datla
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
- Address correspondence to
| |
Collapse
|
17
|
Juntawong P, Bailey-Serres J. Dynamic Light Regulation of Translation Status in Arabidopsis thaliana. FRONTIERS IN PLANT SCIENCE 2012; 3:66. [PMID: 22645595 DOI: 10.3389/fpls.2012.00066/abstract] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 03/20/2012] [Indexed: 05/26/2023]
Abstract
Light, a dynamic environmental parameter, is an essential regulator of plant growth and development. Light-regulated transcriptional networks are well documented, whereas light-regulated post-transcriptional regulation has received limited attention. In this study, dynamics in translation of cytosolic mRNAs were evaluated at the genome-level in Arabidopsis thaliana seedlings grown under a typical light/dark diurnal regime, shifted to darkness at midday, and then re-illuminated. One-hour of unanticipated darkness reduced levels of polysomes by 17% in a manner consistent with inhibition of initiation of translation. This down-regulation of translation was reversed within 10 min of re-illumination. Quantitative comparison of the total cellular population of transcripts (the transcriptome) to those associated with one or more 80S ribosome (the translatome) identified over 1600 mRNAs that were differentially translated in response to light availability. Unanticipated darkness limited both transcription and translation of mRNAs encoding components of the photosynthetic machinery. Many mRNAs encoding proteins associated with the energy demanding process of protein synthesis were stable but sequestered in the dark, in a rapidly reversible manner. A meta-analysis determined these same transcripts were similarly and coordinately regulated in response to changes in oxygen availability. The dark and hypoxia translationally repressed mRNAs lack highly supported candidate RNA-regulatory elements but are characterized by G + C-rich 5'-untranslated regions. We propose that modulation of translation of a subset of cellular mRNAs functions as an energy conservation mechanism.
Collapse
Affiliation(s)
- Piyada Juntawong
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California Riverside, CA, USA
| | | |
Collapse
|
18
|
Juntawong P, Bailey-Serres J. Dynamic Light Regulation of Translation Status in Arabidopsis thaliana. FRONTIERS IN PLANT SCIENCE 2012; 3:66. [PMID: 22645595 PMCID: PMC3355768 DOI: 10.3389/fpls.2012.00066] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 03/20/2012] [Indexed: 05/18/2023]
Abstract
Light, a dynamic environmental parameter, is an essential regulator of plant growth and development. Light-regulated transcriptional networks are well documented, whereas light-regulated post-transcriptional regulation has received limited attention. In this study, dynamics in translation of cytosolic mRNAs were evaluated at the genome-level in Arabidopsis thaliana seedlings grown under a typical light/dark diurnal regime, shifted to darkness at midday, and then re-illuminated. One-hour of unanticipated darkness reduced levels of polysomes by 17% in a manner consistent with inhibition of initiation of translation. This down-regulation of translation was reversed within 10 min of re-illumination. Quantitative comparison of the total cellular population of transcripts (the transcriptome) to those associated with one or more 80S ribosome (the translatome) identified over 1600 mRNAs that were differentially translated in response to light availability. Unanticipated darkness limited both transcription and translation of mRNAs encoding components of the photosynthetic machinery. Many mRNAs encoding proteins associated with the energy demanding process of protein synthesis were stable but sequestered in the dark, in a rapidly reversible manner. A meta-analysis determined these same transcripts were similarly and coordinately regulated in response to changes in oxygen availability. The dark and hypoxia translationally repressed mRNAs lack highly supported candidate RNA-regulatory elements but are characterized by G + C-rich 5'-untranslated regions. We propose that modulation of translation of a subset of cellular mRNAs functions as an energy conservation mechanism.
Collapse
Affiliation(s)
- Piyada Juntawong
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of CaliforniaRiverside, CA, USA
| | - Julia Bailey-Serres
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of CaliforniaRiverside, CA, USA
- *Correspondence: Julia Bailey-Serres, Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California, Riverside, CA 92521, USA. e-mail:
| |
Collapse
|
19
|
Pan MH, Lin J, Prior JL, Piwnica-Worms D. Monitoring molecular-specific pharmacodynamics of rapamycin in vivo with inducible Gal4->Fluc transgenic reporter mice. Mol Cancer Ther 2010; 9:2752-60. [PMID: 20858726 DOI: 10.1158/1535-7163.mct-10-0265] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Rapamycin (Rap), a small-molecule inhibitor of mTOR, is an immunosuppressant, and several Rap analogues are cancer chemotherapeutics. Further pharmacologic development will be significantly facilitated if in vivo reporter models are available to enable monitoring of molecular-specific pharmacodynamic actions of Rap and its analogues. Herein we present the use of a Gal4→Fluc reporter mouse for the study of Rap-induced mTOR/FKBP12 protein-protein interactions in vivo with the use of a mouse two-hybrid transactivation strategy, a derivative of the yeast two-hybrid system applied to live mice. Upon treatment with Rap, a bipartite transactivator was reconstituted, and transcription of a genomic firefly luciferase reporter was activated in a concentration-dependent (K(d) = 2.3 nmol/L) and FK506-competitive (K(i) = 17.1 nmol/L) manner in cellulo, as well as in a temporal and specific manner in vivo. In particular, after a single dose of Rap (4.5 mg/kg, i.p.), peak Rap-induced protein-protein interactions were observed in the liver at 24 hours post treatment, with photon flux signals 600-fold over baseline, which correlated temporally with suppression of p70S6 kinase activity, a downstream effector of mTOR. The Gal4→Fluc reporter mouse provides an intact physiologic system to interrogate protein-protein interactions and molecular-specific pharmacodynamics during drug discovery and lead characterization. Imaging protein interactions and functional proteomics in whole animals in vivo may serve as a basic tool for screening and mechanism-based analysis of small molecules targeting specific protein-protein interactions in human diseases.
Collapse
Affiliation(s)
- Mei-Hsiu Pan
- Molecular Imaging Center, Mallinckrodt Institute of Radiology, BRIGHT Institute, and Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
| | | | | | | |
Collapse
|
20
|
Henriques R, Magyar Z, Monardes A, Khan S, Zalejski C, Orellana J, Szabados L, de la Torre C, Koncz C, Bögre L. Arabidopsis S6 kinase mutants display chromosome instability and altered RBR1-E2F pathway activity. EMBO J 2010; 29:2979-93. [PMID: 20683442 DOI: 10.1038/emboj.2010.164] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2009] [Accepted: 06/29/2010] [Indexed: 12/27/2022] Open
Abstract
The 40S ribosomal protein S6 kinase (S6K) is a conserved component of signalling pathways controlling growth in eukaryotes. To study S6K function in plants, we isolated single- and double-knockout mutations and RNA-interference (RNAi)-silencing lines in the linked Arabidopsis S6K1 and S6K2 genes. Hemizygous s6k1s6k2/++ mutant and S6K1 RNAi lines show high phenotypic instability with variation in size, increased trichome branching, produce non-viable pollen and high levels of aborted seeds. Analysis of their DNA content by flow cytometry, as well as chromosome counting using DAPI staining and fluorescence in situ hybridization, revealed an increase in ploidy and aneuploidy. In agreement with this data, we found that S6K1 associates with the Retinoblastoma-related 1 (RBR1)-E2FB complex and this is partly mediated by its N-terminal LVxCxE motif. Moreover, the S6K1-RBR1 association regulates RBR1 nuclear localization, as well as E2F-dependent expression of cell cycle genes. Arabidopsis cells grown under nutrient-limiting conditions require S6K for repression of cell proliferation. The data suggest a new function for plant S6K as a repressor of cell proliferation and required for maintenance of chromosome stability and ploidy levels.
Collapse
Affiliation(s)
- Rossana Henriques
- Royal Holloway, University of London, School of Biological Sciences, Egham Hill, Egham, UK.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Creff A, Sormani R, Desnos T. The two Arabidopsis RPS6 genes, encoding for cytoplasmic ribosomal proteins S6, are functionally equivalent. PLANT MOLECULAR BIOLOGY 2010; 73:533-546. [PMID: 20437080 DOI: 10.1007/s11103-010-9639-y] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2009] [Accepted: 04/15/2010] [Indexed: 05/26/2023]
Abstract
Many eukaryotic genomes have experienced ancient whole-genome duplication (WGD) followed by massive gene loss. These eliminations were not random since some gene families were preferentially retained as duplicates. The gene balance hypothesis suggests that those genes with dosage reduction can imbalance their interacting partners or complex, resulting in decreased fitness. In Arabidopsis, the cytoplasmic ribosomal proteins (RP) are encoded by gene families with at least two members. We have focused our study on the two RPS6 genes in an attempt to understand why they have been retained as duplicates. We demonstrate that RPS6 function is vital for the plant. We also show that reducing the level of RPS6 accumulation (in the knock-out rps6a or rps6b single mutants, or in the double heterozygous RPS6A/rps6a,RPS6B/rps6b), confers a slow growth phenotype (haplodeficiency). Importantly, we demonstrate that the functions of two RPS6 genes are redundant and interchangeable. Finally, like in most other described Arabidopsis rp mutants, we observed that a reduced RPS6 level slightly alters the dorsoventral leaf patterning. Our results support the idea that the Arabidopsis RPS6 gene duplicates were evolutionarily retained in order to maintain an expression level necessary to sustain the translational demand of the cell, in agreement with the gene balance hypothesis.
Collapse
Affiliation(s)
- Audrey Creff
- Laboratoire de Biologie du Développement des Plantes (LBDP), SBVME/IBEB/DSV/CEA/CNRS/Université Aix-Marseille-II, 13108 St. Paul-lez-Durance, France
| | | | | |
Collapse
|
22
|
Matsuura H, Ishibashi Y, Shinmyo A, Kanaya S, Kato K. Genome-Wide Analyses of Early Translational Responses to Elevated Temperature and High Salinity in Arabidopsis thaliana. ACTA ACUST UNITED AC 2010; 51:448-62. [DOI: 10.1093/pcp/pcq010] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
|
23
|
Tzeng TY, Kong LR, Chen CH, Shaw CC, Yang CH. Overexpression of the lily p70(s6k) gene in Arabidopsis affects elongation of flower organs and indicates TOR-dependent regulation of AP3, PI and SUP translation. PLANT & CELL PHYSIOLOGY 2009; 50:1695-1709. [PMID: 19651701 DOI: 10.1093/pcp/pcp114] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The p70 ribosomal S6 kinase (p70(s6k)) signaling pathway plays a key role in regulating the cell cycle via translational regulation of specific 5'TOP mRNAs. However, the function of this signaling pathway is still poorly understood in plants. Ectopic expression of the lily putative p70(s6k) gene, LS6K1, resulted in up-regulation of NAP (NAC-LIKE, ACTIVATED BY AP3/PI) and PISTILLATA (PI) expression, and significantly inhibited cell expansion for petals and stamens, resulting in the male sterility phenotype in transgenic Arabidopsis. Sequence analysis revealed that the genes involved in petal and stamen development, such as APETALA3 (AP3), PI and SUPERMAN (SUP), probably encode 5'TOP mRNAs. Green fluorescent protein (GFP), fused to oligopyrimidine tract sequences that were identified in the 5'-untranslated region (UTR) of AP3, PI and SUP, was translationally regulated in human cells in response to mitogen stimulation and inhibition by the macrolide antibiotic rapamycin. Furthermore, 35S::LS6K1 significantly up-regulated beta-glucuronidase (GUS) activity in the flower buds of transgenic plants carrying the GUS transgene fused to the AP3 promoter and the 5' UTR. These results have identified a novel role for the p70(s6k) gene in regulating cell division and the expansion of petals and stamens by translational regulation of the 5'TOP mRNAs once ectopically expressed in Arabidopsis.
Collapse
Affiliation(s)
- Tsai-Yu Tzeng
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan ROC
| | | | | | | | | |
Collapse
|
24
|
Branco-Price C, Kaiser KA, Jang CJH, Larive CK, Bailey-Serres J. Selective mRNA translation coordinates energetic and metabolic adjustments to cellular oxygen deprivation and reoxygenation in Arabidopsis thaliana. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2008; 56:743-55. [PMID: 18665916 DOI: 10.1111/j.1365-313x.2008.03642.x] [Citation(s) in RCA: 225] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Cellular oxygen deprivation (hypoxia/anoxia) requires an acclimation response that enables survival during an energy crisis. To gain new insights into the processes that facilitate the endurance of transient oxygen deprivation, the dynamics of the mRNA translation state and metabolites were quantitatively monitored in Arabidopsis thaliana seedlings exposed to a short (2 h) or prolonged (9 h) period of oxygen and carbon dioxide deprivation and following 1 h of re-aeration. Hypoxia stress and reoxygenation promoted adjustments in the levels of polyribosomes (polysomes) that were highly coordinated with cellular ATP content. A quantitative comparison of steady-state and polysomal mRNA populations revealed that over half of the cellular mRNAs were restricted from polysome complexes during the stress, with little or no change in abundance. This selective repression of translation was rapidly reversed upon reoxygenation. Comparison of the adjustment in gene transcripts and metabolites demonstrated that profiling of polysomal mRNAs strongly augments the prediction of cellular processes that are altered during cellular oxygen deprivation. The selective translation of a subset of mRNAs promotes the conservation of ATP and facilitates the transition to anaerobic metabolism during low-oxygen stress.
Collapse
|
25
|
Abercrombie JM, Halfhill MD, Ranjan P, Rao MR, Saxton AM, Yuan JS, Stewart CN. Transcriptional responses of Arabidopsis thaliana plants to As (V) stress. BMC PLANT BIOLOGY 2008; 8:87. [PMID: 18684332 PMCID: PMC2547109 DOI: 10.1186/1471-2229-8-87] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2007] [Accepted: 08/06/2008] [Indexed: 05/20/2023]
Abstract
BACKGROUND Arsenic is toxic to plants and a common environmental pollutant. There is a strong chemical similarity between arsenate [As (V)] and phosphate (Pi). Whole genome oligonucleotide microarrays were employed to investigate the transcriptional responses of Arabidopsis thaliana plants to As (V) stress. RESULTS Antioxidant-related genes (i.e. coding for superoxide dismutases and peroxidases) play prominent roles in response to arsenate. The microarray experiment revealed induction of chloroplast Cu/Zn superoxide dismutase (SOD) (at2g28190), Cu/Zn SOD (at1g08830), as well as an SOD copper chaperone (at1g12520). On the other hand, Fe SODs were strongly repressed in response to As (V) stress. Non-parametric rank product statistics were used to detect differentially expressed genes. Arsenate stress resulted in the repression of numerous genes known to be induced by phosphate starvation. These observations were confirmed with qRT-PCR and SOD activity assays. CONCLUSION Microarray data suggest that As (V) induces genes involved in response to oxidative stress and represses transcription of genes induced by phosphate starvation. This study implicates As (V) as a phosphate mimic in the cell by repressing genes normally induced when available phosphate is scarce. Most importantly, these data reveal that arsenate stress affects the expression of several genes with little or unknown biological functions, thereby providing new putative gene targets for future research.
Collapse
Affiliation(s)
- Jason M Abercrombie
- Department of Plant Sciences, University of Tennessee, 2431 Joe Johnson Blvd., Knoxville, TN 37996-4561, USA
| | - Matthew D Halfhill
- Biology Department, St. Ambrose University, 518 West Locust St., Davenport, IA 52803, USA
| | - Priya Ranjan
- Department of Plant Sciences, University of Tennessee, 2431 Joe Johnson Blvd., Knoxville, TN 37996-4561, USA
| | - Murali R Rao
- Department of Plant Sciences, University of Tennessee, 2431 Joe Johnson Blvd., Knoxville, TN 37996-4561, USA
| | - Arnold M Saxton
- Department of Animal Science, University of Tennessee, 2505 River Dr., Knoxville, TN 37996-4561, USA
| | - Joshua S Yuan
- Department of Plant Sciences, University of Tennessee, 2431 Joe Johnson Blvd., Knoxville, TN 37996-4561, USA
| | - C Neal Stewart
- Department of Plant Sciences, University of Tennessee, 2431 Joe Johnson Blvd., Knoxville, TN 37996-4561, USA
| |
Collapse
|
26
|
Martin J, Masri J, Bernath A, Nishimura RN, Gera J. Hsp70 associates with Rictor and is required for mTORC2 formation and activity. Biochem Biophys Res Commun 2008; 372:578-83. [PMID: 18505677 DOI: 10.1016/j.bbrc.2008.05.086] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Accepted: 05/14/2008] [Indexed: 10/22/2022]
Abstract
mTORC2 is a multiprotein kinase composed of mTOR, mLST8, PRR5, mSIN1 and Rictor. The complex is insensitive to rapamycin and has demonstrated functions controlling cell growth, motility, invasion and cytoskeletal assembly. mTORC2 is the major hydrophobic domain kinase which renders Akt fully active via phosphorylation on serine 473. We isolated Hsp70 as a putative Rictor interacting protein in a yeast two-hybrid assay and confirmed this interaction via co-immunoprecipitation and colocalization experiments. In cells expressing an antisense RNA targeting Hsp70, mTORC2 formation and activity were impaired. Moreover, in cells lacking Hsp70 expression, mTORC2 activity was inhibited following heat shock while controls demonstrated increased mTORC2 activity. These differential effects on mTORC2 activity were specific, in that mTORC1 did not demonstrate Hsp70-dependent alterations under these conditions. These data suggest that Hsp70 is a component of mTORC2 and is required for proper assembly and activity of the kinase both constitutively and following heat shock.
Collapse
Affiliation(s)
- Jheralyn Martin
- Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, 16111 Plummer Street (151), Building 1, Room C111A, Los Angeles, CA 91343, USA
| | | | | | | | | |
Collapse
|
27
|
Meyuhas O. Physiological roles of ribosomal protein S6: one of its kind. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 268:1-37. [PMID: 18703402 DOI: 10.1016/s1937-6448(08)00801-0] [Citation(s) in RCA: 170] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The phosphorylation of ribosomal protein S6 (rpS6), which occurs in response to a wide variety of stimuli on five evolutionarily conserved serine residues, has attracted much attention since its discovery more than three decades ago. However, despite a large body of information on the respective kinases and the signal transduction pathways, the role of this phosphorylation remained obscure. It is only recent that targeting the genes encoding rpS6, the phosphorylatable serine residues or the respective kinases that the unique role of rpS6 and its posttranslational modification have started to be elucidated. This review focuses primarily on the critical role of rpS6 for mouse development, the pathways that transduce various signals into rpS6 phosphorylation, and the physiological functions of this modification. The mechanism(s) underlying the diverse effects of rpS6 phosphorylation on cellular and organismal physiology has yet to be determined. However, a model emerging from the currently available data suggests that rpS6 phosphorylation operates, at least partly, by counteracting positive signals simultaneously induced by rpS6 kinase, and thus might be involved in fine-tuning of the cellular response to these signals.
Collapse
Affiliation(s)
- Oded Meyuhas
- Department of Biochemistry, Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| |
Collapse
|
28
|
Abstract
The TOR (target of rapamycin) pathway is an evolutionarily conserved signaling module regulating cell growth (accumulation of mass) in response to a variety of environmental cues such as nutrient availability, hypoxia, DNA damage and osmotic stress. Its pivotal role in cellular and organismal homeostasis is reflected in the fact that unrestrained signaling activity in mammals is associated with the occurrence of disease states including inflammation, cancer and diabetes. The existence of TOR homologs in unicellular organisms whose growth is affected by environmental factors, such as temperature, nutrients and osmolarity, suggests an ancient role for the TOR signaling network in the surveillance of stress conditions. Here, we will summarize recent advances in the TOR signaling field with special emphasis on how stress conditions impinge on insulin/insulin-like growth factor signaling/TOR signaling.
Collapse
Affiliation(s)
- J H Reiling
- Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, MA 02142-1479, USA
| | | |
Collapse
|
29
|
Um SH, D'Alessio D, Thomas G. Nutrient overload, insulin resistance, and ribosomal protein S6 kinase 1, S6K1. Cell Metab 2006; 3:393-402. [PMID: 16753575 DOI: 10.1016/j.cmet.2006.05.003] [Citation(s) in RCA: 511] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2005] [Revised: 05/01/2006] [Accepted: 05/03/2006] [Indexed: 12/13/2022]
Abstract
Nutrient overload leads to obesity, insulin resistance, and often type 2 diabetes. Whereas increased fat intake is commonly cited as the major factor in diet-induced dysmetabolic states, increased protein consumption also contributes, through elevated circulating amino acids. Recent studies have revealed that ribosomal protein S6 kinase 1, S6K1, an effector of mTOR, is sensitive to both insulin and nutrients, including amino acids. Although S6K1 is an effector of growth, recent reports show that amino acids also negatively affect insulin signaling through mTOR/S6K1 phosphorylation of IRS1. Moreover, rather than signaling through the class 1 PI3K pathway, amino acids appear to mediate mTOR activation through class 3 PI3K, or hVps34. Consistent with this, infusion of amino acids into humans leads to S6K1 activation, inhibition of insulin-induced class 1 PI3K activation, and insulin resistance. Thus, S6K1 may mediate deleterious effects, like insulin resistance, and potentially type 2 diabetes in the face of nutrient excess.
Collapse
Affiliation(s)
- Sung Hee Um
- Department of Genome Science, Genome Research Institute, University of Cincinnati, 2180 E. Galbraith Road, Cincinnati, Ohio 45237, USA
| | | | | |
Collapse
|
30
|
McIntosh KB, Bonham-Smith PC. Ribosomal protein gene regulation: what about plants? ACTA ACUST UNITED AC 2006. [DOI: 10.1139/b06-014] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ribosome is an intricate ribonucleoprotein complex with a multitude of protein constituents present in equimolar amounts. Coordination of the synthesis of these ribosomal proteins (r-proteins) presents a major challenge to the cell. Although most r-proteins are highly conserved, the mechanisms by which r-protein gene expression is regulated often differ widely among species. While the primary regulatory mechanisms coordinating r-protein synthesis in bacteria, yeast, and animals have been identified, the mechanisms governing the coordination of plant r-protein expression remain largely unexplored. In addition, plants are unique among eukaryotes in carrying multiple (often more than two) functional genes encoding each r-protein, which substantially complicates coordinate expression. A survey of the current knowledge regarding coordinated systems of r-protein gene expression in different model organisms suggests that vertebrate r-protein gene regulation provides a valuable comparison for plants.
Collapse
Affiliation(s)
- Kerri B. McIntosh
- Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK S7N 5E2, Canada
| | - Peta C. Bonham-Smith
- Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK S7N 5E2, Canada
| |
Collapse
|
31
|
Mahfouz MM, Kim S, Delauney AJ, Verma DPS. Arabidopsis TARGET OF RAPAMYCIN interacts with RAPTOR, which regulates the activity of S6 kinase in response to osmotic stress signals. THE PLANT CELL 2006; 18:477-90. [PMID: 16377759 PMCID: PMC1356553 DOI: 10.1105/tpc.105.035931] [Citation(s) in RCA: 251] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
TARGET OF RAPAMYCIN (TOR) kinase controls many cellular functions in eukaryotic cells in response to stress and nutrient availability and was shown to be essential for embryonic development in Arabidopsis thaliana. We demonstrated that Arabidopsis RAPTOR1 (a TOR regulatory protein) interacts with the HEAT repeats of TOR and that RAPTOR1 regulates the activity of S6 kinase (S6K) in response to osmotic stress. RAPTOR1 also interacts in vivo with Arabidopsis S6K1, a putative substrate for TOR. S6K1 fused to green fluorescent protein and immunoprecipitated from tobacco (Nicotiana tabacum) leaves after transient expression was active in phosphorylating the Arabidopsis ribosomal S6 protein. The catalytic domain of S6K1 could be phosphorylated by Arabidopsis 3-phosphoinositide-dependent protein kinase-1 (PDK1), indicating the involvement of PDK1 in the regulation of S6K. The S6K1 activity was sensitive to osmotic stress, while PDK1 activity was not affected. However, S6K1 sensitivity to osmotic stress was relieved by co-overexpression of RAPTOR1. Overall, these observations demonstrated the existence of a functional TOR kinase pathway in plants. However, Arabidopsis seedlings do not respond to normal physiological levels of rapamycin, which appears to be due its inability to bind to the Arabidopsis homolog of FKBP12, a protein that is essential for the binding of rapamycin with TOR. Replacement of the Arabidopsis FKBP12 with the human FKBP12 allowed rapamycin-dependent interaction with TOR. Since homozygous mutation in TOR is lethal, it suggests that this pathway is essential for integrating the stress signals into the growth regulation.
Collapse
Affiliation(s)
- Magdy M Mahfouz
- Department of Molecular Genetics and Plant Biotechnology Center, The Ohio State University, Columbus, Ohio 43210, USA
| | | | | | | |
Collapse
|
32
|
Ulm R, Nagy F. Signalling and gene regulation in response to ultraviolet light. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:477-82. [PMID: 16039155 DOI: 10.1016/j.pbi.2005.07.004] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2005] [Accepted: 07/12/2005] [Indexed: 05/03/2023]
Abstract
In contrast to phytochrome-, cryptochrome- and phototropin-sensing systems, about which considerable knowledge has accumulated, the ultraviolet-B (UVB) photoreceptor is not yet known at the molecular level. Information about the downstream signalling events that underlie UVB-provoked physiological responses is limited. Recent whole-genome transcript profiling, isolation of mutants that are impaired in specific UVB-induced responses and detailed photobiological studies suggest that responses that are triggered by shorter wavelength UVB and longer wavelength UVB are mediated by two different sensory systems. The bZIP transcription factor HY5 was recently identified as an important player in the long-wavelength UVB-induced signal transduction cascade. Advances in the development of luciferase-reporter lines will make it feasible to perform high-throughput genetic screens to isolate novel mutants that are impaired in sensing or transducing signals downstream of the putative UVB photoreceptor(s).
Collapse
Affiliation(s)
- Roman Ulm
- Institute of Biology II/Botany, University of Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany.
| | | |
Collapse
|
33
|
Otterhag L, Gustavsson N, Alsterfjord M, Pical C, Lehrach H, Gobom J, Sommarin M. Arabidopsis PDK1: identification of sites important for activity and downstream phosphorylation of S6 kinase. Biochimie 2005; 88:11-21. [PMID: 16125835 DOI: 10.1016/j.biochi.2005.07.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2004] [Accepted: 07/21/2005] [Indexed: 01/14/2023]
Abstract
The Arabidopsis thaliana protein kinase AtPDK1 was identified as a homologue of the mammalian 3-phosphoinositide-dependent protein kinase-1 (PDK1), which is involved in a number of physiological processes including cell growth and proliferation. We now show that AtPDK1, expressed in E. coli as a recombinant protein, undergoes autophosphorylation at several sites. Using mass spectrometry, three phosphorylated amino acid residues, Ser-177, Ser-276 and Ser-382, were identified, followed by mutational analyses to reveal their roles. These residues are not conserved in mammalian PDK1s. Mutation of Ser-276 in AtPDK1 to alanine resulted in an enzyme with no detectable autophosphorylation. Autophosphorylation was significantly reduced in the Ser177Ala mutant but was only slightly reduced in the Ser382Ala mutant. Other identified sites of importance for autophosphorylation and/or activity of AtPDK1 were Asp-167, Thr-176, and Thr-211. Sites in the mammalian PDK1 corresponding to Asp-167 and Thr-211 are essential for PDK1 autophosphorylation and activity. Autophosphorylation was absent in the Asp167Ala mutant while the Thr176Ala and The211Ala mutants exhibited very low but detectable autophosphorylation, pointing to both similarity and difference between mammalian and plant enzymes. We also demonstrate that AtS6k2, an A. thaliana homologue to the mammalian S6 kinases, is an in vitro target of AtPDK1. Our data clearly show that Asp-167, Thr-176, Ser-177, Thr-211, and Ser-276 in AtPDK1 are important for the downstream phosphorylation of AtS6k2. The results confirm that AtPDK1, like mammalian PDK1, needs phosphorylation at several sites for full downstream phosphorylation activity. Finally, we investigated A. thaliana 14-3-3 proteins as potential AtPDK1 regulatory proteins and the effect of phospholipids on the AtPDK1 activity. Nine of the 12 14-3-3 isoforms tested enhanced AtPDK1 activity whereas one isoform suppressed the activity. No significant effects on AtPDK1 activity by the various phospholipids (including phosphoinositides) were evident.
Collapse
Affiliation(s)
- Lotta Otterhag
- Department of Plant Biochemistry, Lund University, P.O. Box 124, SE-22100 Lund, Sweden.
| | | | | | | | | | | | | |
Collapse
|
34
|
Zanetti ME, Chang IF, Gong F, Galbraith DW, Bailey-Serres J. Immunopurification of polyribosomal complexes of Arabidopsis for global analysis of gene expression. PLANT PHYSIOLOGY 2005; 138:624-35. [PMID: 15955926 PMCID: PMC1150383 DOI: 10.1104/pp.105.059477] [Citation(s) in RCA: 173] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2005] [Revised: 02/14/2005] [Accepted: 02/16/2005] [Indexed: 05/03/2023]
Abstract
Immunoaffinity purification of polyribosomes (polysomes) from crude leaf extracts of Arabidopsis (Arabidopsis thaliana) was achieved with transgenic genotypes that overexpress a translational fusion of a ribosomal protein (RP) with a His(6)-FLAG dual epitope tag. In plants with a cauliflower mosaic virus 35S:HF-RPL18 transgene immunopurification with anti-FLAG agarose beads yielded 60-Svedberg ribosomal subunits, intact 80-Svedberg monosomes and polysomes. Sucrose density gradient fractionation of the purified complexes demonstrated that the distribution of polysome size was similar in crude cell extracts and the purified complexes. The immunopurified complexes included putative cytosolic RPs of Arabidopsis and ribosome-associated proteins, as well as full-length transcripts of high and low abundance. Whole-genome profiling using long DNA oligonucleotide-based microarrays provided a high level of reproducibility between polysomal mRNA samples immunopurified from two independent biological replicates (r approximately 0.90). Comparison of immunopurified and total cellular RNA samples revealed that for most of the genes, the mRNAs were associated with the epitope-tagged polysomal complexes, with an average relative level of association of 62.06% +/- 4.39%. The results demonstrate that the immunopurification of polysomes can be a valuable tool for the quantification of mRNAs present in translation complexes in plant cells. This technology can be extended to evaluation of mRNA populations at the cell- or tissue-specific level by regulation of the tagged RP with distinct promoters.
Collapse
Affiliation(s)
- María Eugenia Zanetti
- Department of Botany and Plant Science, Center for Plant Cell Biology, University of California, Riverside, California 92521-0124, USA
| | | | | | | | | |
Collapse
|
35
|
Giavalisco P, Wilson D, Kreitler T, Lehrach H, Klose J, Gobom J, Fucini P. High heterogeneity within the ribosomal proteins of the Arabidopsis thaliana 80S ribosome. PLANT MOLECULAR BIOLOGY 2005; 57:577-91. [PMID: 15821981 DOI: 10.1007/s11103-005-0699-3] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2004] [Accepted: 01/15/2005] [Indexed: 05/17/2023]
Abstract
Proteomic studies have addressed the composition of plant chloroplast ribosomes and 70S ribosomes from the unicellular organism Chlamydomonas reinhardtii But comprehensive characterization of cytoplasmic 80S ribosomes from higher plants has been lacking. We have used two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS) to analyse the cytoplasmic 80S ribosomes from the model flowering plant Arabidopsis thaliana. Of the 80 ribosomal protein families predicted to comprise the cytoplasmic 80S ribosome, we have confirmed the presence of 61; specifically, 27 (84%) of the small 40S subunit and 34 (71%) of the large 60S subunit. Nearly half (45%) of the ribosomal proteins identified are represented by two or more distinct spots in the 2-DE gel indicating that these proteins are either post-translationally modified or present as different isoforms. Consistently, MS-based protein identification revealed that at least one-third (34%) of the identified ribosomal protein families showed expression of two or more family members. In addition, we have identified a number of non-ribosomal proteins that co-migrate with the plant 80S ribosomes during gradient centrifugation suggesting their possible association with the 80S ribosomes. Among them, RACK1 has recently been proposed to be a ribosome-associated protein that promotes efficient translation in yeast. The study, thus provides the basis for further investigation into the function of the other identified non-ribosomal proteins as well as the biological meaning of the various ribosomal protein isoforms.
Collapse
Affiliation(s)
- Patrick Giavalisco
- Max-Planck-Institute for Molecular Genetics, Ihnestr. 73, D-14195 Berlin, Germany
| | | | | | | | | | | | | |
Collapse
|
36
|
Chang IF, Szick-Miranda K, Pan S, Bailey-Serres J. Proteomic characterization of evolutionarily conserved and variable proteins of Arabidopsis cytosolic ribosomes. PLANT PHYSIOLOGY 2005; 137:848-62. [PMID: 15734919 PMCID: PMC1065386 DOI: 10.1104/pp.104.053637] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2004] [Revised: 11/16/2004] [Accepted: 11/23/2004] [Indexed: 05/18/2023]
Abstract
Analysis of 80S ribosomes of Arabidopsis (Arabidopsis thaliana) by use of high-speed centrifugation, sucrose gradient fractionation, one- and two-dimensional gel electrophoresis, liquid chromatography purification, and mass spectrometry (matrix-assisted laser desorption/ionization time-of-flight and electrospray ionization) identified 74 ribosomal proteins (r-proteins), of which 73 are orthologs of rat r-proteins and one is the plant-specific r-protein P3. Thirty small (40S) subunit and 44 large (60S) subunit r-proteins were confirmed. In addition, an ortholog of the mammalian receptor for activated protein kinase C, a tryptophan-aspartic acid-domain repeat protein, was found to be associated with the 40S subunit and polysomes. Based on the prediction that each r-protein is present in a single copy, the mass of the Arabidopsis 80S ribosome was estimated as 3.2 MD (1,159 kD 40S; 2,010 kD 60S), with the 4 single-copy rRNAs (18S, 26S, 5.8S, and 5S) contributing 53% of the mass. Despite strong evolutionary conservation in r-protein composition among eukaryotes, Arabidopsis 80S ribosomes are variable in composition due to distinctions in mass or charge of approximately 25% of the r-proteins. This is a consequence of amino acid sequence divergence within r-protein gene families and posttranslational modification of individual r-proteins (e.g. amino-terminal acetylation, phosphorylation). For example, distinct types of r-proteins S15a and P2 accumulate in ribosomes due to evolutionarily divergence of r-protein genes. Ribosome variation is also due to amino acid sequence divergence and differential phosphorylation of the carboxy terminus of r-protein S6. The role of ribosome heterogeneity in differential mRNA translation is discussed.
Collapse
Affiliation(s)
- Ing-Feng Chang
- Center for Plant Cell Biology, Department of Botany and Plant Sciences, University of California, Riverside, California 92521-0124, USA.
| | | | | | | |
Collapse
|
37
|
Casati P, Walbot V. Crosslinking of ribosomal proteins to RNA in maize ribosomes by UV-B and its effects on translation. PLANT PHYSIOLOGY 2004; 136:3319-32. [PMID: 15466230 PMCID: PMC523391 DOI: 10.1104/pp.104.047043] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Ultraviolet-B (UV-B) photons can cause substantial cellular damage in biomolecules, as is well established for DNA. Because RNA has the same absorption spectrum for UV as DNA, we have investigated damage to this cellular constituent. In maize (Zea mays) leaves, UV-B radiation damages ribosomes by crosslinking cytosolic ribosomal proteins S14, L23a, and L32, and chloroplast ribosomal protein L29 to RNA. Ribosomal damage accumulated during a day of UV-B exposure correlated with a progressive decrease in new protein production; however, de novo synthesis of some ribosomal proteins is increased after 6 h of UV-B exposure. After 16 h without UV-B, damaged ribosomes were eliminated and translation was restored to normal levels. Ribosomal protein S6 and an S6 kinase are phosphorylated during UV-B exposure; these modifications are associated with selective translation of some ribosomal proteins after ribosome damage in mammalian fibroblast cells and may be an adaptation in maize. Neither photosynthesis nor pigment levels were affected significantly by UV-B, demonstrating that the treatment applied is not lethal and that maize leaf physiology readily recovers.
Collapse
Affiliation(s)
- Paula Casati
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA.
| | | |
Collapse
|
38
|
Turck F, Zilbermann F, Kozma SC, Thomas G, Nagy F. Phytohormones participate in an S6 kinase signal transduction pathway in Arabidopsis. PLANT PHYSIOLOGY 2004; 134:1527-35. [PMID: 15064379 PMCID: PMC419828 DOI: 10.1104/pp.103.035873] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2003] [Revised: 01/08/2004] [Accepted: 01/08/2004] [Indexed: 05/20/2023]
Abstract
Addition of fresh medium to stationary cells of Arabidopsis suspension culture induces increased phosphorylation of the S6 ribosomal protein and activation of its cognate kinase, AtS6k. Analysis of the activation response revealed that medium constituents required for S6 kinase activation were the phytohormones 1-naphthylacetic acid (auxin) and kinetin. Pretreatment of cells with anti-auxin or PI3-kinase drugs inhibited this response. Consistent with these findings, LY294002, a PI3-kinase inhibitor, efficiently suppressed phytohormone-induced S6 phosphorylation and translational up-regulation of ribosomal protein S6 and S18A mRNAs without affecting global translation. These data indicate that (1) activation of AtS6k is regulated by phytohormones, at least in part, via a lipid kinase-dependent pathway, that (2) the translational regulation of ribosomal proteins appears to be conserved throughout the plant and animal kingdom, and that (3) these events are hallmarks of a growth-related signal transduction pathway novel in plants.
Collapse
|
39
|
Anthony RG, Henriques R, Helfer A, Mészáros T, Rios G, Testerink C, Munnik T, Deák M, Koncz C, Bögre L. A protein kinase target of a PDK1 signalling pathway is involved in root hair growth in Arabidopsis. EMBO J 2004; 23:572-81. [PMID: 14749726 PMCID: PMC1271803 DOI: 10.1038/sj.emboj.7600068] [Citation(s) in RCA: 212] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2003] [Accepted: 12/15/2003] [Indexed: 11/09/2022] Open
Abstract
Here we report on a lipid-signalling pathway in plants that is downstream of phosphatidic acid and involves the Arabidopsis protein kinase, AGC2-1, regulated by the 3'-phosphoinositide-dependent kinase-1 (AtPDK1). AGC2-1 specifically interacts with AtPDK1 through a conserved C-terminal hydrophobic motif that leads to its phosphorylation and activation, whereas inhibition of AtPDK1 expression by RNA interference abolishes AGC2-1 activity. Phosphatidic acid specifically binds to AtPDK1 and stimulates AGC2-1 in an AtPDK1-dependent manner. AtPDK1 is ubiquitously expressed in all plant tissues, whereas expression of AGC2-1 is abundant in fast-growing organs and dividing cells, and activated during re-entry of cells into the cell cycle after sugar starvation-induced G1-phase arrest. Plant hormones, auxin and cytokinin, synergistically activate the AtPDK1-regulated AGC2-1 kinase, indicative of a role in growth and cell division. Cellular localisation of GFP-AGC2-1 fusion protein is highly dynamic in root hairs and at some stages confined to root hair tips and to nuclei. The agc2-1 knockout mutation results in a reduction of root hair length, suggesting a role for AGC2-1 in root hair growth and development.
Collapse
Affiliation(s)
- Richard G Anthony
- School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, UK
| | - Rossana Henriques
- School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, UK
| | - Anne Helfer
- School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, UK
| | - Tamás Mészáros
- School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, UK
| | - Gabino Rios
- Max-Planck Institut für Züchtungsforschung Carl-von-Linné-Weg 10, Köln, Germany
| | - Christa Testerink
- Department of Plant Physiology, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, Netherlands
| | - Teun Munnik
- Department of Plant Physiology, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, Netherlands
| | - Maria Deák
- MRC Protein Phosphorylation Unit, University of Dundee, Dow Street, Dundee, UK
| | - Csaba Koncz
- Max-Planck Institut für Züchtungsforschung Carl-von-Linné-Weg 10, Köln, Germany
| | - László Bögre
- School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, UK
- School of Biological Sciences, Royal Holloway, University of London, Egham TW20 0EX, UK. Tel.: +44 1784 443407; Fax: +44 1784 434326; E-mail:
| |
Collapse
|
40
|
Abstract
In mammalian, insect, and yeast cells, TOR proteins are essential regulators of cell growth in response to environmental signals including nutrients, mitogens, and stresses. Although many aspects of the TOR-dependent signalling pathway are conserved between animals and fungi, important differences have also been found and are likely to be related to the ecophysiological adaptations of these organisms. The TOR protein also exists in plants. This review will first discuss specific aspects of plants concerning the contribution of cell growth to overall growth, as well as their responses to nutrient starvation, with emphasis on recent results obtained through genetic analysis in the model plant Arabidopsis thaliana. This is followed by the current status of the genetic analysis of the TOR gene in this plant and the search for potential members of a TOR pathway in the Arabidopsis genome.
Collapse
Affiliation(s)
- B Menand
- CEA Cadarache DSV DEVM, Laboratoire du Métabolisme Carboné, UMR 163 CNRS CEA, Univ-Méditerranée UMR 163, Saint-Paul-lez-Durance, France
| | | | | |
Collapse
|
41
|
Williams AJ, Werner-Fraczek J, Chang IF, Bailey-Serres J. Regulated phosphorylation of 40S ribosomal protein S6 in root tips of maize. PLANT PHYSIOLOGY 2003; 132:2086-97. [PMID: 12913163 PMCID: PMC181292 DOI: 10.1104/pp.103.022749] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2003] [Revised: 03/27/2003] [Accepted: 04/02/2003] [Indexed: 05/18/2023]
Abstract
Ribosomal protein S6 (RPS6) is located in the mRNA binding site of the 40S subunit of cytosolic ribosomes. Two maize (Zea mays) rps6 genes were identified that encode polypeptides (30 kD, 11.4 pI) with strong primary amino acid sequence and predicted secondary structure similarity to RPS6 of other eukaryotes. Maize RPS6 was analyzed by the use of two-dimensional gel electrophoresis systems, in vivo labeling with [(32)P]P(i) and immunological detection. Nine RPS6 isoforms were resolved in a two-dimensional basic-urea/sodium dodecyl sulfate-polyacrylamide gel electrophoresis system. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry performed on trypsin-digested isoforms identified four serine (Ser) and one threonine (Thr) residue in the carboxy-terminal region as phosphorylation sites (RRS(238)KLS(241)AAAKAS(247)AAT(250)S(251)A-COOH). Heterogeneity in RPS6 phosphorylation was a consequence of the presence of zero to five phosphorylated residues. Phosphorylated isoforms fell into two groups characterized by (a) sequential phosphorylation of Ser-238 and Ser-241 and (b) the absence of phospho-Ser-238 and presence of phospho-Ser-241. The accumulation of hyper-phosphorylated isoforms with phospho-Ser-238 was reduced in response to oxygen deprivation and heat shock, whereas accumulation of these isoforms was elevated by cold stress. Salt and osmotic stress had no reproducible effect on RPS6 phosphorylation. The reduction in hyper-phosphorylated isoforms under oxygen deprivation was blocked by okadaic acid, a Ser/Thr phosphatase inhibitor. By contrast, the recovery of hyper-phosphorylated isoforms upon re-oxygenation was blocked by LY-294002, an inhibitor of phosphatidylinositol 3-kinases. Thus, differential activity of phosphatase(s) and kinase(s) determine complex heterogeneity in RPS6 phosphorylation.
Collapse
Affiliation(s)
- Alan J Williams
- Center for Plant Cell Biology, Department of Botany and Plant Sciences, University of California, Riverside, California 92521-0124, USA
| | | | | | | |
Collapse
|
42
|
Menand B, Desnos T, Nussaume L, Berger F, Bouchez D, Meyer C, Robaglia C. Expression and disruption of the Arabidopsis TOR (target of rapamycin) gene. Proc Natl Acad Sci U S A 2002; 99:6422-7. [PMID: 11983923 PMCID: PMC122964 DOI: 10.1073/pnas.092141899] [Citation(s) in RCA: 333] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
TOR (target of rapamycin) protein kinases were identified in yeasts, mammals, and Drosophila as central controllers of cell growth in response to nutrient and growth factors. Here we show that Arabidopsis thaliana possesses a single TOR gene encoding a protein able to complex with yeast 12-kDa FK506-binding protein and rapamycin despite the insensitivity of Arabidopsis vegetative growth to rapamycin. Analysis of two T-DNA insertion mutants shows that disruption of AtTOR leads to the premature arrest of endosperm and embryo development. A T-DNA-mediated translational fusion of AtTOR with the GUS reporter gene allows us to show that AtTOR is expressed in primary meristem, embryo, and endosperm, but not in differentiated cells. The implications of these features for the plant TOR pathway are discussed.
Collapse
Affiliation(s)
- Benoît Menand
- Département d'Ecophysiologie Végétale et Microbiologie, Laboratoire du Métabolisme Carboné, Univ-Méditerranée Unité Mixte de Recherche 163, F-13108 Saint-Paul-lez-Durance, Cedex, France
| | | | | | | | | | | | | |
Collapse
|
43
|
Barakat A, Szick-Miranda K, Chang IF, Guyot R, Blanc G, Cooke R, Delseny M, Bailey-Serres J. The organization of cytoplasmic ribosomal protein genes in the Arabidopsis genome. PLANT PHYSIOLOGY 2001; 127:398-415. [PMID: 11598216 DOI: 10.1104/pp.010265.398] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Eukaryotic ribosomes are made of two components, four ribosomal RNAs, and approximately 80 ribosomal proteins (r-proteins). The exact number of r-proteins and r-protein genes in higher plants is not known. The strong conservation in eukaryotic r-protein primary sequence allowed us to use the well-characterized rat (Rattus norvegicus) r-protein set to identify orthologues on the five haploid chromosomes of Arabidopsis. By use of the numerous expressed sequence tag (EST) accessions and the complete genomic sequence of this species, we identified 249 genes (including some pseudogenes) corresponding to 80 (32 small subunit and 48 large subunit) cytoplasmic r-protein types. None of the r-protein genes are single copy and most are encoded by three or four expressed genes, indicative of the internal duplication of the Arabidopsis genome. The r-proteins are distributed throughout the genome. Inspection of genes in the vicinity of r-protein gene family members confirms extensive duplications of large chromosome fragments and sheds light on the evolutionary history of the Arabidopsis genome. Examination of large duplicated regions indicated that a significant fraction of the r-protein genes have been either lost from one of the duplicated fragments or inserted after the initial duplication event. Only 52 r-protein genes lack a matching EST accession, and 19 of these contain incomplete open reading frames, confirming that most genes are expressed. Assessment of cognate EST numbers suggests that r-protein gene family members are differentially expressed.
Collapse
Affiliation(s)
- A Barakat
- Laboratoire Génome et Développement des Plantes, Unité Mixte de Recherche 5096 Centre National de la Recherche Scientifique, Université de Perpignan, 52 Avenue de Villeneuve, 66860 Perpignan cedex, France
| | | | | | | | | | | | | | | |
Collapse
|
44
|
Barakat A, Szick-Miranda K, Chang IF, Guyot R, Blanc G, Cooke R, Delseny M, Bailey-Serres J. The organization of cytoplasmic ribosomal protein genes in the Arabidopsis genome. PLANT PHYSIOLOGY 2001; 127:398-415. [PMID: 11598216 DOI: 10.1104/pp.010265] [Citation(s) in RCA: 208] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Eukaryotic ribosomes are made of two components, four ribosomal RNAs, and approximately 80 ribosomal proteins (r-proteins). The exact number of r-proteins and r-protein genes in higher plants is not known. The strong conservation in eukaryotic r-protein primary sequence allowed us to use the well-characterized rat (Rattus norvegicus) r-protein set to identify orthologues on the five haploid chromosomes of Arabidopsis. By use of the numerous expressed sequence tag (EST) accessions and the complete genomic sequence of this species, we identified 249 genes (including some pseudogenes) corresponding to 80 (32 small subunit and 48 large subunit) cytoplasmic r-protein types. None of the r-protein genes are single copy and most are encoded by three or four expressed genes, indicative of the internal duplication of the Arabidopsis genome. The r-proteins are distributed throughout the genome. Inspection of genes in the vicinity of r-protein gene family members confirms extensive duplications of large chromosome fragments and sheds light on the evolutionary history of the Arabidopsis genome. Examination of large duplicated regions indicated that a significant fraction of the r-protein genes have been either lost from one of the duplicated fragments or inserted after the initial duplication event. Only 52 r-protein genes lack a matching EST accession, and 19 of these contain incomplete open reading frames, confirming that most genes are expressed. Assessment of cognate EST numbers suggests that r-protein gene family members are differentially expressed.
Collapse
Affiliation(s)
- A Barakat
- Laboratoire Génome et Développement des Plantes, Unité Mixte de Recherche 5096 Centre National de la Recherche Scientifique, Université de Perpignan, 52 Avenue de Villeneuve, 66860 Perpignan cedex, France
| | | | | | | | | | | | | | | |
Collapse
|
45
|
Barakat A, Szick-Miranda K, Chang IF, Guyot R, Blanc G, Cooke R, Delseny M, Bailey-Serres J. The organization of cytoplasmic ribosomal protein genes in the Arabidopsis genome. PLANT PHYSIOLOGY 2001; 127:398-415. [PMID: 11598216 PMCID: PMC125077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 03/16/2001] [Revised: 05/16/2001] [Accepted: 07/03/2001] [Indexed: 04/17/2023]
Abstract
Eukaryotic ribosomes are made of two components, four ribosomal RNAs, and approximately 80 ribosomal proteins (r-proteins). The exact number of r-proteins and r-protein genes in higher plants is not known. The strong conservation in eukaryotic r-protein primary sequence allowed us to use the well-characterized rat (Rattus norvegicus) r-protein set to identify orthologues on the five haploid chromosomes of Arabidopsis. By use of the numerous expressed sequence tag (EST) accessions and the complete genomic sequence of this species, we identified 249 genes (including some pseudogenes) corresponding to 80 (32 small subunit and 48 large subunit) cytoplasmic r-protein types. None of the r-protein genes are single copy and most are encoded by three or four expressed genes, indicative of the internal duplication of the Arabidopsis genome. The r-proteins are distributed throughout the genome. Inspection of genes in the vicinity of r-protein gene family members confirms extensive duplications of large chromosome fragments and sheds light on the evolutionary history of the Arabidopsis genome. Examination of large duplicated regions indicated that a significant fraction of the r-protein genes have been either lost from one of the duplicated fragments or inserted after the initial duplication event. Only 52 r-protein genes lack a matching EST accession, and 19 of these contain incomplete open reading frames, confirming that most genes are expressed. Assessment of cognate EST numbers suggests that r-protein gene family members are differentially expressed.
Collapse
Affiliation(s)
- A Barakat
- Laboratoire Génome et Développement des Plantes, Unité Mixte de Recherche 5096 Centre National de la Recherche Scientifique, Université de Perpignan, 52 Avenue de Villeneuve, 66860 Perpignan cedex, France
| | | | | | | | | | | | | | | |
Collapse
|
46
|
Dinkova TD, Aguilar R, Sánchez de Jiménez E. Expression of maize eukaryotic initiation factor (eIF) iso4E is regulated at the translational level. Biochem J 2000; 351 Pt 3:825-31. [PMID: 11042140 PMCID: PMC1221425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
Mechanisms for regulation of gene expression at the translational level have been reported at specific developmental stages in eukaryotes. Control of eukaryotic initiation factor (eIF) 4E availability by insulin/growth factors constitutes a main point of translational regulation. The aim of the present research was to understand the regulatory mechanism(s) behind the differential expression of two main 4E factors present in maize embryonic axes during germination. De novo synthesis of eIFiso4E initiates earlier and is faster than that of eIF4E in maize axes. Insulin addition to maize axes stimulated de novo synthesis of the eIFiso4E protein, but not that of eIF4E. Specific recruitment of the eIFiso4E transcript into polysomes was observed in these axes after insulin stimulation. Inhibitors of the insulin signal-transduction pathway, wortmannin and rapamycin, reversed the insulin effect. In vitro translation of maize poly(A)(+) RNAs by S6 ribosomal protein (rp)-phosphorylated ribosomes demonstrated a strong increase in eIFiso4E synthesis, as compared with its translation by S6 rp-non-phosphorylated ribosomes. Other mRNAs from the poly(A)(+) RNA set, including the eIF4E mRNA, did not show differential translation with regard to the S6-phosphorylated status of the ribosomes. The overall results indicate that eIFiso4E, but not eIF4E, cell content is regulated by de novo synthesis in maize axes during germination, most probably by specific mRNA recruitment into polysomes via a signal-transduction pathway involving S6 rp phosphorylation.
Collapse
Affiliation(s)
- T D Dinkova
- Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México (UNAM), 04510 México, D.F
| | | | | |
Collapse
|
47
|
Harris DM, Myrick TL, Rundle SJ. The Arabidopsis homolog of yeast TAP42 and mammalian alpha4 binds to the catalytic subunit of protein phosphatase 2A and is induced by chilling. PLANT PHYSIOLOGY 1999; 121:609-17. [PMID: 10517853 PMCID: PMC59424 DOI: 10.1104/pp.121.2.609] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/1999] [Accepted: 06/11/1999] [Indexed: 05/18/2023]
Abstract
Type 2A serine/threonine protein phosphatases (PP2A) have been implicated as important mediators of a number of plant growth and developmental processes. In an effort to identify plant PP2A substrates and/or regulators, we performed a yeast two-hybrid screen using an Arabidopsis PP2A catalytic subunit cDNA as bait. All true positives identified by this screen were derived from the same gene, which we have named TAP46 (2A phosphatase associated protein of 46 kD). The TAP46 gene appears to be a single-copy gene and is expressed in all Arabidopsis organs. Transcripts derived from this gene are induced by chilling treatment but not by heat or anaerobic stress. Immunoprecipitation assays using antibodies generated to a peptide spanning amino acids 356 to 366 of TAP46 indicate that TAP46 is associated with a type 2A protein phosphatase in vivo. A search of the database identified TAP46 as a homolog of Saccharomyces cerevisiae TAP42 and mammalian alpha4. These two proteins are known to bind to the catalytic subunit of PP2A and to function in the target-of-rapamycin signaling pathway. Our results identify TAP46 as a plant PP2A-associated protein, with a possible function in the chilling response, and suggest that a target-of-rapamycin-like signaling pathway may exist in plants.
Collapse
Affiliation(s)
- D M Harris
- Department of Biology, Western Carolina University, Cullowhee, North Carolina 28723, USA
| | | | | |
Collapse
|
48
|
Deak M, Casamayor A, Currie RA, Downes CP, Alessi DR. Characterisation of a plant 3-phosphoinositide-dependent protein kinase-1 homologue which contains a pleckstrin homology domain. FEBS Lett 1999; 451:220-6. [PMID: 10371193 DOI: 10.1016/s0014-5793(99)00556-6] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A plant homologue of mammalian 3-phosphoinositide-dependent protein kinase-1 (PDK1) has been identified in Arabidopsis and rice which displays 40% overall identity with human 3-phosphoinositide-dependent protein kinase-1. Like the mammalian 3-phosphoinositide-dependent protein kinase-1, Arabidopsis 3-phosphoinositide-dependent protein kinase-1 and rice 3-phosphoinositide-dependent protein kinase-1 possess a kinase domain at N-termini and a pleckstrin homology domain at their C-termini. Arabidopsis 3-phosphoinositide-dependent protein kinase-1 can rescue lethality in Saccharomyces cerevisiae caused by disruption of the genes encoding yeast 3-phosphoinositide-dependent protein kinase-1 homologues. Arabidopsis 3-phosphoinositide-dependent protein kinase-1 interacts via its pleckstrin homology domain with phosphatidic acid, PtdIns3P, PtdIns(3,4,5)P3 and PtdIns(3,4)P2 and to a lesser extent with PtdIns(4,5)P2 and PtdIns4P. Arabidopsis 3-phosphoinositide-dependent protein kinase-1 is able to activate human protein kinase B alpha (PKB/AKT) in the presence of PtdIns(3,4,5)P3. Arabidopsis 3-phosphoinositide-dependent protein kinase-1 is only the second plant protein reported to possess a pleckstrin homology domain and the first plant protein shown to bind 3-phosphoinositides.
Collapse
Affiliation(s)
- M Deak
- Department of Biochemistry, University of Dundee, UK.
| | | | | | | | | |
Collapse
|
49
|
Bailey-Serres J. Selective translation of cytoplasmic mRNAs in plants. TRENDS IN PLANT SCIENCE 1999; 4:142-148. [PMID: 10322548 DOI: 10.1016/s1360-1385(99)01386-2] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Translation of mRNA is emerging as an important mode of gene regulation in plants. It is frequently controlled at initiation and appears to be regulated by competition for limiting translational components, different requirements for specific factors and cis-acting mRNA elements. Recent studies indicate that interactions between the 5' and 3' ends of the message enhance translation, perhaps by facilitating recruitment of initiation factors or enhancing ribosome recycling. Normal development and environmental stimuli modulate the phosphorylation of components of the mRNA 5'-cap-binding complex, ribosomes and mRNA-binding proteins. These modifications might be responsible for changes in the hierarchy of mRNAs that are in competition for translation.
Collapse
Affiliation(s)
- J Bailey-Serres
- Dept of Botany and Plant Sciences, University of California, Riverside, CA 92521-0124, USA
| |
Collapse
|
50
|
Revenkova E, Masson J, Koncz C, Afsar K, Jakovleva L, Paszkowski J. Involvement of Arabidopsis thaliana ribosomal protein S27 in mRNA degradation triggered by genotoxic stress. EMBO J 1999; 18:490-9. [PMID: 9889204 PMCID: PMC1171142 DOI: 10.1093/emboj/18.2.490] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A recessive Arabidopsis mutant with elevated sensitivity to DNA damaging treatments was identified in one out of 800 families generated by T-DNA insertion mutagenesis. The T-DNA generated a chromosomal deletion of 1287 bp in the promoter of one of three S27 ribosomal protein genes (ARS27A) preventing its expression. Seedlings of ars27A developed normally under standard growth conditions, suggesting wild-type proficiency of translation. However, growth was strongly inhibited in media supplemented with methyl methane sulfate (MMS) at a concentration not affecting the wild type. This inhibition was accompanied by the formation of tumor-like structures instead of auxiliary roots. Wild-type seedlings treated with increasing concentrations of MMS up to a lethal dose never displayed such a trait, neither was this phenotype observed in ars27A plants in the absence of MMS or under other stress conditions. Thus, the hypersensitivity and tumorous growth are mutant-specific responses to the genotoxic MMS treatment. Another important feature of the mutant is its inability to perform rapid degradation of transcripts after UV treatment, as seen in wild-type plants. Therefore, we propose that the ARS27A protein is dispensable for protein synthesis under standard conditions but is required for the elimination of possibly damaged mRNA after UV irradiation.
Collapse
Affiliation(s)
- E Revenkova
- Friedrich Miescher Institute, PO Box 2543, CH-4002 Basel, Switzerland.
| | | | | | | | | | | |
Collapse
|