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Saini LK, Bheri M, Pandey GK. Protein phosphatases and their targets: Comprehending the interactions in plant signaling pathways. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2023; 134:307-370. [PMID: 36858740 DOI: 10.1016/bs.apcsb.2022.11.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
Protein phosphorylation is a vital reversible post-translational modification. This process is established by two classes of enzymes: protein kinases and protein phosphatases. Protein kinases phosphorylate proteins while protein phosphatases dephosphorylate phosphorylated proteins, thus, functioning as 'critical regulators' in signaling pathways. The eukaryotic protein phosphatases are classified as phosphoprotein phosphatases (PPP), metallo-dependent protein phosphatases (PPM), protein tyrosine (Tyr) phosphatases (PTP), and aspartate (Asp)-dependent phosphatases. The PPP and PPM families are serine (Ser)/threonine (Thr) specific phosphatases (STPs) that dephosphorylate Ser and Thr residues. The PTP family dephosphorylates Tyr residues while dual-specificity phosphatases (DsPTPs/DSPs) dephosphorylate Ser, Thr, and Tyr residues. The composition of these enzymes as well as their substrate specificity are important determinants of their functional significance in a number of cellular processes and stress responses. Their role in animal systems is well-understood and characterized. The functional characterization of protein phosphatases has been extensively covered in plants, although the comprehension of their mechanistic basis is an ongoing pursuit. The nature of their interactions with other key players in the signaling process is vital to our understanding. The substrates or targets determine their potential as well as magnitude of the impact they have on signaling pathways. In this article, we exclusively overview the various substrates of protein phosphatases in plant signaling pathways, which are a critical determinant of the outcome of various developmental and stress stimuli.
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Affiliation(s)
- Lokesh K Saini
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India
| | - Malathi Bheri
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India
| | - Girdhar K Pandey
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India.
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Bian C, Guo X, Zhang Y, Wang L, Xu T, DeLong A, Dong J. Protein phosphatase 2A promotes stomatal development by stabilizing SPEECHLESS in Arabidopsis. Proc Natl Acad Sci U S A 2020; 117:13127-13137. [PMID: 32434921 PMCID: PMC7293623 DOI: 10.1073/pnas.1912075117] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Stomatal guard cells control gas exchange that allows plant photosynthesis but limits water loss from plants to the environment. In Arabidopsis, stomatal development is mainly controlled by a signaling pathway comprising peptide ligands, membrane receptors, a mitogen-activated protein kinase (MAPK) cascade, and a set of transcription factors. The initiation of the stomatal lineage requires the activity of the bHLH transcription factor SPEECHLESS (SPCH) with its partners. Multiple kinases were found to regulate SPCH protein stability and function through phosphorylation, yet no antagonistic protein phosphatase activities have been identified. Here, we identify the conserved PP2A phosphatases as positive regulators of Arabidopsis stomatal development. We show that mutations in genes encoding PP2A subunits result in lowered stomatal production in Arabidopsis Genetic analyses place the PP2A function upstream of SPCH. Pharmacological treatments support a role for PP2A in promoting SPCH protein stability. We further find that SPCH directly binds to the PP2A-A subunits in vitro. In plants, nonphosphorylatable SPCH proteins are less affected by PP2A activity levels. Thus, our research suggests that PP2A may function to regulate the phosphorylation status of the master transcription factor SPCH in stomatal development.
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Affiliation(s)
- Chao Bian
- The Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854
- Department of Plant Biology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901
| | - Xiaoyu Guo
- The Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854
| | - Yi Zhang
- The Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854
- Fujian Agriculture and Forestry University-Joint Centre, Horticulture and Metabolic Biology Centre, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, 350002 Fuzhou, People's Republic of China
| | - Lu Wang
- The Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854
- Department of Plant Biology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901
| | - Tongda Xu
- Fujian Agriculture and Forestry University-Joint Centre, Horticulture and Metabolic Biology Centre, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, 350002 Fuzhou, People's Republic of China
| | - Alison DeLong
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, RI 02912
| | - Juan Dong
- The Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854;
- Department of Plant Biology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901
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Fu L, Wang P, Xiong Y. Target of Rapamycin Signaling in Plant Stress Responses. PLANT PHYSIOLOGY 2020; 182:1613-1623. [PMID: 31949028 PMCID: PMC7140942 DOI: 10.1104/pp.19.01214] [Citation(s) in RCA: 76] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 12/21/2019] [Indexed: 05/05/2023]
Abstract
Target of Rapamycin (TOR) is an atypical Ser/Thr protein kinase that is evolutionally conserved among yeasts, plants, and mammals. In plants, TOR signaling functions as a central hub to integrate different kinds of nutrient, energy, hormone, and environmental signals. TOR thereby orchestrates every stage of plant life, from embryogenesis, meristem activation, root, and leaf growth to flowering, senescence, and life span determination. Besides its essential role in the control of plant growth and development, recent research has also shed light on its multifaceted roles in plant environmental stress responses. Here, we review recent findings on the involvement of TOR signaling in plant adaptation to nutrient deficiency and various abiotic stresses. We also discuss the mechanisms underlying how plants cope with such unfavorable conditions via TOR-abscisic acid crosstalk and TOR-mediated autophagy, both of which play crucial roles in plant stress responses. Until now, little was known about the upstream regulators and downstream effectors of TOR in plant stress responses. We propose that the Snf1-related protein kinase-TOR axis plays a role in sensing various stress signals, and predict the key downstream effectors based on recent high-throughput proteomic analyses.
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Affiliation(s)
- Liwen Fu
- Basic Forestry and Proteomics Research Centre, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, Fujian Province 350002, People's Republic of China
| | - Pengcheng Wang
- Shanghai Centre for Plant Stress Biology, Chinese Academy of Sciences Centre for Excellence in Molecular Plant Sciences, Chinese Academy of Sciences, Shanghai 201602, People's Republic of China
| | - Yan Xiong
- Basic Forestry and Proteomics Research Centre, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, Fujian Province 350002, People's Republic of China
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Bheri M, Pandey GK. PP2A Phosphatases Take a Giant Leap in the Post-Genomics Era. Curr Genomics 2019; 20:154-171. [PMID: 31929724 PMCID: PMC6935955 DOI: 10.2174/1389202920666190517110605] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 05/09/2019] [Accepted: 05/09/2019] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND Protein phosphorylation is an important reversible post-translational modifica-tion, which regulates a number of critical cellular processes. Phosphatases and kinases work in a con-certed manner to act as a "molecular switch" that turns-on or - off the regulatory processes driving the growth and development under normal circumstances, as well as responses to multiple stresses in plant system. The era of functional genomics has ushered huge amounts of information to the framework of plant systems. The comprehension of who's who in the signaling pathways is becoming clearer and the investigations challenging the conventional functions of signaling components are on a rise. Protein phosphatases have emerged as key regulators in the signaling cascades. PP2A phosphatases due to their diverse holoenzyme compositions are difficult to comprehend. CONCLUSION In this review, we highlight the functional versatility of PP2A members, deciphered through the advances in the post-genomic era.
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Affiliation(s)
- Malathi Bheri
- Department of Plant Molecular Biology, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi-110021, India
| | - Girdhar K. Pandey
- Department of Plant Molecular Biology, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi-110021, India
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Wang S, Quan L, Li S, You C, Zhang Y, Gao L, Zeng L, Liu L, Qi Y, Mo B, Chen X. The PROTEIN PHOSPHATASE4 Complex Promotes Transcription and Processing of Primary microRNAs in Arabidopsis. THE PLANT CELL 2019; 31:486-501. [PMID: 30674692 PMCID: PMC6447022 DOI: 10.1105/tpc.18.00556] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 11/28/2018] [Accepted: 01/16/2019] [Indexed: 05/02/2023]
Abstract
PROTEIN PHOSPHATASE4 (PP4) is a highly conserved Ser/Thr protein phosphatase found in yeast, plants, and animals. The composition and functions of PP4 in plants are poorly understood. Here, we uncovered the complexity of PP4 composition and function in Arabidopsis (Arabidopsis thaliana) and identified the composition of one form of PP4 containing the regulatory subunit PP4R3A. We show that PP4R3A, together with one of two redundant catalytic subunit genes, PROTEIN PHOSPHATASE X (PPX)1 and PPX2, promotes the biogenesis of microRNAs (miRNAs). PP4R3A is a chromatin-associated protein that interacts with RNA polymerase II and recruits it to the promoters of miRNA-encoding (MIR) genes to promote their transcription. PP4R3A likely also promotes the cotranscriptional processing of miRNA precursors, because it recruits the microprocessor component HYPONASTIC LEAVES1 to MIR genes and to nuclear dicing bodies. Finally, we show that hundreds of introns exhibit splicing defects in pp4r3a mutants. Together, this study reveals roles for Arabidopsis PP4 in transcription and nuclear RNA metabolism.
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Affiliation(s)
- Suikang Wang
- Guangdong Provincial Key Laboratory for Plant Epigenetics, Longhua Institute of Innovative Biotechnology, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China
- Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
- Department of Botany and Plant Sciences, Institute of Integrative Genome Biology, University of California, Riverside, California 92521
| | - Li Quan
- Department of Botany and Plant Sciences, Institute of Integrative Genome Biology, University of California, Riverside, California 92521
- State Key Laboratory of Crop Stress Biology for Arid Areas, College of Agronomy, Northwest A&F University, Yangling, Shanxi 712100, China
| | - Shaofang Li
- Department of Botany and Plant Sciences, Institute of Integrative Genome Biology, University of California, Riverside, California 92521
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Chenjiang You
- Guangdong Provincial Key Laboratory for Plant Epigenetics, Longhua Institute of Innovative Biotechnology, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China
- Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
- Department of Botany and Plant Sciences, Institute of Integrative Genome Biology, University of California, Riverside, California 92521
| | - Yong Zhang
- Department of Botany and Plant Sciences, Institute of Integrative Genome Biology, University of California, Riverside, California 92521
| | - Lei Gao
- Guangdong Provincial Key Laboratory for Plant Epigenetics, Longhua Institute of Innovative Biotechnology, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China
| | - Liping Zeng
- Department of Botany and Plant Sciences, Institute of Integrative Genome Biology, University of California, Riverside, California 92521
| | - Lin Liu
- Guangdong Provincial Key Laboratory for Plant Epigenetics, Longhua Institute of Innovative Biotechnology, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China
| | - Yanhua Qi
- State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310058, China
| | - Beixin Mo
- Guangdong Provincial Key Laboratory for Plant Epigenetics, Longhua Institute of Innovative Biotechnology, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China
| | - Xuemei Chen
- Department of Botany and Plant Sciences, Institute of Integrative Genome Biology, University of California, Riverside, California 92521
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Wang J, Pei L, Jin Z, Zhang K, Zhang J. Overexpression of the protein phosphatase 2A regulatory subunit a gene ZmPP2AA1 improves low phosphate tolerance by remodeling the root system architecture of maize. PLoS One 2017; 12:e0176538. [PMID: 28448624 PMCID: PMC5407761 DOI: 10.1371/journal.pone.0176538] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 04/12/2017] [Indexed: 11/21/2022] Open
Abstract
Phosphate (Pi) limitation is a constraint for plant growth and development in many natural and agricultural ecosystems. In this study, a gene encoding Zea mays L. protein phosphatase 2A regulatory subunit A, designated ZmPP2AA1, was induced in roots by low Pi availability. The function of the ZmPP2AA1 gene in maize was analyzed using overexpression and RNA interference. ZmPP2AA1 modulated root gravitropism, negatively regulated primary root (PR) growth, and stimulated the development of lateral roots (LRs). A detailed characterization of the root system architecture (RSA) in response to different Pi concentrations with or without indole-3-acetic acid and 1-N-naphthylphthalamic acid revealed that auxin was involved in the RSA response to low Pi availability. Overexpression of ZmPP2AA1 enhanced tolerance to Pi starvation in transgenic maize in hydroponic and soil pot experiments. An increased dry weight (DW), root-to-shoot ratio, and total P content and concentration, along with a delayed and reduced accumulation of anthocyanin in overexpressing transgenic maize plants coincided with their highly branched root system and increased Pi uptake capability under low Pi conditions. Inflorescence development of the ZmPP2AA1 overexpressing line was less affected by low Pi stress, resulting in higher grain yield per plant under Pi deprivation. These data reveal the biological function of ZmPP2AA1, provide insights into a linkage between auxin and low Pi responses, and drive new strategies for the efficient utilization of Pi by maize.
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Affiliation(s)
- Jiemin Wang
- School of Life Sciences, Shandong University, Ministry of Education Key Laboratory of Plant Cell Engineering and Germplasm Enhancement, Jinan, China
| | - Laming Pei
- School of Life Sciences, Shandong University, Ministry of Education Key Laboratory of Plant Cell Engineering and Germplasm Enhancement, Jinan, China
- Department of Biotechnology, School of Biological Science and Technology, University of Jinan, Jinan, China
| | - Zhe Jin
- School of Life Sciences, Shandong University, Ministry of Education Key Laboratory of Plant Cell Engineering and Germplasm Enhancement, Jinan, China
| | - Kewei Zhang
- School of Life Sciences, Shandong University, Ministry of Education Key Laboratory of Plant Cell Engineering and Germplasm Enhancement, Jinan, China
| | - Juren Zhang
- School of Life Sciences, Shandong University, Ministry of Education Key Laboratory of Plant Cell Engineering and Germplasm Enhancement, Jinan, China
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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.
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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;
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Durian G, Rahikainen M, Alegre S, Brosché M, Kangasjärvi S. Protein Phosphatase 2A in the Regulatory Network Underlying Biotic Stress Resistance in Plants. FRONTIERS IN PLANT SCIENCE 2016; 7:812. [PMID: 27375664 PMCID: PMC4901049 DOI: 10.3389/fpls.2016.00812] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Accepted: 05/25/2016] [Indexed: 05/20/2023]
Abstract
Biotic stress factors pose a major threat to plant health and can significantly deteriorate plant productivity by impairing the physiological functions of the plant. To combat the wide range of pathogens and insect herbivores, plants deploy converging signaling pathways, where counteracting activities of protein kinases and phosphatases form a basic mechanism for determining appropriate defensive measures. Recent studies have identified Protein Phosphatase 2A (PP2A) as a crucial component that controls pathogenesis responses in various plant species. Genetic, proteomic and metabolomic approaches have underscored the versatile nature of PP2A, which contributes to the regulation of receptor signaling, organellar signaling, gene expression, metabolic pathways, and cell death, all of which essentially impact plant immunity. Associated with this, various PP2A subunits mediate post-translational regulation of metabolic enzymes and signaling components. Here we provide an overview of protein kinase/phosphatase functions in plant immunity signaling, and position the multifaceted functions of PP2A in the tightly inter-connected regulatory network that controls the perception, signaling and responding to biotic stress agents in plants.
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Affiliation(s)
- Guido Durian
- Department of Biochemistry, Molecular Plant Biology, University of TurkuTurku, Finland
| | - Moona Rahikainen
- Department of Biochemistry, Molecular Plant Biology, University of TurkuTurku, Finland
| | - Sara Alegre
- Department of Biochemistry, Molecular Plant Biology, University of TurkuTurku, Finland
| | - Mikael Brosché
- Department of Biochemistry, Molecular Plant Biology, University of TurkuTurku, Finland
| | - Saijaliisa Kangasjärvi
- Department of Biochemistry, Molecular Plant Biology, University of TurkuTurku, Finland
- *Correspondence: Saijaliisa Kangasjärvi,
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Durian G, Rahikainen M, Alegre S, Brosché M, Kangasjärvi S. Protein Phosphatase 2A in the Regulatory Network Underlying Biotic Stress Resistance in Plants. FRONTIERS IN PLANT SCIENCE 2016. [PMID: 27375664 DOI: 10.3389/fpls.2016.00812/abstract] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Biotic stress factors pose a major threat to plant health and can significantly deteriorate plant productivity by impairing the physiological functions of the plant. To combat the wide range of pathogens and insect herbivores, plants deploy converging signaling pathways, where counteracting activities of protein kinases and phosphatases form a basic mechanism for determining appropriate defensive measures. Recent studies have identified Protein Phosphatase 2A (PP2A) as a crucial component that controls pathogenesis responses in various plant species. Genetic, proteomic and metabolomic approaches have underscored the versatile nature of PP2A, which contributes to the regulation of receptor signaling, organellar signaling, gene expression, metabolic pathways, and cell death, all of which essentially impact plant immunity. Associated with this, various PP2A subunits mediate post-translational regulation of metabolic enzymes and signaling components. Here we provide an overview of protein kinase/phosphatase functions in plant immunity signaling, and position the multifaceted functions of PP2A in the tightly inter-connected regulatory network that controls the perception, signaling and responding to biotic stress agents in plants.
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Affiliation(s)
- Guido Durian
- Department of Biochemistry, Molecular Plant Biology, University of Turku Turku, Finland
| | - Moona Rahikainen
- Department of Biochemistry, Molecular Plant Biology, University of Turku Turku, Finland
| | - Sara Alegre
- Department of Biochemistry, Molecular Plant Biology, University of Turku Turku, Finland
| | - Mikael Brosché
- Department of Biochemistry, Molecular Plant Biology, University of Turku Turku, Finland
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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.
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Lillo C, Kataya ARA, Heidari B, Creighton MT, Nemie-Feyissa D, Ginbot Z, Jonassen EM. Protein phosphatases PP2A, PP4 and PP6: mediators and regulators in development and responses to environmental cues. PLANT, CELL & ENVIRONMENT 2014; 37:2631-48. [PMID: 24810976 DOI: 10.1111/pce.12364] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 04/25/2014] [Accepted: 04/28/2014] [Indexed: 05/23/2023]
Abstract
The three closely related groups of serine/threonine protein phosphatases PP2A, PP4 and PP6 are conserved throughout eukaryotes. The catalytic subunits are present in trimeric and dimeric complexes with scaffolding and regulatory subunits that control activity and confer substrate specificity to the protein phosphatases. In Arabidopsis, three scaffolding (A subunits) and 17 regulatory (B subunits) proteins form complexes with five PP2A catalytic subunits giving up to 255 possible combinations. Three SAP-domain proteins act as regulatory subunits of PP6. Based on sequence similarities with proteins in yeast and mammals, two putative PP4 regulatory subunits are recognized in Arabidopsis. Recent breakthroughs have been made concerning the functions of some of the PP2A and PP6 regulatory subunits, for example the FASS/TON2 in regulation of the cellular skeleton, B' subunits in brassinosteroid signalling and SAL proteins in regulation of auxin transport. Reverse genetics is starting to reveal also many more physiological functions of other subunits. A system with key regulatory proteins (TAP46, TIP41, PTPA, LCMT1, PME-1) is present in all eukaryotes to stabilize, activate and inactivate the catalytic subunits. In this review, we present the status of knowledge concerning physiological functions of PP2A, PP4 and PP6 in Arabidopsis, and relate these to yeast and mammals.
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Affiliation(s)
- Cathrine Lillo
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, Stavanger, N-4036, Norway
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Cloning and characterization of TaPP2AbB"-α, a member of the PP2A regulatory subunit in wheat. PLoS One 2014; 9:e94430. [PMID: 24709994 PMCID: PMC3978047 DOI: 10.1371/journal.pone.0094430] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2014] [Accepted: 03/17/2014] [Indexed: 11/19/2022] Open
Abstract
Protein phosphatase 2A (PP2A), a major Serine/Threonine protein phosphatase, consists of three subunits; a highly conserved structural subunit A, a catalytic subunit C, and a highly variable regulatory subunit B which determines the substrate specificity. Although the functional mechanism of PP2A in signaling transduction in Arabidopsis is known, their physiological roles in wheat remain to be characterized. In this study, we identified a novel regulatory subunit B, TaPP2AbB"-α, in wheat (Triticum aestivum L.). Subcellular localization indicated that TaPP2AbB"-α is located in the cell membrane, cytoplasm and nucleus. It interacts with both TaPP2Aa and TaPP2Ac. Expression pattern analyses revealed that TaPP2AbB"-α is strongly expressed in roots, and responds to NaCl, polyethylene glycol (PEG), cold and abscisic acid (ABA) stresses at the transcription level. Transgenic Arabidopsis plants overexpressing TaPP2AbB"-α developed more lateral roots, especially when treated with mannitol or NaCl. These results suggest that TaPP2AbB"-α, in conjunction with the other two PP2A subunits, is involved in multi-stress response, and positively regulates lateral root development under osmotic stress.
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Hu R, Zhu Y, Shen G, Zhang H. TAP46 plays a positive role in the ABSCISIC ACID INSENSITIVE5-regulated gene expression in Arabidopsis. PLANT PHYSIOLOGY 2014; 164:721-34. [PMID: 24357600 PMCID: PMC3912101 DOI: 10.1104/pp.113.233684] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Accepted: 12/17/2013] [Indexed: 05/19/2023]
Abstract
TAP46 is a protein phosphatase2A (PP2A)-associated protein that regulates PP2A activity in Arabidopsis (Arabidopsis thaliana). To study how PP2A is involved in abscisic acid (ABA) signaling in plants, we studied the function of TAP46 in ABA-regulated seed maturation and seedling development. Expression of TAP46 coincides with the action of ABA in developing seeds and during seed germination, and the TAP46 transcript reaches to the highest level in mature seeds. Real-time polymerase chain reaction analysis indicates that external ABA can increase TAP46 transcript level transiently during seed germination. Overexpression of TAP46 increases plant sensitivity to ABA, while tap46 knockdown mutants are less sensitive to ABA during seed germination, suggesting that TAP46 functions positively in ABA signaling. Overexpression of TAP46 also leads to lower PP2A activity, while tap46-1 knockdown mutant displays higher PP2A activity, suggesting that TAP46 negatively regulates PP2A activity in Arabidopsis. Both TAP46 and PP2A interact with the ABA-regulated transcription factor ABA INSENSITIVE5 (ABI5) in vivo, and TAP46's binding to ABI5 can stabilize ABI5. Furthermore, TAP46's binding to the phosphorylated ABI5 may prevent PP2A or PP2A-like protein phosphatases from removing the phosphate from ABI5, thereby maintaining ABI5 in its active form. Overexpression of TAP46 and inhibition of activities of PP2A or PP2A-like protein phosphatases can increase transcript levels of several ABI5-regulated genes, suggesting that TAP46 is a positive factor in the ABA-regulated gene expression in Arabidopsis.
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Robaglia C, Thomas M, Meyer C. Sensing nutrient and energy status by SnRK1 and TOR kinases. CURRENT OPINION IN PLANT BIOLOGY 2012; 15:301-7. [PMID: 22305521 DOI: 10.1016/j.pbi.2012.01.012] [Citation(s) in RCA: 147] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Revised: 01/10/2012] [Accepted: 01/11/2012] [Indexed: 05/18/2023]
Abstract
The perception of nutrient and energy levels inside and outside the cell is crucial to adjust growth and metabolism to available resources. The signaling pathways centered on the conserved TOR and SnRK1/Snf1/AMPK kinases have crucial and numerous roles in nutrient and energy sensing and in translating this information into metabolic and developmental adaptations. In plants evidence is mounting that, like in other eukaryotes, these signaling pathways have pivotal and antagonistic roles in connecting external or intracellular cues to many biological processes, including ribosome biogenesis, regulation of translation, cell division, accumulation of reserves and autophagy. Data on the plant TOR pathway have been hitherto rather scarce but recent findings have shed new light on its roles in plants. Moreover, the distinctive energy metabolism of photosynthetic organisms may reveal new features of these ancestral eukaryotic signaling elements.
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Affiliation(s)
- Christophe Robaglia
- Laboratoire de Génétique et Biophysique des Plantes, UMR 7265, CEA/CNRS, Aix Marseille Université, Faculté des Sciences de Luminy, 163 Avenue de Luminy, Marseille, France
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15
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Antolín-Llovera M, Leivar P, Arró M, Ferrer A, Boronat A, Campos N. Modulation of plant HMG-CoA reductase by protein phosphatase 2A: positive and negative control at a key node of metabolism. PLANT SIGNALING & BEHAVIOR 2011; 6:1127-31. [PMID: 21701259 PMCID: PMC3260709 DOI: 10.4161/psb.6.8.16363] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The enzyme HMG-CoA reductase (HMGR) has a key regulatory role in the mevalonate pathway for isoprenoid biosynthesis, critical not only for normal plant development, but also for the adaptation to demanding environmental conditions. Consistent with this notion, plant HMGR is modulated by many diverse endogenous signals and external stimuli. Protein phosphatase 2A (PP2A) is involved in auxin, abscisic acid, ethylene and brassinosteroid signaling and now emerges as a positive and negative multilevel regulator of plant HMGR, both during normal growth and in response to a variety of stress conditions. The interaction with HMGR is mediated by B" regulatory subunits of PP2A, which are also calcium binding proteins. The new discoveries uncover the potential of PP2A to integrate developmental and calcium-mediated environmental signals in the control of plant HMGR.
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Affiliation(s)
- Meritxell Antolín-Llovera
- Department of Molecular Genetics; Center for Research in Agricultural Genomics (CSIC-IRTA-UAB-UB); Campus Universitat Autònoma de Barcelona; Bellaterra (Cerdanyola del Vallès); Barcelona, Spain
- Departament de Bioquímica i Biologia Molecular; Facultat de Biologia; Universitat de Barcelona; Barcelona, Spain
| | - Pablo Leivar
- Department of Molecular Genetics; Center for Research in Agricultural Genomics (CSIC-IRTA-UAB-UB); Campus Universitat Autònoma de Barcelona; Bellaterra (Cerdanyola del Vallès); Barcelona, Spain
- Departament de Bioquímica i Biologia Molecular; Facultat de Biologia; Universitat de Barcelona; Barcelona, Spain
| | - Montserrat Arró
- Department of Molecular Genetics; Center for Research in Agricultural Genomics (CSIC-IRTA-UAB-UB); Campus Universitat Autònoma de Barcelona; Bellaterra (Cerdanyola del Vallès); Barcelona, Spain
- Departament de Bioquímica i Biologia Molecular; Facultat de Farmàcia; Universitat de Barcelona; Barcelona, Spain
| | - Albert Ferrer
- Department of Molecular Genetics; Center for Research in Agricultural Genomics (CSIC-IRTA-UAB-UB); Campus Universitat Autònoma de Barcelona; Bellaterra (Cerdanyola del Vallès); Barcelona, Spain
- Departament de Bioquímica i Biologia Molecular; Facultat de Farmàcia; Universitat de Barcelona; Barcelona, Spain
| | - Albert Boronat
- Department of Molecular Genetics; Center for Research in Agricultural Genomics (CSIC-IRTA-UAB-UB); Campus Universitat Autònoma de Barcelona; Bellaterra (Cerdanyola del Vallès); Barcelona, Spain
- Departament de Bioquímica i Biologia Molecular; Facultat de Biologia; Universitat de Barcelona; Barcelona, Spain
| | - Narciso Campos
- Department of Molecular Genetics; Center for Research in Agricultural Genomics (CSIC-IRTA-UAB-UB); Campus Universitat Autònoma de Barcelona; Bellaterra (Cerdanyola del Vallès); Barcelona, Spain
- Departament de Bioquímica i Biologia Molecular; Facultat de Biologia; Universitat de Barcelona; Barcelona, Spain
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16
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Abstract
The TOR (target of rapamycin) kinase is present in nearly all eukaryotic organisms and regulates a wealth of biological processes collectively contributing to cell growth. The genome of the model plant Arabidopsis contains a single TOR gene and two RAPTOR (regulatory associated protein of TOR)/KOG1 (Kontroller of growth 1) and GβL/LST8 (G-protein β-subunit-like/lethal with Sec thirteen 8) genes but, in contrast with other organisms, plants appear to be resistant to rapamycin. Disruption of the RAPTOR1 and TOR genes in Arabidopsis results in an early arrest of embryo development. Plants that overexpress the TOR mRNA accumulate more leaf and root biomass, produce more seeds and are more resistant to stress. Conversely, the down-regulation of TOR by constitutive or inducible RNAi (RNA interference) leads to a reduced organ growth, to an early senescence and to severe transcriptomic and metabolic perturbations, including accumulation of sugars and amino acids. It thus seems that plant growth is correlated to the level of TOR expression. We have also investigated the effect of reduced TOR expression on tissue organization and cell division. We suggest that, like in other eukaryotes, the plant TOR kinase could be one of the main contributors to the link between environmental cues and growth processes.
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17
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Ahn CS, Han JA, Lee HS, Lee S, Pai HS. The PP2A regulatory subunit Tap46, a component of the TOR signaling pathway, modulates growth and metabolism in plants. THE PLANT CELL 2011; 23:185-209. [PMID: 21216945 PMCID: PMC3051261 DOI: 10.1105/tpc.110.074005] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 11/29/2010] [Accepted: 12/17/2010] [Indexed: 05/18/2023]
Abstract
Tap42/α4, a regulatory subunit of protein phosphatase 2A, is a downstream effector of the target of rapamycin (TOR) protein kinase, which regulates cell growth in coordination with nutrient and environmental conditions in yeast and mammals. In this study, we characterized the functions and phosphatase regulation of plant Tap46. Depletion of Tap46 resulted in growth arrest and acute plant death with morphological markers of programmed cell death. Tap46 interacted with PP2A and PP2A-like phosphatases PP4 and PP6. Tap46 silencing modulated cellular PP2A activities in a time-dependent fashion similar to TOR silencing. Immunoprecipitated full-length and deletion forms of Arabidopsis thaliana TOR phosphorylated recombinant Tap46 protein in vitro, supporting a functional link between Tap46 and TOR. Tap46 depletion reproduced the signature phenotypes of TOR inactivation, such as dramatic repression of global translation and activation of autophagy and nitrogen mobilization, indicating that Tap46 may act as a positive effector of TOR signaling in controlling those processes. Additionally, Tap46 silencing in tobacco (Nicotiana tabacum) BY-2 cells caused chromatin bridge formation at anaphase, indicating its role in sister chromatid segregation. These findings suggest that Tap46, in conjunction with associated phosphatases, plays an essential role in plant growth and development as a component of the TOR signaling pathway.
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Affiliation(s)
| | | | | | | | - Hyun-Sook Pai
- Department of Biology, Yonsei University, Seoul 120-749, Korea
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18
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País SM, Téllez-Iñón MT, Capiati DA. Serine/threonine protein phosphatases type 2A and their roles in stress signaling. PLANT SIGNALING & BEHAVIOR 2009; 4:1013-5. [PMID: 20009558 PMCID: PMC2819506 DOI: 10.4161/psb.4.11.9783] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Accepted: 08/08/2009] [Indexed: 05/18/2023]
Abstract
Serine/threonine protein phosphatases are ubiquitous enzymes in all eukaryotes but many of their physiological roles in plants remain unknown. The available results have demonstrated critical functions for these enzymes in the regulation of adaptive stress responses, and recent studies have directed attention to the functional roles of Ser/Thr phosphatases type 2A (PP2A) as components of stress signaling pathways. This review is focused primarily on plant PP2As and their participation in the control of biotic and abiotic stress responses.
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Affiliation(s)
- Silvia Marina País
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
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19
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Yoo SJS, Jimenez RH, Sanders JA, Boylan JM, Brautigan DL, Gruppuso PA. The alpha4-containing form of protein phosphatase 2A in liver and hepatic cells. J Cell Biochem 2008; 105:290-300. [PMID: 18543252 DOI: 10.1002/jcb.21830] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The Ser/Thr phosphatase PP2A is a set of multisubunit enzymes that regulate many cellular processes. In yeast, the PP2A regulatory subunit Tap42 forms part of the target of rapamycin (TOR) signaling pathway that links nutrient and energy availability to cell growth. The physiological intersection between the mammalian orthologs of Tap42 and TOR, alpha4 and mTOR, has not been fully characterized. We used two in vivo models of liver growth in the rat, late gestation fetal development and regeneration after partial hepatectomy, to explore the regulation of the alpha4-containing form of PP2A. The alpha4/PP2A catalytic subunit (alpha4/PP2A-C) complex was present in both fetal and adult liver extracts. There was a trend towards higher levels of alpha4 protein in fetal liver, but the complex was more abundant in adult liver. Fractionation of extracts by ion exchange chromatography and transient transfection of the AML12 mouse hepatic cell line indicated that alpha4 associates with PP2A-C but that these complexes have low catalytic activity with both peptide and protein substrates. alpha4 was able to associate with forms of PP2A-C that were both methylated and non-methylated at the carboxy-terminus. The mTOR inhibitor rapamycin did not block the formation of alpha4/PP2A-C in liver or hepatic cells, nor did it appear to modulate PP2A activity. Furthermore, sensitivity to the growth inhibitory effects of rapamycin among a panel of hepatic cell lines did not correlate with levels of alpha4 or alpha4/PP2A-C. Our results indicate that the yeast Tap42/TOR paradigm is not conserved in hepatic cells.
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Affiliation(s)
- Sunny J-S Yoo
- Department of Pediatrics, Rhode Island Hospital and Brown University, Providence, Rhode Island 02903, USA
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20
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Blakeslee JJ, Zhou HW, Heath JT, Skottke KR, Barrios JAR, Liu SY, DeLong A. Specificity of RCN1-mediated protein phosphatase 2A regulation in meristem organization and stress response in roots. PLANT PHYSIOLOGY 2008; 146:539-53. [PMID: 18162590 PMCID: PMC2245836 DOI: 10.1104/pp.107.112995] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2007] [Accepted: 12/17/2007] [Indexed: 05/20/2023]
Abstract
Protein dephosphorylation by the serine/threonine protein phosphatase 2A (PP2A) modulates a broad array of cellular functions. PP2A normally acts as a heterotrimeric holoenzyme complex comprising a catalytic subunit bound by regulatory A and B subunits. Characterization of the regulatory A subunit isoforms (ROOTS CURL IN NAPHTHYLPHTHALAMIC ACID1 [RCN1], PP2AA2, and PP2AA3) of Arabidopsis thaliana PP2A has shown that RCN1 plays a primary role in controlling root and hypocotyl PP2A activity in seedlings. Here we show that hypocotyl and root growth exhibit different requirements for RCN1-mediated regulation of PP2A activity. Roots of rcn1 mutant seedlings exhibit characteristic abnormalities in cell division patterns at the root apical meristem, as well as reduced growth under ionic, osmotic, and oxidative stress conditions. We constructed chimeric A subunit genes and found that restoration of normal root tip development in rcn1 plants requires both regulatory and coding sequences of RCN1, whereas the hypocotyl elongation defect of rcn1 plants can be complemented by either RCN1 or PP2AA3 transgenes. Furthermore, the RCN1 and PP2AA3 proteins exhibit ubiquitous subcellular localization patterns in seedlings and both associate with membrane compartments. Together, these results show that RCN1-containing PP2A has unique functions that cannot be attributed to isoform-specific expression and localization patterns. Postembryonic RCN1 function is required to maintain normal auxin distribution and stem cell function at the root apex. Our data show that RCN1-regulated phosphatase activity plays a unique role in regulating postembryonic root development and stress response.
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Affiliation(s)
- Joshua J Blakeslee
- Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, Rhode Island 02912, USA
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21
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Farkas I, Dombrádi V, Miskei M, Szabados L, Koncz C. Arabidopsis PPP family of serine/threonine phosphatases. TRENDS IN PLANT SCIENCE 2007; 12:169-76. [PMID: 17368080 DOI: 10.1016/j.tplants.2007.03.003] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2006] [Revised: 01/25/2007] [Accepted: 03/02/2007] [Indexed: 05/14/2023]
Abstract
Serine/threonine-specific phosphoprotein phosphatases (PPPs) are ubiquitous enzymes in all eukaryotes, but their regulatory functions are largely unknown in higher plants. The Arabidopsis genome encodes 26 PPP catalytic subunits related to type 1, type 2A and so-called novel phosphatases, including four plant-specific enzymes carrying large N-terminal kelch-domains, but no apparent homologue of the PP2B family. The catalytic subunits of PPPs associate with regulatory protein partners that target them to well defined cellular locations and modulate their activity. Recent studies of phosphatase partners and their interactions have directed attention again to functional dissection of plant PPP families, and highlight their intriguing roles in the regulation of metabolism, cell cycle and development, as well as their roles in light, stress and hormonal signalling.
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Affiliation(s)
- Ilona Farkas
- Department of Medical Chemistry, Research Center for Molecular Medicine, Medical and Health Science Center, University of Debrecen, Egyetem tér 1, Debrecen H-4032, Hungary
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22
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Xu C, Jing R, Mao X, Jia X, Chang X. A wheat (Triticum aestivum) protein phosphatase 2A catalytic subunit gene provides enhanced drought tolerance in tobacco. ANNALS OF BOTANY 2007; 99:439-50. [PMID: 17272305 PMCID: PMC2802960 DOI: 10.1093/aob/mcl285] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2006] [Accepted: 11/21/2006] [Indexed: 05/13/2023]
Abstract
BACKGROUND AND AIMS Multiple copies of genes encoding the catalytic subunit (c) of protein phosphatase 2A (PP2A) are commonly found in plants. For some of these genes, expression is up-regulated under water stress. The aim of this study was to investigate expression and characterization of TaPP2Ac-1 from Triticum aestivum, and to evaluate the effects of TaPP2Ac-1 on Nicotiana benthamiana in response to water stress. METHODS TaPP2Ac-1 cDNA was isolated from wheat by in silico identification and RT-PCR amplification. Transcript levels of TaPP2Ac-1 were examined in wheat responding to water deficit. Copy numbers of TaPP2Ac-1 in wheat genomes and subcellular localization in onion epidermal cells were studied. Enzyme properties of the recombinant TaPP2Ac-1 protein were determined. In addition, studies were carried out in tobacco plants with pCAPE2-TaPP2Ac-1 under water-deficit conditions. KEY RESULTS TaPP2Ac-1 cDNA was cloned from wheat. Transcript levels of TaPP2Ac-1 in wheat seedlings were up-regulated under drought condition. One copy for this TaPP2Ac-1 was present in each of the three wheat genomes. TaPP2Ac-1 fused with GFP was located in the nucleus and cytoplasm of onion epidermis cells. The recombinant TaPP2Ac-1 gene was over-expressed in Escherichia coli and encoded a functional serine/threonine phosphatase. Transgenic tobacco plants over-expressing TaPP2Ac-1 exhibited stronger drought tolerance than non-transgenic tobacco plants. CONCLUSIONS Tobacco plants with pCAPE2-TaPP2Ac-1 appeared to be resistant to water deficit, as shown by their higher capacity to maintain leaf relative water content, leaf cell-membrane stability index, water-retention ability and water use efficiency under water stress. The results suggest that the physiological role of TaPP2Ac-1 is related to drought stress response, possibly through its involvement in drought-responding signal transduction pathways.
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Affiliation(s)
| | - Ruilian Jing
- The National Key Facility for Crop Gene Resources and Genetic Improvement, Key Laboratory of Crop Germplasm & Biotechnology, Ministry of Agriculture, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100081, China
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23
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Aguilera J, Randez-Gil F, Prieto JA. Cold response in Saccharomyces cerevisiae: new functions for old mechanisms. FEMS Microbiol Rev 2007; 31:327-41. [PMID: 17298585 DOI: 10.1111/j.1574-6976.2007.00066.x] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The response of yeast cells to sudden temperature downshifts has received little attention compared with other stress conditions. Like other organisms, both prokaryotes and eukaryotes, in Saccharomyces cerevisiae a decrease in temperature induces the expression of many genes involved in transcription and translation, some of which display a cold-sensitivity phenotype. However, little is known about the role played by many cold-responsive genes, the sensing and regulatory mechanisms that control this response or the biochemical adaptations at or near 0 degrees C. This review focuses on the physiological significance of cold-shock responses, emphasizing the molecular mechanisms that generate and transmit cold signals. There is now enough experimental evidence to conclude that exposure to low temperature protects yeast cells against freeze injury through the cold-induced accumulation of trehalose, glycerol and heat-shock proteins. Recent results also show that changes in membrane fluidity are the primary signal triggering the cold-shock response. Notably, this signal is transduced and regulated through classical stress pathways and transcriptional factors, the high-osmolarity glycerol mitogen-activated protein kinase pathway and Msn2/4p. Alternative cold-stress generators and transducers will also be presented and discussed.
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Affiliation(s)
- Jaime Aguilera
- Department of Biotechnology, Instituto de Agroquímica y Tecnología de los Alimentos, Consejo Superior de Investigaciones Científicas, Burjassot, Valencia, Spain
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24
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Jiang Y. Regulation of the cell cycle by protein phosphatase 2A in Saccharomyces cerevisiae. Microbiol Mol Biol Rev 2006; 70:440-9. [PMID: 16760309 PMCID: PMC1489537 DOI: 10.1128/mmbr.00049-05] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Protein phosphatase 2A (PP2A) has long been implicated in cell cycle regulation in many different organisms. In the yeast Saccharomyces cerevisiae, PP2A controls cell cycle progression mainly through modulation of cyclin-dependent kinase (CDK) at the G(2)/M transition. However, CDK does not appear to be a direct target of PP2A. PP2A affects CDK activity through its roles in checkpoint controls. Inactivation of PP2A downregulates CDK by activating the morphogenesis checkpoint and, consequently, delays mitotic entry. Defects in PP2A also compromise the spindle checkpoint and predispose the cell to an error-prone mitotic exit. In addition, PP2A is involved in controlling the G(1)/S transition and cytokinesis. These findings suggest that PP2A functions in many stages of the cell cycle and its effect on cell cycle progression is pleiotropic.
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Affiliation(s)
- Yu Jiang
- Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
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25
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Smetana JHC, Oliveira CLP, Jablonka W, Aguiar Pertinhez T, Carneiro FRG, Montero-Lomeli M, Torriani I, Zanchin NIT. Low resolution structure of the human alpha4 protein (IgBP1) and studies on the stability of alpha4 and of its yeast ortholog Tap42. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2006; 1764:724-34. [PMID: 16517231 DOI: 10.1016/j.bbapap.2006.01.018] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2005] [Revised: 01/15/2006] [Accepted: 01/20/2006] [Indexed: 12/30/2022]
Abstract
The yeast Tap42 and mammalian alpha4 proteins belong to a highly conserved family of regulators of the type 2A phosphatases, which participate in the rapamycin-sensitive signaling pathway, connecting nutrient availability to cell growth. The mechanism of regulation involves binding of Tap42 to Sit4 and PPH21/22 in yeast and binding of alpha4 to the catalytic subunits of type 2A-related phosphatases PP2A, PP4 and PP6 in mammals. Both recombinant proteins undergo partial proteolysis, generating stable N-terminal fragments. The full-length proteins and alpha4 C-terminal deletion mutants at amino acids 222 (alpha4Delta222), 236 (alpha4Delta236) and 254 (alpha4Delta254) were expressed in E. coli. alpha4Delta254 undergoes proteolysis, producing a fragment similar to the one generated by full-length alpha4, whereas alpha4Delta222 and alpha4Delta236 are highly stable proteins. alpha4 and Tap42 show alpha-helical circular dichroism spectra, as do their respective N-terminal proteolysis resistant products. The cloned truncated proteins alpha4Delta222 and alpha4Delta236, however, possess a higher content of alpha-helix, indicating that the C-terminal region is less structured, which is consistent with its higher sensitivity to proteolysis. In spite of their higher secondary structure content, alpha4Delta222 and alpha4Delta236 showed thermal unfolding kinetics similar to the full-length alpha4. Based on small angle X-ray scattering (SAXS), the calculated radius of gyration for alpha4 and Tap42 were 41.2 +/- 0.8 A and 42.8 +/- 0.7 A and their maximum dimension approximately 142 A and approximately 147 A, respectively. The radii of gyration for alpha4Delta222 and alpha4Delta236 were 21.6 +/- 0.3 A and 25.7 +/- 0.2 A, respectively. Kratky plots show that all studied proteins show variable degree of compactness. Calculation of model structures based on SAXS data showed that alpha4Delta222 and alpha4Delta236 proteins have globular conformation, whereas alpha4 and Tap42 exhibit elongated shapes.
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Affiliation(s)
- Juliana Helena Costa Smetana
- Brazilian Synchrotron Light Laboratory (LNLS), Centro de Biologia Molecular Estrutural, Laboratório Nacional de Luz Síncrotron, R. Giuseppe Máximo Scolfaro, 10.000, Campinas - SP, PO Box 6192-CEP 13084-971, Brazil
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26
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Zheng Y, Jiang Y. The yeast phosphotyrosyl phosphatase activator is part of the Tap42-phosphatase complexes. Mol Biol Cell 2005; 16:2119-27. [PMID: 15689491 PMCID: PMC1073688 DOI: 10.1091/mbc.e04-09-0797] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Phosphotyrosyl phosphatase activator PTPA is a type 2A phosphatase regulatory protein that possesses an ability to stimulate the phosphotyrosyl phosphatase activity of PP2A in vitro. In yeast Saccharomyces cerevisiae, PTPA is encoded by two related genes, RRD1 and RRD2, whose products are 38 and 37% identical, respectively, to the mammalian PTPA. Inactivation of either gene renders yeast cells rapamycin resistant. In this study, we investigate the mechanism underling rapamycin resistance associated with inactivation of PTPA in yeast. We show that the yeast PTPA is an integral part of the Tap42-phosphatase complexes that act downstream of the Tor proteins, the target of rapamycin. We demonstrate a specific interaction of Rrd1 with the Tap42-Sit4 complex and that of Rrd2 with the Tap42-PP2Ac complex. A small portion of PTPA also is found to be associated with the AC dimeric core of PP2A, but the amount is significantly less than that associated with the Tap42-containing complexes. In addition, our results show that the association of PTPA with Tap42-phosphatase complexes is rapamycin sensitive, and importantly, that rapamycin treatment results in release of the PTPA-phosphatase dimer as a functional phosphatase unit.
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Affiliation(s)
- Yin Zheng
- Department of Pharmacology, University of Pittsburgh School of Medicine, PA 15213, USA
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27
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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.
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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
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28
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Crespo JL, Hall MN. Elucidating TOR signaling and rapamycin action: lessons from Saccharomyces cerevisiae. Microbiol Mol Biol Rev 2002; 66:579-91, table of contents. [PMID: 12456783 PMCID: PMC134654 DOI: 10.1128/mmbr.66.4.579-591.2002] [Citation(s) in RCA: 261] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
TOR (target of rapamycin) is a phosphatidylinositol kinase-related protein kinase that controls cell growth in response to nutrients. Rapamycin is an immunosuppressive and anticancer drug that acts by inhibiting TOR. The modes of action of TOR and rapamycin are remarkably conserved from S. cerevisiae to humans. The current understanding of TOR and rapamycin is derived largely from studies with S. cerevisiae. In this review, we discuss the contributions made by S. cerevisiae to understanding rapamycin action and TOR function.
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Affiliation(s)
- José L Crespo
- Division of Biochemistry, Biozentrum, University of Basel, CH-4056 Basel, Switzerland
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29
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Long X, Spycher C, Han ZS, Rose AM, Müller F, Avruch J. TOR deficiency in C. elegans causes developmental arrest and intestinal atrophy by inhibition of mRNA translation. Curr Biol 2002; 12:1448-61. [PMID: 12225660 DOI: 10.1016/s0960-9822(02)01091-6] [Citation(s) in RCA: 202] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND TOR is a phosphatidylinositol kinase (PIK)-related kinase that controls cell growth and proliferation in response to nutritional cues. We describe a C. elegans TOR homolog (CeTOR) and phenotypes associated with CeTOR deficiency. These phenotypes are compared with the response to starvation and the inactivation of a variety of putative TOR targets. RESULTS Whether caused by mutation or RNA interference, TOR deficiency results in developmental arrest at mid-to-late L3, which is accompanied by marked gonadal degeneration and a pronounced intestinal cell phenotype. A population of refractile, autofluorescent intestinal vesicles, which take up the lysosomal dye Neutral Red, increases dramatically in size, while the number of normal intestinal vesicles and the intestinal cytoplasmic volume decrease progressively. This is accompanied by an increase in the gut lumen size and a compromise in the intestine's ability to digest and absorb nutrients. CeTOR-deficient larvae exhibit no significant dauer characteristics, but share some features with starved L3 larvae. Notably, however, starved larvae do not have severe intestinal atrophy. Inactivation of C. elegans p70S6K or TAP42 homologs does not reproduce CeTOR deficiency phenotypes, nor does inactivation of C. elegans TIP41, a putative negative regulator of CeTOR function, rescue CeTOR deficiency. In contrast, inactivating the C. elegans eIF-4G homolog and eIF-2 subunits results in developmental arrest accompanied by the appearance of large, refractile intestinal vesicles and severe intestinal atrophy resembling that of CeTOR deficiency. CONCLUSIONS The developmental arrest and intestinal phenotypes of CeTOR deficiency are due to an inhibition of global mRNA translation. Thus, TOR is a major upstream regulator of overall mRNA translation in C. elegans, as in yeast.
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Affiliation(s)
- Xiaomeng Long
- Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA
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30
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Abstract
Plants are able to survive prolonged exposure to sub-zero temperatures; this ability is enhanced by pre-exposure to low, but above-zero temperatures. This process, known as cold acclimation, is briefly reviewed from the perception of cold, through transduction of the low-temperature signal to functional analysis of cold-induced gene products. The stresses that freezing of apoplastic water imposes on plant cells is considered and what is understood about the mechanisms that plants use to combat those stresses discussed, with particular emphasis on the role of the extracellular matrix.
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Affiliation(s)
- Maggie Smallwood
- Centre for Novel Agricultural Products, Department of Biology, PO Box 373, University of York, York YO1 5YW, UK.
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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.
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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
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Kim HJ, Kim YK, Park JY, Kim J. Light signalling mediated by phytochrome plays an important role in cold-induced gene expression through the C-repeat/dehydration responsive element (C/DRE) in Arabidopsis thaliana. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 29:693-704. [PMID: 12148528 DOI: 10.1046/j.1365-313x.2002.01249.x] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Low temperature induces a number of genes that encode the proteins promoting tolerance to freezing, mediated by ABA-dependent and ABA-independent pathways in plants. The cis-acting element called C/DRE is known to respond to low temperature independently of ABA action. To investigate the signalling and network of ABA-independent pathways, the transgenic Arabidopsis plants were generated containing several copies of the C/DRE derived from cor15a gene with a minimal promoter fused to a GUS reporter gene. The transgenic plants containing four copies of the C/DRE (4C/DRE-GUS) showed responsiveness to cold and drought treatments and were used for characterization of cold signalling and cross-talk. Cold-induced GUS expression was inhibited by okadaic acid at 1 nM, indicating that protein phosphatase 2A might act as a positive regulator. Light was shown to activate cold- and drought-induced GUS expression. Photo-reversibility of the GUS mRNA by red and far-red light with concomitant cold treatment suggests a role of phytochrome as a photoreceptor in mediating light signalling to activate the cold-induced gene expression through the C/DRE. Furthermore, GUS expression analysis in phyA or phyB or phyAphyB mutant backgrounds showed that phytochrome B is a primary photoreceptor responsible for the activation of cold-stress signalling in response to light. Light enhanced the induction kinetics of CBF1, 2, and 3 encoding the cognate transcription factors, and cor15a, in a consecutive manner compared to the dark condition in the cold, suggesting that the connection point between cold and light signalling mediated by phytochrome is at a higher step than the expression of CBF genes.
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Affiliation(s)
- Hyoun-Joung Kim
- Kumho Life and Environmental Science Laboratory, Puk-Gu, Gwang-ju, Korea
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Cutler NS, Pan X, Heitman J, Cardenas ME. The TOR signal transduction cascade controls cellular differentiation in response to nutrients. Mol Biol Cell 2001; 12:4103-13. [PMID: 11739804 PMCID: PMC60779 DOI: 10.1091/mbc.12.12.4103] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2001] [Revised: 09/10/2001] [Accepted: 09/10/2001] [Indexed: 01/05/2023] Open
Abstract
Rapamycin binds and inhibits the Tor protein kinases, which function in a nutrient-sensing signal transduction pathway that has been conserved from the yeast Saccharomyces cerevisiae to humans. In yeast cells, the Tor pathway has been implicated in regulating cellular responses to nutrients, including proliferation, translation, transcription, autophagy, and ribosome biogenesis. We report here that rapamycin inhibits pseudohyphal filamentous differentiation of S. cerevisiae in response to nitrogen limitation. Overexpression of Tap42, a protein phosphatase regulatory subunit, restored pseudohyphal growth in cells exposed to rapamycin. The tap42-11 mutation compromised pseudohyphal differentiation and rendered it resistant to rapamycin. Cells lacking the Tap42-regulated protein phosphatase Sit4 exhibited a pseudohyphal growth defect and were markedly hypersensitive to rapamycin. Mutations in other Tap42-regulated phosphatases had no effect on pseudohyphal differentiation. Our findings support a model in which pseudohyphal differentiation is controlled by a nutrient-sensing pathway involving the Tor protein kinases and the Tap42-Sit4 protein phosphatase. Activation of the MAP kinase or cAMP pathways, or mutation of the Sok2 repressor, restored filamentation in rapamycin treated cells, supporting models in which the Tor pathway acts in parallel with these known pathways. Filamentous differentiation of diverse fungi was also blocked by rapamycin, demonstrating that the Tor signaling cascade plays a conserved role in regulating filamentous differentiation in response to nutrients.
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Affiliation(s)
- N S Cutler
- Department of Genetics, Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA
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Abstract
Rapamycin potently inhibits downstream signaling from the target of rapamycin (TOR) proteins. These evolutionarily conserved protein kinases coordinate the balance between protein synthesis and protein degradation in response to nutrient quality and quantity. The TOR proteins regulate (i) the initiation and elongation phases of translation, (ii) ribosome biosynthesis, (iii) amino acid import, (iv) the transcription of numerous enzymes involved in multiple metabolic pathways, and (v) autophagy. Intriguingly, recent studies have also suggested that TOR signaling plays a critical role in brain development, learning, and memory formation.
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Affiliation(s)
- B Raught
- Department of Biochemistry and McGill Cancer Centre, McGill University, 3655 Promenade Sir-William-Osler, Montréal, QC H3G 1Y6 Canada
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Xiong L, Zhu JK. Abiotic stress signal transduction in plants: Molecular and genetic perspectives. PHYSIOLOGIA PLANTARUM 2001; 112:152-166. [PMID: 11454221 DOI: 10.1034/j.1399-3054.2001.1120202.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Low temperature, drought and salinity are major adverse environmental factors that limit plant productivity. Understanding the mechanisms by which plants perceive and transduce these stress signals to initiate adaptive responses is essential for engineering stress-tolerant crop plants. Molecular and biochemical studies suggest that abiotic stress signaling in plants involves receptor-coupled phosphorelay, phosphoinositol-induced Ca2+ changes, mitogen-activated protein kinase cascades and transcriptional activation of stress-responsive genes. In addition, protein posttranslational modifications and adapter or scaffold-mediated protein-protein interactions are also important in abiotic stress signal transduction. Most of these signaling modules, however, have not been genetically established to function in plant abiotic stress signal transduction. To overcome the scarcity of abiotic stress-specific phenotypes for conventional genetic screens, molecular genetic analysis using stress-responsive promoter-driven reporter is suggested as an alternative approach to genetically dissect abiotic stress signaling networks in plants.
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Affiliation(s)
- Liming Xiong
- Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA
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Zolnierowicz S. Type 2A protein phosphatase, the complex regulator of numerous signaling pathways. Biochem Pharmacol 2000; 60:1225-35. [PMID: 11007961 DOI: 10.1016/s0006-2952(00)00424-x] [Citation(s) in RCA: 159] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Type 2A protein phosphatase (PP2A) comprises a diverse family of phosphoserine- and phosphothreonine-specific enzymes ubiquitously expressed in eukaryotic cells. Common to all forms of PP2A is a catalytic subunit (PP2Ac) which can form two distinct complexes, one with a structural subunit termed PR65/A and another with an alpha4 protein. The PR65/A-PP2Ac dimer may further associate with a regulatory subunit and form a trimeric holoenzyme. To date, three distinct families of regulatory subunits, which control substrate selectivity and phosphatase activity and target PP2A holoenzymes to their substrates, have been identified. Other molecular mechanisms that regulate PP2Ac function include phosphorylation, carboxyl methylation, inhibition by intracellular protein inhibitors (I(1)(PP2A) and I(2)(PP2A)), and stimulation by ceramide. PP2A dephosphorylates many proteins in vitro, but in vivo protein kinases and transcription factors appear to represent two major sets of substrates. Several natural compounds can inhibit PP2A activity and are used to study its function. Mutations in genes encoding PR65/A subunits have been identified in several different human cancers and the PP2A inhibitor, termed fostriecin, is being tested as an anticancer drug. Thus, a more thorough understanding of PP2A structure and function may lead to the development of novel strategies against human diseases.
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Affiliation(s)
- S Zolnierowicz
- Intercollegiate Faculty of Biotechnology UG-MUG, Gdansk, Poland.
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Awotunde OS, Sugajska E, Zolnierowicz S, Muszyńska G. Characterisation of two protein phosphatase 2A holoenzymes from maize seedlings. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1480:65-76. [PMID: 11004556 DOI: 10.1016/s0167-4838(00)00097-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Two holoenzymes of protein phosphatase 2A (PP2A), designated PP2AI and PP2AII, were purified from maize seedlings. The subunit composition of maize holoenzymes generally resembled those of animal PP2A. Using SDS/PAGE and Western blots with antibodies generated against peptides derived from animal PP2A, we established the subunit composition of plant protein phosphatase 2A. In both maize holoenzymes, a 38000 catalytic (PP2Ac) and a 66000 constant regulatory subunit (A) constituting the core dimer of PP2A were present. In addition, PP2AI (180000-200000) contained a protein of 57000 which reacted with antibodies generated against the peptide (EFDYLKSLEIEE) conserved in all eukaryotic Balpha regulatory subunits. In contrast, none of the proteins visualised in PP2AII (140000-160000) by double staining reacted with these antibodies. The activity of PP2AI measured with (32)P-labelled phosphorylase a in the presence of protamine and ammonium sulfate is about two times higher than that of PP2AII. PP2AI and PP2AII displayed different patterns of activation by protamine, polylysine and histone H1 and exhibit high sensitivity toward inhibition by okadaic acid. The data obtained provide direct biochemical evidence for the existence in plants of PP2A holoenzymes composed of a catalytic subunit complexed with one or two regulatory subunits.
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Affiliation(s)
- O S Awotunde
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
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Deruère J, Jackson K, Garbers C, Söll D, Delong A. The RCN1-encoded A subunit of protein phosphatase 2A increases phosphatase activity in vivo. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 1999; 20:389-399. [PMID: 10607292 DOI: 10.1046/j.1365-313x.1999.00607.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine-specific protein phosphatase, comprises a catalytic C subunit and two distinct regulatory subunits, A and B. The RCN1 gene encodes one of three A regulatory subunits in Arabidopsis thaliana. A T-DNA insertion mutation at this locus impairs root curling, seedling organ elongation and apical hypocotyl hook formation. We have used in vivo and in vitro assays to gauge the impact of the rcn1 mutation on PP2A activity in seedlings. PP2A activity is decreased in extracts from rcn1 mutant seedlings, and this decrease is not due to a reduction in catalytic subunit expression. Roots of mutant seedlings exhibit increased sensitivity to the phosphatase inhibitors okadaic acid and cantharidin in organ elongation assays. Shoots of dark-grown, but not light-grown seedlings also show increased inhibitor sensitivity. Furthermore, cantharidin treatment of wild-type seedlings mimics the rcn1 defect in root curling, root waving and hypocotyl hook formation assays. In roots of wild-type seedlings, RCN1 mRNA is expressed at high levels in root tips, and accumulates to lower levels in the pericycle and lateral root primordia. In shoots, RCN1 is expressed in the apical hook and the basal, rapidly elongating cells in etiolated hypocotyls, and in the shoot meristem and leaf primordia of light-grown seedlings. Our results show that the wild-type RCN1-encoded A subunit functions as a positive regulator of the PP2A holoenzyme, increasing activity towards substrates involved in organ elongation and differential cell elongation responses such as root curling.
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Affiliation(s)
- J Deruère
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut, USA
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