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Lokdarshi A, von Arnim AG, Akuoko TK. Modulation of GCN2 activity under excess light stress by osmoprotectants and amino acids. PLANT SIGNALING & BEHAVIOR 2022; 17:2115747. [PMID: 36093942 PMCID: PMC9481134 DOI: 10.1080/15592324.2022.2115747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 08/10/2022] [Accepted: 08/11/2022] [Indexed: 06/15/2023]
Abstract
The protein kinase GCN2 (General Control Nonderepressible2) and its phosphorylation target, the eukaryotic translation initiation factor (eIF)2α represent the core module of the plant's integrated stress response, a signaling pathway widely conserved in eukaryotes that can rapidly regulate translation in response to stressful conditions. Recent findings indicate that the Arabidopsis thaliana GCN2 protein operates under the command of reactive oxygen species (ROS) emanating from the chloroplast under a variety of abiotic stresses such as excess light. To get deeper insights into the mechanism of GCN2 activation under excess light, we assessed the role of amino acids in view of the classic function of GCN2 as a sensor of amino acid status. Additionally, given that osmoprotectants can counteract ROS-related stresses, we tested their ability to mitigate GCN2 activity. Our results demonstrate that certain amino acids and osmoprotectants attenuate eIF2α-phosphorylation under excess light stress to some degree. Future investigations into the biochemical mechanisms of these natural compounds on GCN2 signaling activity will provide better insights into the GCN2-eIF2α regulation.
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Affiliation(s)
- Ansul Lokdarshi
- Department of Biology, Valdosta State University, Valdosta, GA, USA
| | - Albrecht G von Arnim
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, USA
- UT-ORNL Graduate School of Genome Science and Technology, the University of Tennessee, Knoxville, TN, USA
| | - Teressa K Akuoko
- Department of Biology, Valdosta State University, Valdosta, GA, USA
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Sonawala U, Dinkeloo K, Danna CH, McDowell JM, Pilot G. Review: Functional linkages between amino acid transporters and plant responses to pathogens. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2018; 277:79-88. [PMID: 30466603 DOI: 10.1016/j.plantsci.2018.09.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 08/11/2018] [Accepted: 09/12/2018] [Indexed: 06/09/2023]
Abstract
Upon infection, plant pathogens become dependent on their hosts for nutrition. Therefore, the interaction between the two organisms is tightly linked to the availability and flux of nutrients in the plant. The plant's nitrogen metabolism is reprogrammed during pathogen attack, likely reflecting plant's response to invasion by the pathogen and active modification by the pathogen to promote feeding. Several lines of evidence indicate that plant-derived amino acids are an important source of nitrogen for diverse pathogens. Moreover, amino acid homeostasis is interconnected with the plant's immune signaling pathways. Here, we critically examine the knowns and unknowns about connections between plant-encoded amino acid transporters and resistance or susceptibility to pathogens and pests. We use recent insights into sugar transporters to frame a perspective with potential applicability to amino acids and other nutrients. We emphasize different approaches that have provided insight in this topic and we conclude with suggestions to fill gaps in foundational knowledge and explore new avenues for disease control.
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Affiliation(s)
- Unnati Sonawala
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, 24060 VA, USA
| | - Kasia Dinkeloo
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, 24060 VA, USA
| | - Cristian H Danna
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - John M McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, 24060 VA, USA.
| | - Guillaume Pilot
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, 24060 VA, USA.
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3
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Kocira S, Szparaga A, Kocira A, Czerwińska E, Wójtowicz A, Bronowicka-Mielniczuk U, Koszel M, Findura P. Modeling Biometric Traits, Yield and Nutritional and Antioxidant Properties of Seeds of Three Soybean Cultivars Through the Application of Biostimulant Containing Seaweed and Amino Acids. FRONTIERS IN PLANT SCIENCE 2018; 9:388. [PMID: 29636764 PMCID: PMC5880921 DOI: 10.3389/fpls.2018.00388] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Accepted: 03/09/2018] [Indexed: 05/14/2023]
Abstract
In recent years, attempts have been made to use preparations that allow obtaining high and good quality yields, while reducing the application of pesticides and mineral fertilizers. These include biostimulants that are safe for the natural environment and contribute to the improvement of yield size and quality, especially after the occurrence of stressors. Their use is advisable in the case of crops sensitive to such biotic stress factors like low temperatures or drought. One of these is soybean which is a very important plant from the economic viewpoint. Field experiments were established in the years 2014-2016 in a random block design in four replicates on experimental plots of 10 m2. Three soybean cultivars: Annushka, Mavka, and Atlanta were planted in the third decade of April. Fylloton biostimulant was used at 0.7% or 1% concentrations as single spraying (BBCH 13-15) or double spraying (BBCH 13-15, BBCH 61) in the vegetation period. The number of seeds per 1 m2, seed yield, thousand seed weight, number of pods per plant, number of nodes in the main shoot, height of plants, and protein and fat contents in seeds were determined. The content of phenolic compounds, antioxidant capacity and antioxidant effect of soybean seeds were assayed as well. Foliar treatment of soybean with Fylloton stimulated the growth and yield of plants without compromising their nutritional and nutraceutical properties. The double application of the higher concentration of Fylloton was favorable for the plant height, seed number and soybean yield. Moreover, the highest number of pods was obtained after single treatment of plants with the lower biostimulant concentration. There was also a positive effect of using this biostimulant on the content and activity of some bioactive compounds, such as phenolics and flavonoids, and on the reducing power.
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Affiliation(s)
- Sławomir Kocira
- Department of Machinery Exploitation and Production Process Management, Faculty of Production Engineering, University of Life Sciences in Lublin, Lublin, Poland
- *Correspondence: Sławomir Kocira
| | - Agnieszka Szparaga
- Department of Agrobiotechnology, Faculty of Mechanical Engineering, Koszalin University of Technology, Koszalin, Poland
| | - Anna Kocira
- Institute of Agricultural Sciences, State School of Higher Education in Chełm, Chełm, Poland
| | - Ewa Czerwińska
- Department of Biomedical Engineering, Faculty of Technology and Education, Koszalin University of Technology, Koszalin, Poland
| | - Agnieszka Wójtowicz
- Department of Food Process Engineering, Faculty of Production Engineering, University of Life Sciences in Lublin, Lublin, Poland
| | - Urszula Bronowicka-Mielniczuk
- Department of Applied Mathematics and Computer Sciences, Faculty of Production Engineering, University of Life Sciences in Lublin, Lublin, Poland
| | - Milan Koszel
- Department of Machinery Exploitation and Production Process Management, Faculty of Production Engineering, University of Life Sciences in Lublin, Lublin, Poland
| | - Pavol Findura
- Department of Machines and Production Biosystems, Faculty of Engineering, Slovak University of Agriculture in Nitra, Nitra, Slovakia
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Chen J, Huang M, Cao F, Pardha-Saradhi P, Zou Y. Urea application promotes amino acid metabolism and membrane lipid peroxidation in Azolla. PLoS One 2017; 12:e0185230. [PMID: 28945775 PMCID: PMC5612470 DOI: 10.1371/journal.pone.0185230] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2017] [Accepted: 09/09/2017] [Indexed: 11/25/2022] Open
Abstract
A pot experiment was conducted to evaluate the effect of urea on nitrogen metabolism and membrane lipid peroxidation in Azolla pinnata. Compared to controls, the application of urea to A. pinnata resulted in a 44% decrease in nitrogenase activity, no significant change in glutamine synthetase activity, 660% higher glutamic-pyruvic transaminase, 39% increase in free amino acid levels, 22% increase in malondialdehyde levels, 21% increase in Na+/K+- levels, 16% increase in Ca2+/Mg2+-ATPase levels, and 11% decrease in superoxide dismutase activity. In terms of H2O2 detoxifying enzymes, peroxidase activity did not change and catalase activity increased by 64% in urea-treated A. pinnata. These findings suggest that urea application promotes amino acid metabolism and membrane lipid peroxidation in A. pinnata.
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Affiliation(s)
- Jiana Chen
- Southern Regional Collaborative Innovation Center for Grain and Oil Crops (CICGO), Hunan Agricultural University, Changsha, China
| | - Min Huang
- Southern Regional Collaborative Innovation Center for Grain and Oil Crops (CICGO), Hunan Agricultural University, Changsha, China
- * E-mail:
| | - Fangbo Cao
- Southern Regional Collaborative Innovation Center for Grain and Oil Crops (CICGO), Hunan Agricultural University, Changsha, China
| | - P. Pardha-Saradhi
- Department of Environmental Studies, University of Delhi, Delhi, India
| | - Yingbin Zou
- Southern Regional Collaborative Innovation Center for Grain and Oil Crops (CICGO), Hunan Agricultural University, Changsha, China
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Guerra D, Chapiro SM, Pratelli R, Yu S, Jia W, Leary J, Pilot G, Callis J. Control of Amino Acid Homeostasis by a Ubiquitin Ligase-Coactivator Protein Complex. J Biol Chem 2017; 292:3827-3840. [PMID: 28100770 PMCID: PMC5339764 DOI: 10.1074/jbc.m116.766469] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Indexed: 11/06/2022] Open
Abstract
Intercellular amino acid transport is essential for the growth of all multicellular organisms, and its dysregulation is implicated in developmental disorders. By an unknown mechanism, amino acid efflux is stimulated in plants by overexpression of a membrane-localized protein (GLUTAMINE DUMPER 1 (GDU1)) that requires a ubiquitin ligase (LOSS OF GDU 2 (LOG2). Here we further explore the physiological consequences of the interaction between these two proteins. LOG2 ubiquitin ligase activity is necessary for GDU1-dependent tolerance to exogenous amino acids, and LOG2 self-ubiquitination was markedly stimulated by the GDU1 cytosolic domain, suggesting that GDU1 functions as an adaptor or coactivator of amino acid exporter(s). However, other consequences more typical of a ligase-substrate relationship are observed: disruption of the LOG2 gene increased the in vivo half-life of GDU1, mass spectrometry confirmed that LOG2 ubiquitinates GDU1 at cytosolic lysines, and GDU1 protein levels decreased upon co-expression with active, but not enzymatically inactive LOG2. Altogether these data indicate LOG2 negatively regulates GDU1 protein accumulation by a mechanism dependent upon cytosolic GDU1 lysines. Although GDU1-lysine substituted protein exhibited diminished in vivo ubiquitination, overexpression of GDU1 lysine mutants still conferred amino acid tolerance in a LOG2-dependent manner, consistent with GDU1 being both a substrate and facilitator of LOG2 function. From these data, we offer a model in which GDU1 activates LOG2 to stimulate amino acid export, a process that could be negatively regulated by GDU1 ubiquitination and LOG2 self-ubiquitination.
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Affiliation(s)
- Damian Guerra
- From the Department of Molecular and Cellular Biology, University of California, Davis, Davis, California 95616 and
| | - Sonia M Chapiro
- From the Department of Molecular and Cellular Biology, University of California, Davis, Davis, California 95616 and
| | - Réjane Pratelli
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
| | - Shi Yu
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
| | - Weitao Jia
- From the Department of Molecular and Cellular Biology, University of California, Davis, Davis, California 95616 and
| | - Julie Leary
- From the Department of Molecular and Cellular Biology, University of California, Davis, Davis, California 95616 and
| | - Guillaume Pilot
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
| | - Judy Callis
- From the Department of Molecular and Cellular Biology, University of California, Davis, Davis, California 95616 and
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Kang SM, Radhakrishnan R, You YH, Khan AL, Lee KE, Lee JD, Lee IJ. Enterobacter asburiae KE17 association regulates physiological changes and mitigates the toxic effects of heavy metals in soybean. PLANT BIOLOGY (STUTTGART, GERMANY) 2015; 17:1013-22. [PMID: 25940948 DOI: 10.1111/plb.12341] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Accepted: 04/28/2015] [Indexed: 06/04/2023]
Abstract
This study aimed to elucidate the role played by Enterobacter asburiae KE17 in the growth and metabolism of soybeans during copper (100 μm Cu) and zinc (100 μm Zn) toxicity. When compared to controls, plants grown under Cu and Zn stress exhibited significantly lower growth rates, but inoculation with E. asburiae KE17 increased growth rates of stressed plants. The concentrations of plant hormones (abscisic acid and salicylic acid) and rates of lipid peroxidation were higher in plants under heavy metal stress, while total chlorophyll, carotenoid content and total polyphenol concentration were lower. While the bacterial treatment reduced the abscisic acid and salicylic acid content and lipid peroxidation rate of Cu-stressed plants, it also increased the concentration of photosynthetic pigments and total polyphenol. Moreover, the heavy metals induced increased accumulation of free amino acids such as aspartic acid, threonine, serine, glycine, alanine, leucine, isoleucine, tyrosine, proline and gamma-aminobutyric acid, while E. asburiae KE17 significantly reduced concentrations of free amino acids in metal-affected plants. Co-treatment with E. asburiae KE17 regulated nutrient uptake by enhancing nitrogen content and inhibiting Cu and Zn accumulation in soybean plants. The results of this study suggest that E. asburiae KE17 mitigates the effects of Cu and Zn stress by reprogramming plant metabolic processes.
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Affiliation(s)
- S-M Kang
- School of Applied Biosciences, Kyungpook National University, Daegu, Korea
| | - R Radhakrishnan
- School of Applied Biosciences, Kyungpook National University, Daegu, Korea
| | - Y-H You
- Korean Agricultural Culture Collection, Agricultural Microbiology Division, National Academy of Agricultural Science, RDA, Daegu, Korea
| | - A-L Khan
- Department of Biological Sciences and Chemistry, University of Nizwa, Nizwa, Oman
| | - K-E Lee
- School of Ecology and Environmental Science, Kyungpook National University, Sangju, Korea
| | - J-D Lee
- School of Applied Biosciences, Kyungpook National University, Daegu, Korea
| | - I-J Lee
- School of Applied Biosciences, Kyungpook National University, Daegu, Korea
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Yu S, Pratelli R, Denbow C, Pilot G. Suppressor mutations in the Glutamine Dumper1 protein dissociate disturbance in amino acid transport from other characteristics of the Gdu1D phenotype. FRONTIERS IN PLANT SCIENCE 2015; 6:593. [PMID: 26300894 PMCID: PMC4523740 DOI: 10.3389/fpls.2015.00593] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 07/17/2015] [Indexed: 05/05/2023]
Abstract
Intracellular amino acid transport across plant membranes is critical for metabolic pathways which are often split between different organelles. In addition, transport of amino acids across the plasma membrane enables the distribution of organic nitrogen through the saps between leaves and developing organs. Amino acid importers have been studied for more than two decades, and their role in this process is well-documented. While equally important, amino acid exporters are not well-characterized. The over-expression of GDU1, encoding a small membrane protein with one transmembrane domain, leads to enhancement of amino acid export by Arabidopsis cells, glutamine secretion at the leaf margin, early senescence and size reduction of the plant, possibly caused by the stimulation of amino acid exporter(s). Previous work reported the identification of suppressor mutations of the GDU1 over-expression phenotype, which affected the GDU1 and LOG2 genes, the latter encoding a membrane-bound ubiquitin ligase interacting with GDU1. The present study focuses on the characterization of three additional suppressor mutations affecting GDU1. Size, phenotype, glutamine transport and amino acid tolerance were recorded for recapitulation plants and over-expressors of mutagenized GDU1 proteins. Unexpectedly, the over-expression of most mutated GDU1 led to plants with enhanced amino acid export, but failing to display secretion of glutamine and size reduction. The results show that the various effects triggered by GDU1 over-expression can be dissociated from one another by mutagenizing specific residues. The fact that these residues are not necessarily conserved suggests that the diverse biochemical properties of the GDU1 protein are not only born by the characterized transmembrane and VIMAG domains. These data provide a better understanding of the structure/function relationships of GDU1 and may enable modifying amino acid export in plants without detrimental effects on plant fitness.
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Affiliation(s)
| | | | | | - Guillaume Pilot
- *Correspondence: Guillaume Pilot, Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, 511 Latham Hall, 220 AG Quad Lane, Blacksburg, VA 24061, USA,
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8
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Pratelli R, Pilot G. Regulation of amino acid metabolic enzymes and transporters in plants. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:5535-56. [PMID: 25114014 DOI: 10.1093/jxb/eru320] [Citation(s) in RCA: 191] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Amino acids play several critical roles in plants, from providing the building blocks of proteins to being essential metabolites interacting with many branches of metabolism. They are also important molecules that shuttle organic nitrogen through the plant. Because of this central role in nitrogen metabolism, amino acid biosynthesis, degradation, and transport are tightly regulated to meet demand in response to nitrogen and carbon availability. While much is known about the feedback regulation of the branched biosynthesis pathways by the amino acids themselves, the regulation mechanisms at the transcriptional, post-transcriptional, and protein levels remain to be identified. This review focuses mainly on the current state of our understanding of the regulation of the enzymes and transporters at the transcript level. Current results describing the effect of transcription factors and protein modifications lead to a fragmental picture that hints at multiple, complex levels of regulation that control and coordinate transport and enzyme activities. It also appears that amino acid metabolism, amino acid transport, and stress signal integration can influence each other in a so-far unpredictable fashion.
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Affiliation(s)
- Réjane Pratelli
- Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24060, USA
| | - Guillaume Pilot
- Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24060, USA
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9
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Khan AL, Lee IJ. Endophytic Penicillium funiculosum LHL06 secretes gibberellin that reprograms Glycine max L. growth during copper stress. BMC PLANT BIOLOGY 2013; 13:86. [PMID: 23721090 PMCID: PMC3674946 DOI: 10.1186/1471-2229-13-86] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Accepted: 05/27/2013] [Indexed: 05/23/2023]
Abstract
BACKGROUND Heavy metal pollution in crop fields is one of the major issues in sustainable agriculture production. To improve crop growth and reduce the toxic effects of metals is an ideal strategy. Understanding the resilience of gibberellins producing endophytic fungi associated with crop plants in metal contaminated agriculture fields could be an important step towards reducing agrochemical pollutions. In present study, it was aimed to screen and identify metal resistant endophyte and elucidate its role in rescuing crop plant growth and metabolism during metal stress. RESULTS Fungal endophyte, Penicillium funiculosum LHL06, was identified to possess higher growth rate in copper (Cu) and cadmium contaminated mediums as compared to other endophytes (Metarhizium anisopliae, Promicromonospora sp. and Exophiala sp.). P. funiculosum had high biosorption potential toward copper as compared to cadmium. An endophyte-metal-plant interaction was assessed by inoculating the host Glycine max L. plants with P. funiculosum during Cu (100 μM) stress. The Cu application adversely affected the biomass, chlorophyll and total protein content of non-inoculated control plants. The control plants unable to synthesis high carbon, hydrogen and nitrogen because the roots had lower access to phosphorous, potassium, sulphur and calcium during Cu treatment. Conversely, P. funiculosum-association significantly increased the plant biomass, root physiology and nutrients uptake to support higher carbon, hydrogen and nitrogen assimilation in shoot. The metal-removal potential of endophyte-inoculated plants was significantly higher than control as the endophyte-association mediated the Cu uptake via roots into shoots. The symbiosis rescued the host-plant growth by minimizing Cu-induced electrolytic leakage and lipid peroxidation while increasing reduces glutathione activities to avoid oxidative stress. P. funiculosum-association synthesized higher quantities of proline and glutamate as compared to control. Stress-responsive abscisic acid was significantly down-regulated in the plant-metal-microbe association. CONCLUSION The endophyte P. funiculosum symbiosis counteracted the Cu stress and reprogrammed soybean plant growth. Such growth promoting and stress mediating endophytes can be applied at field levels to help in bioremediation of the polluted agricultural fields.
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Affiliation(s)
- Abdul Latif Khan
- Department of Biological Sciences & Chemistry, University of Nizwa, Nizwa 616, Sultanate of Oman
- School of Applied Biosciences, College of Agriculture and Life Sciences, Kyungpook National University, Daegu, 701-702, Republic of Korea
- Kohat University of Science & Technology, Kohat, Pakistan
| | - In-Jung Lee
- Department of Biological Sciences & Chemistry, University of Nizwa, Nizwa 616, Sultanate of Oman
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Pratelli R, Guerra DD, Yu S, Wogulis M, Kraft E, Frommer WB, Callis J, Pilot G. The ubiquitin E3 ligase LOSS OF GDU2 is required for GLUTAMINE DUMPER1-induced amino acid secretion in Arabidopsis. PLANT PHYSIOLOGY 2012; 158:1628-42. [PMID: 22291198 PMCID: PMC3320174 DOI: 10.1104/pp.111.191965] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Amino acids serve as transport forms for organic nitrogen in the plant, and multiple transport steps are involved in cellular import and export. While the nature of the export mechanism is unknown, overexpression of GLUTAMINE DUMPER1 (GDU1) in Arabidopsis (Arabidopsis thaliana) led to increased amino acid export. To gain insight into GDU1's role, we searched for ethyl-methanesulfonate suppressor mutants and performed yeast-two-hybrid screens. Both methods uncovered the same gene, LOSS OF GDU2 (LOG2), which encodes a RING-type E3 ubiquitin ligase. The interaction between LOG2 and GDU1 was confirmed by glutathione S-transferase pull-down, in vitro ubiquitination, and in planta coimmunoprecipitation experiments. Confocal microscopy and subcellular fractionation indicated that LOG2 and GDU1 both localized to membranes and were enriched at the plasma membrane. LOG2 expression overlapped with GDU1 in the xylem and phloem tissues of Arabidopsis. The GDU1 protein encoded by the previously characterized intragenic suppressor mutant log1-1, with an arginine in place of a conserved glycine, failed to interact in the multiple assays, suggesting that the Gdu1D phenotype requires the interaction of GDU1 with LOG2. This hypothesis was supported by suppression of the Gdu1D phenotype after reduction of LOG2 expression using either artificial microRNAs or a LOG2 T-DNA insertion. Altogether, in accordance with the emerging bulk of data showing membrane protein regulation via ubiquitination, these data suggest that the interaction of GDU1 and the ubiquitin ligase LOG2 plays a significant role in the regulation of amino acid export from plant cells.
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Mangelsen E, Wanke D, Kilian J, Sundberg E, Harter K, Jansson C. Significance of light, sugar, and amino acid supply for diurnal gene regulation in developing barley caryopses. PLANT PHYSIOLOGY 2010; 153:14-33. [PMID: 20304969 PMCID: PMC2862414 DOI: 10.1104/pp.110.154856] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2010] [Accepted: 03/16/2010] [Indexed: 05/21/2023]
Abstract
The caryopses of barley (Hordeum vulgare), as of all cereals, are complex sink organs optimized for starch accumulation and embryo development. While their early to late development has been studied in great detail, processes underlying the caryopses' diurnal adaptation to changes in light, temperature, and the fluctuations in phloem-supplied carbon and nitrogen have remained unknown. In an attempt to identify diurnally affected processes in developing caryopses at the early maturation phase, we monitored global changes of both gene expression and metabolite levels. We applied the 22 K Barley1 GeneChip microarray and identified 2,091 differentially expressed (DE) genes that were assigned to six major diurnal expression clusters. Principal component analysis and other global analyses demonstrated that the variability within the data set relates to genes involved in circadian regulation, storage compound accumulation, embryo development, response to abiotic stress, and photosynthesis. The correlation of amino acid and sugar profiles with expression trajectories led to the identification of several hundred potentially metabolite-regulated DE genes. A comparative analysis of our data set and publicly available microarray data disclosed suborgan-specific expression of almost all diurnal DE genes, with more than 350 genes specifically expressed in the pericarp, endosperm, or embryo tissues. Our data reveal a tight linkage between day/night cycles, changes in light, and the supply of carbon and nitrogen. We present a model that suggests several phases of diurnal gene expression in developing barley caryopses, summarized as starvation and priming, energy collection and carbon fixation, light protection and chaperone activity, storage and growth, and embryo development.
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Affiliation(s)
- Elke Mangelsen
- Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, SE-75007 Uppsala, Sweden.
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Pratelli R, Voll LM, Horst RJ, Frommer WB, Pilot G. Stimulation of nonselective amino acid export by glutamine dumper proteins. PLANT PHYSIOLOGY 2010; 152:762-73. [PMID: 20018597 PMCID: PMC2815850 DOI: 10.1104/pp.109.151746] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2009] [Accepted: 12/14/2009] [Indexed: 05/17/2023]
Abstract
Phloem and xylem transport of amino acids involves two steps: export from one cell type to the apoplasm, and subsequent import into adjacent cells. High-affinity import is mediated by proton/amino acid cotransporters, while the mechanism of export remains unclear. Enhanced expression of the plant-specific type I membrane protein Glutamine Dumper1 (GDU1) has previously been shown to induce the secretion of glutamine from hydathodes and increased amino acid content in leaf apoplasm and xylem sap. In this work, tolerance to low concentrations of amino acids and transport analyses using radiolabeled amino acids demonstrate that net amino acid uptake is reduced in the glutamine-secreting GDU1 overexpressor gdu1-1D. The net uptake rate of phenylalanine decreased over time, and amino acid net efflux was increased in gdu1-1D compared with the wild type, indicating increased amino acid export from cells. Independence of the export from proton gradients and ATP suggests that overexpression of GDU1 affects a passive export system. Each of the seven Arabidopsis (Arabidopsis thaliana) GDU genes led to similar phenotypes, including increased efflux of a wide spectrum of amino acids. Differences in expression profiles and functional properties suggested that the GDU genes fulfill different roles in roots, vasculature, and reproductive organs. Taken together, the GDUs appear to stimulate amino acid export by activating nonselective amino acid facilitators.
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