1
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Williamson G, Harris T, Bizior A, Hoskisson PA, Pritchard L, Javelle A. Biological ammonium transporters: evolution and diversification. FEBS J 2024; 291:3786-3810. [PMID: 38265636 DOI: 10.1111/febs.17059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 12/14/2023] [Accepted: 01/09/2024] [Indexed: 01/25/2024]
Abstract
Although ammonium is the preferred nitrogen source for microbes and plants, in animal cells it is a toxic product of nitrogen metabolism that needs to be excreted. Thus, ammonium movement across biological membranes, whether for uptake or excretion, is a fundamental and ubiquitous biological process catalysed by the superfamily of the Amt/Mep/Rh transporters. A remarkable feature of the Amt/Mep/Rh family is that they are ubiquitous and, despite sharing low amino acid sequence identity, are highly structurally conserved. Despite sharing a common structure, these proteins have become involved in a diverse range of physiological process spanning all domains of life, with reports describing their involvement in diverse biological processes being published regularly. In this context, we exhaustively present their range of biological roles across the domains of life and after explore current hypotheses concerning their evolution to help to understand how and why the conserved structure fulfils diverse physiological functions.
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Affiliation(s)
- Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Paul Alan Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Leighton Pritchard
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
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2
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Pflüger T, Gschell M, Zhang L, Shnitsar V, Zabadné AJ, Zierep P, Günther S, Einsle O, Andrade SLA. How sensor Amt-like proteins integrate ammonium signals. SCIENCE ADVANCES 2024; 10:eadm9441. [PMID: 38838143 DOI: 10.1126/sciadv.adm9441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 04/30/2024] [Indexed: 06/07/2024]
Abstract
Unlike aquaporins or potassium channels, ammonium transporters (Amts) uniquely discriminate ammonium from potassium and water. This feature has certainly contributed to their repurposing as ammonium receptors during evolution. Here, we describe the ammonium receptor Sd-Amt1, where an Amt module connects to a cytoplasmic diguanylate cyclase transducer module via an HAMP domain. Structures of the protein with and without bound ammonium were determined to 1.7- and 1.9-Ångstrom resolution, depicting the ON and OFF states of the receptor and confirming the presence of a binding site for two ammonium cations that is pivotal for signal perception and receptor activation. The transducer domain was disordered in the crystals, and an AlphaFold2 prediction suggests that the helices linking both domains are flexible. While the sensor domain retains the trimeric fold formed by all Amt family members, the HAMP domains interact as pairs and serve to dimerize the transducer domain upon activation.
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Affiliation(s)
- Tobias Pflüger
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Mathias Gschell
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Lin Zhang
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Volodymyr Shnitsar
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Annas J Zabadné
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Paul Zierep
- Faculty of Chemistry and Pharmacy, Institute for Pharmaceutical Sciences, University Freiburg, Hermann-Herder-Str. 9, 79104 Freiburg, Germany
| | - Stefan Günther
- Faculty of Chemistry and Pharmacy, Institute for Pharmaceutical Sciences, University Freiburg, Hermann-Herder-Str. 9, 79104 Freiburg, Germany
| | - Oliver Einsle
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
- BIOSS Centre for Biological Signaling Studies, University Freiburg, Schänzlerstr. 1, 79104 Freiburg, Germany
| | - Susana L A Andrade
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
- BIOSS Centre for Biological Signaling Studies, University Freiburg, Schänzlerstr. 1, 79104 Freiburg, Germany
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3
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Williamson G, Bizior A, Harris T, Pritchard L, Hoskisson P, Javelle A. Biological ammonium transporters from the Amt/Mep/Rh superfamily: mechanism, energetics, and technical limitations. Biosci Rep 2024; 44:BSR20211209. [PMID: 38131184 PMCID: PMC10794816 DOI: 10.1042/bsr20211209] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 12/12/2023] [Accepted: 12/21/2023] [Indexed: 12/23/2023] Open
Abstract
The exchange of ammonium across cellular membranes is a fundamental process in all domains of life and is facilitated by the ubiquitous Amt/Mep/Rh transporter superfamily. Remarkably, despite a high structural conservation in all domains of life, these proteins have gained various biological functions during evolution. It is tempting to hypothesise that the physiological functions gained by these proteins may be explained at least in part by differences in the energetics of their translocation mechanisms. Therefore, in this review, we will explore our current knowledge of energetics of the Amt/Mep/Rh family, discuss variations in observations between different organisms, and highlight some technical drawbacks which have hampered effects at mechanistic characterisation. Through the review, we aim to provide a comprehensive overview of current understanding of the mechanism of transport of this unique and extraordinary Amt/Mep/Rh superfamily of ammonium transporters.
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Affiliation(s)
- Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Leighton Pritchard
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
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4
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Jain D, Schmidt W. Protein Phosphorylation Orchestrates Acclimations of Arabidopsis Plants to Environmental pH. Mol Cell Proteomics 2024; 23:100685. [PMID: 38000714 PMCID: PMC10837763 DOI: 10.1016/j.mcpro.2023.100685] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2023] [Revised: 10/18/2023] [Accepted: 11/16/2023] [Indexed: 11/26/2023] Open
Abstract
Environment pH (pHe) is a key parameter dictating a surfeit of conditions critical to plant survival and fitness. To elucidate the mechanisms that recalibrate cytoplasmic and apoplastic pH homeostasis, we conducted a comprehensive proteomic/phosphoproteomic inventory of plants subjected to transient exposure to acidic or alkaline pH, an approach that covered the majority of protein-coding genes of the reference plant Arabidopsis thaliana. Our survey revealed a large set-of so far undocumented pHe-dependent phospho-sites, indicative of extensive post-translational regulation of proteins involved in the acclimation to pHe. Changes in pHe altered both electrogenic H+ pumping via P-type ATPases and H+/anion co-transport processes, putatively leading to altered net trans-plasma membrane translocation of H+ ions. In pH 7.5 plants, the transport (but not the assimilation) of nitrogen via NRT2-type nitrate and AMT1-type ammonium transporters was induced, conceivably to increase the cytosolic H+ concentration. Exposure to both acidic and alkaline pH resulted in a marked repression of primary root elongation. No such cessation was observed in nrt2.1 mutants. Alkaline pH decreased the number of root hairs in the wild type but not in nrt2.1 plants, supporting a role of NRT2.1 in developmental signaling. Sequestration of iron into the vacuole via alterations in protein abundance of the vacuolar iron transporter VTL5 was inversely regulated in response to high and low pHe, presumptively in anticipation of associated changes in iron availability. A pH-dependent phospho-switch was also observed for the ABC transporter PDR7, suggesting changes in activity and, possibly, substrate specificity. Unexpectedly, the effect of pHe was not restricted to roots and provoked pronounced changes in the shoot proteome. In both roots and shoots, the plant-specific TPLATE complex components AtEH1 and AtEH2-essential for clathrin-mediated endocytosis-were differentially phosphorylated at multiple sites in response to pHe, indicating that the endocytic cargo protein trafficking is orchestrated by pHe.
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Affiliation(s)
- Dharmesh Jain
- Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, Academia Sinica and National Chung-Hsing University, Taipei, Taiwan; Graduate Institute of Biotechnology, National Chung-Hsing University, Taichung, Taiwan; Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
| | - Wolfgang Schmidt
- Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, Academia Sinica and National Chung-Hsing University, Taipei, Taiwan; Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan; Biotechnology Center, National Chung-Hsing University, Taichun, Taiwan; Genome and Systems Biology Degree Program, College of Life Science, National Taiwan University, Taipei, Taiwan.
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5
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Cao H, Liu Q, Liu X, Ma Z, Zhang J, Li X, Shen L, Yuan J, Zhang Q. Phosphatidic acid regulates ammonium uptake by interacting with AMMONIUM TRANSPORTER 1;1 in Arabidopsis. PLANT PHYSIOLOGY 2023; 193:1954-1969. [PMID: 37471275 DOI: 10.1093/plphys/kiad421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Revised: 06/26/2023] [Accepted: 06/27/2023] [Indexed: 07/22/2023]
Abstract
Ammonium (NH4+) is a key inorganic nitrogen source in cellular amino acid biosynthesis. The coupling of transcriptional and posttranslational regulation of AMMONIUM TRANSPORTER (AMT) ensures that NH4+ acquisition by plant roots is properly balanced, which allows for rapid adaptation to a variety of nitrogen conditions. Here, we report that phospholipase D (PLD)-derived phosphatidic acid (PA) interacts with AMT1;1 to mediate NH4+ uptake in Arabidopsis (Arabidopsis thaliana). We examined pldα1 pldδ-knockout mutants and found that a reduced PA level increased seedling growth under nitrogen deficiency and inhibited root growth upon NH4+ stress, which was consistent with the enhanced accumulation of cellular NH4+. PA directly bound to AMT1;1 and inhibited its transport activity. Mutation of AMT1;1 R487 to Gly (R487G) resulted in abolition of PA suppression and, subsequently, enhancement of ammonium transport activity in vitro and in vivo. Observations of AMT1;1-GFP showed suppressed endocytosis under PLD deficiency or by mutation of the PA-binding site in AMT1;1. Endocytosis was rescued by PA in the pldα1 pldδ mutant but not in the mutant AMT1;1R487G-GFP line. Together, these findings demonstrated PA-based shutoff control of plant NH4+ transport and point to a broader paradigm of lipid-transporter function.
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Affiliation(s)
- Hongwei Cao
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Qingyun Liu
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Xiao Liu
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Zhaokun Ma
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Jixiu Zhang
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Xuebing Li
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Like Shen
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Jingya Yuan
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Qun Zhang
- State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
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6
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Chen YN, Ho CH. CIPK15-mediated inhibition of NH 4+ transport protects Arabidopsis from submergence. Heliyon 2023; 9:e20235. [PMID: 37810036 PMCID: PMC10560025 DOI: 10.1016/j.heliyon.2023.e20235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2023] [Revised: 07/18/2023] [Accepted: 09/14/2023] [Indexed: 10/10/2023] Open
Abstract
Ammonium (NH4+) serves as a vital nitrogen source for plants, but it can turn toxic when it accumulates in excessive amounts. Toxicity is aggravated under hypoxic/anaerobic conditions, e.g., during flooding or submergence, due to a lower assimilation capacity. AMT1; 1 mediates NH4+ uptake into roots. Under conditions of oxygen-deficiency, i.e., submergence, the CBL-interacting protein kinase OsCIPK15 has been shown to trigger SnRK1A signaling, promoting starch mobilization, thereby the increasing availability of ATP, reduction equivalents and acceptors for NH4+ assimilation in rice. Our previous study in Arabidopsis demonstrates that AtCIPK15 phosphorylates AMT1; 1 whose activity is under allosteric feedback control by phosphorylation of T460 in the cytosolic C-terminus. Here we show that submergence cause higher NH4+ accumulation in wild-type, plant but not of nitrate, nor in a quadruple amt knock-out mutant. In addition, submergence triggers rapid accumulation of AtAMT1;1 and AtCIPK15 transcripts as well as AMT1 phosphorylation. Significantly, cipk15 knock-out mutants do not exhibit an increase in AMT1 phosphorylation; however, they do display heightened sensitivity to submergence. These findings suggest that CIPK15 suppresses AMT activity, resulting in decreased NH4+ accumulation during submergence, a period when NH4+ assimilation capacity may be impaired.
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Affiliation(s)
- Yen-Ning Chen
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Cheng-Hsun Ho
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
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7
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Choi SJ, Lee Z, Jeong E, Kim S, Seo JS, Um T, Shim JS. Signaling pathways underlying nitrogen transport and metabolism in plants. BMB Rep 2023; 56:56-64. [PMID: 36658636 PMCID: PMC9978367] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Indexed: 01/21/2023] Open
Abstract
Nitrogen (N) is an essential macronutrient required for plant growth and crop production. However, N in soil is usually insufficient for plant growth. Thus, chemical N fertilizer has been extensively used to increase crop production. Due to negative effects of N rich fertilizer on the environment, improving N usage has been a major issue in the field of plant science to achieve sustainable production of crops. For that reason, many efforts have been made to elucidate how plants regulate N uptake and utilization according to their surrounding habitat over the last 30 years. Here, we provide recent advances focusing on regulation of N uptake, allocation of N by N transporting system, and signaling pathway controlling N responses in plants. [BMB Reports 2023; 56(2): 56-64].
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Affiliation(s)
- Su Jeong Choi
- School of Biological Sciences and Technology, Chonnam National University, Gwangju 61186, Korea
| | - Zion Lee
- School of Biological Sciences and Technology, Chonnam National University, Gwangju 61186, Korea
| | - Eui Jeong
- School of Biological Sciences and Technology, Chonnam National University, Gwangju 61186, Korea
| | - Sohyun Kim
- School of Biological Sciences and Technology, Chonnam National University, Gwangju 61186, Korea
| | - Jun Sung Seo
- Crop Biotechnology Institute, Green Bio Science and Technology, Seoul National University, Pyeongchang 25354, Korea
| | - Taeyoung Um
- Agriculture and Life Sciences Research Institute, Kangwon National University, Chuncheon 24341, Korea
| | - Jae Sung Shim
- School of Biological Sciences and Technology, Chonnam National University, Gwangju 61186, Korea,Corresponding author. Tel: +82-62-530-0507; Fax: +82-62-530-2199; E-mail:
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8
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Hui J, An X, Li Z, Neuhäuser B, Ludewig U, Wu X, Schulze WX, Chen F, Feng G, Lambers H, Zhang F, Yuan L. The mycorrhiza-specific ammonium transporter ZmAMT3;1 mediates mycorrhiza-dependent nitrogen uptake in maize roots. THE PLANT CELL 2022; 34:4066-4087. [PMID: 35880836 PMCID: PMC9516061 DOI: 10.1093/plcell/koac225] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 06/18/2022] [Indexed: 06/15/2023]
Abstract
Most plant species can form symbioses with arbuscular mycorrhizal fungi (AMFs), which may enhance the host plant's acquisition of soil nutrients. In contrast to phosphorus nutrition, the molecular mechanism of mycorrhizal nitrogen (N) uptake remains largely unknown, and its physiological relevance is unclear. Here, we identified a gene encoding an AMF-inducible ammonium transporter, ZmAMT3;1, in maize (Zea mays) roots. ZmAMT3;1 was specifically expressed in arbuscule-containing cortical cells and the encoded protein was localized at the peri-arbuscular membrane. Functional analysis in yeast and Xenopus oocytes indicated that ZmAMT3;1 mediated high-affinity ammonium transport, with the substrate NH4+ being accessed, but likely translocating uncharged NH3. Phosphorylation of ZmAMT3;1 at the C-terminus suppressed transport activity. Using ZmAMT3;1-RNAi transgenic maize lines grown in compartmented pot experiments, we demonstrated that substantial quantities of N were transferred from AMF to plants, and 68%-74% of this capacity was conferred by ZmAMT3;1. Under field conditions, the ZmAMT3;1-dependent mycorrhizal N pathway contributed >30% of postsilking N uptake. Furthermore, AMFs downregulated ZmAMT1;1a and ZmAMT1;3 protein abundance and transport activities expressed in the root epidermis, suggesting a trade-off between mycorrhizal and direct root N-uptake pathways. Taken together, our results provide a comprehensive understanding of mycorrhiza-dependent N uptake in maize and present a promising approach to improve N-acquisition efficiency via plant-microbe interactions.
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Affiliation(s)
- Jing Hui
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, MOE, China Agricultural University, Beijing, 100193, China
| | - Xia An
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, MOE, China Agricultural University, Beijing, 100193, China
| | - Zhibo Li
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, MOE, China Agricultural University, Beijing, 100193, China
| | - Benjamin Neuhäuser
- Department of Nutritional Crop Physiology, Institute of Crop Science, University of Hohenheim, Stuttgart, 70593, Germany
| | - Uwe Ludewig
- Department of Nutritional Crop Physiology, Institute of Crop Science, University of Hohenheim, Stuttgart, 70593, Germany
| | - Xuna Wu
- Department of Plant Systems Biology, Institute for Physiology and Biotechnology of Plants, University of Hohenheim, Stuttgart, 70593, Germany
| | - Waltraud X Schulze
- Department of Plant Systems Biology, Institute for Physiology and Biotechnology of Plants, University of Hohenheim, Stuttgart, 70593, Germany
| | - Fanjun Chen
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, MOE, China Agricultural University, Beijing, 100193, China
| | - Gu Feng
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, MOE, China Agricultural University, Beijing, 100193, China
| | - Hans Lambers
- School of Biological Science and Institute of Agriculture, University of Western Australia, Perth, WA6009, Australia
| | - Fusuo Zhang
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, MOE, China Agricultural University, Beijing, 100193, China
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9
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Williamson G, Brito AS, Bizior A, Tamburrino G, Dias Mirandela G, Harris T, Hoskisson PA, Zachariae U, Marini AM, Boeckstaens M, Javelle A. Coexistence of Ammonium Transporter and Channel Mechanisms in Amt-Mep-Rh Twin-His Variants Impairs the Filamentation Signaling Capacity of Fungal Mep2 Transceptors. mBio 2022; 13:e0291321. [PMID: 35196127 PMCID: PMC9040831 DOI: 10.1128/mbio.02913-21] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Accepted: 01/26/2022] [Indexed: 12/01/2022] Open
Abstract
Ammonium translocation through biological membranes, by the ubiquitous Amt-Mep-Rh family of transporters, plays a key role in all domains of life. Two highly conserved histidine residues protrude into the lumen of the pore of these transporters, forming the family's characteristic Twin-His motif. It has been hypothesized that the motif is essential to confer the selectivity of the transport mechanism. Here, using a combination of in vitro electrophysiology on Escherichia coli AmtB, in silico molecular dynamics simulations, and in vivo yeast functional complementation assays, we demonstrate that variations in the Twin-His motif trigger a mechanistic switch between a specific transporter, depending on ammonium deprotonation, to an unspecific ion channel activity. We therefore propose that there is no selective filter that governs specificity in Amt-Mep-Rh transporters, but the inherent mechanism of translocation, dependent on the fragmentation of the substrate, ensures the high specificity of the translocation. We show that coexistence of both mechanisms in single Twin-His variants of yeast Mep2 transceptors disrupts the signaling function and so impairs fungal filamentation. These data support a signaling process driven by the transport mechanism of the fungal Mep2 transceptors. IMPORTANCE Fungal infections represent a significant threat to human health and cause huge damage to crop yields worldwide. The dimorphic switch between yeast and filamentous growth is associated with the virulence of pathogenic fungi. Of note, fungal Mep2 proteins of the conserved Amt-Mep-Rh family play a transceptor role in the induction of filamentation; however, the signaling mechanism remains largely unknown. Amt-Mep-Rh proteins ensure the specific scavenging of NH4+ through a mechanism relying on substrate deprotonation, thereby preventing competition and translocation of similar-sized K+. Our multidisciplinary approaches using E. coli AmtB, Saccharomyces cerevisiae, and Candida albicans Mep2 show that double variation of the family-defining Twin-His motif triggers a mechanistic switch from a specific transporter to an unspecific ion channel with both mechanisms still coexisting in single variants. Moreover, we show that this mechanistic alteration is associated with loss of signaling ability of Mep2, supporting a transport mechanism-driven process in filamentation induction.
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Affiliation(s)
- Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Ana Sofia Brito
- Biology of Membrane Transport Laboratory, Department of Molecular Biology, Université Libre de Bruxelles, Gosselies, Belgium
| | - Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Giulia Tamburrino
- Computational Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Gaëtan Dias Mirandela
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
- Biology of Membrane Transport Laboratory, Department of Molecular Biology, Université Libre de Bruxelles, Gosselies, Belgium
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Ulrich Zachariae
- Computational Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Anna Maria Marini
- Biology of Membrane Transport Laboratory, Department of Molecular Biology, Université Libre de Bruxelles, Gosselies, Belgium
| | - Mélanie Boeckstaens
- Biology of Membrane Transport Laboratory, Department of Molecular Biology, Université Libre de Bruxelles, Gosselies, Belgium
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
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10
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Chen YN, Ho CH. Concept of Fluorescent Transport Activity Biosensor for the Characterization of the Arabidopsis NPF1.3 Activity of Nitrate. SENSORS 2022; 22:s22031198. [PMID: 35161943 PMCID: PMC8839256 DOI: 10.3390/s22031198] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 01/24/2022] [Accepted: 01/31/2022] [Indexed: 02/01/2023]
Abstract
The NRT1/PTR FAMILY (NPF) in Arabidopsis (Arabidopsis thaliana) plays a major role as a nitrate transporter. The first nitrate transporter activity biosensor NiTrac1 converted the dual-affinity nitrate transceptor NPF6.3 into fluorescence activity sensors. To test whether this approach is transferable to other members of this family, screening for genetically encoded fluorescence transport activity sensor was performed with the member of the NPF family in Arabidopsis. In this study, NPF1.3, an uncharacterized member of NPF in Arabidopsis, was converted into a transporter activity biosensor NiTrac-NPF1.3 that responds specifically to nitrate. The emission ratio change of NiTrac-NPF1.3 triggered by the addition of nitrate reveals the important function of NPF1.3 in nitrate transport in Arabidopsis. A functional analysis of Xenopus laevis oocytes confirmed that NPF1.3 plays a role as a nitrate transporter. This new technology is applicable in plant and medical research.
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11
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Wang Y, Xuan YM, Wang SM, Fan DM, Wang XC, Zheng XQ. Genome-wide identification, characterization, and expression analysis of the ammonium transporter gene family in tea plants (Camellia sinensis L.). PHYSIOLOGIA PLANTARUM 2022; 174:e13646. [PMID: 35129836 DOI: 10.1111/ppl.13646] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 01/30/2022] [Accepted: 02/02/2022] [Indexed: 06/14/2023]
Abstract
As a preferred nitrogen form, ammonium (NH4 + ) transport via specific transporters is particularly important for the growth and development of tea plants (Camellia sinensis L.). However, our understanding of the functions of the AMT family in tea plants is limited. We identified and named 16 putative AMT genes according to phylogenetic analysis. All CsAMT genes were divided into three groups, distributed on 12 chromosomes with only one segmental duplication repetition. The CsAMT genes showed different expression levels in different organs, and most of them were expressed mainly in the apical buds and roots. Complementation analysis of yeast mutants showed that CsAMTs restored the uptake of NH4 + . This study provides insights into the genome-wide distribution and spatial expression of AMT genes in tea plants.
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Affiliation(s)
- Yu Wang
- Tea Research Institute, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, China
| | - Yi-Min Xuan
- Tea Research Institute, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, China
| | - Shu-Mao Wang
- Tea Research Institute, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, China
| | - Dong-Mei Fan
- Tea Research Institute, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, China
| | - Xiao-Chang Wang
- Tea Research Institute, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, China
| | - Xin-Qiang Zheng
- Tea Research Institute, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, China
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12
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Nitrogen Uptake in Plants: The Plasma Membrane Root Transport Systems from a Physiological and Proteomic Perspective. PLANTS 2021; 10:plants10040681. [PMID: 33916130 PMCID: PMC8066207 DOI: 10.3390/plants10040681] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 03/26/2021] [Accepted: 03/29/2021] [Indexed: 11/17/2022]
Abstract
Nitrogen nutrition in plants is a key determinant in crop productivity. The availability of nitrogen nutrients in the soil, both inorganic (nitrate and ammonium) and organic (urea and free amino acids), highly differs and influences plant physiology, growth, metabolism, and root morphology. Deciphering this multifaceted scenario is mandatory to improve the agricultural sustainability. In root cells, specific proteins located at the plasma membrane play key roles in the transport and sensing of nitrogen forms. This review outlines the current knowledge regarding the biochemical and physiological aspects behind the uptake of the individual nitrogen forms, their reciprocal interactions, the influences on root system architecture, and the relations with other proteins sustaining fundamental plasma membrane functionalities, such as aquaporins and H+-ATPase. This topic is explored starting from the information achieved in the model plant Arabidopsis and moving to crops in agricultural soils. Moreover, the main contributions provided by proteomics are described in order to highlight the goals and pitfalls of this approach and to get new hints for future studies.
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13
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Chen HY, Chen YN, Wang HY, Liu ZT, Frommer WB, Ho CH. Feedback inhibition of AMT1 NH 4+-transporters mediated by CIPK15 kinase. BMC Biol 2020; 18:196. [PMID: 33317525 PMCID: PMC7737296 DOI: 10.1186/s12915-020-00934-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 11/24/2020] [Indexed: 11/24/2022] Open
Abstract
Background Ammonium (NH4+), a key nitrogen form, becomes toxic when it accumulates to high levels. Ammonium transporters (AMTs) are the key transporters responsible for NH4+ uptake. AMT activity is under allosteric feedback control, mediated by phosphorylation of a threonine in the cytosolic C-terminus (CCT). However, the kinases responsible for the NH4+-triggered phosphorylation remain unknown. Results In this study, a functional screen identified protein kinase CBL-Interacting Protein Kinase15 (CIPK15) as a negative regulator of AMT1;1 activity. CIPK15 was able to interact with several AMT1 paralogs at the plasma membrane. Analysis of AmTryoshka, an NH4+ transporter activity sensor for AMT1;3 in yeast, and a two-electrode-voltage-clamp (TEVC) of AMT1;1 in Xenopus oocytes showed that CIPK15 inhibits AMT activity. CIPK15 transcript levels increased when seedlings were exposed to elevated NH4+ levels. Notably, cipk15 knockout mutants showed higher 15NH4+ uptake and accumulated higher amounts of NH4+ compared to the wild-type. Consistently, cipk15 was hypersensitive to both NH4+ and methylammonium but not nitrate (NO3−). Conclusion Taken together, our data indicate that feedback inhibition of AMT1 activity is mediated by the protein kinase CIPK15 via phosphorylation of residues in the CCT to reduce NH4+-accumulation. Supplementary information The online version contains supplementary material available at 10.1186/s12915-020-00934-w.
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Affiliation(s)
- Hui-Yu Chen
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Yen-Ning Chen
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Hung-Yu Wang
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Zong-Ta Liu
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Wolf B Frommer
- Institute for Molecular Physiology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.,Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya, 464-8601, Japan
| | - Cheng-Hsun Ho
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan.
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14
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Hao DL, Zhou JY, Yang SY, Huang YN, Su YH. Functional and Regulatory Characterization of Three AMTs in Maize Roots. FRONTIERS IN PLANT SCIENCE 2020; 11:884. [PMID: 32676086 PMCID: PMC7333355 DOI: 10.3389/fpls.2020.00884] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Accepted: 05/29/2020] [Indexed: 06/11/2023]
Abstract
Maize grows in nitrate-dominated dryland soils, but shortly upon localized dressing of nitrogen fertilizers, ammonium is retained as a noticeable form of nitrogen source available to roots. Thus in addition to nitrate, the absorption of ammonium can be an important strategy that promotes rapid plant growth at strong nitrogen demanding stages. The present study reports the functional characterization of three root-expressed ammonium transporters (AMTs), aiming at finding out functional and regulatory properties that correlate with efficient nitrogen acquisition of maize. Using a stable electrophysiological recording method we previously established in Xenopus laevis oocytes that integrates the capture of currents in response to voltage ramps with onsite stability controls, we demonstrate that all three ZmAMT1s engage NH4 + uniporting as ammonium uptake mechanisms. The K m value for ZmAMT1.1a, 1.1b, or ZmAMT1.3 is, respectively, 9.9, 15.6, or 18.6 μM, indicating a typical high-affinity transport of NH4 + ions. Importantly, the uptake currents of these ZmAMT1s are markedly amplified upon extracellular acidification. A pH drop from 7.4 to 5.4 results in a 140.8%, 64.1% or a 120.7% increase of ammonium uptake activity through ZmAMT1.1a, 1.1b, or ZmAMT1.3. Since ammonium uptake by plant roots accompanies a spontaneous acidification to the root medium, the functional promotion of ZmAMT1.1a, 1.1b, and ZmAMT1.3 by low pH is in line with the facilitated ammonium uptake activity in maize roots. Furthermore, the expression of the three ZmAMT1 genes is induced under ammonium-dominated conditions. Thus we describe a facilitated ammonium uptake strategy in maize roots by functional and expression regulations of ZmAMT1 transporters that may coordinate with efficient acquisition of this form of nitrogen source when available.
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15
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Hao DL, Zhou JY, Yang SY, Qi W, Yang KJ, Su YH. Function and Regulation of Ammonium Transporters in Plants. Int J Mol Sci 2020; 21:E3557. [PMID: 32443561 PMCID: PMC7279009 DOI: 10.3390/ijms21103557] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2020] [Revised: 05/11/2020] [Accepted: 05/13/2020] [Indexed: 02/07/2023] Open
Abstract
Ammonium transporter (AMT)-mediated acquisition of ammonium nitrogen from soils is essential for the nitrogen demand of plants, especially for those plants growing in flooded or acidic soils where ammonium is dominant. Recent advances show that AMTs additionally participate in many other physiological processes such as transporting ammonium from symbiotic fungi to plants, transporting ammonium from roots to shoots, transferring ammonium in leaves and reproductive organs, or facilitating resistance to plant diseases via ammonium transport. Besides being a transporter, several AMTs are required for the root development upon ammonium exposure. To avoid the adverse effects of inadequate or excessive intake of ammonium nitrogen on plant growth and development, activities of AMTs are fine-tuned not only at the transcriptional level by the participation of at least four transcription factors, but also at protein level by phosphorylation, pH, endocytosis, and heterotrimerization. Despite these progresses, it is worth noting that stronger growth inhibition, not facilitation, unfortunately occurs when AMT overexpression lines are exposed to optimal or slightly excessive ammonium. This implies that a long road remains towards overcoming potential limiting factors and achieving AMT-facilitated yield increase to accomplish the goal of persistent yield increase under the present high nitrogen input mode in agriculture.
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Affiliation(s)
- Dong-Li Hao
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; (D.-L.H.); (J.-Y.Z.); (S.-Y.Y.)
| | - Jin-Yan Zhou
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; (D.-L.H.); (J.-Y.Z.); (S.-Y.Y.)
| | - Shun-Ying Yang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; (D.-L.H.); (J.-Y.Z.); (S.-Y.Y.)
| | - Wei Qi
- College of Resources and Environment, Shandong Agricultural University, Taian 271018, China;
| | - Ke-Jun Yang
- Agro-Tech Extension and Service Center, Zhucheng 262200, China;
| | - Yan-Hua Su
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; (D.-L.H.); (J.-Y.Z.); (S.-Y.Y.)
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16
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Hao DL, Yang SY, Liu SX, Zhou JY, Huang YN, Véry AA, Sentenac H, Su YH. Functional Characterization of the Arabidopsis Ammonium Transporter AtAMT1;3 With the Emphasis on Structural Determinants of Substrate Binding and Permeation Properties. FRONTIERS IN PLANT SCIENCE 2020; 11:571. [PMID: 32528489 PMCID: PMC7256485 DOI: 10.3389/fpls.2020.00571] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 04/17/2020] [Indexed: 05/13/2023]
Abstract
AtAMT1;3 is a major contributor to high-affinity ammonium uptake in Arabidopsis roots. Using a stable electrophysiological recording strategy, we demonstrate in Xenopus laevis oocytes that AtAMT1;3 functions as a typical high-affinity NH4 + uniporter independent of protons and Ca2+. The findings that AtAMT1;3 transports methylammonium (MeA+, a chemical analog of NH4 +) with extremely low affinity (K m in the range of 2.9-6.1 mM) led to investigate the mechanisms underlying substrate binding. Homologous modeling and substrate docking analyses predicted that the deduced substrate binding motif of AtAMT1;3 facilitates the binding of NH4 + ions but loosely accommodates the binding of MeA+ to a more superficial location of the permeation pathway. Amongst point mutations tested based on this analysis, P181A resulted in both significantly increased current amplitudes and substrate binding affinity, whereas F178I led to opposite effects. Thus these 2 residues, which flank W179, a major structural component of the binding site, are also important determinants of AtAMT1;3 transport capacity by being involved in substrate binding. The Q365K mutation neighboring the histidine residue H378, which confines the substrate permeation tunnel, affected only the current amplitudes but not the binding affinities, providing evidence that Q365 mainly controls the substrate diffusion rate within the permeation pathway.
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Affiliation(s)
- Dong-Li Hao
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
| | - Shun-Ying Yang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
| | - Shu-Xia Liu
- Department of Computational Biology, Beijing Computing Center, Beijing, China
| | - Jin-Yan Zhou
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
| | - Ya-Nan Huang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
| | - Anne-Aliénor Véry
- BPMP, Univ Montpellier, CNRS, INRAE, Institut Agro, Montpellier, France
| | - Hervé Sentenac
- BPMP, Univ Montpellier, CNRS, INRAE, Institut Agro, Montpellier, France
- *Correspondence: Hervé Sentenac,
| | - Yan-Hua Su
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
- Yan-Hua Su,
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17
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Wu X, Liu T, Zhang Y, Duan F, Neuhäuser B, Ludewig U, Schulze WX, Yuan L. Ammonium and nitrate regulate NH4+ uptake activity of Arabidopsis ammonium transporter AtAMT1;3 via phosphorylation at multiple C-terminal sites. JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:4919-4930. [PMID: 31087098 PMCID: PMC6760267 DOI: 10.1093/jxb/erz230] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Accepted: 05/04/2019] [Indexed: 05/03/2023]
Abstract
In plants, nutrient transporters require tight regulation to ensure optimal uptake in complex environments. The activities of many nutrient transporters are post-translationally regulated by reversible phosphorylation, allowing rapid adaptation to variable environmental conditions. Here, we show that the Arabidopsis root epidermis-expressed ammonium transporter AtAMT1;3 was dynamically (de-)phosphorylated at multiple sites in the cytosolic C-terminal region (CTR) responding to ammonium and nitrate signals. Under ammonium resupply rapid phosphorylation of a Thr residue (T464) in the conserved part of the CTR (CTRC) effectively inhibited AtAMT1;3-dependent NH4+ uptake. Moreover, phosphorylation of Thr (T494), one of three phosphorylation sites in the non-conserved part of the CTR (CRTNC), moderately decreased the NH4+ transport activity of AtAMT1;3, as deduced from functional analysis of phospho-mimic mutants in yeast, oocytes, and transgenic Arabidopsis. Double phospho-mutants indicated a role of T494 in fine-tuning the NH4+ transport activity when T464 was non-phosphorylated. Transient dephosphorylation of T494 with nitrate resupply closely paralleled a transient increase in ammonium uptake. These results suggest that T464 phosphorylation at the CTRC acts as a prime switch to prevent excess ammonium influx, while T494 phosphorylation at the CTRNC fine tunes ammonium uptake in response to nitrate. This provides a sophisticated regulatory mechanism for plant ammonium transporters to achieve optimal ammonium uptake in response to various nitrogen forms.
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Affiliation(s)
- Xiangyu Wu
- Key Lab of Plant-Soil Interaction, MOE, College Resources and Environmental Sciences, China Agricultural University, Beijing, China
| | - Ting Liu
- Key Lab of Plant-Soil Interaction, MOE, College Resources and Environmental Sciences, China Agricultural University, Beijing, China
- College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei, China
| | - Yongjian Zhang
- Key Lab of Plant-Soil Interaction, MOE, College Resources and Environmental Sciences, China Agricultural University, Beijing, China
| | - Fengying Duan
- Key Lab of Plant-Soil Interaction, MOE, College Resources and Environmental Sciences, China Agricultural University, Beijing, China
| | - Benjamin Neuhäuser
- Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, Stuttgart, Germany
| | - Uwe Ludewig
- Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, Stuttgart, Germany
| | - Waltraud X Schulze
- Institute for Physiology and Biotechnology of Plants, Plant Systems Biology, University of Hohenheim, Garbenstraße, Stuttgart, Germany
| | - Lixing Yuan
- Key Lab of Plant-Soil Interaction, MOE, College Resources and Environmental Sciences, China Agricultural University, Beijing, China
- Correspondence:
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18
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Michniewicz M, Ho CH, Enders TA, Floro E, Damodaran S, Gunther LK, Powers SK, Frick EM, Topp CN, Frommer WB, Strader LC. TRANSPORTER OF IBA1 Links Auxin and Cytokinin to Influence Root Architecture. Dev Cell 2019; 50:599-609.e4. [PMID: 31327740 DOI: 10.1016/j.devcel.2019.06.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 05/29/2019] [Accepted: 06/14/2019] [Indexed: 10/26/2022]
Abstract
Developmental processes that control root system architecture are critical for soil exploration by plants, allowing for uptake of water and nutrients. Conversion of the auxin precursor indole-3-butyric acid (IBA) to active auxin (indole-3-acetic acid; IAA) modulates lateral root formation. However, mechanisms governing IBA-to-IAA conversion have yet to be elucidated. We identified TRANSPORTER OF IBA1 (TOB1) as a vacuolar IBA transporter that limits lateral root formation. Moreover, TOB1, which is transcriptionally regulated by the phytohormone cytokinin, is necessary for the ability of cytokinin to exert inhibitory effects on lateral root production. The increased production of lateral roots in tob1 mutants, TOB1 transport of IBA into the vacuole, and cytokinin-regulated TOB1 expression provide a mechanism linking cytokinin signaling and IBA contribution to the auxin pool to tune root system architecture.
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Affiliation(s)
- Marta Michniewicz
- Department of Biology, Washington University, St. Louis, MO 63130, USA
| | - Cheng-Hsun Ho
- Institute for Molecular Physiology, Heinrich Heine Universität Düsseldorf, Institute for Biotransformative Molecules (WPI-ITbM), Nagoya University, Nagoya, Japan; Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan
| | - Tara A Enders
- Department of Biology, Washington University, St. Louis, MO 63130, USA
| | - Eric Floro
- Donald Danforth Plant Science Center, St. Louis, MO 63132, USA
| | - Suresh Damodaran
- Department of Biology, Washington University, St. Louis, MO 63130, USA
| | - Lauren K Gunther
- Department of Biology, Washington University, St. Louis, MO 63130, USA
| | - Samantha K Powers
- Department of Biology, Washington University, St. Louis, MO 63130, USA
| | - Elizabeth M Frick
- Department of Biology, Washington University, St. Louis, MO 63130, USA
| | | | - Wolf B Frommer
- Institute for Molecular Physiology, Heinrich Heine Universität Düsseldorf, Institute for Biotransformative Molecules (WPI-ITbM), Nagoya University, Nagoya, Japan
| | - Lucia C Strader
- Department of Biology, Washington University, St. Louis, MO 63130, USA; Center for Engineering MechanoBiology, Washington University, St. Louis, MO 63130, USA; Center for Science & Engineering of Living Systems, Washington University, St. Louis, MO 63130, USA.
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19
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Zhu Y, Hao Y, Liu H, Sun G, Chen R, Song S. Identification and characterization of two ammonium transporter genes in flowering Chinese cabbage ( Brassica campestris). PLANT BIOTECHNOLOGY (TOKYO, JAPAN) 2018; 35:59-70. [PMID: 31275038 PMCID: PMC6543737 DOI: 10.5511/plantbiotechnology.18.0202a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Accepted: 02/02/2018] [Indexed: 06/09/2023]
Abstract
Ammonium transporters (AMTs), which include AMT1 and AMT2 subfamilies, have been identified and partially characterized in many plants. In this study, two AMT2-type genes from Brassica campestris, namely BcAMT2 and BcAMT2like, were identified and characterized. BcAMT2 and BcAMT2like are 2666 bp and 2952 bp, encode proteins of 490 and 489 amino acids, respectively, and contain five exons and four introns. Transient expression of these proteins labelled with green fluorescence protein in onion epidermal cells indicated that both are located on the plasma membrane. When expressing BcAMT2 or BcAMT2like, the mutant yeast strain 31019b could grow on medium containing 2 mM ammonium as the only nitrogen source when expressing BcAMT2 or BcAMT2like, indicating that both are functional AMT genes. Quantitative PCR results showed that BcAMT2 and BcAMT2like were expressed in all tissues, but they displayed different expression patterns in the reproductive stages. BcAMT2s transcript levels in leaves were positively correlated with ammonium concentration and external pH. Moreover, the expression BcAMT2s responded to diurnal change. Furthermore, the uncharged form of ammonium, i.e., ammonia, might also be transported by BcAMT2s. These results provide new insights into the molecular mechanisms underlying ammonium absorption and transportation by the AMT2 subfamily in B. campestris.
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Affiliation(s)
- Yunna Zhu
- College of Horticulture, South China Agricultural University, 510642, Guangzhou, People’s Republic of China
| | - Yanwei Hao
- College of Horticulture, South China Agricultural University, 510642, Guangzhou, People’s Republic of China
| | - Houcheng Liu
- College of Horticulture, South China Agricultural University, 510642, Guangzhou, People’s Republic of China
| | - Guangwen Sun
- College of Horticulture, South China Agricultural University, 510642, Guangzhou, People’s Republic of China
| | - Riyuan Chen
- College of Horticulture, South China Agricultural University, 510642, Guangzhou, People’s Republic of China
| | - Shiwei Song
- College of Horticulture, South China Agricultural University, 510642, Guangzhou, People’s Republic of China
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20
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Chen XL, Zhang B, Chng YR, Ong JLY, Chew SF, Wong WP, Lam SH, Nakada T, Ip YK. Ammonia exposure affects the mRNA and protein expression levels of certain Rhesus glycoproteins in the gills of climbing perch. ACTA ACUST UNITED AC 2017; 220:2916-2931. [PMID: 28576822 DOI: 10.1242/jeb.157123] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 05/30/2017] [Indexed: 01/08/2023]
Abstract
The freshwater climbing perch, Anabas testudineus, is an obligate air-breathing and euryhaline teleost capable of active ammonia excretion and tolerant of high concentrations of environmental ammonia. As Rhesus glycoproteins (RhGP/Rhgp) are known to transport ammonia, this study aimed to obtain the complete cDNA coding sequences of various rhgp isoforms from the gills of A. testudineus, and to determine their mRNA and protein expression levels during 6 days of exposure to 100 mmol l-1 NH4Cl. The subcellular localization of Rhgp isoforms in the branchial epithelium was also examined in order to elucidate the type of ionocyte involved in active ammonia excretion. Four rhgp (rhag, rhbg, rhcg1 and rhcg2) had been identified from the gills of A. testudineus They had conserved amino acid residues for NH4+ binding, NH4+ deprotonation, channel gating and lining of the vestibules. Despite inwardly directed NH3 and NH4+ gradients, there were significant increases in the mRNA expression levels of the four branchial rhgp in A. testudineus at certain time points during 6 days of ammonia exposure, with significant increases in the protein abundances of Rhag and Rhcg2 on day 6. Immunofluorescence microscopy revealed a type of ammonia-inducible Na+/K+-ATPase α1c-immunoreactive ionocyte with apical Rhag and basolateral Rhcg2 in the gills of fish exposed to ammonia for 6 days. Hence, active ammonia excretion may involve NH4+ entering the ionocyte through the basolateral Rhcg2 and being excreted through the apical Rhag, driven by a transapical membrane electrical potential generated by the apical cystic fibrosis transmembrane conductance regulator Cl- channel, as suggested previously.
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Affiliation(s)
- Xiu L Chen
- Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore
| | - Biyan Zhang
- Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore
| | - You R Chng
- Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore
| | - Jasmine L Y Ong
- Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore
| | - Shit F Chew
- Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Republic of Singapore
| | - Wai P Wong
- Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore
| | - Siew H Lam
- Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore.,NUS Environmental Research Institute, National University of Singapore, Kent Ridge, Singapore 117411, Republic of Singapore
| | - Tsutomu Nakada
- Department of Molecular Pharmacology, Shinshu University School of Medicine, Matsumoto, Nagano 390-8621, Japan
| | - Yuen K Ip
- Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore
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21
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Berg GM, Driscoll S, Hayashi K, Ross M, Kudela R. Variation in growth rate, carbon assimilation, and photosynthetic efficiency in response to nitrogen source and concentration in phytoplankton isolated from upper San Francisco Bay. JOURNAL OF PHYCOLOGY 2017; 53:664-679. [PMID: 28328165 PMCID: PMC5518194 DOI: 10.1111/jpy.12535] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 03/02/2017] [Indexed: 05/15/2023]
Abstract
Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH4+ ), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (Fv /Fm ) was a sensitive indicator of NH4+ toxicity, manifested by a suppression of Fv /Fm in a dose-dependent manner. Two chlorophytes were the least sensitive to NH4+ inhibition, at concentrations of >3,000 μmoles NH4+ · L-1 , followed by two estuarine diatoms that were sensitive at concentrations >1,000 μmoles NH4+ · L-1 , followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 μmoles NH4+ · L-1 . At non-inhibiting concentrations of NH4+ , the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO3- ), whereas the other grew significantly faster on NH4+ . All four diatoms tested grew faster on NH4+ compared with NO3- . We showed that in cases where growth rates were faster on NH4+ than they were on NO3- , the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH4+ dominates the total N pool and they will also not have a growth advantage when NO3- is dominant, as long as N concentrations are sufficient.
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Affiliation(s)
- Gry Mine Berg
- Applied Marine Sciences911 Center StreetSanta CruzCalifornia95060USA
| | - Sara Driscoll
- Applied Marine Sciences911 Center StreetSanta CruzCalifornia95060USA
| | - Kendra Hayashi
- Ocean Sciences DepartmentUniversity of California1156 High StreetSanta CruzCalifornia95064USA
| | - Melissa Ross
- Applied Marine Sciences911 Center StreetSanta CruzCalifornia95060USA
| | - Raphael Kudela
- Ocean Sciences DepartmentUniversity of California1156 High StreetSanta CruzCalifornia95064USA
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22
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Hao D, Yang S, Huang Y, Su Y. Identification of structural elements involved in fine-tuning of the transport activity of the rice ammonium transporter OsAMT1;3. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2016; 108:99-108. [PMID: 27423220 DOI: 10.1016/j.plaphy.2016.07.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 07/01/2016] [Accepted: 07/03/2016] [Indexed: 05/13/2023]
Abstract
Ammonium transporters (AMTs) are major routes for plant uptake of the NH4+-form nitrogen. Plant AMTs mediate predominantly the uptake of NH4+ and to a lesser extent, its organic analog methylammonium (MeA+). Mutagenesis studies on potential phosphorylation residues have achieved solid recognition that alteration of the phosphorylation status can result in allosteric regulation and impair the functionality of plant AMTs. However, molecular insights to the fine-tuning of a functional ammonium transporter remain less clear. In this report, we demonstrate that the rice root expressed OsAMT1;3 (Oryza sativa ammonium transporter 1;3) functions as a typical high-affinity NH4+ transporter and is weakly permeable to MeA+ using growth assays in NH4+ uptake defective yeast cells and electrophysiological measurements in Xenopus oocytes. Upon screening of six point mutations generated with the transporter, we identified two amino acid residues involved in the functional modulation of OsAMT1;3. The H199E mutation caused loss of transport activity whereas other five mutations retained the functionality of OsAMT1;3. Furthermore, the L56F mutation enabled respectively 5- and 3.5 -fold increased capability for NH4+ and MeA+ uptake with several-fold decreased affinity (Km) and accelerated Vmax values. Surprisingly, yeast cells expressing the L56F mutation shown increased Na+ toxicity leading to a speculation that enhanced Na+ permeation occurred with this mutation. The phenomenon was further supported by the observation of significant Na+ uptake current in oocytes. Our results seemingly support a speculation that the L56F mutation of OsAMT1;3 widens the substrate passage tunnel and allows enhanced permeability to NH4+ and larger ions MeA+ and Na+.
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Affiliation(s)
- Dongli Hao
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shunying Yang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
| | - Yanan Huang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yanhua Su
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
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Garnett T, Plett D, Heuer S, Okamoto M. Genetic approaches to enhancing nitrogen-use efficiency (NUE) in cereals: challenges and future directions. FUNCTIONAL PLANT BIOLOGY : FPB 2015; 42:921-941. [PMID: 32480734 DOI: 10.1071/fp15025] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Accepted: 06/24/2015] [Indexed: 05/03/2023]
Abstract
Over 100million tonnes of nitrogen (N) fertiliser are applied globally each year to maintain high yields in agricultural crops. The rising price of N fertilisers has made them a major cost for farmers. Inefficient use of N fertiliser leads to substantial environmental problems through contamination of air and water resources and can be a significant economic cost. Consequently, there is considerable need to improve the way N fertiliser is used in farming systems. The efficiency with which crops use applied N fertiliser - the nitrogen-use efficiency (NUE) - is currently quite low for cereals. This is the case in both high yielding environments and lower yielding environments characteristic of cereal growing regions of Australia. Multiple studies have attempted to identify the genetic basis of NUE, but the utility of the results is limited because of the complex nature of the trait and the magnitude of genotype by environment interaction. Transgenic approaches have been applied to improve plant NUE but with limited success, due, in part, to a combination of the complexity of the trait but also due to lack of accurate phenotyping methods. This review documents these two approaches and suggests future directions in improving cereal NUE with a focus on the Australian cereal industry.
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Affiliation(s)
- Trevor Garnett
- Australian Centre for Plant Functional Genomics, School of Agriculture Food and Wine, University of Adelaide, Adelaide, SA 5064, Australia
| | - Darren Plett
- Australian Centre for Plant Functional Genomics, School of Agriculture Food and Wine, University of Adelaide, Adelaide, SA 5064, Australia
| | - Sigrid Heuer
- Australian Centre for Plant Functional Genomics, School of Agriculture Food and Wine, University of Adelaide, Adelaide, SA 5064, Australia
| | - Mamoru Okamoto
- Australian Centre for Plant Functional Genomics, School of Agriculture Food and Wine, University of Adelaide, Adelaide, SA 5064, Australia
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24
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Fontenot EB, Ditusa SF, Kato N, Olivier DM, Dale R, Lin WY, Chiou TJ, Macnaughtan MA, Smith AP. Increased phosphate transport of Arabidopsis thaliana Pht1;1 by site-directed mutagenesis of tyrosine 312 may be attributed to the disruption of homomeric interactions. PLANT, CELL & ENVIRONMENT 2015; 38:2012-22. [PMID: 25754174 DOI: 10.1111/pce.12522] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 02/06/2015] [Accepted: 02/14/2015] [Indexed: 05/20/2023]
Abstract
Members of the Pht1 family of plant phosphate (Pi) transporters play vital roles in Pi acquisition from soil and in planta Pi translocation to maintain optimal growth and development. The study of the specificities and biochemical properties of Pht1 transporters will contribute to improving the current understanding of plant phosphorus homeostasis and use-efficiency. In this study, we show through split in vivo interaction methods and in vitro analysis of microsomal root tissues that Arabidopsis thaliana Pht1;1 and Pht1;4 form homomeric and heteromeric complexes. Transient and heterologous expression of the Pht1;1 variants, Pht1;1(Y312D), Pht1;1(Y312A) and Pht1;1(Y312F), was used to analyse the role of a putative Pi binding residue (Tyr 312) in Pht1;1 transporter oligomerization and function. The homomeric interaction among Pht1;1 proteins was disrupted by mutation of Tyr 312 to Asp, but not to Ala or Phe. In addition, the Pht1;1(Y312D) variant conferred enhanced Pi transport when expressed in yeast cells. In contrast, mutation of Tyr 312 to Ala or Phe did not affect Pht1;1 transport kinetics. Our study demonstrates that modifications to the Pht1;1 higher-order structure affects Pi transport, suggesting that oligomerization may serve as a regulatory mechanism for modulating Pi uptake.
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Affiliation(s)
- Elena B Fontenot
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Sandra Feuer Ditusa
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Naohiro Kato
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Danielle M Olivier
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Renee Dale
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Wei-Yi Lin
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 11529, Taiwan, China
| | - Tzyy-Jen Chiou
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 11529, Taiwan, China
| | - Megan A Macnaughtan
- Department of Chemistry, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Aaron P Smith
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70803, USA
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25
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Neuhäuser B, Dynowski M, Ludewig U. Switching substrate specificity of AMT/MEP/ Rh proteins. Channels (Austin) 2015; 8:496-502. [PMID: 25483282 DOI: 10.4161/19336950.2014.967618] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In organisms from all kingdoms of life, ammonia and its conjugated ion ammonium are transported across membranes by proteins of the AMT/Rh family. Efficient and successful growth often depends on sufficient ammonium nutrition. The proteins mediating this transport, the so called Ammonium Transporter (AMT) or Rhesus like (Rh) proteins, share a very similar trimeric overall structure and a high sequence similarity even throughout the kingdoms. Even though structural components of the transport mechanism, like an external substrate recruitment site, an essential twin histidine pore motif, a phenylalanine gate and the hydrophobic pore are strongly conserved and have been analyzed in detail by molecular dynamic simulations and mutational studies, the substrate(s), which pass the central pores of the AMT/Rh subunits, NH4(+), NH3 + H(+), NH4(+) + H(+) or NH3, are still a matter of debate for most proteins, including the best characterized AmtB protein from Escherichia coli. The lack of a robust expression system for functional analysis has hampered proof of structural and mutational studies, although the NH3 transport function for Rh-like proteins is rarely disputed. In plant transporters belonging to the subfamily AMT1, transport is associated with electrical currents, while some plant transporters, notably of the AMT2 type, were suggested to transport NH3 across the membrane, without associated ionic currents. Here we summarize data in favor of each substrate for the distinct AMT/Rh classes, discuss mutants and how they differ in structure and functionality. A common mechanism with deprotonation and subsequent NH3 transport through the central subunit pore is suggested.
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Affiliation(s)
- Benjamin Neuhäuser
- a Institute of Crop Science; Nutritional Crop Physiology ; University of Hohenheim ; Stuttgart , Germany
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26
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Bao A, Liang Z, Zhao Z, Cai H. Overexpressing of OsAMT1-3, a High Affinity Ammonium Transporter Gene, Modifies Rice Growth and Carbon-Nitrogen Metabolic Status. Int J Mol Sci 2015; 16:9037-63. [PMID: 25915023 PMCID: PMC4463577 DOI: 10.3390/ijms16059037] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2015] [Revised: 04/11/2015] [Accepted: 04/13/2015] [Indexed: 11/16/2022] Open
Abstract
AMT1-3 encodes the high affinity NH₄⁺ transporter in rice roots and is predominantly expressed under nitrogen starvation. In order to evaluate the effect of AMT1-3 gene on rice growth, nitrogen absorption and metabolism, we generated AMT1-3-overexpressing plants and analyzed the growth phenotype, yield, carbon and nitrogen metabolic status, and gene expression profiles. Although AMT1-3 mRNA accumulated in transgenic plants, these plants displayed significant decreases in growth when compared to the wild-type plants. The nitrogen uptake assay using a 15N tracer revealed poor nitrogen uptake ability in AMT1-3-overexpressing plants. We found significant decreases in AMT1-3-overexpressing plant leaf carbon and nitrogen content accompanied with a higher leaf C/N ratio. Significant changes in soluble proteins and carbohydrates were also observed in AMT1-3-overexpressing plants. In addition, metabolite profile analysis demonstrated significant changes in individual sugars, organic acids and free amino acids. Gene expression analysis revealed distinct expression patterns of genes that participate in carbon and nitrogen metabolism. Additionally, the correlation between the metabolites and gene expression patterns was consistent in AMT1-3-overexpressing plants under both low and high nitrogen growth conditions. Therefore, we hypothesized that the carbon and nitrogen metabolic imbalance caused by AMT1-3 overexpressing attributed to the poor growth and yield of transgenic plants.
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Affiliation(s)
- Aili Bao
- Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Microelement Research Center, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
| | - Zhijun Liang
- Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Microelement Research Center, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
| | - Zhuqing Zhao
- Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Microelement Research Center, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
| | - Hongmei Cai
- Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Microelement Research Center, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
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27
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Yang S, Hao D, Cong Y, Jin M, Su Y. The rice OsAMT1;1 is a proton-independent feedback regulated ammonium transporter. PLANT CELL REPORTS 2015; 34:321-30. [PMID: 25433856 DOI: 10.1007/s00299-014-1709-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2014] [Revised: 10/20/2014] [Accepted: 11/19/2014] [Indexed: 05/22/2023]
Abstract
Functional identification of a relatively lower affinity ammonium transporter, OsAMT1;1, which is a proton-independent feedback regulated ammonium transporter in rice. Rice genome contains at least 12 ammonium transporters, though their functionality has not been clearly resolved. Here, we demonstrate the functional properties of OsAMT1;1 applying functional complementation and (15)NH4 (+) uptake determination in yeast cells in combination with electrophysiological measurements in Xenopus oocytes. Our results show that OsAMT1;1 is a NH4 (+) transporter with relatively lower affinity to NH4 (+) (110-129 μM in oocytes and yeast cells, respectively). Under our experimental conditions, OsAMT1;1-mediated NH4 (+) uptake or current is not significantly modulated by extra- or intracellular pH gradient, suggesting that this transporter probably functions as a NH4 (+) uniporter. Inhibition of yeast growth or currents elicited from oocytes by ammonium assimilation inhibitor L-methionine sulfoximine indicates that NH4 (+) transport by OsAMT1;1 is likely feedback regulated by accumulation of the substrate. In addition, effects of phosphorylation inhibitors imply that NH4 (+) uptake by OsAMT1;1 is also modulated by tyrosine-specific protein kinase or calcium-regulated serine/threonine-specific protein phosphatase involved phosphorylation processes.
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Affiliation(s)
- Shunying Yang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, No. 71, East Beijing Road, Nanjing, 210008, China
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28
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Straub D, Ludewig U, Neuhäuser B. A nitrogen-dependent switch in the high affinity ammonium transport in Medicago truncatula. PLANT MOLECULAR BIOLOGY 2014; 86:485-94. [PMID: 25164101 DOI: 10.1007/s11103-014-0243-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 08/18/2014] [Indexed: 05/26/2023]
Abstract
Ammonium transporters (AMTs) are crucial for the high affinity primary uptake and translocation of ammonium in plants. In the model legume Medicago truncatula, the genomic set of AMT-type ammonium transporters comprises eight members. Only four genes were abundantly expressed in young seedlings, both in roots and shoots. While the expression of all AMTs in the shoot was not affected by the nitrogen availability, the dominating MtAMT1;1 gene was repressed by nitrogen in roots, despite that cellular nitrogen concentrations were far above deficiency levels. A contrasting de-repression by nitrogen was observed for MtAMT1;4 and MtAMT2;1, which were both expressed at intermediate level. Weak expression was found for MtAMT1;2 and MtAMT2;3, while the other AMTs were not detected in young seedlings. When expressed from their endogenous promoters, translational fusion proteins of MtAMT1;1 and MtAMT2;1 with green fluorescent protein were co-localized in the plasma membrane of rhizodermal cells, but also detected in cortical root layers. Both transporter proteins similarly functionally complemented a yeast strain that is deficient in high affinity ammonium transport, both at acidic and neutral pH. The uptake into yeast mediated by these transporters saturated with Km AMT1;1 = 89 µM and Km AMT2;1 = 123 µM, respectively. When expressed in oocytes, MtAMT1;1 mediated much larger (15)N-ammonium uptake than MtAMT2;1, but NH4 (+) currents were only recorded for MtAMT1;1. These currents saturated with a voltage-dependent Km = 90 µM at -80 mV. The cellular localization and regulation of the AMTs suggests that MtAMT1;1 encodes the major high affinity ammonium transporter gene in low nitrogen grown young M. truncatula roots and despite the similar localization and substrate affinity, MtAMT2;1 appears functionally distinct and more important at higher nitrogen supply.
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Affiliation(s)
- Daniel Straub
- Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, Fruwirthstr. 20, 70593, Stuttgart, Germany
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29
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Jones AM, Xuan Y, Xu M, Wang RS, Ho CH, Lalonde S, You CH, Sardi MI, Parsa SA, Smith-Valle E, Su T, Frazer KA, Pilot G, Pratelli R, Grossmann G, Acharya BR, Hu HC, Engineer C, Villiers F, Ju C, Takeda K, Su Z, Dong Q, Assmann SM, Chen J, Kwak JM, Schroeder JI, Albert R, Rhee SY, Frommer WB. Border Control--A Membrane-Linked Interactome of Arabidopsis. Science 2014; 344:711-6. [DOI: 10.1126/science.1251358] [Citation(s) in RCA: 162] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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30
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Neuhäuser B, Ludewig U. Uncoupling of ionic currents from substrate transport in the plant ammonium transporter AtAMT1;2. J Biol Chem 2014; 289:11650-11655. [PMID: 24634212 PMCID: PMC4002075 DOI: 10.1074/jbc.c114.552802] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Revised: 03/13/2014] [Indexed: 12/20/2022] Open
Abstract
The ammonium flux across prokaryotic, plant, and animal membranes is regulated by structurally related ammonium transporters (AMT) and/or related Rhesus (Rh) glycoproteins. Several plant AMT homologs, such as AtAMT1;2 from Arabidopsis, elicit ionic, ammonium-dependent currents when expressed in oocytes. By contrast, functional evidence for the transport of NH3 and the lack of coupled ionic currents has been provided for many Rh proteins. Furthermore, despite high resolution structures the transported substrate in many bacterial homologs, such as AmtB from Escherichia coli, is still unclear. In a heterologous genetic screen in yeast, AtAMT1;2 mutants with reduced transport activity were identified based on the resistance of yeast to the toxic transport analog methylamine. When expressed in oocytes, the reduced transport capacity was confirmed for either of the mutants Q67K, M72I,and W145S. Structural alignments suggest that these mutations were dispersed at subunit contact sites of trimeric AMTs, without direct contact to the pore lumen. Surprisingly, and in contrast to the wild type AtAMT1;2 transporter, ionic currents were not associated with the substrate transport in these mutants. Whether these data suggest that the wild type AtAMT1;2 functions as H(+)/NH3 co-transporter, as well as how the strict substrate coupling with protons is lost by the mutations, is discussed.
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Affiliation(s)
- Benjamin Neuhäuser
- Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, Fruwirthstrasse 20, D-70593 Stuttgart, Germany.
| | - Uwe Ludewig
- Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, Fruwirthstrasse 20, D-70593 Stuttgart, Germany
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31
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Bai L, Ma X, Zhang G, Song S, Zhou Y, Gao L, Miao Y, Song CP. A Receptor-Like Kinase Mediates Ammonium Homeostasis and Is Important for the Polar Growth of Root Hairs in Arabidopsis. THE PLANT CELL 2014; 26:1497-1511. [PMID: 24769480 PMCID: PMC4036567 DOI: 10.1105/tpc.114.124586] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Revised: 03/30/2014] [Accepted: 04/09/2014] [Indexed: 05/19/2023]
Abstract
Ammonium (NH4+) is both a necessary nutrient and an important signal in plants, but can be toxic in excess. Ammonium sensing and regulatory mechanisms in plant cells have not been fully elucidated. To decipher the complex network of NH4+ signaling, we analyzed [Ca2+]cyt-associated protein kinase (CAP) genes, which encode signaling components that undergo marked changes in transcription levels in response to various stressors. We demonstrated that CAP1, a tonoplast-localized receptor-like kinase, regulates root hair tip growth by maintaining cytoplasmic Ca2+ gradients. A CAP1 knockout mutant (cap1-1) produced elevated levels of cytoplasmic NH4+. Furthermore, root hair growth of cap1-1 was inhibited on Murashige and Skoog medium, but NH4+ depletion reestablished the Ca2+ gradient necessary for normal growth. The lower net NH4+ influx across the vacuolar membrane and relatively alkaline cytosolic pH of cap1-1 root hairs implied that mutation of CAP1 increased NH4+ accumulation in the cytoplasm. Furthermore, CAP1 functionally complemented the npr1 (nitrogen permease reactivator protein) kinase yeast mutant, which is defective in high-affinity NH4+ uptake via MEP2 (methylammonium permease 2), distinguishing CAP1 as a cytosolic modulator of NH4+ levels that participates in NH4+ homeostasis-regulated root hair growth by modulating tip-focused cytoplasmic Ca2+ gradients.
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Affiliation(s)
- Ling Bai
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China
| | - Xiaonan Ma
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China
| | - Guozeng Zhang
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China
| | - Shufei Song
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China
| | - Yun Zhou
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China
| | - Lijie Gao
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China
| | - Yuchen Miao
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China
| | - Chun-Peng Song
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China
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32
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Ho CH, Frommer WB. Fluorescent sensors for activity and regulation of the nitrate transceptor CHL1/NRT1.1 and oligopeptide transporters. eLife 2014; 3:e01917. [PMID: 24623305 PMCID: PMC3950950 DOI: 10.7554/elife.01917] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
To monitor nitrate and peptide transport activity in vivo, we converted the dual-affinity nitrate transceptor CHL1/NRT1.1/NPF6.3 and four related oligopeptide transporters PTR1, 2, 4, and 5 into fluorescence activity sensors (NiTrac1, PepTrac). Substrate addition to yeast expressing transporter fusions with yellow fluorescent protein and mCerulean triggered substrate-dependent donor quenching or resonance energy transfer. Fluorescence changes were nitrate/peptide-specific, respectively. Like CHL1, NiTrac1 had biphasic kinetics. Mutation of T101A eliminated high-affinity transport and blocked the fluorescence response to low nitrate. NiTrac was used for characterizing side chains considered important for substrate interaction, proton coupling, and regulation. We observed a striking correlation between transport activity and sensor output. Coexpression of NiTrac with known calcineurin-like proteins (CBL1, 9; CIPK23) and candidates identified in an interactome screen (CBL1, KT2, WNKinase 8) blocked NiTrac1 responses, demonstrating the suitability for in vivo analysis of activity and regulation. The new technology is applicable in plant and medical research. DOI:http://dx.doi.org/10.7554/eLife.01917.001 About 1% of global energy output is used to produce nitrogen-enriched fertiliser to improve crop yields, but much of this energy is wasted because plants absorb only a fraction of the nitrogen that is applied as fertiliser. Even worse, the excess nitrogen leaches into water sources, poisoning the environment and causing health problems. However, to date, most efforts to increase the efficiency of nitrogen uptake in plants have been unsuccessful. The key to improving the uptake efficiency of a nutrient is to identify obstacles in its journey from the soil to cells inside the plant. The first obstacle that nitrate ions encounter is the membrane of the cells on the surface of the roots of the plant. Many researchers believe that it would be possible to increase the amount of nitrogen absorbed by the plant if more was known about the ways that plants control how nitrate ions and other chemicals enter cells. The cell membrane contains gated pores called transporters that allow particular molecules to pass through it. Although the transporters responsible for the uptake of nitrate ions, peptides, and ammonium ions (the main nitrogen compounds that plants acquire) have been identified, current experimental techniques cannot determine when and where a specific transporter is active within a living plant. This makes it difficult to know where to target modifications and to determine how effective they have been at each step. The nitrate transporter also acts as an antenna that measures nitrate concentration to ensure it is used optimally in the plant, but current techniques cannot show how this actually works. Now, Ho and Frommer have exploited the fact that a transporter changes shape as it does its job to create sensors that can track the movement of nitrate and peptides through the cell membrane. By using fluorescent proteins to monitor how the shape of the transporter changes, Ho and Frommer were able to measure how structural mutations and regulatory proteins influenced the movement of nitrate and peptides through the membrane. For efficiency, all of this work was performed in yeast cells. The next goal is to use the technique in plants to uncover how they adjust to changes in nutrient levels in the soil. DOI:http://dx.doi.org/10.7554/eLife.01917.002
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Affiliation(s)
- Cheng-Hsun Ho
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Wolf B Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
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33
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Li B, Li G, Kronzucker HJ, Baluška F, Shi W. Ammonium stress in Arabidopsis: signaling, genetic loci, and physiological targets. TRENDS IN PLANT SCIENCE 2014; 19:107-14. [PMID: 24126103 DOI: 10.1016/j.tplants.2013.09.004] [Citation(s) in RCA: 135] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2013] [Revised: 09/06/2013] [Accepted: 09/13/2013] [Indexed: 05/22/2023]
Abstract
Ammonium (NH4(+)) toxicity is a significant ecological and agricultural issue, and an important phenomenon in cell biology. As a result of increasing soil nitrogen input and atmospheric deposition, plants have to deal with unprecedented NH4(+) stress from sources below and above ground. In this review, we describe recent advances in elucidating the signaling pathways and identifying the main physiological targets and genetic loci involved in the effects of NH4(+) stress in the roots and shoots of Arabidopsis thaliana. We outline new experimental approaches that are being used to study NH4(+) toxicity in Arabidopsis and propose an integrated view of behavior and signaling in response to NH4(+) stress in the Arabidopsis system.
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Affiliation(s)
- Baohai Li
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, No. 71 East Beijing Road, Nanjing 210008, China
| | - Guangjie Li
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, No. 71 East Beijing Road, Nanjing 210008, China
| | - Herbert J Kronzucker
- Department of Biological Sciences, University of Toronto, 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada
| | - František Baluška
- Institute of Cellular and Molecular Botany, University of Bonn, Kirschallee 1, Bonn, D-53115, Germany
| | - Weiming Shi
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, No. 71 East Beijing Road, Nanjing 210008, China.
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34
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Bai L, Zhou Y, Ma X, Gao L, Song CP. Arabidopsis CAP1-mediated ammonium sensing required reactive oxygen species in plant cell growth. PLANT SIGNALING & BEHAVIOR 2014; 9:e29582. [PMID: 25763633 PMCID: PMC4205142 DOI: 10.4161/psb.29582] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 06/13/2014] [Accepted: 06/13/2014] [Indexed: 05/24/2023]
Abstract
[Ca(2+)]cyt-associated protein kinase (CAP) gene 1 is a receptor-like kinase that belongs to CrRLK1L (Catharanthus roseus Receptor like kinase) subfamily. CAP1 has been identified as a novel modulator of NH4(+) in the tonoplast, which regulates root hair growth by maintaining the cytoplasmic Ca(2+) gradients. Different expression pattern of tonoplast intrinsic protein (TIP2;3) in the CAP1 knock out mutant and wild type on Murashige and Skoog (MS) medium suggested that CAP1 influences transport activity to regulate the compartmentalization of NH4(+) into vacuole. Lower expression level of Oxidative Signal-Inducible1(OXI1) in the cap1-1 root and the abnormal reactive oxygen species (ROS) gradient in root hair of cap1-1 on MS medium indicated that ROS signaling involve in CAP1-regulated root hair growth. Wild-type-like ROS distribution pattern in the cap1-1 root hair can be reestablished in seedlings grown on NH4(+) deficient medium, which indicated that CAP1 functions as a sensor for NH4(+) signaling in maintaining tip-focused ROS gradient in root hairs polar growth.
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De Michele R, Ast C, Loqué D, Ho CH, Andrade SLA, Lanquar V, Grossmann G, Gehne S, Kumke MU, Frommer WB. Fluorescent sensors reporting the activity of ammonium transceptors in live cells. eLife 2013; 2:e00800. [PMID: 23840931 PMCID: PMC3699834 DOI: 10.7554/elife.00800] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Accepted: 05/18/2013] [Indexed: 01/14/2023] Open
Abstract
Ammonium serves as key nitrogen source and metabolic intermediate, yet excess causes toxicity. Ammonium uptake is mediated by ammonium transporters, whose regulation is poorly understood. While transport can easily be characterized in heterologous systems, measuring transporter activity in vivo remains challenging. Here we developed a simple assay for monitoring activity in vivo by inserting circularly-permutated GFP into conformation-sensitive positions of two plant and one yeast ammonium transceptors (‘AmTrac’ and ‘MepTrac’). Addition of ammonium to yeast cells expressing the sensors triggered concentration-dependent fluorescence intensity (FI) changes that strictly correlated with the activity of the transporter. Fluorescence-based activity sensors present a novel technology for monitoring the interaction of the transporters with their substrates, the activity of transporters and their regulation in vivo, which is particularly valuable in the context of analytes for which no radiotracers exist, as well as for cell-specific and subcellular transport processes that are otherwise difficult to track. DOI:http://dx.doi.org/10.7554/eLife.00800.001 Ammonium provides a vital source of nitrogen for bacteria, fungi and plants, and is produced by animals as a waste product of metabolism. High levels of ammonium can be toxic, so all organisms need to control their uptake or excretion of this substance. Ammonium transporters, which are highly conserved from bacteria to plants to humans, are essential for this process but, along with transporters in general, they are hard to study. Their activity can be examined in vitro by expressing them in heterologous systems—that is, in cells other than those in which they are naturally found. But in vivo studies must rely on indirect techniques such as monitoring radioactive isotopes or membrane potentials, and these cannot distinguish between the activity of ammonium transporters and uptake of ammonium through other routes. One approach that has been successful in other fields is the use of fluorescent proteins that can signal conformational changes—such as those that occur when a transporter is activated—by a shift in fluorescence. Green fluorescent protein (GFP) is a commonly used fluorescent indicator, and a particularly useful variant is ‘circularly permutated GFP’. This is GFP in which parts of the amino acid sequence have been rearranged without fundamentally changing the overall structure or function of the protein. Circularly permutated GFP can be fused to another protein in such a way that a conformational change in the second protein triggers a change in fluorescence that can be detected by fluorescence spectroscopy or microscopy. Now, De Michele et al. have applied this approach to the study of both plant and yeast ammonium transporters. They constructed a library of fusion proteins made up of circularly permutated GFP and an ammonium transporter from the plant Arabidopsis thaliana—and found one version that functioned normally as a transporter but also produced a detectable change in fluorescence that correlated precisely with transporter activity. De Michele et al. then used the same method to produce fluorescent indicator fusion proteins of two more ammonium transporters—a second isoform from Arabidopsis and one from yeast. These fluorescent sensors should be a great boon to researchers studying the ammonium transport system. Moreover, this approach could in theory be applied to other transporter proteins that are currently difficult to study, and so could help to open up research into a variety of transport processes. DOI:http://dx.doi.org/10.7554/eLife.00800.002
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Affiliation(s)
- Roberto De Michele
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.,Institute of Plant Genetics, Italian National Research Council (CNR-IGV), Palermo, Italy
| | - Cindy Ast
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.,NanoPolyPhotonik, Fraunhofer Institute for Applied Polymer Research, Potsdam-Golm, Germany
| | - Dominique Loqué
- Feedstocks Division, Joint BioEnergy Institute, Emeryville, United States
| | - Cheng-Hsun Ho
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Susana LA Andrade
- Department of Biochemistry, Institute for Organic Chemistry and Biochemistry, and BIOSS Center for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
| | - Viviane Lanquar
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Guido Grossmann
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Sören Gehne
- Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany
| | - Michael U Kumke
- Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany
| | - Wolf B Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
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De Michele R, Ast C, Loqué D, Ho CH, Andrade SLA, Lanquar V, Grossmann G, Gehne S, Kumke MU, Frommer WB. Fluorescent sensors reporting the activity of ammonium transceptors in live cells. eLife 2013; 2:e00800. [PMID: 23840931 DOI: 10.7554/elife.00800.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Accepted: 05/18/2013] [Indexed: 05/26/2023] Open
Abstract
Ammonium serves as key nitrogen source and metabolic intermediate, yet excess causes toxicity. Ammonium uptake is mediated by ammonium transporters, whose regulation is poorly understood. While transport can easily be characterized in heterologous systems, measuring transporter activity in vivo remains challenging. Here we developed a simple assay for monitoring activity in vivo by inserting circularly-permutated GFP into conformation-sensitive positions of two plant and one yeast ammonium transceptors ('AmTrac' and 'MepTrac'). Addition of ammonium to yeast cells expressing the sensors triggered concentration-dependent fluorescence intensity (FI) changes that strictly correlated with the activity of the transporter. Fluorescence-based activity sensors present a novel technology for monitoring the interaction of the transporters with their substrates, the activity of transporters and their regulation in vivo, which is particularly valuable in the context of analytes for which no radiotracers exist, as well as for cell-specific and subcellular transport processes that are otherwise difficult to track. DOI:http://dx.doi.org/10.7554/eLife.00800.001.
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Affiliation(s)
- Roberto De Michele
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
- Institute of Plant Genetics, Italian National Research Council (CNR-IGV), Palermo, Italy
| | - Cindy Ast
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
- NanoPolyPhotonik, Fraunhofer Institute for Applied Polymer Research, Potsdam-Golm, Germany
| | - Dominique Loqué
- Feedstocks Division, Joint BioEnergy Institute, Emeryville, United States
| | - Cheng-Hsun Ho
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Susana LA Andrade
- Department of Biochemistry, Institute for Organic Chemistry and Biochemistry, and BIOSS Center for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
| | - Viviane Lanquar
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Guido Grossmann
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Sören Gehne
- Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany
| | - Michael U Kumke
- Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany
| | - Wolf B Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
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Hall JA, Yan D. The molecular basis of K+ exclusion by the Escherichia coli ammonium channel AmtB. J Biol Chem 2013; 288:14080-14086. [PMID: 23546877 DOI: 10.1074/jbc.m113.457952] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Members of the Amt family of channels mediate the transport of ammonium. The form of ammonium, NH3 or NH4(+), carried by these proteins remains controversial, and the mechanism by which they select against K(+) ions is unclear. We describe here a set of Escherichia coli AmtB proteins carrying mutations at the conserved twin-histidine site within the conduction pore that have altered substrate specificity and now transport K(+). Subsequent work established that AmtB-mediated K(+) uptake occurred against a concentration gradient and was membrane potential-dependent. These findings indicate that the twin-histidine element serves as a filter to prevent K(+) conduction and strongly support the notion that Amt proteins transport cations (NH4(+) or, in mutant proteins, K(+)) rather than NH3 gas molecules through their conduction pores.
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Affiliation(s)
- Jason A Hall
- Division of Biological Sciences, University of California San Diego, La Jolla, California 92093-0374.
| | - Dalai Yan
- Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120
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Yuan L, Gu R, Xuan Y, Smith-Valle E, Loqué D, Frommer WB, von Wirén N. Allosteric regulation of transport activity by heterotrimerization of Arabidopsis ammonium transporter complexes in vivo. THE PLANT CELL 2013; 25:974-84. [PMID: 23463773 PMCID: PMC3634700 DOI: 10.1105/tpc.112.108027] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Ammonium acquisition by plant roots is mediated by AMMONIUM TRANSPORTERs (AMTs), ubiquitous membrane proteins with essential roles in nitrogen nutrition in all organisms. In microbial and plant cells, ammonium transport activity is controlled by ammonium-triggered feedback inhibition to prevent cellular ammonium toxicity. Data from heterologous expression in yeast indicate that oligomerization of plant AMTs is critical for allosteric regulation of transport activity, in which the conserved cytosolic C terminus functions as a trans-activator. Employing the coexpressed transporters AMT1;1 and AMT1;3 from Arabidopsis thaliana as a model, we show here that these two isoforms form functional homo- and heterotrimers in yeast and plant roots and that AMT1;3 carrying a phosphomimic residue in its C terminus regulates both homo- and heterotrimers in a dominant-negative fashion in vivo. (15)NH4(+) influx studies further indicate that allosteric inhibition represses ammonium transport activity in roots of transgenic Arabidopsis expressing a phosphomimic mutant together with functional AMT1;3 or AMT1;1. Our study demonstrates in planta a regulatory role in transport activity of heterooligomerization of transporter isoforms, which may enhance their versatility for signal exchange in response to environmental triggers.
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Affiliation(s)
- Lixing Yuan
- Department of Plant Nutrition, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
| | - Riliang Gu
- Department of Plant Nutrition, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
| | - Yuanhu Xuan
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Erika Smith-Valle
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Dominique Loqué
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
- Joint Bioenergy Institute, Emeryville, California 94608
| | - Wolf B. Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Nicolaus von Wirén
- Molecular Plant Nutrition, Leibniz Institute for Plant Genetics and Crop Plant Research, 06466 Gatersleben, Germany
- Address correspondence to
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Retracted article: ammonium transport proteins from Archaeoglobus fulgidus. J Physiol Biochem 2013; 69:963. [PMID: 23385667 DOI: 10.1007/s13105-012-0205-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Accepted: 07/26/2012] [Indexed: 10/28/2022]
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Pantoja O. High affinity ammonium transporters: molecular mechanism of action. FRONTIERS IN PLANT SCIENCE 2012; 3:34. [PMID: 22645581 PMCID: PMC3355798 DOI: 10.3389/fpls.2012.00034] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2011] [Accepted: 02/06/2012] [Indexed: 05/26/2023]
Abstract
The importance of the family of high affinity ammonium transporters is demonstrated by the presence of these proteins in all domains of life, including bacteria, archaea, fungi, plants, and humans. The majority of the proteins that have been studied from this family show high affinity and selectivity for ammonium, are impermeable to alkaline cations, saturate rapidly at low millimolar concentrations and most of them, are also permeable to methylammonium. Crystallization of homologue proteins from bacteria and archaea has demonstrated that the functional entity corresponds to a trimer, with each monomer maintaining a conductive pore. Through molecular modeling, it has been demonstrated that even though the identity of the proteins between bacteria/archaea with those from plants is below 25%, the latter seem to maintain similar tertiary and quaternary structures, an observation that has helped to address the functionality of conserved residues by means of mutational analysis. Results have shown that changes in the extracellular binding site of some plant transporters may result in their inhibition or reduction in transport activity, while in Escherichia coli, dissimilar replacements like Phe/Ala or Ser/Leu that eliminate possible π-interactions or H-bonds with ammonium, respectively, lead to more active transporters. Active mutants with changes in the pair of conserved His in the center of the transporter suggest these residues are dispensable. Additional mutations have identified other important amino acids, both in the entrance of the pore and in cytoplasmic loops. Regulation of this family of transporters can be achieved by interactions of the C-terminal with cytoplasmic loops within the same monomer, or with a neighbor in the trimer. Depending on the interacting residues, these contacts may lead to the activation or inhibition of the protein. The aim of this review is to critically evaluate the newest findings on the role of the proposed amino acids that structure the ammonium pathway, as well as highlight the importance of additional residues that have been identified through mutational analyses.
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Affiliation(s)
- Omar Pantoja
- Instituto de Biotecnología, Universidad Nacional Autónoma de MéxicoCuernavaca, México
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De Michele R, Loqué D, Lalonde S, Frommer WB. Ammonium and urea transporter inventory of the selaginella and physcomitrella genomes. FRONTIERS IN PLANT SCIENCE 2012; 3:62. [PMID: 22639655 PMCID: PMC3355718 DOI: 10.3389/fpls.2012.00062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Accepted: 03/14/2012] [Indexed: 05/05/2023]
Abstract
Ammonium and urea are important nitrogen sources for autotrophic organisms. Plant genomes encode several families of specific transporters for these molecules, plus other uptake mechanisms such as aquaporins and ABC transporters. Selaginella and Physcomitrella are representatives of lycophytes and bryophytes, respectively, and the recent completion of their genome sequences provided us with an opportunity for comparative genome studies, with special emphasis on the adaptive processes that accompanied the conquest of dry land and the evolution of a vascular system. Our phylogenetic analysis revealed that the number of genes encoding urea transporters underwent a progressive reduction during evolution, eventually down to a single copy in vascular plants. Conversely, no clear evolutionary pattern was found for ammonium transporters, and their number and distribution in families varies between species. In particular Selaginella, similar to rice, favors the AMT2/MEP family of ammonium transporters over the plant-specific AMT1 type. In comparison, Physcomitrella presents several members belonging to both families.
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Affiliation(s)
- Roberto De Michele
- Department of Plant Biology, Carnegie Institution for ScienceStanford, CA, USA
- Plant Genetics Institute, National Research Council of ItalyPalermo, Italy
| | | | - Sylvie Lalonde
- Department of Plant Biology, Carnegie Institution for ScienceStanford, CA, USA
| | - Wolf B. Frommer
- Department of Plant Biology, Carnegie Institution for ScienceStanford, CA, USA
- *Correspondence: Wolf B. Frommer, Department of Plant Biology, Carnegie Institution for Science, 260 Panama Street, Stanford, CA 94305, USA. e-mail:
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The pivotal twin histidines and aromatic triad of the Escherichia coli ammonium channel AmtB can be replaced. Proc Natl Acad Sci U S A 2011; 108:13270-4. [PMID: 21775672 DOI: 10.1073/pnas.1108451108] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In Escherichia coli, each subunit of the trimeric channel protein AmtB carries a hydrophobic pore for transport of NH(4)(+) across the cytoplasmic membrane. Positioned along this substrate conduction pathway are two conserved elements--a pair of hydrogen-bonded histidines (H168/H318) located within the pore itself and a set of aromatic residues (F107/W148/F215) at its periplasmic entrance--thought to be critical to AmtB function. Using site-directed mutagenesis and suppressor genetics, we examined the requirement for these elements in NH(4)(+) transport. This analysis shows that AmtB can accommodate, by either direct substitution or suppressor generation, acidic residues at one or both positions of the H168/H318 twin-histidine site while retaining near wild-type activity. Similarly, study of the F107/W148/F215 triad indicates that good-to-excellent AmtB function is preserved upon individual and simultaneous replacement of these aromatic amino acids with aliphatic residues. Our findings lead us to conclude that these elements and their component parts are not required for AmtB function, but instead serve to optimize its performance.
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Graff L, Obrdlik P, Yuan L, Loqué D, Frommer WB, von Wirén N. N-terminal cysteines affect oligomer stability of the allosterically regulated ammonium transporter LeAMT1;1. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:1361-73. [PMID: 21127027 DOI: 10.1093/jxb/erq379] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
AMMONIUM TRANSPORTER (AMT) proteins are conserved in all domains of life and mediate the transport of ammonium or ammonia across cell membranes. AMTs form trimers and use intermolecular interaction between subunits to regulate activity. So far, binding forces that stabilize AMT protein complexes are not well characterized. High temperature or reducing agents released mono- and dimeric forms from trimeric complexes formed by AMT1;1 from Arabidopsis and tomato. However, in the paralogue LeAMT1;3, trimeric complexes were not detected. LeAMT1;3 differs from the other AMTs by an unusually short N-terminus, suggesting a role for the N-terminus in oligomer stability. Truncation of the N-terminus in LeAMT1;1 destabilized the trimer and led to loss of functionality when expressed in yeast. Swapping of the N-terminus between LeAMT1;1 and LeAMT1;3 showed that sequences in the N-terminus of LeAMT1;1 are necessary and sufficient for stabilization of the interaction among the subunits. Two N-terminal cysteine residues are highly conserved among AMT1 transporters in plants but are lacking in LeAMT1;3. C3S or C27S variants of LeAMT1;1 showed reduced complex stability, which coincided with lower transport capacity for the substrate analogue methylammonium. Both cysteine-substituted LeAMT1;1 variants showed weaker interactions with the wildtype as determined by a quantitative analysis of the complex stability using the mating-based split-ubiquitin assay. These data indicate that the binding affinity of AMT1 subunits is stabilized by cysteines in the N-terminus and suggest a role for disulphide bridge formation via apoplastic N-terminal cysteine residues.
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Affiliation(s)
- Lucile Graff
- Institute for Plant Nutrition, University of Hohenheim, D-70593 Stuttgart, Germany
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Lanquar V, Frommer WB. Adjusting ammonium uptake via phosphorylation. PLANT SIGNALING & BEHAVIOR 2010; 5:736-8. [PMID: 20418663 PMCID: PMC3001575 DOI: 10.4161/psb.5.6.11696] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2010] [Accepted: 03/03/2010] [Indexed: 05/22/2023]
Abstract
In plants, AMT/MEP/Rh superfamily mediates high affinity ammonium uptake. AMT/MEP transporters form a trimeric complex, which requires a productive interaction between subunits in order to be functional. The AMT/MEP C-terminal domain is highly conserved in more than 700 AMT homologs from cyanobacteria to higher plants with no cases found to be lacking this domain. AMT1;1 exists in active and inactive states, probably controlled by the spatial positioning of the C-terminus. Ammonium triggers the phosphorylation of a conserved threonine residue (T460) in the C-terminus of AMT1;1 in a time- and concentration-dependent manner. The T460 phosphorylation level correlates with a decrease of root ammonium uptake. We propose that ammonium-induced phosphorylation modulates ammonium uptake as a general mechanism to protect against ammonium toxicity.
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Affiliation(s)
- Viviane Lanquar
- Department of Plant Biology, Carnegie Institution for Science, Stanford, CA, USA
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Lanquar V, Loqué D, Hörmann F, Yuan L, Bohner A, Engelsberger WR, Lalonde S, Schulze WX, von Wirén N, Frommer WB. Feedback inhibition of ammonium uptake by a phospho-dependent allosteric mechanism in Arabidopsis. THE PLANT CELL 2009; 21:3610-22. [PMID: 19948793 PMCID: PMC2798313 DOI: 10.1105/tpc.109.068593] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Revised: 09/23/2009] [Accepted: 11/06/2009] [Indexed: 05/18/2023]
Abstract
The acquisition of nutrients requires tight regulation to ensure optimal supply while preventing accumulation to toxic levels. Ammonium transporter/methylamine permease/rhesus (AMT/Mep/Rh) transporters are responsible for ammonium acquisition in bacteria, fungi, and plants. The ammonium transporter AMT1;1 from Arabidopsis thaliana uses a novel regulatory mechanism requiring the productive interaction between a trimer of subunits for function. Allosteric regulation is mediated by a cytosolic C-terminal trans-activation domain, which carries a conserved Thr (T460) in a critical position in the hinge region of the C terminus. When expressed in yeast, mutation of T460 leads to inactivation of the trimeric complex. This study shows that phosphorylation of T460 is triggered by ammonium in a time- and concentration-dependent manner. Neither Gln nor l-methionine sulfoximine-induced ammonium accumulation were effective in inducing phosphorylation, suggesting that roots use either the ammonium transporter itself or another extracellular sensor to measure ammonium concentrations in the rhizosphere. Phosphorylation of T460 in response to an increase in external ammonium correlates with inhibition of ammonium uptake into Arabidopsis roots. Thus, phosphorylation appears to function in a feedback loop restricting ammonium uptake. This novel autoregulatory mechanism is capable of tuning uptake capacity over a wide range of supply levels using an extracellular sensory system, potentially mediated by a transceptor (i.e., transporter and receptor).
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Affiliation(s)
- Viviane Lanquar
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Dominique Loqué
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Friederike Hörmann
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Lixing Yuan
- Key Lab of Plant Nutrition, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
| | - Anne Bohner
- Molecular Plant Nutrition, Leibniz-Institute for Plant Genetics and Crop Plant Research, 06466 Gatersleben, Germany
| | | | - Sylvie Lalonde
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | | | - Nicolaus von Wirén
- Molecular Plant Nutrition, Leibniz-Institute for Plant Genetics and Crop Plant Research, 06466 Gatersleben, Germany
| | - Wolf B. Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
- Address correspondence to
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