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Urbanavičiūtė I, Bonfiglioli L, Pagnotta MA. One Hundred Candidate Genes and Their Roles in Drought and Salt Tolerance in Wheat. Int J Mol Sci 2021; 22:ijms22126378. [PMID: 34203629 PMCID: PMC8232269 DOI: 10.3390/ijms22126378] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 06/03/2021] [Accepted: 06/09/2021] [Indexed: 12/31/2022] Open
Abstract
Drought and salinity are major constraints to agriculture. In this review, we present an overview of the global situation and the consequences of drought and salt stress connected to climatic changes. We provide a list of possible genetic resources as sources of resistance or tolerant traits, together with the previous studies that focused on transferring genes from the germplasm to cultivated varieties. We explained the morphological and physiological aspects connected to hydric stresses, described the mechanisms that induce tolerance, and discussed the results of the main studies. Finally, we described more than 100 genes associated with tolerance to hydric stresses in the Triticeae. These were divided in agreement with their main function into osmotic adjustment and ionic and redox homeostasis. The understanding of a given gene function and expression pattern according to hydric stress is particularly important for the efficient selection of new tolerant genotypes in classical breeding. For this reason, the current review provides a crucial reference for future studies on the mechanism involved in hydric stress tolerance and the use of these genes in mark assistance selection (MAS) to select the wheat germplasm to face the climatic changes.
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Li J, Sun P, Xia Y, Zheng G, Sun J, Jia H. A Stress-Associated Protein, PtSAP13, From Populus trichocarpa Provides Tolerance to Salt Stress. Int J Mol Sci 2019; 20:ijms20225782. [PMID: 31744233 PMCID: PMC6888306 DOI: 10.3390/ijms20225782] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 11/12/2019] [Accepted: 11/15/2019] [Indexed: 01/19/2023] Open
Abstract
The growth and production of poplars are usually affected by unfavorable environmental conditions such as soil salinization. Thus, enhancing salt tolerance of poplars will promote their better adaptation to environmental stresses and improve their biomass production. Stress-associated proteins (SAPs) are a novel class of A20/AN1 zinc finger proteins that have been shown to confer plants' tolerance to multiple abiotic stresses. However, the precise functions of SAP genes in poplars are still largely unknown. Here, the expression profiles of Populus trichocarpa SAPs in response to salt stress revealed that PtSAP13 with two AN1 domains was up-regulated dramatically during salt treatment. The β-glucuronidase (GUS) staining showed that PtSAP13 was accumulated dominantly in leaf and root, and the GUS signal was increased under salt condition. The Arabidopsis transgenic plants overexpressing PtSAP13 exhibited higher seed germination and better growth than wild-type (WT) plants under salt stress, demonstrating that overexpression of PtSAP13 increased salt tolerance. Higher activities of antioxidant enzymes were found in PtSAP13-overexpressing plants than in WT plants under salt stress. Transcriptome analysis revealed that some stress-related genes, including Glutathione peroxidase 8, NADP-malic enzyme 2, Response to ABA and Salt 1, WRKYs, Glutathione S-Transferase, and MYBs, were induced by salt in transgenic plants. Moreover, the pathways of flavonoid biosynthesis and metabolic processes, regulation of response to stress, response to ethylene, dioxygenase activity, glucosyltransferase activity, monooxygenase activity, and oxidoreductase activity were specially enriched in transgenic plants under salt condition. Taken together, our results demonstrate that PtSAP13 enhances salt tolerance through up-regulating the expression of stress-related genes and mediating multiple biological pathways.
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Affiliation(s)
- Jianbo Li
- Experimental Center of Forestry in North China, Chinese Academy of Forestry, Beijing 102300, China; (Y.X.); (G.Z.); (J.S.)
- State Key Laboratory of Tree Genetics and Breeding, Chinese Academy of Forestry, Beijing 100091, China;
- Correspondence: (J.L.); (H.J.)
| | - Pei Sun
- State Key Laboratory of Tree Genetics and Breeding, Chinese Academy of Forestry, Beijing 100091, China;
- Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
| | - Yongxiu Xia
- Experimental Center of Forestry in North China, Chinese Academy of Forestry, Beijing 102300, China; (Y.X.); (G.Z.); (J.S.)
| | - Guangshun Zheng
- Experimental Center of Forestry in North China, Chinese Academy of Forestry, Beijing 102300, China; (Y.X.); (G.Z.); (J.S.)
| | - Jingshuang Sun
- Experimental Center of Forestry in North China, Chinese Academy of Forestry, Beijing 102300, China; (Y.X.); (G.Z.); (J.S.)
| | - Huixia Jia
- State Key Laboratory of Tree Genetics and Breeding, Chinese Academy of Forestry, Beijing 100091, China;
- Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
- Correspondence: (J.L.); (H.J.)
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Kale D, Spurny P, Shamayeva K, Spurna K, Kahoun D, Ganser D, Zayats V, Ludwig J. The S. cerevisiae cation translocation protein Trk1 is functional without its “long hydrophilic loop” but LHL regulates cation translocation activity and selectivity. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1861:1476-1488. [DOI: 10.1016/j.bbamem.2019.06.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 06/14/2019] [Accepted: 06/17/2019] [Indexed: 10/26/2022]
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Keisham M, Mukherjee S, Bhatla SC. Mechanisms of Sodium Transport in Plants-Progresses and Challenges. Int J Mol Sci 2018; 19:E647. [PMID: 29495332 PMCID: PMC5877508 DOI: 10.3390/ijms19030647] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Revised: 02/14/2018] [Accepted: 02/22/2018] [Indexed: 01/01/2023] Open
Abstract
Understanding the mechanisms of sodium (Na⁺) influx, effective compartmentalization, and efflux in higher plants is crucial to manipulate Na⁺ accumulation and assure the maintenance of low Na⁺ concentration in the cytosol and, hence, plant tolerance to salt stress. Na⁺ influx across the plasma membrane in the roots occur mainly via nonselective cation channels (NSCCs). Na⁺ is compartmentalized into vacuoles by Na⁺/H⁺ exchangers (NHXs). Na⁺ efflux from the plant roots is mediated by the activity of Na⁺/H⁺ antiporters catalyzed by the salt overly sensitive 1 (SOS1) protein. In animals, ouabain (OU)-sensitive Na⁺, K⁺-ATPase (a P-type ATPase) mediates sodium efflux. The evolution of P-type ATPases in higher plants does not exclude the possibility of sodium efflux mechanisms similar to the Na⁺, K⁺-ATPase-dependent mechanisms characteristic of animal cells. Using novel fluorescence imaging and spectrofluorometric methodologies, an OU-sensitive sodium efflux system has recently been reported to be physiologically active in roots. This review summarizes and analyzes the current knowledge on Na⁺ influx, compartmentalization, and efflux in higher plants in response to salt stress.
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Affiliation(s)
- Monika Keisham
- Laboratory of Plant Physiology and Biochemistry, Department of Botany, University of Delhi, Delhi 110007, India.
| | - Soumya Mukherjee
- Laboratory of Plant Physiology and Biochemistry, Department of Botany, University of Delhi, Delhi 110007, India.
- Department of Botany, Jangipur College, University of Kalyani, West Bengal 742213, India.
| | - Satish C Bhatla
- Laboratory of Plant Physiology and Biochemistry, Department of Botany, University of Delhi, Delhi 110007, India.
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Essential and Beneficial Trace Elements in Plants, and Their Transport in Roots: a Review. Appl Biochem Biotechnol 2016; 181:464-482. [PMID: 27687587 DOI: 10.1007/s12010-016-2224-3] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 08/26/2016] [Indexed: 01/09/2023]
Abstract
The essentiality of 14 mineral elements so far have been reported in plant nutrition. Eight of these elements were known as micronutrients due to their lower concentrations in plants (usually ≤100 mg/kg/dw). However, it is still challenging to mention an exact number of plant micronutrients since some elements have not been strictly proposed yet either as essential or beneficial. Micronutrients participate in very diverse metabolic processes, including from the primary and secondary metabolism to the cell defense, and from the signal transduction to the gene regulation, energy metabolism, and hormone perception. Thus, the attempt to understand the molecular mechanism(s) behind their transport has great importance in terms of basic and applied plant sciences. Moreover, their deficiency or toxicity also caused serious disease symptoms in plants, even plant destruction if not treated, and many people around the world suffer from the plant-based dietary deficiencies or metal toxicities. In this sense, shedding some light on this issue, the 13 mineral elements (Fe, B, Cu, Mn, Mo, Si, Zn, Ni, Cl, Se, Na, Al, and Co), required by plants at trace amounts, has been reviewed with the primary focus on the transport proteins (transporters/channels) in plant roots. So, providing the compiled but extensive information about the structural and functional roles of micronutrient transport genes/proteins in plant roots.
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Ariyarathna HACK, Francki MG. Phylogenetic relationships and protein modelling revealed two distinct subfamilies of group II HKT genes between crop and model grasses. Genome 2016; 59:509-17. [PMID: 27203707 DOI: 10.1139/gen-2016-0035] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Molecular evolution of large protein families in closely related species can provide useful insights on structural functional relationships. Phylogenetic analysis of the grass-specific group II HKT genes identified two distinct subfamilies, I and II. Subfamily II was represented in all species, whereas subfamily I was identified only in the small grain cereals and possibly originated from an ancestral gene duplication post divergence from the coarse grain cereal lineage. The core protein structures were highly analogous despite there being no more than 58% amino acid identity between members of the two subfamilies. Distinctly variable regions in known functional domains, however, indicated functional divergence of the two subfamilies. The subsets of codons residing external to known functional domains predicted signatures of positive Darwinian selection potentially identifying new domains of functional divergence and providing new insights on the structural function and relationships between protein members of the two subfamilies.
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Affiliation(s)
- H A Chandima K Ariyarathna
- a School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley WA 6009, Australia.,b State Agricultural Biotechnology Centre, Murdoch University, Murdoch WA 6150, Australia
| | - Michael G Francki
- b State Agricultural Biotechnology Centre, Murdoch University, Murdoch WA 6150, Australia.,c Department of Agriculture and Food Western Australia, 3 Baron Hay Ct, South Perth WA 6151, Australia
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Model of Cation Transportation Mediated by High-Affinity Potassium Transporters (HKTs) in Higher Plants. Biol Proced Online 2015; 17:1. [PMID: 25698907 PMCID: PMC4334588 DOI: 10.1186/s12575-014-0013-3] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Accepted: 12/06/2014] [Indexed: 01/18/2023] Open
Abstract
Trk/Ktr/HKT transporters probably were evolved from simple K+ channels KcsA. HKT transporters, which mediate Na+-uniport or Na+/K+-symport, maintain K+/Na+ homeostasis and increase salinity tolerance, can be classified into three subfamilies in higher plants. In this review, we systematically analyzed the characteristics of amino acids sequences and physiological functions of HKT transporters in higher plant. Furthermore, we depicted the hypothetical models of cations selection and transportation mediated by HKT transporters according to the highly conserved structure for the goal of better understanding the cations transportation processes.
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Ariyarathna HACK, Ul-Haq T, Colmer TD, Francki MG. Characterization of the multigene family TaHKT 2;1 in bread wheat and the role of gene members in plant Na(+) and K(+) status. BMC PLANT BIOLOGY 2014; 14:159. [PMID: 24920193 PMCID: PMC4079177 DOI: 10.1186/1471-2229-14-159] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Accepted: 06/04/2014] [Indexed: 05/20/2023]
Abstract
BACKGROUND A member of the TaHKT2;1 multigene family was previously identified as a Na(+) transporter with a possible role in root Na(+) uptake. In the present study, the existing full-length cDNA of this member was used as a basis to query the International Wheat Genome Survey Sequence to identify all members of the TaHKT2;1 family. Individual TaHKT2;1 genes were subsequently studied for gene and predicted protein structures, promoter variability, tissue expression and their role in Na(+) and K(+) status of wheat. RESULTS Six TaHKT2;1 genes were characterized which included four functional genes (TaHKT2;1 7AL-1, TaHKT2;1 7BL-1, TaHKT2;1 7BL-2 and TaHKT2;1 7DL-1) and two pseudogenes (TaHKT2;1 7AL-2 and TaHKT2;1 7AL-3), on chromosomes 7A, 7B and 7D of hexaploid wheat. Variability in protein domains for cation specificity and in cis-regulatory elements for salt response in gene promoters, were identified amongst the functional TaHKT2;1 members. The functional genes were expressed under low and high NaCl conditions in roots and leaf sheaths, but were down regulated in leaf blades. Alternative splicing events were evident in TaHKT2;1 7AL-1. Aneuploid lines null for each functional gene were grown in high NaCl nutrient solution culture to identify potential role of each TaHKT2;1 member. Aneuploid lines null for TaHKT2;1 7AL-1, TaHKT2;1 7BL-1 and TaHKT2;1 7BL-2 showed no difference in Na(+) concentration between Chinese Spring except for higher Na(+) in sheaths. The same aneuploid lines had lower K(+) in roots, sheath and youngest fully expanded leaf but only under high (200 mM) NaCl in the external solution. There was no difference in Na(+) or K(+) concentration for any treatment between aneuploid line null for the TaHKT2;1 7DL-1 gene and Chinese Spring. CONCLUSIONS TaHKT2;1 is a complex family consisting of pseudogenes and functional members. TaHKT2;1 genes do not have an apparent role in controlling root Na(+) uptake in bread wheat seedlings under experimental conditions in this study, contrary to existing hypotheses. However, TaHKT2;1 genes or, indeed other genes in the same chromosome region on 7AL, are candidates that may control Na(+) transport from root to sheath and regulate K(+) levels in different plant tissues.
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Affiliation(s)
- HA Chandima K Ariyarathna
- School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley 6009, Western Australia
- State Agricultural Biotechnology Centre, Murdoch University, Murdoch 6150, Western Australia
| | - Tanveer Ul-Haq
- School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley 6009, Western Australia
- State Agricultural Biotechnology Centre, Murdoch University, Murdoch 6150, Western Australia
- College of Agriculture, D. G. Khan, University of Agriculture Faisalabad, Faisalabad 38040, Pakistan
| | - Timothy D Colmer
- School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley 6009, Western Australia
| | - Michael G Francki
- State Agricultural Biotechnology Centre, Murdoch University, Murdoch 6150, Western Australia
- Department of Agriculture and Food Western Australia, South Perth 6151, Western Australia
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Shankar A, Singh A, Kanwar P, Srivastava AK, Pandey A, Suprasanna P, Kapoor S, Pandey GK. Gene expression analysis of rice seedling under potassium deprivation reveals major changes in metabolism and signaling components. PLoS One 2013; 8:e70321. [PMID: 23922980 PMCID: PMC3726378 DOI: 10.1371/journal.pone.0070321] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 06/17/2013] [Indexed: 01/09/2023] Open
Abstract
Plant nutrition is one of the important areas for improving the yield and quality in crops as well as non-crop plants. Potassium is an essential plant nutrient and is required in abundance for their proper growth and development. Potassium deficiency directly affects the plant growth and hence crop yield and production. Recently, potassium-dependent transcriptomic analysis has been performed in the model plant Arabidopsis, however in cereals and crop plants; such a transcriptome analysis has not been undertaken till date. In rice, the molecular mechanism for the regulation of potassium starvation responses has not been investigated in detail. Here, we present a combined physiological and whole genome transcriptomic study of rice seedlings exposed to a brief period of potassium deficiency then replenished with potassium. Our results reveal that the expressions of a diverse set of genes annotated with many distinct functions were altered under potassium deprivation. Our findings highlight altered expression patterns of potassium-responsive genes majorly involved in metabolic processes, stress responses, signaling pathways, transcriptional regulation, and transport of multiple molecules including K+. Interestingly, several genes responsive to low-potassium conditions show a reversal in expression upon resupply of potassium. The results of this study indicate that potassium deprivation leads to activation of multiple genes and gene networks, which may be acting in concert to sense the external potassium and mediate uptake, distribution and ultimately adaptation to low potassium conditions. The interplay of both upregulated and downregulated genes globally in response to potassium deprivation determines how plants cope with the stress of nutrient deficiency at different physiological as well as developmental stages of plants.
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Affiliation(s)
- Alka Shankar
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India
| | - Amarjeet Singh
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India
| | - Poonam Kanwar
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India
| | - Ashish Kumar Srivastava
- Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Mumbai, India
| | - Amita Pandey
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India
| | - Penna Suprasanna
- Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Mumbai, India
| | - Sanjay Kapoor
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India
| | - Girdhar K. Pandey
- Department of Plant Molecular Biology, University of Delhi South Campus, Dhaula Kuan, New Delhi, India
- * E-mail:
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AtHKT1;1 mediates nernstian sodium channel transport properties in Arabidopsis root stelar cells. PLoS One 2011; 6:e24725. [PMID: 21931830 PMCID: PMC3170383 DOI: 10.1371/journal.pone.0024725] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Accepted: 08/19/2011] [Indexed: 11/19/2022] Open
Abstract
The Arabidopsis AtHKT1;1 protein was identified as a sodium (Na+) transporter by heterologous expression in Xenopus laevis oocytes and Saccharomyces cerevisiae. However, direct comparative in vivo electrophysiological analyses of a plant HKT transporter in wild-type and hkt loss-of-function mutants has not yet been reported and it has been recently argued that heterologous expression systems may alter properties of plant transporters, including HKT transporters. In this report, we analyze several key functions of AtHKT1;1-mediated ion currents in their native root stelar cells, including Na+ and K+ conductances, AtHKT1;1-mediated outward currents, and shifts in reversal potentials in the presence of defined intracellular and extracellular salt concentrations. Enhancer trap Arabidopsis plants with GFP-labeled root stelar cells were used to investigate AtHKT1;1-dependent ion transport properties using patch clamp electrophysiology in wild-type and athkt1;1 mutant plants. AtHKT1;1-dependent currents were carried by sodium ions and these currents were not observed in athkt1;1 mutant stelar cells. However, K+ currents in wild-type and athkt1;1 root stelar cell protoplasts were indistinguishable correlating with the Na+ over K+ selectivity of AtHKT1;1-mediated transport. Moreover, AtHKT1;1-mediated currents did not show a strong voltage dependence in vivo. Unexpectedly, removal of extracellular Na+ caused a reduction in AtHKT1;1-mediated outward currents in Columbia root stelar cells and Xenopus oocytes, indicating a role for external Na+ in regulation of AtHKT1;1 activity. Shifting the NaCl gradient in root stelar cells showed a Nernstian shift in the reversal potential providing biophysical evidence for the model that AtHKT1;1 mediates passive Na+ channel transport properties.
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Horie T, Brodsky DE, Costa A, Kaneko T, Lo Schiavo F, Katsuhara M, Schroeder JI. K+ transport by the OsHKT2;4 transporter from rice with atypical Na+ transport properties and competition in permeation of K+ over Mg2+ and Ca2+ ions. PLANT PHYSIOLOGY 2011; 156:1493-507. [PMID: 21610181 PMCID: PMC3135959 DOI: 10.1104/pp.110.168047] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Accepted: 05/20/2011] [Indexed: 05/18/2023]
Abstract
Members of class II of the HKT transporters, which have thus far only been isolated from grasses, were found to mediate Na(+)-K(+) cotransport and at high Na(+) concentrations preferred Na(+)-selective transport, depending on the ionic conditions. But the physiological functions of this K(+)-transporting class II of HKT transporters remain unknown in plants, with the exception of the unique class II Na(+) transporter OsHKT2;1. The genetically tractable rice (Oryza sativa; background Nipponbare) possesses two predicted K(+)-transporting class II HKT transporter genes, OsHKT2;3 and OsHKT2;4. In this study, we have characterized the ion selectivity of the class II rice HKT transporter OsHKT2;4 in yeast and Xenopus laevis oocytes. OsHKT2;4 rescued the growth defect of a K(+) uptake-deficient yeast mutant. Green fluorescent protein-OsHKT2;4 is targeted to the plasma membrane in transgenic plant cells. OsHKT2;4-expressing oocytes exhibited strong K(+) permeability. Interestingly, however, K(+) influx in OsHKT2;4-expressing oocytes did not require stimulation by extracellular Na(+), in contrast to other class II HKT transporters. Furthermore, OsHKT2;4-mediated currents exhibited permeabilities to both Mg(2+) and Ca(2+) in the absence of competing K(+) ions. Comparative analyses of Ca(2+) and Mg(2+) permeabilities in several HKT transporters, including Arabidopsis thaliana HKT1;1 (AtHKT1;1), Triticum aestivum HKT2;1 (TaHKT2;1), OsHKT2;1, OsHKT2;2, and OsHKT2;4, revealed that only OsHKT2;4 and to a lesser degree TaHKT2;1 mediate Mg(2+) transport. Interestingly, cation competition analyses demonstrate that the selectivity of both of these class II HKT transporters for K(+) is dominant over divalent cations, suggesting that Mg(2+) and Ca(2+) transport via OsHKT2;4 may be small and would depend on competing K(+) concentrations in plants.
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Corratgé-Faillie C, Jabnoune M, Zimmermann S, Véry AA, Fizames C, Sentenac H. Potassium and sodium transport in non-animal cells: the Trk/Ktr/HKT transporter family. Cell Mol Life Sci 2010; 67:2511-32. [PMID: 20333436 PMCID: PMC11115768 DOI: 10.1007/s00018-010-0317-7] [Citation(s) in RCA: 158] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2009] [Revised: 02/10/2010] [Accepted: 02/15/2010] [Indexed: 02/06/2023]
Abstract
Bacterial Trk and Ktr, fungal Trk and plant HKT form a family of membrane transporters permeable to K(+) and/or Na(+) and characterized by a common structure probably derived from an ancestral K(+) channel subunit. This transporter family, specific of non-animal cells, displays a large diversity in terms of ionic permeability, affinity and energetic coupling (H(+)-K(+) or Na(+)-K(+) symport, K(+) or Na(+) uniport), which might reflect a high need for adaptation in organisms living in fluctuating or dilute environments. Trk/Ktr/HKT transporters are involved in diverse functions, from K(+) or Na(+) uptake to membrane potential control, adaptation to osmotic or salt stress, or Na(+) recirculation from shoots to roots in plants. Structural analyses of bacterial Ktr point to multimeric structures physically interacting with regulatory subunits. Elucidation of Trk/Ktr/HKT protein structures along with characterization of mutated transporters could highlight functional and evolutionary relationships between ion channels and transporters displaying channel-like features.
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Affiliation(s)
- C. Corratgé-Faillie
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, 2 Place Viala, 34060 Montpellier Cedex 2, France
| | - M. Jabnoune
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, 2 Place Viala, 34060 Montpellier Cedex 2, France
- Present Address: Plant Biotechnology Laboratory, DBMV, University of Lausanne, 1015 Lausanne, Switzerland
| | - S. Zimmermann
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, 2 Place Viala, 34060 Montpellier Cedex 2, France
| | - A.-A. Véry
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, 2 Place Viala, 34060 Montpellier Cedex 2, France
| | - C. Fizames
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, 2 Place Viala, 34060 Montpellier Cedex 2, France
| | - H. Sentenac
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, 2 Place Viala, 34060 Montpellier Cedex 2, France
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Horie T, Horie R, Chan WY, Leung HY, Schroeder JI. Calcium Regulation of Sodium Hypersensitivities of sos3 and athkt1 Mutants. ACTA ACUST UNITED AC 2006; 47:622-33. [PMID: 16540484 DOI: 10.1093/pcp/pcj029] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
T-DNA disruption mutations in the AtHKT1 gene have previously been shown to suppress the salt sensitivity of the sos3 mutant. However, both sos3 and athkt1 single mutants show sodium (Na+) hypersensitivity. In the present study we further analyzed the underlying mechanisms for these non-additive and counteracting Na+ sensitivities by characterizing athkt1-1 sos3 and athkt1-2 sos3 double mutant plants. Unexpectedly, mature double mutant plants grown in soil clearly showed an increased Na+ hypersensitivity compared with wild-type plants when plants were subjected to salinity stress. The salt sensitive phenotype of athkt1 sos3 double mutant plants was similar to that of athkt1 plants, which showed chlorosis in leaves and stems. The Na+ content in xylem sap samples of soil-grown athkt1 sos3 double and athkt1 single mutant plants showed dramatic Na+ overaccumulation in response to salinity stress. Salinity stress analyses using basic minimal nutrient medium and Murashige-Skoog (MS) medium revealed that athkt1 sos3 double mutant plants show a more athkt1 single mutant-like phenotype in the presence of 3 mM external Ca2+, but show a more sos3 single mutant-like phenotype in the presence of 1 mM external Ca2+. Taken together multiple analyses demonstrate that the external Ca2+ concentration strongly impacts the Na+ stress response of athkt1 sos3 double mutants. Furthermore, the presented findings show that SOS3 and AtHKT1 are physiologically distinct major determinants of salinity resistance such that sos3 more strongly causes Na+ overaccumulation in roots, whereas athkt1 causes an increase in Na+ levels in the xylem sap and shoots and a concomitant Na+ reduction in roots.
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Affiliation(s)
- Tomoaki Horie
- Division of Biological Sciences, Cell and Developmental Biology Section, and Center for Molecular Genetics, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA
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Verslues PE, Agarwal M, Katiyar-Agarwal S, Zhu J, Zhu JK. Methods and concepts in quantifying resistance to drought, salt and freezing, abiotic stresses that affect plant water status. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2006; 45:523-39. [PMID: 16441347 DOI: 10.1111/j.1365-313x.2005.02593.x] [Citation(s) in RCA: 712] [Impact Index Per Article: 39.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The abiotic stresses of drought, salinity and freezing are linked by the fact that they all decrease the availability of water to plant cells. This decreased availability of water is quantified as a decrease in water potential. Plants resist low water potential and related stresses by modifying water uptake and loss to avoid low water potential, accumulating solutes and modifying the properties of cell walls to avoid the dehydration induced by low water potential and using protective proteins and mechanisms to tolerate reduced water content by preventing or repairing cell damage. Salt stress also alters plant ion homeostasis, and under many conditions this may be the predominant factor affecting plant performance. Our emphasis is on experiments that quantify resistance to realistic and reproducible low water potential (drought), salt and freezing stresses while being suitable for genetic studies where a large number of lines must be analyzed. Detailed protocols for the use of polyethylene glycol-infused agar plates to impose low water potential stress, assay of salt tolerance based on root elongation, quantification of freezing tolerance and the use of electrolyte leakage experiments to quantify cellular damage induced by freezing and low water potential are also presented.
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Affiliation(s)
- Paul E Verslues
- Institute for Integrative Genome Biology and Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA
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15
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Kuroda T, Bihler H, Bashi E, Slayman CL, Rivetta A. Chloride channel function in the yeast TRK-potassium transporters. J Membr Biol 2005; 198:177-92. [PMID: 15216418 DOI: 10.1007/s00232-004-0671-1] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2003] [Revised: 02/27/2004] [Indexed: 01/22/2023]
Abstract
The TRK proteins-Trk1p and Trk2p- are the main agents responsible for "active" accumulation of potassium by the yeast Saccharomyces cerevisiae. In previous studies, inward currents measured through those proteins by whole-cell patch-clamping proved very unresponsive to changes of extracellular potassium concentration, although they did increase with extracellular proton concentration-qualitatively as expected for H(+) coupling to K(+) uptake. These puzzling observations have now been explored in greater detail, with the following major findings: a) the large inward TRK currents are not carried by influx of either K(+) or H(+), but rather by an efflux of chloride ions; b) with normal expression levels for Trk1p and Trk2p in potassium-replete cells, the inward TRK currents are contributed approximately half by Trk1p and half by Trk2p; but c) strain background strongly influences the absolute magnitude of these currents, which are nearly twice as large in W303-derived spheroplasts as in S288c-derived cells (same cell-size and identical recording conditions); d) incorporation of mutations that increase cell size (deletion of the Golgi calcium pump, Pmr1p) or that upregulate the TRK2 promoter, can further substantially increase the TRK currents; e) removal of intracellular chloride (e.g., replacement by sulfate or gluconate) reveals small inward currents that are K(+)-dependent and can be enhanced by K(+) starvation; and f) finally, the latter currents display two saturating kinetic components, with preliminary estimates of K(0.5) at 46 micro M [K(+)](out) and 6.8 m M [K(+)](out), and saturating fluxes of approximately 5 m M/min and approximately 10 m M/min (referred to intracellular water). These numbers are compatible with the normal K(+)-transport properties of Trk1p and Trk2p, respectively.
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Affiliation(s)
- T Kuroda
- Department of Cellular and Molecular Physiology, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
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16
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Zeng GF, Pypaert M, Slayman CL. Epitope Tagging of the Yeast K+ Carrier Trk2p Demonstrates Folding That Is Consistent with a Channel-like Structure. J Biol Chem 2004; 279:3003-13. [PMID: 14570869 DOI: 10.1074/jbc.m309760200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
TRK family proteins, which mediate the concentrative uptake of potassium by plant cells, fungi, and bacteria, resemble primitive potassium channels in sequence and have recently been proposed actually to fold like potassium channels in a 4-MPM motif (Durell, S. R., and Guy, H. R. (1999) Biophys. J. 77, 789 - 807), instead of like conventional substrate porters in the 12-TM motif (Gaber, R. F., Styles, C. A., and Fink, G. R. (1988) Mol. Cell. Biol. 8, 2848-2859). The known fungal members of this family possess a very long hydrophilic loop, positioned intracellularly in the K(+)-channel model and extracellularly in the substrate porter model. This and two shorter hydrophilic segments have been tested as topological markers for the true folding pattern of TRK proteins using Saccharomyces cerevisiae Trk2p. Hemagglutinin epitope tags were inserted into all three segments, and the enhanced green fluorescent protein (EGFP) was fused to the C terminus of Trk2p. The gene constructs were expressed from a high copy plasmid, and sidedness of the tags was determined by native fluorescence (EGFP), indirect immunofluorescence, and immunoelectron microscopy. Both the long-loop tag and the C-terminal EGFP fusion allowed abundant protein to reach the plasma membrane and support normal yeast growth. In all determinations, the long-loop tag was localized to the inner surface of the yeast cell plasma membrane, thus strongly supporting the channel-like folding model. Additional observations showed (i). membrane-associated Trk2p to lie in proteolipid rafts; (ii). significant tagged protein, expressed from the plasmid, to be sequestered in cytoplasmic vesicular-tubular clusters; and (iii). suppression of such clusters by yeast growth in 5-10% glycerol. This chaperone-like effect may assist other membrane proteins (overexpressed or heterologously expressed) to function within the yeast plasma membrane.
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Affiliation(s)
- Ge-Fei Zeng
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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17
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Gao X, Ren Z, Zhao Y, Zhang H. Overexpression of SOD2 increases salt tolerance of Arabidopsis. PLANT PHYSIOLOGY 2003; 133:1873-81. [PMID: 14630955 PMCID: PMC300740 DOI: 10.1104/pp.103.026062] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2003] [Revised: 06/11/2003] [Accepted: 09/11/2003] [Indexed: 05/18/2023]
Abstract
The yeast (Schizosaccharomyces pombe) SOD2 (Sodium2) gene was introduced into Arabidopsis under the control of the cauliflower mosaic virus 35S promoter. Transformants were selected for their ability to grow on medium containing kanamycin. Southern- and northern-blot analyses confirmed that SOD2 was transferred into the Arabidopsis genome. There were no obvious morphological or developmental differences between the transgenic and wild-type (wt) plants. Several transgenic homozygous lines and wt plants (control) were evaluated for salt tolerance and gene expression. Overexpression of SOD2 in Arabidopsis improved seed germination and seedling salt tolerance. Analysis of Na+ and K+ contents of the symplast and apoplast in the parenchyma cells of the root cortex and mesophyll cells in the spongy tissue of the leaf showed that transgenic lines accumulated less Na+ and more K+ in the symplast than the wt plants did. The photosynthetic rate and the fresh weight of the transgenic lines were distinctly higher than that of wt plants after NaCl treatment. Results from different tests indicated that the expression of the SOD2 gene promoted a higher level of salt tolerance in vivo in transgenic Arabidopsis plants.
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Affiliation(s)
- Xiuhua Gao
- Key Laboratory of Plant Stress Research, College of Life Science, Shandong Normal University, Jinan 250014, China
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18
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Berthomieu P, Conéjéro G, Nublat A, Brackenbury WJ, Lambert C, Savio C, Uozumi N, Oiki S, Yamada K, Cellier F, Gosti F, Simonneau T, Essah PA, Tester M, Véry AA, Sentenac H, Casse F. Functional analysis of AtHKT1 in Arabidopsis shows that Na(+) recirculation by the phloem is crucial for salt tolerance. EMBO J 2003; 22:2004-14. [PMID: 12727868 PMCID: PMC156079 DOI: 10.1093/emboj/cdg207] [Citation(s) in RCA: 348] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Two allelic recessive mutations of Arabidopsis, sas2-1 and sas2-2, were identified as inducing sodium overaccumulation in shoots. The sas2 locus was found (by positional cloning) to correspond to the AtHKT1 gene. Expression in Xenopus oocytes revealed that the sas2-1 mutation did not affect the ionic selectivity of the transporter but strongly reduced the macro scopic (whole oocyte current) transport activity. In Arabidopsis, expression of AtHKT1 was shown to be restricted to the phloem tissues in all organs. The sas2-1 mutation strongly decreased Na(+) concentration in the phloem sap. It led to Na(+) overaccumulation in every aerial organ (except the stem), but to Na(+) underaccumulation in roots. The sas2 plants displayed increased sensitivity to NaCl, with reduced growth and even death under moderate salinity. The whole set of data indicates that AtHKT1 is involved in Na(+) recirculation from shoots to roots, probably by mediating Na(+) loading into the phloem sap in shoots and unloading in roots, this recirculation removing large amounts of Na(+) from the shoot and playing a crucial role in plant tolerance to salt.
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Affiliation(s)
- Pierre Berthomieu
- Biochimie et Physiologie Moléculaire des Plantes, UMR 5004, ENSA M INRA CNRS UMII and UMR Agronomie Ecophysiologie des Plantes sous Stress Environnementaux, INRA ENSA.M, 34060 Montpellier Cedex 2, France.
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19
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Véry AA, Sentenac H. Molecular mechanisms and regulation of K+ transport in higher plants. ANNUAL REVIEW OF PLANT BIOLOGY 2003; 54:575-603. [PMID: 14503004 DOI: 10.1146/annurev.arplant.54.031902.134831] [Citation(s) in RCA: 305] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Potassium (K+) plays a number of important roles in plant growth and development. Over the past few years, molecular approaches associated with electrophysiological analyses have greatly advanced our understanding of K+ transport in plants. A large number of genes encoding K+ transport systems have been identified, revealing a high level of complexity. Characterization of some transport systems is providing exciting information at the molecular level on functions such as root K+ uptake and secretion into the xylem sap, K+ transport in guard cells, or K+ influx into growing pollen tubes. In this review, we take stock of this recent molecular information. The main families of plant K+ transport systems (Shaker and KCO channels, KUP/HAK/KT and HKT transporters) are described, along with molecular data on how these systems are regulated. Finally, we discuss a few physiological questions on which molecular studies have shed new light.
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Affiliation(s)
- Anne-Aliénor Véry
- UMR 5004 CNRS/ENSA-M/INRA/UM2, Place Viala, 34060 Montpellier, France.
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20
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Laurie S, Feeney KA, Maathuis FJM, Heard PJ, Brown SJ, Leigh RA. A role for HKT1 in sodium uptake by wheat roots. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 32:139-49. [PMID: 12383080 DOI: 10.1046/j.1365-313x.2002.01410.x] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The high affinity potassium transporter, HKT1 from wheat was introduced into Florida wheat in sense and antisense orientation under control of a ubiquitin promoter. Ten transgenic lines expressing the transgene were identified and two of these showed strong down-regulation of the native HKT1 transcript. One line (271) was expressing the antisense construct and the other (223) was expressing a truncated sense construct. The two lines were examined further for phenotype relating to cation transport. Membrane depolarisations were measured in low (0.1 mm) K+ and high (100 mm) NaCl. Under these conditions there was no difference between line 271 and the control at low K+, but at high Na+ there was a rapid depolarisation that was significantly larger in control plants. 22Na uptake was measured in this line and there was a significant decrease in uptake at 100 mm NaCl in the transgenic line when compared with the control. The two transgenic lines were grown at high NaCl (200 mm) and analysed for growth and root sodium content. Lines 271 and 223 showed enhanced growth under salinity when compared with the control and had lower sodium in the root. Secondary ion mass spectrometry (SIMS) analysis of transverse sections of the root showed that Na+ and K+ were strongly localised to stelar regions when compared with other ions, and that the Na+ : K+ ratios were reduced in salt-stressed transgenic tissue when compared with the control.
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Affiliation(s)
- Sophie Laurie
- IACR Long Ashton, Crop Performance and Improvement Division, Long Ashton, Bristol, BS41 9AF, UK.
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21
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Abstract
Studying salt stress is an important means to the understanding of plant ion homeostasis and osmo-balance. Salt stress research also benefits agriculture because soil salinity significantly limits plant productivity on agricultural lands. Decades of physiological and molecular studies have generated a large body of literature regarding potential salt tolerance determinants. Recent advances in applying molecular genetic analysis and genomics tools in the model plant Arabidopsis thaliana are shading light on the molecular nature of salt tolerance effectors and regulatory pathways.
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Affiliation(s)
- Liming Xiong
- Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, Tel. (520) 626-2229, Fax (520) 621-7186,
| | - Jian-Kang Zhu
- Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, Tel. (520) 626-2229, Fax (520) 621-7186,
- Corresponding author
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22
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Senn ME, Rubio F, Bañuelos MA, Rodríguez-Navarro A. Comparative functional features of plant potassium HvHAK1 and HvHAK2 transporters. J Biol Chem 2001; 276:44563-9. [PMID: 11562376 DOI: 10.1074/jbc.m108129200] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Plant K(+) transporters of the HAK family belong to four rather divergent phylogenetic clusters, although most of the transporters belong to clusters I or II. A simple phylogenetic analysis of fungal and plant HAK transporters suggests that an original HAK gene duplicated even before fungi and plants diverged, generating transporters that at present fulfill different functions in the plant. The HvHAK1 transporter belongs to cluster I and mediates high-affinity K(+) uptake in barley roots, but no function is known for the cluster II transporter, HvHAK2, which is not functional in yeast. The function of HvHAK2 was investigated by constructing HvHAK1-HAK2 chimeric transporters, which were not functional even when they included only short fragments of HvHAK2. Then, amino acids characteristic of cluster II in the N terminus and in the first transmembrane domain were introduced into HvHAK1. All of these changes increased the Rb(+) K(m), introducing minimal changes in the Na(+) K(m), which suggested that HvHAK2 is a low-affinity, Na(+)-sensitive K(+) transporter. Using a K(+)-defective Escherichia coli mutant, we functionally expressed HvHAK2 and found that the predicted characteristics were correct, as well as discovering that the bacterial expression of HvHAK2 is functional at pH 5.5 but not at 7.5. We discuss whether HvHAK2 may be a tonoplast transporter effective for vacuolar K(+) depletion in K(+) starved plants.
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Affiliation(s)
- M E Senn
- Departamento de Biotecnologia, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Politécnica de Madrid, 28040 Madrid, Spain
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23
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Liu W, Fairbairn DJ, Reid RJ, Schachtman DP. Characterization of two HKT1 homologues from Eucalyptus camaldulensis that display intrinsic osmosensing capability. PLANT PHYSIOLOGY 2001; 127:283-94. [PMID: 11553756 PMCID: PMC117984 DOI: 10.1104/pp.127.1.283] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2001] [Revised: 03/19/2001] [Accepted: 05/13/2001] [Indexed: 05/18/2023]
Abstract
Plants have multiple potassium (K(+)) uptake and efflux mechanisms that are expressed throughout plant tissues to fulfill different physiological functions. Several different classes of K(+) channels and carriers have been identified at the molecular level in plants. K(+) transporters of the HKT1 superfamily have been cloned from wheat (Triticum aestivum), Arabidopsis, and Eucalyptus camaldulensis. The functional characteristics as well as the primary structure of these transporters are diverse with orthologues found in bacterial and fungal genomes. In this report, we provide a detailed characterization of the functional characteristics, as expressed in Xenopus laevis oocytes, of two cDNAs isolated from E. camaldulensis that encode proteins belonging to the HKT1 superfamily of K(+)/Na(+) transporters. The transport of K(+) in EcHKT-expressing oocytes is enhanced by Na(+), but K(+) was also transported in the absence of Na(+). Na(+) is transported in the absence of K(+) as has been demonstrated for HKT1 and AtHKT1. Overall, the E. camaldulensis transporters show some similarities and differences in ionic selectivity to HKT1 and AtHKT1. One striking difference between HKT1 and EcHKT is the sensitivity to changes in the external osmolarity of the solution. Hypotonic solutions increased EcHKT induced currents in oocytes by 100% as compared with no increased current in HKT1 expressing or uninjected oocytes. These osmotically sensitive currents were not enhanced by voltage and may mediate water flux. The physiological function of these osmotically induced increases in currents may be related to the ecological niches that E. camaldulensis inhabits, which are periodically flooded. Therefore, the osmosensing function of EcHKT may provide this species with a competitive advantage in maintaining K(+) homeostasis under certain conditions.
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Affiliation(s)
- W Liu
- CSIRO Plant Industry Horticulture Unit, G.P.O. Box 350, Glen Osmond, South Australia 5064, Australia
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24
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Kato Y, Sakaguchi M, Mori Y, Saito K, Nakamura T, Bakker EP, Sato Y, Goshima S, Uozumi N. Evidence in support of a four transmembrane-pore-transmembrane topology model for the Arabidopsis thaliana Na+/K+ translocating AtHKT1 protein, a member of the superfamily of K+ transporters. Proc Natl Acad Sci U S A 2001; 98:6488-93. [PMID: 11344270 PMCID: PMC33495 DOI: 10.1073/pnas.101556598] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Arabidopsis thaliana AtHKT1 protein, a Na(+)/K(+) transporter, is capable of mediating inward Na(+) currents in Xenopus laevis oocytes and K(+) uptake in Escherichia coli. HKT1 proteins are members of a superfamily of K(+) transporters. These proteins have been proposed to contain eight transmembrane segments and four pore-forming regions arranged in a mode similar to that of a K(+) channel tetramer. However, computer analysis of the AtHKT1 sequence identified eleven potential transmembrane segments. We have investigated the membrane topology of AtHKT1 with three different techniques. First, a gene fusion alkaline phosphatase study in E. coli clearly defined the topology of the N-terminal and middle region of AtHKT1, but the model for membrane folding of the C-terminal region had to be refined. Second, with a reticulocyte-lysate supplemented with dog-pancreas microsomes, we demonstrated that N-glycosylation occurs at position 429 of AtHKT1. An engineered unglycosylated protein variant, N429Q, mediated Na(+) currents in X. laevis oocytes with the same characteristics as the wild-type protein, indicating that N-glycosylation is not essential for the functional expression and membrane targeting of AtHKT1. Five potential glycosylation sites were introduced into the N429Q. Their pattern of glycosylation supported the model based on the E. coli-alkaline phosphatase data. Third, immunocytochemical experiments with FLAG-tagged AtHKT1 in HEK293 cells revealed that the N and C termini of AtHKT1, and the regions containing residues 135-142 and 377-384, face the cytosol, whereas the region of residues 55-62 is exposed to the outside. Taken together, our results show that AtHKT1 contains eight transmembrane-spanning segments.
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Affiliation(s)
- Y Kato
- Graduate School of Bioagricultural Sciences and Bioscience Center, Nagoya University, Nagoya 464-8601, Japan
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