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      Humic Acid Confers HIGH-AFFINITY K + TRANSPORTER 1-Mediated Salinity Stress Tolerance in Arabidopsis

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          Abstract

          Excessive salt disrupts intracellular ion homeostasis and inhibits plant growth, which poses a serious threat to global food security. Plants have adapted various strategies to survive in unfavorable saline soil conditions. Here, we show that humic acid (HA) is a good soil amendment that can be used to help overcome salinity stress because it markedly reduces the adverse effects of salinity on Arabidopsis thaliana seedlings. To identify the molecular mechanisms of HA-induced salt stress tolerance in Arabidopsis, we examined possible roles of a sodium influx transporter HIGH-AFFINITY K + TRANSPORTER 1 (HKT1). Salt-induced root growth inhibition in HKT1 overexpressor transgenic plants ( HKT1-OX) was rescued by application of HA, but not in wild-type and other plants. Moreover, salt-induced degradation of HKT1 protein was blocked by HA treatment. In addition, the application of HA to HKT1-OX seedlings led to increased distribution of Na + in roots up to the elongation zone and caused the reabsorption of Na + by xylem and parenchyma cells. Both the influx of the secondary messenger calcium and its cytosolic release appear to function in the destabilization of HKT1 protein under salt stress. Taken together, these results suggest that HA could be applied to the field to enhance plant growth and salt stress tolerance via post-transcriptional control of the HKT1 transporter gene under saline conditions.

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          Most cited references 74

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          Salt tolerance conferred by overexpression of a vacuolar Na+/H+ antiport in Arabidopsis.

          Agricultural productivity is severely affected by soil salinity. One possible mechanism by which plants could survive salt stress is to compartmentalize sodium ions away from the cytosol. Overexpression of a vacuolar Na+/H+ antiport from Arabidopsis thaliana in Arabidopsis plants promotes sustained growth and development in soil watered with up to 200 millimolar sodium chloride. This salinity tolerance was correlated with higher-than-normal levels of AtNHX1 transcripts, protein, and vacuolar Na+/H+ (sodium/proton) antiport activity. These results demonstrate the feasibility of engineering salt tolerance in plants.
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            Na+ tolerance and Na+ transport in higher plants.

             M. Tester (2003)
            Tolerance to high soil [Na(+)] involves processes in many different parts of the plant, and is manifested in a wide range of specializations at disparate levels of organization, such as gross morphology, membrane transport, biochemistry and gene transcription. Multiple adaptations to high [Na(+)] operate concurrently within a particular plant, and mechanisms of tolerance show large taxonomic variation. These mechanisms can occur in all cells within the plant, or can occur in specific cell types, reflecting adaptations at two major levels of organization: those that confer tolerance to individual cells, and those that contribute to tolerance not of cells per se, but of the whole plant. Salt-tolerant cells can contribute to salt tolerance of plants; but we suggest that equally important in a wide range of conditions are processes involving the management of Na(+) movements within the plant. These require specific cell types in specific locations within the plant catalysing transport in a coordinated manner. For further understanding of whole plant tolerance, we require more knowledge of cell-specific transport processes and the consequences of manipulation of transporters and signalling elements in specific cell types.
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              Regulation of SOS1, a plasma membrane Na+/H+ exchanger in Arabidopsis thaliana, by SOS2 and SOS3.

              Maintaining low levels of sodium ions in the cell cytosol is critical for plant growth and development. Biochemical studies suggest that Na(+)/H(+) exchangers in the plasma membrane of plant cells contribute to cellular sodium homeostasis by transporting sodium ions out of the cell; however, these exchangers have not been identified at the molecular level. Genetic analysis has linked components of the salt overly sensitive pathway (SOS1-3) to salt tolerance in Arabidopsis thaliana. The predicted SOS1 protein sequence and comparisons of sodium ion accumulation in wild-type and sos1 plants suggest that SOS1 is involved directly in the transport of sodium ions across the plasma membrane. To demonstrate the transport capability of SOS1, we studied Na(+)/H(+)-exchange activity in wild-type and sos plants using highly purified plasma membrane vesicles. The results showed that plasma membrane Na(+)/H(+)-exchange activity was present in wild-type plants treated with 250 mM NaCl, but this transport activity was reduced by 80% in similarly treated sos1 plants. In vitro addition of activated SOS2 protein (a protein kinase) increased Na(+)/H(+)-exchange activity in salt-treated wild-type plants 2-fold relative to transport without added protein. However, the addition of activated SOS2 did not have any stimulatory effect on the exchange activity in sos1 plants. Although vesicles of sos2 and sos3 plants had reduced plasma membrane Na(+)/H(+)-exchange activity, transport activity in both increased with the addition of activated SOS2 protein. These results demonstrate that SOS1 contributes to plasma membrane Na(+)/H(+) exchange and that SOS2 and SOS3 regulate SOS1 transport activity.
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                Author and article information

                Journal
                Mol Cells
                Mol. Cells
                ksmcb
                Molecules and Cells
                Korean Society for Molecular and Cellular Biology
                1016-8478
                0219-1032
                31 December 2017
                20 December 2017
                : 40
                : 12
                : 966-975
                Affiliations
                [1 ]Division of Applied Life Science (BK21Plus), Plant Molecular Biology and Biotechnology Research Center (PMBBRC), Research Institute of Life Sciences (RILS), Gyeongsang National University, Jinju 52828, Korea
                [2 ]Institute of Glocal Disease Control, Konkuk University, Seoul 05029, Korea
                [3 ]Department of Biomedical Science and Engineering, Konkuk University, Seoul 05029, Korea
                [4 ]Department of Agriculture Chemistry and Food Science & Technology, Institute of Agriculture and Life Science (IALS), Gyeongsang National University, Jinju 52828, Korea
                [5 ]College of Pharmacy and Research Institute of Pharmaceutical Science, PMBBRC, Gyeongsang National University, Jinju 52828, Korea
                Author notes
                [* ]Correspondence: kim1312@ 123456gnu.ac.kr (WYK); jycha@ 123456gnu.ac.kr (JYC)
                Article
                molce-40-12-966
                10.14348/molcells.2017.0229
                5750715
                29276942
                9af279c7-b4f1-45bc-9b98-1b9a72c601f7
                © The Korean Society for Molecular and Cellular Biology. All rights reserved.

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/.

                Categories
                Article

                arabidopsis, calcium, hkt1, humic acid, salt stress

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