| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
First published online July 1, 2009; 10.1104/pp.109.137802 Plant Physiology 151:210-222 (2009) © 2009 American Society of Plant Biologists OPEN ACCESS ARTICLE
Loss of Halophytism by Interference with SOS1 Expression1,[W],[OA]Departments of Plant Biology and Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (D.-H.O., Q.Z., Y.L., H.J.B.); Division of Applied Life Science (BK21 Program) and Environmental Biotechnology National Core Research Center, Graduate School of Gyeongsang National University, Jinju 660–701, Korea (D.-H.O., S.-M.H., S.Y.L., J.D.B., D.-J.Y.); Instituto de Recursos Naturales y Agrobiología, Consejo Superior de Investigaciones Científicas, Seville 41012, Spain (E.L., F.J.Q., X.J., J.M.P.), Key Laboratory of Plant Stress Research, College of Life Science, Shandong Normal University, Jinan 250014, China (Q.Z., Y.Z.); Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, Guangxi University, Nanning, Guangxi 530005, China (Y.L.); and Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907 (M.P.D., R.A.B.)
The contribution of SOS1 (for Salt Overly Sensitive 1), encoding a sodium/proton antiporter, to plant salinity tolerance was analyzed in wild-type and RNA interference (RNAi) lines of the halophytic Arabidopsis (Arabidopsis thaliana)-relative Thellungiella salsuginea. Under all conditions, SOS1 mRNA abundance was higher in Thellungiella than in Arabidopsis. Ectopic expression of the Thellungiella homolog ThSOS1 suppressed the salt-sensitive phenotype of a Saccharomyces cerevisiae strain lacking sodium ion (Na+) efflux transporters and increased salt tolerance of wild-type Arabidopsis. thsos1-RNAi lines of Thellungiella were highly salt sensitive. A representative line, thsos1-4, showed faster Na+ accumulation, more severe water loss in shoots under salt stress, and slower removal of Na+ from the root after removal of stress compared with the wild type. thsos1-4 showed drastically higher sodium-specific fluorescence visualized by CoroNa-Green, a sodium-specific fluorophore, than the wild type, inhibition of endocytosis in root tip cells, and cell death in the adjacent elongation zone. After prolonged stress, Na+ accumulated inside the pericycle in thsos1-4, while sodium was confined in vacuoles of epidermis and cortex cells in the wild type. RNAi-based interference of SOS1 caused cell death in the root elongation zone, accompanied by fragmentation of vacuoles, inhibition of endocytosis, and apoplastic sodium influx into the stele and hence the shoot. Reduction in SOS1 expression changed Thellungiella that normally can grow in seawater-strength sodium chloride solutions into a plant as sensitive to Na+ as Arabidopsis.
Accompanying the production and accumulation of osmolytes and other protective molecules, an important aspect of plant responses leading to salt stress tolerance is the regulation of uptake, reexport, and control over the distribution of sodium ions (Na+; Hasegawa et al., 2000  ; Tester and Davenport, 2003). Na+ appear to enter the root by several pathways (Essah et al., 2003; Pardo et al., 2006), although the nature of participating genes and their interaction in pathways require further investigation. Once Na+ has entered the root endodermis, a tissue that represents a barrier to ions (Peng et al., 2004), it is generally assumed that the ion enters the xylem following the movement of water to aerial parts of the plant. Despite substantial efflux of Na+ across the plasma membrane of root cells, the net flux of Na+ is unidirectional from soil to roots and then to the shoot, except for possible recirculation via the phloem (Tester and Davenport, 2003). In a range of species, the severity of damaging symptoms is positively correlated with the content of Na+ reaching photosynthetic tissues (Davenport et al., 2005; Ren et al., 2005; Munns et al., 2006). However, halophytic species can accumulate very high amounts of Na+ in vacuoles, such that Na+ may account for most of the total cellular osmotic potential (Tester and Davenport, 2003), and the presence of Na+ accelerates growth in euhalophytes to some degree (Adams et al., 1998). Emerging as the major advantage of halophytes appears to be their exceptional control over Na+ influx combined with export mechanisms, the ability to coordinate its distribution to various tissues, and efficient sequestration of Na+ into vacuoles. These characteristics are of particular advantage when plants are subjected to a sudden increase of Na+ salts in their environment (Hasegawa et al., 2000), whereas gradual increases in Na+ may be tolerated even by plants that are not halophytic in nature.
Na+-ATPases, major Na+ export systems in organisms such as fungi and the moss Physcomitrella patens, have not been found in higher plants (Lunde et al., 2007
In Arabidopsis, the SOS1 gene is most strongly expressed in the epidermis of the root tip region and in cells adjacent to vascular tissues (Shi et al., 2002
Thellungiella salsuginea (salt cress), which had before been called T. halophila by us, is a close relative of Arabidopsis, which has become a model to study the genetic basis of this plant's extreme tolerance to a variety of abiotic stress factors, including salinity (Inan et al., 2004 Here, we wished to explore the role(s) by which ThSOS1, the SOS1 homolog in Thellungiella, could be involved in shaping the halophytic character of the species using ectopic expression of the gene in yeast and in Arabidopsis and Thellungiella SOS1-RNA interference (RNAi) lines. The results identified ThSOS1 as a genetic element whose activity limits Na+ accumulation and affects the distribution of Na+ ions at high concentration, thus acting as a major tolerance determinant.
Thellungiella Expresses SOS1 at Higher Levels Than Arabidopsis
ThSOS1 (EF207775) is most closely related to Arabidopsis SOS1 (AtSOS1; At2g01980) in the deduced amino acid sequences (83% identity) among SOS1 coding regions from other plants (Supplemental Fig. S1). ThSOS1 exists as a single-copy gene in the Thellungiella genome (data not shown). Transcript abundance of SOS1 was compared between Arabidopsis and Thellungiella by reverse transcription (RT)-PCR. Reference genes were selected among genes more than 90% identical in their sequence identities between both species, while they showed unaltered expression levels under stress conditions (Czechowski et al., 2005
ThSOS1 Expression Suppressed the Salt-Sensitive Phenotype of a Yeast Strain Lacking Na+ Transporters and Increased the Salt Tolerance in Arabidopsis
The Saccharomyces cerevisiae strain AXT3K (
Transgenic Arabidopsis expressing ThSOS1 under control of the cauliflower mosaic virus-35S promoter were analyzed together with AtSOS1-overexpressing lines (Shi et al., 2003 ) for SOS1 expression and salt tolerance (Fig. 3
). The transgenic lines showed various levels of SOS1 expression, highest in a ThSOS1-overexpressing line (Fig. 3A, line 30). The survival rates of the wild type and SOS1-overexpressing lines were quantified by rescuing the seedlings onto nonsaline medium after a brief stress. Seedlings that resumed growth were counted as survivors (Fig. 3B). The survival rates of SOS1-overexpressing lines were proportional to the level of SOS1 under stress (r2 = 0.95), regardless of SOS1 origin, indicating that expression strength/mRNA stability or protein amount/activity are determining factors in tolerance acquisition. However, even the highest tolerance observed in line 30 (Fig. 3B) did not approach that shown by wild-type Thellungiella (Inan et al., 2004).
RNAi-Based Reduction of ThSOS1 Expression Resulted in Decreased Salt Tolerance with Faster Na+ Accumulation in Shoots We have developed transgenic Thellungiella transformed with a ThSOS1 RNAi vector (Fig. 4A ). Two lines, designated thsos1-4 and thsos1-6, were used for further analyses. Both showed 3:1 segregation in BASTA resistance and salt sensitivity, indicating a single insertion locus of the RNAi construct (data not shown).
Seedlings on plates (Fig. 4B) and mature plants grown in artificial soil (Supplemental Fig. S3A) showed a salt-sensitive phenotype in the RNAi lines. Shoots of RNAi line plants showed partial bleaching and root growth stopped at 200 mM NaCl, while the wild type and vector control (thsos1-11) continued to grow without symptoms in NaCl solutions up to 300 mM (Fig. 4, B and C). The abundance of ThSOS1 mRNA was determined by quantitative real-time PCR in roots and shoots with or without salt stress. The decline of SOS1 mRNA by RNAi was more prominent under salt stress, where thsos1-4 showed 30% and 84% and thsos1-6 showed 17% and 40% of wild-type expression in the shoot and root, respectively (Fig. 4D). A similar reduction in SOS1 transcript amount persisted throughout development and at different strengths of NaCl (Supplemental Figs. S3B and S5). The vector control (thsos1-11) showed no significant difference in ThSOS1 expression from the wild type (data not shown). To further characterize the role of ThSOS1 in the stress response, 2-week-old plants of wild type and thsos1-4 were transferred to 200 mM NaCl and fresh weight and water and ion contents of shoots were measured, using inductively coupled plasma-optical emission spectrometry. Wild-type shoots continued to gain weight, but thsos1-4 shoots showed no growth after day 4 (Fig. 5A ). Water content was deduced from a comparison of the fresh and dry weights of seedling shoots. Salt-stressed wild-type shoots maintained water content slightly lower than the unstressed control throughout the experiments. However, a more significant decrease in water content in thsos1-4 shoots became apparent after 7 d (Fig. 5B). In contrast to the wild type, which showed a linear, gradual increase of Na+ in the leaves, sodium content in thsos1-4 leaves peaked by day 4 and later declined, most probably by leakage due to the loss of water (Fig. 5C). Loss of potassium was observed in both the wild type and thsos1-4, with a seemingly insignificant higher decrease in thsos1-4 during later times of the experiment (Fig. 5D). These results already pointed to ThSOS1 as important and required for the ability to tolerate extremely high levels of NaCl.
The changes in ion content of stressed plants after removal of the stress were compared between the wild type and thsos1-4 (Fig. 6 ). Hydroponically grown plants were treated by increasing NaCl stepwise to the nonlethal concentration of 150 mM within 2 weeks, transferred to medium without NaCl, and harvested to determine Na+ and K+ concentrations. Both shoots and roots of thsos1-4 showed higher Na+ (Fig. 6, A and C) and lower K+ (Fig. 6, B and D) contents compared with the wild type. In the wild type, shoot ion contents did not change over a 72-h period after removal of the plants from NaCl solutions, while thsos1-4 showed gradual decreases in Na+ and increases in K+, eventually converging on the Na+ contents observed in the wild type (Fig. 6, A and B). The roots of wild-type plants exhibited a sharp drop in Na+ ion content within 1 h after removal of NaCl, while the efflux of Na+ ions was much slower in thsos1-4 roots, which failed to reach the level of Na+ content in the wild type at 72 h (Fig. 6C). To assess the contribution of ThSOS1 to the reduction of net sodium uptake in the short term, wild-type and thsos1-4 plants were transferred to hydroponic medium supplemented with 0.1, 1, and 10 mM and the Na+ content was determined after 15 and 30 min and 2 and 48 h. Roots of line thsos1-4 started to show significantly greater Na+ contents than the wild type after 2 h of salt imposition (Supplemental Fig. S4).
Down-Regulation of ThSOS1 Resulted in Increased Sodium Accumulation in the Root Tip and Cell Death in the Elongation Zone To determine the role of ThSOS1 in specific cell types in the roots, the distribution of sodium was imaged using the fluorescent, sodium-specific dye CoroNa-Green AM (Invitrogen), as outlined in "Materials and Methods," comparing wild-type and thsos1-4 seedling roots by confocal microscopy. Incubations in 150 mM NaCl did not result in rapid differences between the wild type and thsos1-4, but within 24 h thsos1-4 roots showed higher fluorescence in the meristematic region than the wild type (Fig. 7, A and B ). When the vacuolar fluorescence intensities of root cortex cells from five individual plants from each line were quantified, the wild type showed a mean relative value of fluorescence intensity of 29.68 (SD = 9.43; arbitrary units), while the mean was 68.80 (SD = 16.89) for thsos1-4 (Fig. 7C).
Cellular events in the root tip region at this time point were observed by CoroNa Green AM and FM4-64 (Invitrogen). In the wild type, CoroNa Green specifically stained the prevacuolar compartment of irregular shape in the meristematic and expanding cells (Fig. 7D). Cells of thsos1-4 showed significantly stronger CoroNa-Green fluorescence in small round intracellular vacuoles, which converged into one or two large bodies within 24 h in medium with 150 mM NaCl (Fig. 7E). Interestingly, the endocytotic inclusion of the FM4-64 dye, which was apparent in the wild type (Fig. 7D, arrows in inset), was absent in thsos1-4 root cells (Fig. 7E, inset). Neither the shape of vacuoles nor endocytosis was affected under normal conditions in the wild type or thsos1-4 (data not shown). Whereas wild-type plants did not show any symptoms even during longer term exposure to salt (Fig. 7F), increasing Na+-specific fluorescence in thsos1-4 was followed by cell death within and adjacent to the elongation zone, visualized by intracellular staining of propidium iodide (Fig. 7G, arrow). The number of thsos1-4 seedlings showing higher fluorescence and/or cell death at the root tip and elongation zone increased to two-third of the tested seedlings (10 of 15) within 36 h of stress, and the primary root of all thsos1-4 seedlings (10 of 10) had died within 48 h.
To visualize Na+ distribution in the stele, wild-type and thsos1-4 seedlings were incubated for longer times at low concentrations of CoroNa Green (see "Materials and Methods"). Fluorescein diacetate was used as a control in separate experiments to ensure that dyes penetrated to the vasculature (data not shown). In the wild type, Na+ was confined in the vacuoles of epidermis, cortex, and, less pronounced, endodermis cells, and fluorescence was absent from pericycle cells and cells within the vasculature after treatment with 150 mM NaCl for up to 4 d (Fig. 8, A, B, E, G, and I
). In contrast, cell damage in the elongation zone in thsos1-4 extended to the older sections of the root as the stress continued (Fig. 8, C and D), resulting in compromised cells with intensive intracellular staining of propidium iodide (Fig. 8F, arrow 1). Strongest CoroNa Green fluorescence was observed in cells adjacent to structurally compromised cells (Fig. 8F, arrow 2). While epidermis and cortex cells were either terminally damaged or failed to confine Na+ to vacuoles, the Na+-specific fluorescence was also found in cells inside the pericycle (Fig. 8H, arrows). Within 4 d of incubation, pericycle cells revealed damage and CoroNa Green stained xylem vessels (Fig. 8J) in thsos1-4 at the low concentration of NaCl (150 mM), which was not recognized in wild-type plants as a stressful condition, as shown in Figure 8I and also suggested by microarray experiments (Gong et al., 2005
The higher accumulation of Na+ ions inside the endodermis of thsos1-4 was confirmed by scanning electron microscopy and energy-dispersive x-ray microanalysis (SEM-EDX) in the roots of mature plants (Fig. 9 ). After treatment with 250 mM NaCl for 2 d, thsos1-4 root accumulated more than twice the amount of Na+ than wild-type root, concurrent with a dramatic decrease of K+ in the vacuole of xylem parenchyma that resulted in a more than 12 times higher Na+-K+ ratio. In contrast, cortex cells did not show a significant difference between the wild type and thsos1-4.
In Arabidopsis, the SOS pathway has been documented as an essential component of the ion homeostasis system. The known signal transduction components of the pathway, a complex of SOS2 and SOS3, control the activity of SOS1, a plasma membrane-localized Na+/H+ antiporter (Qiu et al., 2002 ; Quintero et al., 2002; Chinnusamy et al., 2006). The importance of this mechanism in the glycophyte Arabidopsis notwithstanding (Shi et al., 2002, 2003), questions remained about the relative impact of this pathway in a naturally salt-tolerant species. We used the halophytic Arabidopsis relative Thellungiella (Bressan et al., 2001) to address this question.
While the sequence of SOS1 is highly conserved between Thellungiella and Arabidopsis (Oh et al., 2007 Complementation by SOS1 cDNAs of a yeast mutant lacking Na+ transporters suggested that ThSOS1 can function in Na+ exclusion more efficiently than AtSOS1, especially at higher levels of NaCl (Fig. 2, A and B). Coexpression of AtSOS2/3 indicated that ThSOS1 was activated by Arabidopsis SOS signaling components (Fig. 2B), indicating conservation of the pathway in Thellungiella. However, no significant differences in Na+/H+ exchange rates were found in plasma membrane vesicles from cells expressing AtSOS1 or ThSOS1 (Fig. 2D). These results indicate that the two highly conserved SOS1 proteins are substantially equivalent, and the long-term effect of differential specific activity or protein abundance, too subtle to be discriminated in transport ion assays, may become amplified over time to render cells with improved salt tolerance. This is in agreement with the correlation between the salt tolerance of Arabidopsis transgenic lines and the expression level of SOS1, regardless of the origin of the protein (Fig. 3).
Sodium fluxes into and out of Thellungiella roots have been studied in comparison with Arabidopsis (Wang et al., 2006
The RNAi-induced reduction of SOS1 led to faster leaf senescence accompanied by severe shoot water loss during salt stress (Figs. 4B and 5B; Supplemental Fig. S3A). This water loss in RNAi lines was not based on impaired stomatal conductance, as the RNAi plants showed severe stress symptoms even at 100% humidity (data not shown). The phenotype was strictly Na+ specific; the RNAi lines did not show differences compared with the wild type at K+ concentrations up to 300 mM (Fig. 4B). The phenotype rather appeared related to the rate of Na+ accumulation during the initial stages of exposure to high Na+ and not to the absolute amount of Na+ in the shoots after long-term exposure. Generally, tolerant species that have been categorized as Na+ excluders accumulate large amounts of the ion over time, but this accumulation proceeds more slowly than in sensitive "sodium-including" species (Tester and Davenport, 2003
A main objective was to observe the accumulation and distribution of Na+ ions in cell lineages of the root, considering that we lack information on the genetic makeup that allows halophytic multicellular plants to achieve control over the rate of Na+ accumulation. Sodium uptake was followed using the membrane-permeable fluorescent dye CoroNa-Green that binds Na+ ions only after it has been confined within cells (Meier et al., 2006
Early during salt stress, thsos1-4 roots showed little differences when compared with the wild type in intensity or distribution of the Na+-specific fluorescence (data not shown). Observable changes eventually originated at the root tip region, which began to show stronger fluorescence signals in thsos1-4, indicating SOS1's function in Na+ exclusion (Fig. 7, A–C). Propidium iodide, which stained cell walls and dead cells, revealed that increased Na+ fluorescence was accompanied by a gradual loss of membrane integrity, initially confined to cells of the elongation zone (Fig. 7G), spreading to cells of the root hair zone over time (Fig. 8, C and F). It appears that Na+ exclusion by SOS1 is most critical in cells that expand and consequently take up water, whereas cells closer to the quiescent center seem to be protected by the absence of large vacuoles. These observations correspond with results from a recent study that identified the beginning of the elongation zone as the most responsive to salt stress along the longitudinal axis of the primary root (Dinneny et al., 2008
In roots incubated for an extended time (18 h) with the dye, wild-type plants showed significantly lower Na+-specific fluorescence in cells of the pericycle and the stele (Fig. 8, E, G, and I). This visual observation matched studies using x-ray microanalysis for the localization of Na+ in roots and confirmed the root endodermis as a major barrier controlling ion influx into the stele (Peng et al., 2004
New evidence has revealed SOS1 and the SOS pathway with a function not only as a Na+ exporter but as a mediator of intracellular Ca2+ and pH homeostasis (Cheng et al., 2004
SOS1 activity could protect endocytosis of cells in the root tip and elongation zone and ultimately sustain membrane integrity, thus providing an essential stop-gap measure or temporary protective solution allowing for other defensive measures to become established in the plants. Supporting this view is the fact that cells in Thellungiella wild-type roots that developed after the plants had adapted to increased salinity showed a stronger fluorescence than cells that developed during the stress imposition period (Fig. 8B, compare areas 1 and 2). Apparently, the halophyte achieved adaptation in newly developed root cells within less than 2 d, which was absent from thsos1-4 roots that suffered extensive damage, cell death, and uncontrolled apoplastic Na+ influx into the root stele and shoot (Fig. 8D). Stress "preparedness" by Thellungiella seems to extend to other functions, because the plant contains, compared with Arabidopsis, higher amounts of metabolites, including Pro, trehalose, inositols, and several organic acids and substantially unique yet unknown compounds (Taji et al., 2004
Transformation of Yeast and Plants
Transformation and salt treatment of yeast AXT3K mutant and Arabidopsis (Arabidopsis thaliana Columbia wild type) were performed as described (Shi et al., 2003
All plants were grown under 14-h-day and 10-h-night conditions. For the assessment of salt tolerance of Arabidopsis expressing ThSOS1 and AtSOS1, seedlings were transferred to medium containing 200 mM NaCl as described (Shi et al., 2003
All analyses used pools of 10 plants for each sample. For the interspecific comparison, 2-week-old (for Arabidopsis) or 3-week-old (for Thellungiella) plants, thus accounting for identical growth stage (Gong et al., 2005
For measurement of ion contents in the seedling shoot, medium containing 200 mM NaCl was placed in single compartments of a half-divided petri dish. Two-week-old seedlings were grown vertically with their shoot placed in the empty compartment not contacting the medium. Harvested shoot samples were dried, dissolved in HNO3, and analyzed by inductively coupled plasma-optical emission spectrometry (Optima 2000; Perkin-Elmer). For measurement of ion contents in hydoponically grown plants, atomic absorption spectrophotometry (Perkin-Elmer 1100B) was applied to saps extracted from leaf and root frozen samples as described (Gorham et al., 1994 SEM-EDX was used on frozen sections of leaves and roots harvested from 3-week-old hydroponically grown plants. Samples were mounted in slots of copper holders, fixed with OCT Compound (BDH), and dipped into a bath of slush nitrogen prior to transfer under vacuum into the cryopreparation chamber (CT1500; Oxford Instruments) attached to the scanning electron microscope (DSM 960; Zeiss). The chamber temperature was left to rise from –163°C to –90°C and set for 10 min for ice sublimation before sputter coating with gold (2 min). Samples were analyzed with an ATW detector interfaced with a Link ISIS analyzer (Oxford Instruments) under the following conditions: accelerating voltage, 15 kV; takeoff angle, 42°C; collecting time of x-ray counts, 100 s; working distance between sample and detector, 24 mm. Measurements were performed by focusing on exposed vacuoles of specific cells.
Vesicles of the yeast plasma membrane were produced by two-phase partitioning as described previously (Martinez-Atienza et al., 2007
One week-old seedlings were stained and observed by confocal microscopy (TCS SP2 RBB; Leica) after salt treatment on medium containing 1.1% type A agar (Sigma-Aldrich). Staining to reveal Na+ content was performed as described (Mazel et al., 2004
The following materials are available in the online version of this article.
We thank Drs. Qingqui Gong, Shisong Ma, and Valeriy Poroyko for discussions and Drs. Francoise Quigley and Valeriy Poroyko for Thellungiella SOS1 cDNAs. Received February 28, 2009; accepted June 27, 2009; published July 1, 2009.
1 This work was supported by the World Class University Program (grant no. R32–10148), the Environmental Biotechnology National Core Research Center Project (grant no. R15–2003–012–01002–00), the Biogreen 21 Project of the Rural Development Administration (grant no. 20070301034030), the National Science Foundation (grant no. DBI–0223905), University of Illinois at Urbana-Champaign and Purdue University institutional funds, the Spanish Ministerio de Ciencia e Innovacion (grant no. BFU2006–06968), and the Brain Korea 21 Program (scholarships to S.-M.H.).  The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Hans J. Bohnert (hbohnert{at}illinois.edu).
[W] The online version of this article contains Web-only data.
[OA] Open Access articles can be viewed online without a subscription. www.plantphysiol.org/cgi/doi/10.1104/pp.109.137802 * Corresponding author; e-mail hbohnert{at}illinois.edu.
Adams P, Nelson DE, Yamada S, Chmara W, Jensen RG, Bohnert HJ, Griffiths H (1998) Growth and development of Mesembryanthemum crystallinum (Aizoaceae). New Phytol 138: 171–190[CrossRef][Web of Science] Amtmann A (2009) Learning from evolution: Thellungiella generates new knowledge on essential and critical components of abiotic stress tolerance in plants. Mol Plant 2: 3–12 Berthomieu P, Conejero G, Nublat A, Brackenbury WJ, Lambert C, Savio C, Uozumi N, Oiki S, Yamada K, Cellier F, et al (2003) Functional analysis of AtHKT1 in Arabidopsis shows that Na+ recirculation by the phloem is crucial for salt tolerance. EMBO J 22: 2004–2014[CrossRef][Web of Science][Medline] Bressan RA, Zhang C, Zhang H, Hasegawa PM, Bohnert HJ, Zhu JK (2001) Learning from the Arabidopsis experience: the next gene search paradigm. Plant Physiol 127: 1354–1360 Cheng NH, Pittman JK, Zhu JK, Hirschi KD (2004) The protein kinase SOS2 activates the Arabidopsis H+/Ca2+ antiporter CAX1 to integrate calcium transport and salt tolerance. J Biol Chem 279: 2922–2926 Chinnusamy V, Zhu J, Zhu JK (2006) Salt stress signaling and mechanisms of plant salt tolerance. Genet Eng (N Y) 27: 141–177[CrossRef][Medline] Chung JS, Zhu JK, Bressan RA, Hasegawa PM, Shi H (2008) Reactive oxygen species mediate Na+-induced SOS1 mRNA stability in Arabidopsis. Plant J 53: 554–565[CrossRef][Web of Science][Medline] Czechowski T, Stitt M, Altmann T, Udvardi MK, Scheible WR (2005) Genome-wide identification and testing of superior reference genes for transcript normalization in Arabidopsis. Plant Physiol 139: 5–17 Davenport R, James RA, Zakrisson-Plogander A, Tester M, Munns R (2005) Control of sodium transport in durum wheat. Plant Physiol 137: 807–818 Demidchik V, Maathuis FJ (2007) Physiological roles of nonselective cation channels in plants: from salt stress to signalling and development. New Phytol 175: 387–404[CrossRef][Web of Science][Medline] Dhonukshe P, Aniento F, Hwang I, Robinson DG, Mravec J, Stierhof YD, Friml J (2007) Clathrin-mediated constitutive endocytosis of PIN auxin efflux carriers in Arabidopsis. Curr Biol 17: 520–527[CrossRef][Medline] Dhonukshe P, Baluska F, Schlicht M, Hlavacka A, Samaj J, Friml J, Gadella TW Jr (2006) Endocytosis of cell surface material mediates cell plate formation during plant cytokinesis. Dev Cell 10: 137–150[CrossRef][Web of Science][Medline] Dinneny JR, Long TA, Wang JY, Jung JW, Mace D, Pointer S, Barron C, Brady SM, Schiefelbein J, Benfey PN (2008) Cell identity mediates the response of Arabidopsis roots to abiotic stress. Science 320: 942–945 Essah PA, Davenport R, Tester M (2003) Sodium influx and accumulation in Arabidopsis. Plant Physiol 133: 307–318 Geldner N, Hyman DL, Wang X, Schumacher K, Chory J (2007) Endosomal signaling of plant steroid receptor kinase BRI1. Genes Dev 21: 1598–1602 Gong Q, Li P, Ma S, Indu Rupassara S, Bohnert HJ (2005) Salinity stress adaptation competence in the extremophile Thellungiella halophila in comparison with its relative Arabidopsis thaliana. Plant J 44: 826–839[Web of Science][Medline] Gorham J, Papa R, Aloy-Lleonart M (1994) Varietal differences in sodium uptake in barley cultivars exposed to soil salinity or salt spray. J Exp Bot 45: 895–901 Hasegawa PM, Bressan RA, Zhu JK, Bohnert HJ (2000) Plant cellular and molecular responses to high salinity. Annu Rev Plant Physiol Plant Mol Biol 51: 463–499[CrossRef][Web of Science] Inan G, Zhang Q, Li P, Wang Z, Cao Z, Zhang H, Zhang C, Quist TM, Goodwin SM, Zhu J, et al (2004) Salt cress: a halophyte and cryophyte Arabidopsis relative model system and its applicability to molecular genetic analyses of growth and development of extremophiles. Plant Physiol 135: 1718–1737 Katiyar-Agarwal S, Zhu J, Kim K, Agarwal M, Fu X, Huang A, Zhu JK (2006) The plasma membrane Na+/H+ antiporter SOS1 interacts with RCD1 and functions in oxidative stress tolerance in Arabidopsis. Proc Natl Acad Sci USA 103: 18816–18821 Kawasaki S, Borchert C, Deyholos M, Wang H, Brazille S, Kawai K, Galbraith D, Bohnert HJ (2001) Gene expression profiles during the initial phase of salt stress in rice. Plant Cell 13: 889–905 Läuchli A, James RA, Huang CX, McCully M, Munns R (2008) Cell-specific localization of Na+ in roots of durum wheat and possible control points for salt exclusion. Plant Cell Environ 31: 1565–1574[Medline] Leshem Y, Melamed-Book N, Cagnac O, Ronen G, Nishri Y, Solomon M, Cohen G, Levine A (2006) Suppression of Arabidopsis vesicle-SNARE expression inhibited fusion of H2O2-containing vesicles with tonoplast and increased salt tolerance. Proc Natl Acad Sci USA 103: 18008–18013 Li J, Yang H, Peer WA, Richter G, Blakeslee J, Bandyopadhyay A, Titapiwantakun B, Undurraga S, Khodakovskaya M, Richards EL, et al (2005) Arabidopsis H+-PPase AVP1 regulates auxin-mediated organ development. Science 310: 121–125 Lunde C, Drew DP, Jacobs AK, Tester M (2007) Exclusion of Na+ via sodium ATPase (PpENA1) ensures normal growth of Physcomitrella patens under moderate salt stress. Plant Physiol 144: 1786–1796 Martinez-Atienza J, Jiang X, Garciadeblas B, Mendoza I, Zhu JK, Pardo JM, Quintero FJ (2007) Conservation of the salt overly sensitive pathway in rice. Plant Physiol 143: 1001–1012 Mazel A, Leshem Y, Tiwari BS, Levine A (2004) Induction of salt and osmotic stress tolerance by overexpression of an intracellular vesicle trafficking protein AtRab7 (AtRabG3e). Plant Physiol 134: 118–128 Meier SD, Kovalchuk Y, Rose CR (2006) Properties of the new fluorescent Na+ indicator CoroNa Green: comparison with SBFI and confocal Na+ imaging. J Neurosci Methods 155: 251–259[CrossRef][Web of Science][Medline] Munns R, James RA, Lauchli A (2006) Approaches to increasing the salt tolerance of wheat and other cereals. J Exp Bot 57: 1025–1043 Murphy AS, Bandyopadhyay A, Holstein SE, Peer WA (2005) Endocytotic cycling of PM proteins. Annu Rev Plant Biol 56: 221–251[CrossRef][Medline] Oh DH, Gong Q, Ulanov A, Zhang Q, Li Y, Ma W, Yun DJ, Bressan RA, Bohnert HJ (2007) Sodium stress in the halophyte Thellungiella halophila and transcriptional changes in a thsos1-RNA interference line. J Integr Plant Biol 49: 1484–1496[CrossRef][Web of Science] Ottow EA, Brinker M, Teichmann T, Fritz E, Kaiser W, Brosche M, Kangasjarvi J, Jiang X, Polle A (2005) Populus euphratica displays apoplastic sodium accumulation, osmotic adjustment by decreases in calcium and soluble carbohydrates, and develops leaf succulence under salt stress. Plant Physiol 139: 1762–1772 Pardo JM, Cubero B, Leidi EO, Quintero FJ (2006) Alkali cation exchangers: roles in cellular homeostasis and stress tolerance. J Exp Bot 57: 1181–1199 Peng YH, Zhu YF, Mao YQ, Wang SM, Su WA, Tang ZC (2004) Alkali grass resists salt stress through high [K+] and an endodermis barrier to Na+. J Exp Bot 55: 939–949 Qiu QS, Guo Y, Dietrich MA, Schumaker KS, Zhu JK (2002) Regulation of SOS1, a plasma membrane Na+/H+ exchanger in Arabidopsis thaliana, by SOS2 and SOS3. Proc Natl Acad Sci USA 99: 8436–8441 Quintero FJ, Ohta M, Shi H, Zhu JK, Pardo JM (2002) Reconstitution in yeast of the Arabidopsis SOS signaling pathway for Na+ homeostasis. Proc Natl Acad Sci USA 99: 9061–9066 Reichardt I, Stierhof YD, Mayer U, Richter S, Schwarz H, Schumacher K, Jurgens G (2007) Plant cytokinesis requires de novo secretory trafficking but not endocytosis. Curr Biol 17: 2047–2053[CrossRef][Web of Science][Medline] Ren ZH, Gao JP, Li LG, Cai XL, Huang W, Chao DY, Zhu MZ, Wang ZY, Luan S, Lin HX (2005) A rice quantitative trait locus for salt tolerance encodes a sodium transporter. Nat Genet 37: 1141–1146[CrossRef][Web of Science][Medline] Rus A, Lee BH, Munoz-Mayor A, Sharkhuu A, Miura K, Zhu JK, Bressan RA, Hasegawa PM (2004) AtHKT1 facilitates Na+ homeostasis and K+ nutrition in planta. Plant Physiol 136: 2500–2511 Shabala L, Cuin TA, Newman IA, Shabala S (2005) Salinity-induced ion flux patterns from the excised roots of Arabidopsis sos mutants. Planta 222: 1041–1050[CrossRef][Web of Science][Medline] Shi H, Ishitani M, Kim C, Zhu JK (2000) The Arabidopsis thaliana salt tolerance gene SOS1 encodes a putative Na+/H+ antiporter. Proc Natl Acad Sci USA 97: 6896–6901 Shi H, Lee BH, Wu SJ, Zhu JK (2003) Overexpression of a plasma membrane Na+/H+ antiporter gene improves salt tolerance in Arabidopsis thaliana. Nat Biotechnol 21: 81–85[CrossRef][Web of Science][Medline] Shi H, Quintero FJ, Pardo JM, Zhu JK (2002) The putative plasma membrane Na+/H+ antiporter SOS1 controls long-distance Na+ transport in plants. Plant Cell 14: 465–477 Shoji T, Suzuki K, Abe T, Kaneko Y, Shi H, Zhu JK, Rus A, Hasegawa PM, Hashimoto T (2006) Salt stress affects cortical microtubule organization and helical growth in Arabidopsis. Plant Cell Physiol 47: 1158–1168 Soldati T, Schliwa M (2006) Powering membrane traffic in endocytosis and recycling. Nat Rev Mol Cell Biol 7: 897–908[CrossRef][Web of Science][Medline] Sun F, Zhang W, Hu H, Li B, Wang Y, Zhao Y, Li K, Liu M, Li X (2008) Salt modulates gravity signaling pathway to regulate growth direction of primary roots in Arabidopsis. Plant Physiol 146: 178–188 Sutter JU, Sieben C, Hartel A, Eisenach C, Thiel G, Blatt MR (2007) Abscisic acid triggers the endocytosis of the Arabidopsis KAT1 K+ channel and its recycling to the plasma membrane. Curr Biol 17: 1396–1402[CrossRef][Medline] Taji T, Seki M, Satou M, Sakurai T, Kobayashi M, Ishiyama K, Narusaka Y, Narusaka M, Zhu JK, Shinozaki K (2004) Comparative genomics in salt tolerance between Arabidopsis and Arabidopsis-related halophyte salt cress using Arabidopsis microarray. Plant Physiol 135: 1697–1709 Tester M, Davenport R (2003) Na+ tolerance and Na+ transport in higher plants. Ann Bot (Lond) 91: 503–527 Vera-Estrella R, Barkla BJ, Garcia-Ramirez L, Pantoja O (2005) Salt stress in Thellungiella halophila activates Na+ transport mechanisms required for salinity tolerance. Plant Physiol 139: 1507–1517 Volkov V, Amtmann A (2006) Thellungiella halophila, a salt-tolerant relative of Arabidopsis thaliana, has specific root ion-channel features supporting K+/Na+ homeostasis under salinity stress. Plant J 48: 342–353[CrossRef][Web of Science][Medline] Wang B, Davenport RJ, Volkov V, Amtmann A (2006) Low unidirectional sodium influx into root cells restricts net sodium accumulation in Thellungiella halophila, a salt-tolerant relative of Arabidopsis thaliana. J Exp Bot 57: 1161–1170 Yamaguchi T, Aharon GS, Sottosanto JB, Blumwald E (2005) Vacuolar Na+/H+ antiporter cation selectivity is regulated by calmodulin from within the vacuole in a Ca2+- and pH-dependent manner. Proc Natl Acad Sci USA 102: 16107–16112 Related articles in Plant Physiol.:
This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ASPB Publications | PLANT PHYSIOLOGY® | THE PLANT CELL | |
|---|---|---|---|
TOP
ABSTRACT
RESULTS
(EF1
ena1-4 
