Function, Intracellular Localization and the Importance in Salt Tolerance of a Vacuolar Na+/H+ Antiporter from Rice

Abstract

We examined the function and intracellular localization of the product of the Na(+)/H(+) antiporter gene (OsNHX1) cloned from rice (Oryza sativa). OsNHX1 has the ability to suppress Na(+), Li(+) and hygromycin sensitivity of yeast nhx1 mutants and sensitivity to a high K(+) concentration, a novel phenotype of the nhx1 mutants. Analysis using rice cells expressing a fusion protein of OsNHX1 and green fluorescent protein and Western blot analysis using antibodies specific for OsNHX1 confirmed the localization of OsNHX1 on the tonoplasts. These results indicate that the OsNHX1 gene encodes a vacuolar (Na(+), K(+))/H(+) antiporter. Treatment with high concentrations of NaCl and KCl increased the transcript levels of OsNHX1 in rice roots and shoots. In addition, overexpression of OsNHX1 improved the salt tolerance of transgenic rice cells and plants. These results suggest that OsNHX1 on the tonoplasts plays important roles in the compartmentation of Na(+) and K(+) highly accumulated in the cytoplasm into the vacuoles, and the amount of the antiporter is one of the most important factors determining salt tolerance in rice.

A Plant Ca2+ Pump, ACA2, Relieves Salt Hypersensitivity in Yeast

“…In plants, the significant contribution of the NHX1 homologue to salt tolerance is well documented (59,60). Interestingly, blocking a related kinase, Ca 2ϩ -dependent protein kinase, results in increases in [Na ϩ ] cyt in rice cells due to the lack of activation of a likely vacuolar Na ϩ /H ϩ antiporter (3).…”

Regulation by salt of vacuolar H+-ATPase and H+-pyrophosphatase activities and Na+/H+exchange

“…77 The overexpression of the Na + /H + antiporter gene clone from OsNHX1, improved the salt tolerance of transgenic rice cells and plants. 73 The role of tonoplast Na + /H + antiporter in plant salt tolerance has been reinforced by several evidences showing that exposure to salt promotes the increase of Na + /H + antiport activity 35,42,46,51,53,97,98 (Fig. 3).…”

“…3). Some reports show upregulation of NHX genes, 22,56,[72][73][74][75][76][77]79,80,99 increased protein abundance 56,[74][75][76] or regulation at protein activity level. 46,100 Garbarino and co-workers 97,100 have shown that the inducible Na + /H + antiporter activity observed in tonoplast from barley roots grown in the presence of NaCl was due to activation of an existing protein rather than to de novo protein synthesis, since the rapid induction was observed in the presence of inhibitors of protein synthesis.…”

“…71 The first plant Na + /H + antiporter, AtNHX1, was isolated from Arabidopsis by functional genetic complementation of a yeast mutant defective for endosomal Na + / H + activity, 21,22 and its overexpression suppressed some of the saltsensitive phenotypes of the nhx1 yeast strain. 22 Since then, several Na + /H + antiporter genes have been characterized in plants such as rice, 72,73 Atriplex gmelini, 74 B. vulgaris, 75 Brassica napus, 76 cotton, 77 wheat [78][79][80] and grapevine. 81 Six AtNHX isoforms were found in Arabidopsis, and for five of them Na + /H + transport activity has been demonstrated 82,83 (Fig.…”

Rice Shaker Potassium Channel OsKAT1 Confers Tolerance to Salinity Stress on Yeast and Rice Cells

“…In Arabidopsis (Arabidopsis thaliana), the plasma membrane Na 1 /H 1 antiporter SOS1 catalyzes Na 1 extrusion from cells (Shi et al, 2003). Vacuolar sequestration of Na 1 is also effective at lowering Na 1 concentration in the cytoplasm and is mediated by the NHX family of vacuolar Na 1 /H 1 antiporters, such as AtNHX1 in Arabidopsis (Apse et al, 1999) and OsNHX1 in rice (Fukuda et al, 2004). HKT-type transporters are involved in regulating cation homeostasis under salt stress in Arabidopsis (Sunarpi et al, 2005) and rice (Ren et al, 2005).…”