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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Loss of Halophytism by Interference with SOS1 Expression^1,[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.

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).

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.137802

^* Corresponding author; e-mail hbohnert{at}illinois.edu.

Received February 28, 2009; accepted June 27, 2009; published July 1, 2009.

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