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Soil Bacteria Confer Plant Salt Tolerance by Tissue-Specific Regulation of the Sodium Transporter HKT1

June 2008 , Volume 21 , Number  6
Pages  737 - 744

Huiming Zhang,1 Mi-Seong Kim,1 Yan Sun,1 Scot E. Dowd,2 Huazhong Shi,1 and Paul W. Paré1

1Texas Tech University; Department of Chemistry, Biochemistry and Biology Lubbock 79409, U.S.A.; 2United States Department of Agriculture--Agricultural Research Service, Livestock Issues Research Unit; RT 3 Box 214 FM 1294; Lubbock, TX 79403, U.S.A.

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Accepted 6 February 2008.

Elevated sodium (Na+) decreases plant growth and, thereby, agricultural productivity. The ion transporter high-affinity K+ transporter (HKT)1 controls Na+ import in roots, yet dysfunction or overexpression of HKT1 fails to increase salt tolerance, raising questions as to HKT1's role in regulating Na+ homeostasis. Here, we report that tissue-specific regulation of HKT1 by the soil bacterium Bacillus subtilis GB03 confers salt tolerance in Arabidopsis thaliana. Under salt stress (100 mM NaCl), GB03 concurrently down- and upregulates HKT1 expression in roots and shoots, respectively, resulting in lower Na+ accumulation throughout the plant compared with controls. Consistent with HKT1 participation in GB03-induced salt tolerance, GB03 fails to rescue salt-stressed athkt1 mutants from stunted foliar growth and elevated total Na+ whereas salt-stressed Na+ export mutants sos3 show GB03-induced salt tolerance with enhanced shoot and root growth as well as reduced total Na+. These results demonstrate that tissue-specific regulation of HKT1 is critical for managing Na+ homeostasis in salt-stressed plants, as well as underscore the breadth and sophistication of plant--microbe interactions.

© 2008 The American Phytopathological Society