This Article Full Text (PDF) All Versions of this Article: 21/7/1875    most recent tpc.109.210710v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Plant Cell Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Farquharson, K. L. Search for Related Content PubMed PubMed Citation Articles by Farquharson, K. L. Agricola Articles by Farquharson, K. L.

IN BRIEF

Targeted Overexpression of a Sodium Transporter in the Root Stele Increases Salinity Tolerance

Science Editor

kfarquharson{at}aspb.org

Soil salinity poses a major threat to global agricultural productivity. An elevated concentration of shoot Na⁺ causes stress in many crops growing in saline soils (reviewed in Tester and Davenport, 2003). Arabidopsis HKT1;1 (for high affinity potassium transporter1;1), a plasma membrane protein expressed in the root stele, mediates salinity tolerance by retrieving Na⁺ from the transpiration stream and thereby reducing Na⁺ levels in the shoot (Mäser et al., 2002; Sunarpi et al., 2005; Davenport et al., 2007).

In an effort to boost salinity tolerance by minimizing Na⁺ accumulation in Arabidopsis shoots, Møller et al. (pages 2163–2178) produced plants that overexpress HKT1;1 either constitutively or in a cell-type–specific manner. They used an enhancer trap system to generate plants that overexpress HKT1;1 specifically in (1) the pericycle and (2) the vascular bundle of the stele of mature roots. Cell-type specificity of the transgene was confirmed by RT-PCR analysis of laser-dissected stelar root cells and by mRNA in situ hybridization. Furthermore, patch clamp analysis showed that protoplasts derived from pericycle cells overexpressing HKT1;1 had an increased electrogenic transport capacity for Na⁺, which is consistent with increased amounts of active HKT1;1 protein being present in the plasma membrane.

The researchers monitored the effect of overexpression of HKT1;1 on Na⁺ transport using radiolabeled sodium (²²Na⁺). Whereas targeted overexpression of HKT1;1 did not affect the unidirectional influx of ²²Na⁺ into the roots, stelar-specific overexpression of HKT1;1 decreased ²²Na⁺ flux from the roots to the shoot by 28 to 59%. Inductively coupled plasma atomic emission spectroscopy analysis confirmed that overexpression of HKT1;1 specifically in the stele reduced the concentration of Na⁺ in the shoot by 37 to 64% and increased retention in the root by up to twofold. X-ray microanalysis of cryogenically frozen roots demonstrated that this was due to retention of Na⁺ within xylem parenchyma and cortical cells. By contrast, constitutive overexpression of HKT1;1 increased both the unidirectional influx of ²²Na⁺ into the root and the flux of ²²Na⁺ to the shoot.

Finally, the authors found that targeted overexpression of HKT1;1 improved a plant's ability to withstand salt stress (see figure). The total dry mass of plants overexpressing HKT1;1 specifically in stelar root cells was not significantly affected by a 5-d salt treatment compared with control plants (although the stature of one of the lines was reduced by HKT1;1 overexpression itself). However, salt treatment resulted in a significant reduction in the total dry biomass of untransformed parental lines as well as transgenic plants constitutively overexpressing HKT1;1.

View larger version (87K): [in this window] [in a new window] [as a PowerPoint slide]   Hydroponically grown plants overexpressing HKT1 specifically in the stele continued to thrive in the presence of 100 mM NaCl (A), whereas control plants (B) as well as plants constitutively overexpressing HKT1 (data not shown) exhibited signs of salt stress.

Footnotes

www.plantcell.org/cgi/doi/10.1105/tpc.109.210710

REFERENCES

Davenport, R.J., Muñoz-Mayor, A., Jha, D., Essah, P.A., Rus, A., and Tester, M. (2007). The Na⁺ transporter AtHKT1 controls xylem retrieval of Na⁺ in Arabidopsis. Plant Cell Environ. 30: 497–507.[CrossRef][Medline]

Mäser, P., et al. (2002). Altered shoot/root Na⁺ distribution and bifurcating salt sensitivity in Arabidopsis by genetic disruption of the Na⁺ transporter AtHKT1. FEBS Lett. 531: 157–161.[CrossRef][Web of Science][Medline]

Møller, I.S., Gilliham, M., Jha, D., Mayo, G.M., Roy, S.J., Coates, J.C., Haseloff, J., and Tester, M. (2009). Shoot Na⁺ exclusion and increased salinity tolerance engineered by cell type–specific alteration of Na⁺ transport in Arabidopsis. Plant Cell 21: 2163–2178.[Abstract/Free Full Text]

Sunarpi, et al. (2005). Enhanced salt tolerance mediated by AtHKT1 transporter-induced Na⁺ unloading from xylem vessels to xylem parenchyma cells. Plant J. 44: 928–938.[CrossRef][Web of Science][Medline]

Tester, M., and Davenport, R.J. (2003). Na⁺ tolerance and Na⁺ transport in higher plants. Ann. Bot. (Lond.) 91: 503–527.[Abstract/Free Full Text]

Related articles in Plant Cell:

Shoot Na⁺ Exclusion and Increased Salinity Tolerance Engineered by Cell Type–Specific Alteration of Na⁺ Transport in Arabidopsis

Inge S. Møller, Matthew Gilliham, Deepa Jha, Gwenda M. Mayo, Stuart J. Roy, Juliet C. Coates, Jim Haseloff, and Mark Tester
Plant Cell 2009 21: 2163-2178. [Abstract] [Full Text]  

This Article Full Text (PDF) All Versions of this Article: 21/7/1875    most recent tpc.109.210710v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Plant Cell Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Farquharson, K. L. Search for Related Content PubMed PubMed Citation Articles by Farquharson, K. L. Agricola Articles by Farquharson, K. L.