Wheat grain yield on saline soils is improved by an ancestral Na+ transporter gene

Journal name:
Nature Biotechnology
Volume:
30,
Pages:
360–364
Year published:
DOI:
doi:10.1038/nbt.2120
Received
Accepted
Published online

The ability of wheat to maintain a low sodium concentration ([Na+]) in leaves correlates with improved growth under saline conditions1, 2. This trait, termed Na+ exclusion, contributes to the greater salt tolerance of bread wheat relative to durum wheat3, 4. To improve the salt tolerance of durum wheat, we explored natural diversity in shoot Na+ exclusion within ancestral wheat germplasm. Previously, we showed that crossing of Nax2, a gene locus in the wheat relative Triticum monococcum into a commercial durum wheat (Triticum turgidum ssp. durum var. Tamaroi) reduced its leaf [Na+] (ref. 5). Here we show that a gene in the Nax2 locus, TmHKT1;5-A, encodes a Na+-selective transporter located on the plasma membrane of root cells surrounding xylem vessels, which is therefore ideally localized to withdraw Na+ from the xylem and reduce transport of Na+ to leaves. Field trials on saline soils demonstrate that the presence of TmHKT1;5-A significantly reduces leaf [Na+] and increases durum wheat grain yield by 25% compared to near-isogenic lines without the Nax2 locus.

At a glance

Figures

  1. TmHKT1;5-A expression in yeast (S. cerevisiae) and X. laevis oocytes.
    Figure 1: TmHKT1;5-A expression in yeast (S. cerevisiae) and X. laevis oocytes.

    (a) Growth of yeast expressing TmHKT1;5A, OsHKT1;5 and empty-vector control in AP media31 with 10 mM NaCl. (b) Growth of yeast without added NaCl. (c) Currents elicited by TmHKT1;5-A cRNA–injected oocyte when bathed in Na+- or K+-glutamate solution clamped at −120 mV; in water-injected oocytes no inward currents were detected. (dg) Current-voltage (I-V) curve of TmHKT1;5-A-injected oocytes exposed to different concentrations of Na+ (n = 5) (d), K+ (n = 4) (e), 1 mM Na+ plus different K+ (n = 5) (f) and 10 mM Na+ plus different K+ (g). Average currents from water-injected controls at each voltage have been subtracted in all cases.

  2. Localization of TmHKT1;5-A and its encoded protein, and its transcriptional regulation by salt.
    Figure 2: Localization of TmHKT1;5-A and its encoded protein, and its transcriptional regulation by salt.

    (a) Plasma membrane (PM) localization of YFPdouble colonTmHKT1;5-A in Arabidopsis mesophyll protoplasts; ECFPdouble colonRop11 (ref. 32) was used as plasma membrane marker. Scale bar, 10 μM. Images were captured using the following wavelengths: YFP (excitation, 514 nm; emission, 525–538 nm), CFP (excitation, 405 nm; emission, 450–490 nm) and chlorophyll auto fluorescence (excitation, 448 nm; emission, 640–740 nm). (b) Tissue localization of TmHKT1;5-A using in situ PCR on 21-d-old roots grown in 2 mM NaCl; cells in which transcript is present stain blue. From top to bottom, TmHKT1;5-A primers in Tamaroi [−] Nax2 (the near-isogenic line without Nax2/TmHKT1;5-A) to confirm absence in lines without Nax2; TmHKT1;5-A primers in Tamaroi [+] Nax2 (the near-isogenic line with Nax2/TmHKT1;5-A), demonstrating the stelar localization of TmHKT1;5-A; 18S rRNA in Tamaroi [+] Nax2 as a positive control to show presence of cDNA in all cell-types; a no RT (reverse transcription) control was included to show lack of genomic DNA contamination; c, cortex; en, endodermis; p, pericycle; x, xylem; xp, xylem parenchyma; scale bars, 100 μM. (c) TmHKT1;5-A is highly expressed in roots of line 149 (derived from a cross of T. monococcum and durum wheat to contains Nax2) and Tamaroi [+] Nax2 compared to Tamaroi [−] Nax2, and shoots of all genotypes after 3 weeks in 20 μM NaCl (clear bars). Additionally, in 3-week-old roots expression of TmHKT1;5-A was not found to be inducible by increasing [Na+]ext from 20 μM to 50 mM for 3 d before harvest in the roots or shoots of any germplasm tested (filled bars). R, roots; S, shoots. Data presented as mean ± s.e.m. (n = 6; three biological replicates per treatment with each replicate comprising two pooled plants, with qPCR performed in triplicate).

  3. Variation in salinity across a commercially farmed field, and the relative increase in grain yield due to the presence of TmHKT1:5-A.
    Figure 3: Variation in salinity across a commercially farmed field, and the relative increase in grain yield due to the presence of TmHKT1:5-A.

    (a) Apparent electrical conductivity (ECa) of a salinity–affected field near Moree in northern New South Wales, Australia. Numbers indicate location of field trial site in 2008 (1) and 2009 (2). (b) Relative increase in grain yield of Tamaroi [+] TmHKT1;5-A compared to Tamaroi. *, P < 0.05.

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References

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Author information

  1. These authors have contributed equally to this work.

    • Rana Munns,
    • Richard A James &
    • Bo Xu

Affiliations

  1. CSIRO Plant Industry, Canberra, Australian Capital Territory, Australia.

    • Rana Munns,
    • Richard A James &
    • Caitlin S Byrt
  2. School of Plant Biology, University of Western Australia, Crawley, Western Australia, Australia.

    • Rana Munns
  3. School of Agriculture, Food and Wine and Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, Australia.

    • Bo Xu,
    • Asmini Athman,
    • Simon J Conn,
    • Charlotte Jordans,
    • Caitlin S Byrt,
    • Stephen D Tyerman,
    • Mark Tester,
    • Darren Plett &
    • Matthew Gilliham
  4. Australian Centre for Plant Functional Genomics, Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, Australia.

    • Bo Xu,
    • Caitlin S Byrt,
    • Mark Tester &
    • Darren Plett
  5. Australian Research Council Centre of Excellence in Plant Energy Biology, Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, Australia.

    • Bo Xu,
    • Asmini Athman,
    • Stephen D Tyerman &
    • Matthew Gilliham
  6. Australian Research Council Centre of Excellence in Plant Cell Walls, Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, Australia.

    • Caitlin S Byrt
  7. NSW Department of Primary Industries, Tamworth, New South Wales, Australia.

    • Ray A Hare

Contributions

R.M., R.A.J., R.A.H., M.T., D.P. and M.G. conceived the project and planned experiments. R.M. and M.G. supervised the research. B.X. performed all Xenopus, yeast and protoplast experiments and R.A.J. performed field research. C.S.B. performed wheat genotyping. S.D.T. assisted with electrophysiology experiments. S.J.C., A.A. and C.J. performed in situ PCR and qPCR. M.G., D.P., R.A.J. and R.M. wrote the manuscript. All authors commented on the manuscript.

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The authors declare no competing financial interests.

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