Structural variations in wheat HKT1;5 underpin differences in Na+ transport capacity

Abstract

An important trait associated with the salt tolerance of wheat is the exclusion of sodium ions (Na+) from the shoot. We have previously shown that the sodium transporters TmHKT1;5-A and TaHKT1;5-D, from Triticum monoccocum (Tm) and Triticum aestivum (Ta), are encoded by genes underlying the major shoot Na+-exclusion loci Nax1 and Kna1, respectively. Here, using heterologous expression, we show that the affinity (K m) for the Na+ transport of TmHKT1;5-A, at 2.66 mM, is higher than that of TaHKT1;5-D at 7.50 mM. Through 3D structural modelling, we identify residues D471/a gap and D474/G473 that contribute to this property. We identify four additional mutations in amino acid residues that inhibit the transport activity of TmHKT1;5-A, which are predicted to be the result of an occlusion of the pore. We propose that the underlying transport properties of TmHKT1;5-A and TaHKT1;5-D contribute to their unique ability to improve Na+ exclusion in wheat that leads to an improved salinity tolerance in the field.

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Authors

Contributions

BX, MH, DP, and MG conceived the project out of work initiated by RM and MT. BX performed all experiments except the structural modelling and predictions (SW) and the cloning and original characterisation of TmHKT1;5-AK118E/L339P/Y379M (CSB). SDT advised on electrophysiology and analysis. MG, MH, and DP supervised the work. BX, SW, CSB, MH, and MG wrote the paper. All authors provided comment.

Corresponding authors

Correspondence to Maria Hrmova or Matthew Gilliham.

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Funding

This work was supported by the Grains Research and Development Corporation (UA00145, M.G.), the University of Adelaide Australian Postgraduate Award and the CJ Everald postgraduate scholarship (S.W.), and the Australian Research Council through the following schemes: Discovery (DP120100900, M.H.), Centre of Excellence (CE140100008, M.G., R.M., S.D.T), Future Fellowship (FT130100709, M.G.), and DECRA (DE150100837, C.S.B.).

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Xu, B., Waters, S., Byrt, C.S. et al. Structural variations in wheat HKT1;5 underpin differences in Na+ transport capacity. Cell. Mol. Life Sci. 75, 1133–1144 (2018). https://doi.org/10.1007/s00018-017-2716-5

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Keywords

  • Gatekeeper cells
  • Salt exclusion
  • Ion transport
  • Structure–function
  • Einkorn
  • Bread
  • Salt tolerance
  • Xenopus
  • Mutagenesis
  • Yeast
  • High-affinity K+ transporter