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 D(471)/a gap and D(474)/G(473) 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.