Description:
<jats:title>Summary</jats:title><jats:p>Bread wheat (<jats:italic>Triticum aestivum</jats:italic> L.) has a major salt tolerance locus, <jats:italic>Kna1,</jats:italic> responsible for the maintenance of a high cytosolic K<jats:sup>+</jats:sup>/Na<jats:sup>+</jats:sup> ratio in the leaves of salt stressed plants. The <jats:italic>Kna1</jats:italic> locus encompasses a large <jats:styled-content style="fixed-case">DNA</jats:styled-content> fragment, the distal 14% of chromosome 4<jats:styled-content style="fixed-case">DL</jats:styled-content>. Limited recombination has been observed at this locus making it difficult to map genetically and identify the causal gene. Here, we decipher the function of <jats:italic>Ta<jats:styled-content style="fixed-case">HKT</jats:styled-content>1;5‐D,</jats:italic> a candidate gene underlying the <jats:italic>Kna1</jats:italic> locus. Transport studies using the heterologous expression systems <jats:italic>Saccharomyces cerevisiae</jats:italic> and <jats:italic>Xenopus laevis</jats:italic> oocytes indicated that Ta<jats:styled-content style="fixed-case">HKT</jats:styled-content>1;5‐D is a Na<jats:sup>+</jats:sup>‐selective transporter. Transient expression in <jats:italic>Arabidopsis thaliana</jats:italic> mesophyll protoplasts and <jats:italic>in situ</jats:italic> polymerase chain reaction indicated that <jats:italic>Ta<jats:styled-content style="fixed-case">HKT</jats:styled-content>1;5‐D</jats:italic> is localised on the plasma membrane in the wheat root stele. <jats:styled-content style="fixed-case">RNA</jats:styled-content> interference‐induced silencing decreased the expression of <jats:italic>Ta<jats:styled-content style="fixed-case">HKT</jats:styled-content>1;5‐D</jats:italic> in transgenic bread wheat lines which led to an increase in the Na<jats:sup>+</jats:sup> concentration in the leaves. This indicates that <jats:italic>Ta<jats:styled-content style="fixed-case">HKT</jats:styled-content>1;5‐D</jats:italic> retrieves Na<jats:sup>+</jats:sup> from the xylem vessels in the root and has an important role in restricting the transport of Na<jats:sup>+</jats:sup> from the root to the leaves in bread wheat. Thus, <jats:italic>Ta<jats:styled-content style="fixed-case">HKT</jats:styled-content>1;5‐D</jats:italic> confers the essential salinity tolerance mechanism in bread wheat associated with the <jats:italic>Kna1</jats:italic> locus via shoot Na<jats:sup>+</jats:sup> exclusion and is critical in maintaining a high K<jats:sup>+</jats:sup>/Na<jats:sup>+</jats:sup> ratio in the leaves. These findings show there is potential to increase the salinity tolerance of bread wheat by manipulation of <jats:italic><jats:styled-content style="fixed-case">HKT</jats:styled-content>1;5</jats:italic> genes.</jats:p>