Barley sodium content is regulated by natural variants of the Na(+) transporter HvHKT1;5

During plant growth, sodium (Na(+)) in the soil is transported via the xylem from the root to the shoot. While excess Na(+) is toxic to most plants, non-toxic concentrations have been shown to improve crop yields under certain conditions, such as when soil K(+) is low. We quantified grain Na(+) across a barley genome-wide association study panel grown under non-saline conditions and identified variants of a Class 1 HIGH-AFFINITY-POTASSIUM-TRANSPORTER (HvHKT1;5)-encoding gene responsible for Na(+) content variation under these conditions. A leucine to proline substitution at position 189 (L189P) in HvHKT1;5 disturbs its characteristic plasma membrane localisation and disrupts Na(+) transport. Under low and moderate soil Na(+), genotypes containing HvHKT1:5(P189) accumulate high concentrations of Na(+) but exhibit no evidence of toxicity. As the frequency of HvHKT1:5(P189) increases significantly in cultivated European germplasm, we cautiously speculate that this non-functional variant may enhance yield potential in non-saline environments, possibly by offsetting limitations of low available K(+).