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+. Kelly Houston et al. report a genome-wide association study for sodium content in barley to find genetic variants that may improve yield under low soil K(+)levels. They identify variants of the Na+ transporter-encoding gene HvHKT1;5 as important for sodium content variation in non-saline conditions.