Wheat grain yield on saline soils is improved by an ancestral Na ⁺ transporter gene

The ability of wheat to maintain a low sodium concentration ([Na ⁺]) in leaves correlates with improved growth under saline conditions. This trait, termed Na ⁺ exclusion, contributes to the greater salt tolerance of bread wheat relative to durum wheat. To improve the salt tolerance of durum wheat, we explored natural diversity in shoot Na ⁺ exclusion within ancestral wheat germplasm. Previously, we showed that crossing of Nax2, a gene locus in the wheat relative Triticum monococcum into a commercial durum wheat (Triticum turgidum ssp. durum var. Tamaroi) reduced its leaf [Na ⁺] (ref. 5). Here we show that a gene in the Nax2 locus, TmHKT1;5-A, encodes a Na ⁺-selective transporter located on the plasma membrane of root cells surrounding xylem vessels, which is therefore ideally localized to withdraw Na ⁺ from the xylem and reduce transport of Na ⁺ to leaves. Field trials on saline soils demonstrate that the presence of TmHKT1;5-A significantly reduces leaf [Na ⁺] and increases durum wheat grain yield by 25% compared to near-isogenic lines without the Nax2 locus.