A teosinte-derived allele of an HKT1 family sodium transporter improves salt tolerance in maize

The sodium cation (Na⁺) is the predominant cation with deleterious effects on crops in salt-affected agricultural areas. Salt tolerance of crop can be improved by increasing shoot Na⁺ exclusion. Therefore, it is crucial to identify and use genetic variants of various crops that promote shoot Na⁺ exclusion. Here, we show that a HKT1 family gene ZmNC3 (Zea mays L. Na⁺ Content 3; designated ZmHKT1;2) confers natural variability in shoot-Na⁺ accumulation and salt tolerance in maize. ZmHKT1;2 encodes a Na⁺-preferential transporter localized in the plasma membrane, which mediates shoot Na⁺ exclusion, likely by withdrawing Na⁺ from the root xylem flow. A naturally occurring nonsynonymous SNP (SNP947-G) increases the Na⁺ transport activity of ZmHKT1;2, promoting shoot Na⁺ exclusion and salt tolerance in maize. SNP947-G first occurred in the wild grass teosinte (at a allele frequency of 43%) and has become a minor allele in the maize population (allele frequency 6.1%), suggesting that SNP947-G is derived from teosinte and that the genomic region flanking SNP947 likely has undergone selection during domestication or post-domestication dispersal of maize. Moreover, we demonstrate that introgression of the SNP947-G ZmHKT1;2 allele into elite maize germplasms reduces shoot Na⁺ content by up to 80% and promotes salt tolerance. Taken together, ZmNC3/ZmHKT1;2 was identified as an important QTL promoting shoot Na⁺ exclusion, and its favourable allele provides an effective tool for developing salt-tolerant maize varieties.