A domestication‐associated reduction in K + ‐preferring HKT transporter activity underlies maize shoot K + accumulation and salt tolerance

Summary Maize was domesticated from Balsas teosinte c . 10 000 yr ago. Previous studies have suggested that increased tolerance to environmental stress occurred during maize domestication. However, the underlying genetic basis remains largely unknown. We used a maize (W22)–teosinte recombinant inbred line (RIL) to investigate the salt wild‐type tolerance aspects of maize domestication. We revealed that ZmHKT2 is a major QTL that regulates K + homeostasis in saline soils. ZmHKT2 encodes a K + ‐preferring HKT family transporter and probably reduces shoot K + content by removing K + ions from root‐to‐shoot flowing xylem sap, ZmHKT2 deficiency increases xylem sap and shoot K + concentrations, and increases salt tolerance. A coding sequence polymorphism in the ZmHKT2 W22 allele (SNP389‐G) confers an amino acid variant ZmHKT2 that increases xylem sap K + concentration, thereby increasing shoot K + content and salt tolerance. Additional analyses showed that SNP389‐G first existed in teosinte (allele frequency 56% in assayed accessions), then swept through the maize population (allele frequency 98%), and that SNP389‐G probably underwent positive selection during maize domestication. We conclude that a domestication‐associated reduction in K + transport activity in ZmHKT2 underlies maize shoot K + content and salt tolerance, and propose that CRISPR‐based editing of ZmHKT2 might provide a feasible strategy for improving maize salt tolerance.