Soybean CHX‐type ion transport protein GmSALT3 confers leaf Na<sup>+</sup> exclusion via a root derived mechanism, and Cl<sup>−</sup> exclusion via a shoot derived process
Yue Qu, Rongxia Guan, Jayakumar Bose, Sam W. Henderson, Stefanie Wege, Lijuan Qiu, Matthew Gilliham
Abstract
Abstract Soybean ( Glycine max ) yields are threatened by multiple stresses including soil salinity. GmSALT3 (a cation‐proton exchanger protein) confers net shoot exclusion for both Na + and Cl − and improves salt tolerance of soybean; however, how the ER‐localized GmSALT3 achieves this is unknown. Here, GmSALT3's function was investigated in heterologous systems and near isogenic lines that contained the full‐length GmSALT3 (NIL‐T; salt‐tolerant) or a truncated transcript Gmsalt3 (NIL‐S; salt‐sensitive). GmSALT3 restored growth of K + ‐uptake‐defective Escherichia coli and contributed towards net influx and accumulation of Na + , K + and Cl − in Xenopus laevis oocytes, while Gmsalt3 was non‐functional. Time‐course analysis of NILs confirmed shoot Cl − exclusion occurs distinctly from Na + exclusion. Grafting showed that shoot Na + exclusion occurs via a root xylem‐based mechanism; in contrast, NIL‐T plants exhibited significantly greater Cl − content in both the stem xylem and phloem sap compared to NIL‐S, indicating that shoot Cl − exclusion likely depends upon novel phloem‐based Cl − recirculation. NIL‐T shoots grafted on NIL‐S roots contained low shoot Cl − , which confirmed that Cl − recirculation is dependent on the presence of GmSALT3 in shoots. Overall, these findings provide new insights on GmSALT3's impact on salinity tolerance and reveal a novel mechanism for shoot Cl − exclusion in plants.