GhCHX6A and GhKEA1D Enhance Salt Tolerance by Regulating Na + /K + Homeostasis in Cotton

ABSTRACT The cation/proton antiporter (CPA2) family plays key roles in regulating plant ion balance and pH homeostasis, particularly in response to salt stress. In this study, a total of 76 CPA2 members were identified in Gossypium hirsutum , phylogenetically classified into 62 GhCHXs and 14 GhKEAs . Through RNA‐Seq data analysis, we found that the expression levels of GhCHX6A and GhKEA1D were significantly upregulated under salt stress. The subcellular localization test showed that GhCHX6A is localized to the vacuolar membrane, while GhKEA1D is localized to the thylakoid membrane. Yeast functional complementation assays revealed that GhCHX6A and GhKEA1D exhibit Na + and K + transport activities, respectively. Silencing of these genes via virus‐induced gene silencing (VIGS) dampened cotton salt tolerance, manifested as aggravated wilting, increased accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), decreased chlorophyll content, and disrupted Na + /K + balance in cotton tissues. These results indicate that GhCHX6A and GhKEA1D enhance salt tolerance in upland cotton by regulating Na + /K + transport to maintain ion homeostasis and alleviate oxidative damage.