CBL3 and CIPK18 are required for the function of NHX5 and NHX6 in mediating Li+ homeostasis in Arabidopsis.

Arabidopsis NHX5 and NHX6 are endosomal Na+,K+/H+ antiporters that function in mediating Na+, K+ and pH homeostasis. Here, we report that NHX5 and NHX6 mediate Li+ homeostasis in Arabidopsis. We found that the nhx5 nhx6 double mutant was defective in growth and had a high pale rate under Li+ stress; complementation with either NHX5 or NHX6 restored the growth of the double mutant under LiCl treatments. We further found that CBL3 and CIPK18 collaborate with NHX5 and NHX6 in controlling seedling growth. CBL3 and CIPK18 are involved in the NHX5- and NHX6-mediated response to Li+ stress but not to salt or low K+ stress. In addition, NHX5 and NHX6 coordinate NHX8, a plasma membrane antiporter, in mediating Li+ homeostasis. NHX8 may function differently from NHX5 and NHX6 in mediating Li+ homeostasis. NHX8 was not controlled by CBL3 and CIPK18. Overall, CBL3 and CIPK18 are required for the function of NHX5 and NHX6 in mediating Li+ homeostasis in Arabidopsis.