ZxSOS1 is essential for long-distance transport and spatial distribution of Na+ and K+ in the xerophyte Zygophyllum xanthoxylum

Background and aims Two major adaptive strategies used by Zygophyllum xanthoxylum , a C 3 succulent xerophyte, against arid environments are absorbing a great quantity of Na + from low-salinity soil which is efficiently transported to the leaves, and maintaining the stability of K + concentration in those leaves. The plasma membrane Na + /H + antiporter SOS1 has been suggested to be involved in Na + transport and correlated with K + nutrition in glycophytes. In this study, we investigated the function of the plasma membrane Na + /H + antiporter ZxSOS1 in long-distance transport and spatial distribution of Na + and K + in the xerophyte Z. xanthoxylum . Methods The responses of ZxSOS1 to NaCl, KCl treatments and osmotic stress were investigated by semi-quantitative RT-PCR, then the role of ZxSOS1 in regulating plant growth and Na + , K + transport and spatial distribution in Z. xanthoxylum was studied by using post-transcriptional gene silencing. Results We found that ZxSOS1 was preferentially expressed in roots and was induced and regulated by salt treatments and osmotic stress. Using post-transcriptional gene silencing, we found that ZxSOS1 -silenced plants exhibited reduced growth rate compared to wild-type (WT) plants under both normal and saline conditions. ZxSOS1 -silenced plants accumulated more Na + in their roots but less Na + in leaves and stems than WT under 50 mM NaCl. Furthermore, ZxSOS1 -silenced plants had a lower net K + uptake rate than WT plants under both normal and saline conditions, and more interestingly, accumulated less K + in leaves under normal conditions than WT plants. ZxSOS1 -silenced plants also showed a decreased concentration and spatial distribution of K + in leaves and roots than WT under 50 mM NaCl. In addition, ZxSOS1 -silenced plants possessed an increased selective transport (ST) capacity for K + over Na + from root to stem while a decreased ST value from stem to leaf compared with WT plants when both were grown in 50 mM NaCl. Conclusions These results demonstrate that ZxSOS1 is not only essential in long-distance transport and spatial distribution of Na + and even K + , but also vital for regulating K + and Na + transport system and maintaining Na + and K + homeostasis in Z. xanthoxylum , thereby regulating its normal growth.