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

摘要

Background and aims: Two major adaptive strategies used by Zygophyllum xanthoxylum, a C₃ 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.