Coordination of AtHKT1;1 and AtSOS1 facilitates Na+ and K+ homeostasis in Arabidopsis thaliana under salt stress

Reducing Na+ accumulation and maintaining K+ stability in plant is one of the key strategies for improving salt tolerance. AtHKT1;1 and AtSOS1 are not only the salt tolerance determinants themselves, but also mediate K+ uptake and transport indirectly. To assess the contribution of AtHKT1;1 and AtSOS1 to Na+ homeostasis and K+ nutrition in plant, net Na+ and K+ uptake rate, Na+ and K+ distributions in Arabidopsis thaliana wild type (WT), hkt1;1 mutant (athkt1;1) and sos1 mutant (atsos1) were investigated. Results showed that under 2.5 mM K+ plus 25 or 100 mM NaCl, athkt1;1 shoot concurrently accumulated more Na+ and less K+ than did WT shoot, suggesting that AtHKT1;1 was critical for controlling Na+ and K+ distribution in plant; while atsos1 root accumulated more Na+ and absorbed lower K+ than did WT root, implying that AtSOS1 was determiner of Na+ excretion and K+ acquisition. Under 0.01 mM K+, athkt1;1 absorbed lower Na+ than did WT with 100 mM NaCl, suggesting that AtHKT1;1 is involved in Na+ uptake in roots; while atsos1 shoot accumulated less Na+ than did WT shoot no matter with 25 or 100 mM NaCl, implying that AtSOS1 played a key role in controlling long-distance Na+ transport from root to shoot. We present a model in which coordination of AtHKT1;1 and AtSOS1 facilitates Na+ and K+ homeostasis in A. thaliana under salt stress: under the normal K+, the major function of AtHKT1;1 is Na+ unloading and AtSOS1 is mainly involved in Na+ exclusion, whereas under the low K+, AtHKT1;1 may play a dominant role in Na+ uptake and AtSOS1 may be mainly involved in Na+ loading into the xylem.