The Role Of PtSOS1,PtAKT1in Salt Tolerance Of Halophyte Puccinellia Tenuiflora

P. tenuiflora is a monocotyledonous halophyte found in north China, and used as forage as well as for soil improvement. Our previous studies suggested that restricting unidirectional Na+influx into roots with a strong selectivity for K+over Na+was thought to be contributed to the salt tolerance of P. tenuiflora. However, the molecular mechanisms of selectivity for K+over Na+in the regulation of salt tolerance remains unknown. The plasma membrane Na+/H+antiporter (SOS1) was proved to be a Na+efflux protein and also involved in K+uptake and transport, PtSOS1may be contributed to maintain selective transport capacity for K+over Na+(ST) by roots under salt conditions; plants AKT1-type channels (AKT1) exhibited a high selectivity for K+over other monovalent cations and were reputed to specifically mediate K+uptake by roots under K+deficiency or salt stress, PtAKT1may play an key role in selective absorption capacity for K+over Na+(SA) by roots in P. tenuiflora exposed to salt conditions. In this study, to reveal the role of PtSOS1, PtAKT1in salt tolerance of halophyte P. tenuiflora, we isolated cDNAs for Na+/H+antiporter gene (PtSOS1) and AKT1-type K+channels (PtAKT1) from P. tenuiflora, and Na+and K+accumulations in P. tenuiflora exposed to various NaCl, KCl and NaCl plus different KCl treatments were investigated, respectively. The results are as follows;(1) PtSOS1consisted of1143amino acid residues with a cyclic nucleotide binding domain located at centrally in the long C-terminal tail and shared higher similarity with the known plasma membrane Na+/H+antiporters(over57%); PtAKT1consists of895amino acid residues and shares high similarity with the known AKT1-type channels (over60%).(2) The expression levels of PtSOS1in root increased significantly with the increase of external NaCl (25-150mM), accompanied by an increase of selective transport (ST) capacity for K+over Na+by roots.(3) Transcription levels of PtSOS1in root and ST values increased under0.1-1mM KCl, then declined sharply under5-10mM KCl.(4) Under150mM NaCl, PtSOS1expression levels in root and ST values at0.1mM KCl was significantly lower than that at5mM KCl with the prolonging of treatment time.(5) A significantly positive correlation was found between PtSOSI expression levels and ST values in root exposed to150mM NaCl plus0.1or5mM KCl treatments, suggesting that PtSOSI may be the major component of selective transport capacity for K+over Na+under salt conditions.(6) No significant differences were observed in the expression of PtAKT1in root or whole plant K+concentrations among KCl treatments, indicating that PtAKT1contributes to maintain K+uptake by roots under K+deficiency.(7) The expression of PtAKTl in root at150mM NaCl plus0.1or5mM KCl was significantly higher than that at25mM NaCl plus0.1or5mM KCl treatment for6-48h.. However, the expression of PtAKTl or whole plant K+concentrations in root was down-regulated by different concentrations of NaCl plus KCl treatments for with the increase of treatment time (48-96h), and there were no significant differences in the expression levels of PtAKT1in root or whole plant K concentrations among treatments for48-96h.. SA values in root at150mM NaCl plus0.1or5mM KCl was significantly higher than that at25mM NaCl plus0.1or5mM KCl treatment for6-96h. Furthermore, a significantly positive correlation was found between selective absorption capacity for K+over Na+values and PtAKT1expression levels in root under various concentrations of NaC1plus KCl treatments, suggesting that PtAKT1may play an important role in selective absorption capacity for K+over+Na by roots in P. tenuiflora exposed to salt conditions.In summary, we proposed that PtSOS1seems likely to be the major component of selective transport capacity for K+over Na+and hence salt tolerance of P. tenuiflora. Finally, we hypothesized a function model of SOS1in regulating K+and Na+transport system in the membrane of xylem parenchyma cells by sustaining the membrane integrity under salt stress. In addition, PtAKT1may contribute to maintaining selective absorption capacity for K+over Na+by roots in response to salt stress.