Function Analyses Of Rice Potassium Transporter OsHAKx In Responses To Salt Stress

Agricultural lands increasingly suffer from the intensification of soil salinization,hence,investigating the mechanism of plant salt tolerance and cultivating haloduric crops have become an urgent task.So far,sodium(Na+)transport concerned with plant salt-tolerance has been researched intensively.Under salt stress,plants could restrict Na+ uptake,active Na+ exclusion back to the soil solution,and compartmentalize excessive Na+ into vacuoles,resulting in reduction of Na+ accumulation in cells,especially in the cytoplasm.Simultaneously,the excessive extracellular and intracellular Na+ offten lead to potassium(K)nutrition deficency.So how to maintain the plant cytoplasmic Na+/K+homeostasis is essential for plant salt-tolerance.K+ and Na+ are similar in both physical and chemical properties,thus Na+ could competitively inhibit K+ absorption.When Na+ toxicity in cells could not be effectively relieved,it would eventually destruct intracellular potassium homeostasis in cells.The KT/HAK/KUP transporter family is an important K+ uptake and transport systems in plants,which mediate K+ absorption from the soil and K+ distribution among different tissues.In this study,we determined the functions of OsHAKx transport protein,and the roles of maintaining Na+/K+ homeostasis in rice response to salt stress.We performed phenotype analysis,quantitative analyses,subcellular localization analyses,the functional complementation tests in yeast cells,etc.The main results were listed as follows:1.We found OsHAKx expression couldn be induced by high salinity treatment.The Tos17 insertion mutant oshakxs exhibited more sensitive to salt stress than wild type under 130 mM NaCl,as determined by the shoot growth significant inhibition and chlorosis of leaves.2.The ion contents and net absorption rate analysis of all OsHAKx genotypes showed:Compared to the wild type,oshakx accumulated significant more Na+ and less K+ in shoots,Na+ net absorption rate of oshakx was significantly higher than WT,while the K+ net absorption rate was significantly lower than WT.3.RT-PCR analysis in various organs of WT plants showed that OsHAKx was expressed in the whole plant,and the transcripts were more abundant in the flag leaf and the sheath of flag leaf.Subcellular localization analysis showed OsHAKx localized at cytoplasmic membrane.4.The transporter activity of OsHAKx was assayed by using yeast functional complementation,We found the OsHAKx expression exactly eased the growth defect of a K+ uptake-deficient mutant of yeast strain CY162.Besides,K+ absorption mediated by OsHAKx could mantain Na+/K+ steady-state and enhance the salt tolerance of CY162 cells.Overall,we demonstrat that OsHAKx participate in responses to salinity stress.K+absorption mediates by OsHAKx may play an importantent role in the maintenance of Na+/K+ homeostasis and improving the salt resistance of rice.