The Effect Of Potassium Transporter OsHAK18 Mutation On Potassium Transport And Salt Resistance In Rice

Soil salinization is an obstacle for agriculture production which threatens seriouslyplant productivity and food supply.Rice is a staple food crop worldwide,while it is very sensitive to soil salinity.Potassium(K)is the most abundant essential cation in plants,it plays critical roles in various physiological and biochemical processes such as maintaining charge balance,regulating cell swelling,promoting photosynthesis and protein synthesis.Increasing K availability and uptake can improve plant tolerance to salinity stress.The transporters belonging to HAK/KUT/KT family have been isolated and predicted as the major contributors of K uptake and translocation,and are involved in salt tolerance in plants.There are at least 27 HAK/KUT/KT members in rice genome,while only three of them have been functionally characterized..In this study,we detected the expression patterns and functions of OsHAK18 both in heterogeneous expression systems and rice(cv.Nipponbare).A series of molecular and physiological experiments with two OsHAK18 knockout(KO)of Tosl7 insertion mutants together with wild type(WT)were used to identify the physiological function of OsHAK18.The main results were summarized as follows.1.By transforming OsHAK18 fused GFP in rice protoplast,we detected that OsHAK18 is located not only in plasma membrane,but also in endosome-like and intracellular punctate localization.GUS staining analysis of OsHAK18-promoter-GUS transgenic rice indicated that OsHAK18 was mainly expressed in the column,rhizome,leaf sheath,leaf blade,glume,stamen and pistil.2.We planted OsHAK18 KO and WT lines in hydroponic solution with different K concentrations.When the K concentration was 0.1 mM,the KO lines showed significant lower biomass,K concentration and accumulation in the roots in comparison to WT,while K concentration in the shoot and the shoot to root ratio of K concentration were significantly higher in the KO lines compared with WT lines.However,there were no significant differences of K concentration in entire rice plant and the shoot to root ratio of K concentration of KO line between the mutants and WT.In addition,the K concentration in xylem sap of KO lines was much lower than that of the WT lines when grown in low K solution,while no significant difference of the xylem K concentration was obtained between them at high K solution.Furthermore,,the K concentration in the phloem sap of KO lines was significantly decreased compared with WT lines.Taking these results together,it could be deduced that OsHAK18 plays important role in K translocation,especially the redistribution of K from above ground parts to roots in rice when K supply was limited.3.The expression of OsHAK18 was enhanced largely by salt stress.In comparison to WT,OsHAK18 KO mutants displayed weaker salt tolerance,lower K+ but higher Na+concentration,and higher Na+/K+ ratio in the shoot.These results implicate that OsHAK18 takes a role in enhancing rice salt tolerance.In conclusion,OsHAK18 participates' in K+ circulation from shoot to root in rice grown in low K+ medium.Because OsHAK18 KO also reduced Na+ translocation from shoot to root,it is likely OsHAK18 transporter distinguish less between K+ and Na+comparing to several charicterized OsHAKs.Thus,it may promote the circulation of K+or Na+ from shoot to root in the low K+ or high Na+ environment,and enhances rice plant low K+ or high Na+ tolerance.