Study On The Function Of NHX5 And NHX6 In Regulating The Auxin Transporter PIN6 In Arabidopsis

Plant Na~+/H~+ exchangers(NHXs)play an important role in growth and development.Studies have shown that the Arabidopsis endosomal antiporters At NHX5 and At NHX6 regulate growth and development.However,the mechanisms behind the action of At NHX5 and At NHX6 remain to be studied.Auxin is a key phytohormone that regulates plant development.Auxin needs to be transported to specific cells or tissues by auxin transporters.PIN6,an auxin transporter located in the endoplasmic reticulum and plasma membranes,is critical for auxin homeostasis and plant development.The purpose of this study is to understand whether or not At NHX5 and At NHX6 regulate plant development by controlling PIN6 activity and hence cellular auxin levels.We generated PIN6 overexpression lines and analyzed their development.The main results are as follows:1.We first generated PIN6 overexpression lines.UBQ10::PIN6(Col-0)lines were hybridized with nhx5,nhx6 single mutants and nhx5 nhx6 double mutants,respectively,to generate the PIN6-overexpressing lines of UBQ10::PIN6(nhx5),UBQ10::PIN6(nhx6)and UBQ10::PIN6(nhx5 nhx6),respectively.2.RT-PCR analysis showed that the expression levels of the PIN6 gene in nhx5,nhx6 and nhx5 nhx6 were the same as that of the wild type,indicating that At NHX5 and At NHX6 do not affect PIN6 expression.However,the fluorescence of PIN6-GFP in leaf veins was reduced in nhx5,nhx6 and nhx5 nhx6,indicating that At NHX5 and At NHX6 regulate PIN6 distribution in leaf veins.3.We analyzed the growth of the overexpression line PIN6/nhx5 nhx6.The overexpression line was small in size.It had small rosettes,reduced cotyledon angles,short siliques,and increased chlorophylls.It produced less siliques with decreased seed yields.Seed abortion happened frequently.Flowers were small,with a high rate of abnormality in stamen development.These results suggest that At NHX5 and At NHX6 regulate PIN6 function.In conclusion,our studies indicate that At NHX5 and At NHX6 regulate PIN6 function;At NHX5 and At NHX6 may regulate plant development by controlling PIN6 function and hence cellular auxin levels.