title: Nax loci affect SOS1-like Na+/H+ exchanger expression and activity in wheat.
abstract: Salinity stress tolerance in durum wheat is strongly associated with a plant's ability to control Na(+) delivery to the shoot. Two loci, termed Nax1 and Nax2, were recently identified as being critical for this process and the sodium transporters HKT1;4 and HKT1;5 were identified as the respective candidate genes. These transporters retrieve Na(+) from the xylem, thus limiting the rates of Na(+) transport from the root to the shoot. In this work, we show that the Nax loci also affect activity and expression levels of the SOS1-like Na(+)/H(+) exchanger in both root cortical and stelar tissues. Net Na(+) efflux measured in isolated steles from salt-treated plants, using the non-invasive ion flux measuring MIFE technique, decreased in the sequence: Tamaroi (parental line)>Nax1=Nax2>Nax1:Nax2 lines. This efflux was sensitive to amiloride (a known inhibitor of the Na(+)/H(+) exchanger) and was mirrored by net H(+) flux changes. TdSOS1 relative transcript levels were 6-10-fold lower in Nax lines compared with Tamaroi. Thus, it appears that Nax loci confer two highly complementary mechanisms, both of which contribute towards reducing the xylem Na(+) content. One enhances the retrieval of Na(+) back into the root stele via HKT1;4 or HKT1;5, whilst the other reduces the rate of Na(+) loading into the xylem via SOS1. It is suggested that such duality plays an important adaptive role with greater versatility for responding to a changing environment and controlling Na(+) delivery to the shoot.
authors.affiliation: School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia.
authors.forename: Min
authors.initials: M
authors.lastname: Zhu
authors.affiliation: School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia.
authors.forename: Lana
authors.initials: L
authors.lastname: Shabala
authors.affiliation: School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs Platz 2, D-97082 Würzburg, Germany.
authors.forename: Tracey A
authors.initials: TA
authors.lastname: Cuin
authors.affiliation: School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia.
authors.forename: Xin
authors.initials: X
authors.lastname: Huang
authors.affiliation: School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia.
authors.forename: Meixue
authors.initials: M
authors.lastname: Zhou
authors.affiliation: School of Plant Biology and ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Crawley WA 6009, Australia CSIRO Agriculture, Canberra, ACT 2601, Australia.
authors.forename: Rana
authors.initials: R
authors.lastname: Munns
authors.affiliation: School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia Sergey.Shabala@utas.edu.au.
authors.forename: Sergey
authors.initials: S
authors.lastname: Shabala
mesh_terms: D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D056426:Genetic Loci; D007477:Ions; D008954:Models, Biological; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D014908:Triticum / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D007477:Ions; D010940:Plant Proteins; D012333:RNA, Messenger; D017923:Sodium-Hydrogen Exchangers; D012965:Sodium Chloride; D011188:Potassium
keywords: HKT transporter; potassium; salinity stress; sequestration; sodium; xylem loading.