Nax loci affect SOS1-like Na+/H+ exchanger expression and activity in wheat.

Min Zhu,Rana Munns,Sergey Shabala,Lana Shabala,Meixue Zhou,Xin Huang,Tracey A Cuin

doi:10.1093/jxb/erv493

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.

Highlights

Soil salinity severely affects plant growth and limits agricultural crop production (Qadir et al, 2014; Shabala et al, 2014)
We show that the Nax loci affect activity and expression levels of the SOS1-like Na+/H+ exchanger in both root cortical and stelar tissues
H+ fluxes measured in response to salt treatment were lower for the Nax lines compared with Tamaroi (Fig. 1B), with steady-state H+ flux values being Tamaroi>Nax1=Nax 2>Nax1:Nax2 lines (Fig. 1B)

Summary

Introduction

Soil salinity severely affects plant growth and limits agricultural crop production (Qadir et al, 2014; Shabala et al, 2014). These loci are not present in modern durum or bread wheat, so they were crossed into the current durum cultivar Tamaroi, and near-isogenic lines were developed containing either the Nax or Nax loci or both These lines had lower rates of Na+ transport from the roots to the shoots, the result of a lower rate of net Na+ loading into the xylem (James et al, 2006). It was localized on the plasma membrane of cells surrounding the xylem and, when crossed into an elite Australian durum cultivar, was found to confer a yield benefit of 25% on saline soil in a farmer’s field (Munns et al, 2012).

Methods

Results

Conclusion