A Glycine max sodium/hydrogen exchanger enhances salt tolerance through maintaining higher Na+ efflux rate and K+/Na+ ratio in Arabidopsis

Tian-Jie Sun,Jun Yang,Jie Zhang,Chun-Yan Yang,Ren-Zhi Cao,Dong-Mei Wang,Long Fan

doi:10.1186/s12870-019-2084-4

Tian-Jie Sun, Jun Yang + Show 5 more

Open Access

https://doi.org/10.1186/s12870-019-2084-4

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Abstract

BackgroundSoybean (Glycine max (L.)) is one the most important oil-yielding cash crops. However, the soybean production has been seriously restricted by salinization. It is therefore crucial to identify salt tolerance-related genes and reveal molecular mechanisms underlying salt tolerance in soybean crops. A better understanding of how plants resist salt stress provides insights in improving existing soybean varieties as well as cultivating novel salt tolerant varieties. In this study, the biological function of GmNHX1, a NHX-like gene, and the molecular basis underlying GmNHX1-mediated salt stress resistance have been revealed.ResultsWe found that the transcription level of GmNHX1 was up-regulated under salt stress condition in soybean, reaching its peak at 24 h after salt treatment. By employing the virus-induced gene silencing technique (VIGS), we also found that soybean plants became more susceptible to salt stress after silencing GmNHX1 than wild-type and more silenced plants wilted than wild-type under salt treatment. Furthermore, Arabidopsis thaliana expressing GmNHX1 grew taller and generated more rosette leaves under salt stress condition compared to wild-type. Exogenous expression of GmNHX1 resulted in an increase of Na+ transportation to leaves along with a reduction of Na+ absorption in roots, and the consequent maintenance of a high K+/Na+ ratio under salt stress condition. GmNHX1-GFP-transformed onion bulb endothelium cells showed fluorescent pattern in which GFP fluorescence signals enriched in vacuolar membranes. Using the non-invasive micro-test technique (NMT), we found that the Na+ efflux rate of both wild-type and transformed plants after salt treatment were significantly higher than that of before salt treatment. Additionally, the Na+ efflux rate of transformed plants after salt treatment were significantly higher than that of wild-type. Meanwhile, the transcription levels of three osmotic stress-related genes, SKOR, SOS1 and AKT1 were all up-regulated in GmNHX1-expressing plants under salt stress condition.ConclusionVacuolar membrane-localized GmNHX1 enhances plant salt tolerance through maintaining a high K+/Na+ ratio along with inducing the expression of SKOR, SOS1 and AKT1. Our findings provide molecular insights on the roles of GmNHX1 and similar sodium/hydrogen exchangers in regulating salt tolerance.

Highlights

Soybean (Glycine max (L.)) is one the most important oil-yielding cash crops
GmNHX1 gene is related to salt stress resistance in plants In order to examine the relation between GmNHX1 and the response to salt stress in soybeans, we examined the transcription level of GmNHX1 in soybean variety “Jidou7”
We observed an increase of GmNHX1 gene expression after salt treatment and the peak of its expression was at 24 h post treatment, reaching approximately 10-fold of that of before treatment (0 hpt)

Summary

Introduction

Soybean (Glycine max (L.)) is one the most important oil-yielding cash crops. the soybean production has been seriously restricted by salinization. It is crucial to identify salt tolerance-related genes and reveal molecular mechanisms underlying salt tolerance in soybean crops. A better understanding of how plants resist salt stress provides insights in improving existing soybean varieties as well as cultivating novel salt tolerant varieties. The biological function of GmNHX1, a NHX-like gene, and the molecular basis underlying GmNHX1-mediated salt stress resistance have been revealed. Na+/H+ exchangers (NHXs) are integral membrane transporters that catalyze the electroneutral exchange of K+ or Na+ for H+ and are implicated in cell expansion [4], development [5], ion homeostasis [6] and salt tolerance [7]. In Arabidopsis, NHXs that localize in vacuolar and plasma membrane are generally considered critical for maintaining Na+/K+ homeostasis [8]. NHX5 and NHX6, function as pH regulators of Golgi, trans-Golgi network, and pre-vacuolar compartments, regulating the sorting of newly synthesized peptides and the direction of Golgi-cargo movement [9]

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