The Recretohalophyte Tamarix TrSOS1 Gene Confers Enhanced Salt Tolerance to Transgenic Hairy Root Composite Cotton Seedlings Exhibiting Virus-Induced Gene Silencing of GhSOS1.

Benning Che,Bingjun Yu,Yongmei Liu,Jiajia Fang,Li Jiang,Cong Cheng

doi:10.3390/ijms20122930

Abstract

The salt overly sensitive 1 (SOS1) gene encodes the plasma membrane Na+/H+ antiporter, SOS1, that is mainly responsible for extruding Na+ from the cytoplasm and reducing the Na+ content in plants under salt stress and is considered a vital determinant in conferring salt tolerance to the plant. However, studies on the salt tolerance function of the TrSOS1 gene of recretohalophytes, such as Tamarix, are limited. In this work, the effects of salt stress on cotton seedlings transformed with tobacco-rattle-virus-based virus-induced gene silencing (VIGS) of the endogenous GhSOS1 gene, or Agrobacterium rhizogenes strain K599-mediated TrSOS1-transgenic hairy root composite cotton plants exhibiting VIGS of GhSOS1 were first investigated. Then, with Arabidopsis thaliana AtSOS1 as a reference, differences in the complementation effect of TrSOS1 or GhSOS1 in a yeast mutant were compared under salt treatment. Results showed that compared to empty-vector-transformed plants, GhSOS1-VIGS-transformed cotton plants were more sensitive to salt stress and had reduced growth, insufficient root vigor, and increased Na+ content and Na+/K+ ratio in roots, stems, and leaves. Overexpression of TrSOS1 enhanced the salt tolerance of hairy root composite cotton seedlings exhibiting GhSOS1-VIGS by maintaining higher root vigor and leaf relative water content (RWC), and lower Na+ content and Na+/K+ ratio in roots, stems, and leaves. Transformations of TrSOS1, GhSOS1, or AtSOS1 into yeast NHA1 (Na+/H+ antiporter 1) mutant reduced cellular Na+ content and Na+/K+ ratio, increased K+ level under salt stress, and had good growth complementation in saline conditions. In particular, the ability of TrSOS1 or GhSOS1 to complement the yeast mutant was better than that of AtSOS1. This may indicate that TrSOS1 is an effective substitute and confers enhanced salt tolerance to transgenic hairy root composite cotton seedlings, and even the SOS1 gene from salt-tolerant Tamarix or cotton may have higher efficiency than salt-sensitive Arabidopsis in regulating Na+ efflux, maintaining Na+ and K+ homeostasis, and therefore contributing to stronger salt tolerance.

Highlights

Soil salinity is one of the major abiotic stress factors that adversely affects plant growth and development, reducing crop quality and yield [1,2]
The cotton seedlings transformed with the empty vector or pTRV2-GhSOS1 (GhSOS1-virus-induced gene silencing (VIGS)) grew well (Figure S1b-left), but GhSOS1 expression was only markedly downregulated in both the true leaves and roots of the latter, showing the effective silencing of the GhSOS1 gene (Figure S1b-right)
When the empty vector and GhSOS1-VIGS-transformed cotton plants were exposed to 200 mM NaCl for seven days, the growth of both was obviously inhibited, but the latter displayed smaller leaves, lower plant dry weight and leaf chlorophyll content, and a higher relative electrolytic leakage (REL) value and MDA content in the leaves and roots (Figure 1a–f), which suggests more severe salt injury or sensitivity to the GhSOS1-VIGS-transformed cotton plants than the empty-vector-transformed cotton plants

Summary

Introduction

Soil salinity is one of the major abiotic stress factors that adversely affects plant growth and development, reducing crop quality and yield [1,2]. NaCl is the most soluble and abundant salt released into the soil and is the major cause of salt stress on plants or crops [3]. Osmotic stress, nutritional imbalance, and oxidative damage are the main causes of salt injury in plants. Plant cells can be protected through several strategies, such as Na+ extrusion out of the plasma membrane, ionic imbalances in the vacuole, stress signal transduction, and expression of effector genes encoding ion transporters, channels, enzymes involved in osmolyte biosynthesis and antioxidant systems, etc. Ionic toxicity by the accumulation of Na+ and Cl− is the primary and dominant factor of salt injury in plants [6], crops such as cotton, rice, and barley, are more sensitive to Na+ than to Cl− [7]. Many studies have reported on the mechanisms of maintaining low Na+ in the cytoplasm from two synergistic aspects, i.e., Na+ extrusion out of the cytoplasm into the apoplast and vacuolar compartmentalization through membrane-bound Na+/H+

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