Abstract
An obligate halophyte, Salicornia brachiata grows in salt marshes and is considered to be a potential resource of salt- and drought-responsive genes. It is important to develop an understanding of the mechanisms behind enhanced salt tolerance. To increase this understanding, a novel SbSRP gene was cloned, characterized, over-expressed, and functionally validated in the model plant Nicotiana tabacum. The genome of the halophyte S. brachiata contains two homologs of an intronless SbSRP gene of 1,262 bp in length that encodes for a stress-related protein. An in vivo localization study confirmed that SbSRP is localized on the plasma membrane. Transgenic tobacco plants (T1) that constitutively over-express the SbSRP gene showed improved salinity and osmotic stress tolerance. In comparison to Wild Type (WT) and Vector Control (VC) plants, transgenic lines showed elevated relative water and chlorophyll content, lower malondialdehyde content, lower electrolyte leakage and higher accumulation of proline, free amino acids, sugars, polyphenols, and starch under abiotic stress treatments. Furthermore, a lower build-up of H2O2 content and superoxide-radicals was found in transgenic lines compared to WT and VC plants under stress conditions. Transcript expression of Nt-APX (ascorbate peroxidase), Nt-CAT (catalase), Nt-SOD (superoxide dismutase), Nt-DREB (dehydration responsive element binding factor), and Nt-AP2 (apetala2) genes was higher in transgenic lines under stress compared to WT and VC plants. The results suggested that overexpression of membrane-localized SbSRP mitigates salt and osmotic stress in the transgenic tobacco plant. It was hypothesized that SbSRP can be a transporter protein to transmit the environmental stimuli downward through the plasma membrane. However, a detailed study is required to ascertain its exact role in the abiotic stress tolerance mechanism. Overall, SbSRP is a potential candidate to be used for engineering salt and osmotic tolerance in crops.
Highlights
About 450 million small-scale producers around the world are dependent on agriculture for their sustenance
The Salicornia brachiata stress-related protein (SbSRP) gene was cloned from an extreme halophyte S. brachiata and functionally characterized using transgenic approach
Morphological, biochemical, and physiological analyses of T1 transgenic tobacco lines showed that transgenic plants are more tolerant to salinity and osmotic stress than wild type plants
Summary
About 450 million small-scale producers around the world are dependent on agriculture for their sustenance. The Intergovernmental Panel on Climate Change (IPCC) reported that high temperatures, salinity, floods, drought, and deterioration of arable land severely affect the agricultural economy in the developing world (Annan et al, 2009). About 800 million ha of land are salt-affected worldwide and soil salinity is gradually increasing (Munns, 2005; Tuteja et al, 2011). An adverse impact is envisaged for the agricultural economy of developing countries, major precautionary steps are needed to develop adaptive strategies for sustainable agriculture according to the changing environment (Ashraf and Foolad, 2007; Tuteja et al, 2011). The ions that cause high salinity are Na+ and Cl− as they prevail in seawater Halophytes utilize these ions for a large portion of their osmotic change (Flowers et al, 2010). Plants have evolutionarily conserved mechanisms to endure harsh conditions by expressing enzymes, transcription regulators and other factors that function in pathways directed by phytohormones, such as abscisic acid (ABA), and second messengers, such as Ca2+ (Mukhopadhyay and Tyagi, 2015)
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