AUTHOR=Udawat Pushpika , Jha Rajesh K. , Mishra Avinash , Jha Bhavanath 

TITLE=Overexpression of a Plasma Membrane-Localized SbSRP-Like Protein Enhances Salinity and Osmotic Stress Tolerance in Transgenic Tobacco

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.00582

DOI=10.3389/fpls.2017.00582

ISSN=1664-462X

ABSTRACT=<p>An obligate halophyte, <italic>Salicornia brachiata</italic> 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 <italic>SbSRP</italic> gene was cloned, characterized, over-expressed, and functionally validated in the model plant <italic>Nicotiana tabacum</italic>. The genome of the halophyte <italic>S. brachiata</italic> contains two homologs of an intronless <italic>SbSRP</italic> gene of 1,262 bp in length that encodes for a stress-related protein. An <italic>in vivo</italic> localization study confirmed that <italic>Sb</italic>SRP is localized on the plasma membrane. Transgenic tobacco plants (T1) that constitutively over-express the <italic>SbSRP</italic> 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 H<sub>2</sub>O<sub>2</sub> content and superoxide-radicals was found in transgenic lines compared to WT and VC plants under stress conditions. Transcript expression of <italic>Nt-APX</italic> (ascorbate peroxidase), <italic>Nt-CAT</italic> (catalase), <italic>Nt-SOD</italic> (superoxide dismutase), <italic>Nt-DREB</italic> (dehydration responsive element binding factor), and <italic>Nt-AP2</italic> (apetala2) genes was higher in transgenic lines under stress compared to WT and VC plants. The results suggested that overexpression of membrane-localized <italic>Sb</italic>SRP mitigates salt and osmotic stress in the transgenic tobacco plant. It was hypothesized that <italic>Sb</italic>SRP 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, <italic>SbSRP</italic> is a potential candidate to be used for engineering salt and osmotic tolerance in crops.</p>