A Novel Gene SbSI-2 Encoding Nuclear Protein from a Halophyte Confers Abiotic Stress Tolerance in E. coli and Tobacco

Salicornia brachiata is an extreme halophyte that grows luxuriantly in coastal marshes. Previously, we have reported isolation and characterization of ESTs from Salicornia with large number of novel/unknown salt-responsive gene sequences. In this study, we have selected a novel salt-inducible gene SbSI-2 (Salicornia brachiata salt-inducible-2) for functional characterization. Bioinformatics analysis revealed that SbSI-2 protein has predicted nuclear localization signals and a strong protein-protein interaction domain. Transient expression of the RFP:SbSI2 fusion protein confirmed that SbSI-2 is a nuclear-localized protein. Genomic organization study showed that SbSI-2 is intronless and has a single copy in Salicornia genome. Quantitative RT-PCR analysis revealed higher SbSI-2 expression under salt stress and desiccation conditions. The SbSI-2 gene was transformed in E. coli and tobacco for functional characterization. pET28a-SbSI-2 recombinant E. coli cells showed higher tolerance to desiccation and salinity compared to vector alone. Transgenic tobacco plants overexpressing SbSI-2 have improved salt- and osmotic tolerance, accompanied by better growth parameters, higher relative water content, elevated accumulation of compatible osmolytes, lower Na(+) and ROS accumulation and lesser electrolyte leakage than the wild-type. Overexpression of the SbSI-2 also enhanced transcript levels of ROS-scavenging genes and some stress-related transcription factors under salt and osmotic stresses. Taken together, these results demonstrate that SbSI-2 might play an important positive modulation role in abiotic stress tolerance. This identifies SbSI-2 as a novel determinant of salt/osmotic tolerance and suggests that it could be a potential bioresource for engineering abiotic stress tolerance in crop plants.