Ectopic expression of a grapevine alkaline α-galactosidase seed imbibition protein VvSIP enhanced salinity tolerance in transgenic tobacco plants

Alpha-galactosidase seed imbibition protein (VvSIP) isolated from Vitis vinifera is up-regulated upon salt stress and mediates osmotic stress responses in a tolerant grapevine cultivar. So far, little is known about the putative role of this stress-responsive gene. In the present study, VvSIP function was investigated in model tobacco plants via Agrobacterium-mediated genetic transformation. Our results showed that overexpression of VvSIP exhibited increased tolerance to salinity at germination and late vegetative stage in transgenic Nicotiana benthamiana compared to the nontransgenic plants based on the measurement of the germination rate and biomass production. High salt concentrations of 200 and 400 mM NaCl in greenhouse-grown pot assay resulted in better relative water content, higher leaf osmotic potential, and leaf water potential in transgenic lines when compared to the wild-type (WT) plants. These physiological changes attributed to efficient osmotic adjustment improved plant performance and tolerance to salinity compared to the WT. Moreover, the VvSIP-expressing lines SIP1 and SIP2 showed elevated amounts of chlorophyll with lower malondialdehyde content indicating a reduced lipid peroxidation required to maintain membrane stability. When subjected to high salinity conditions, the transgenic tobacco VvSIP exhibited higher soluble sugar content, which may suggest an enhancement of the carbohydrate metabolism. Our findings indicate that the VvSIP is involved in plant salt tolerance by functioning as a positive regulator of osmotic adjustment and sugar metabolism, both of which are responsible for stress mitigation. Such a candidate gene is highly suitable to alleviate environmental stresses and thus could be a promising candidate for crop improvement.