TsDHN-2, a unique dehydrin protein from Thellungiella and its role in salt tolerance

Abstract

Salt stress, or salinity, is one of the most common environmental stresses affecting crop yield worldwide. Due to the prevalence of salinity stress, it is not surprising that plants have evolved mechanisms to tolerate osmotic and ionic stress caused by salinity. Dehydrins are intrinsically unstructured proteins that accumulate in photosynthetic organisms under dehydrating conditions, such as salinity, and are thought to confer stress tolerance through the stabilization of cellular membranes. Thellungiella salsuginea, a close relative of Arabidopsis thaliana, is a halophyte that thrives in the Canadian sub-Arctic (Yukon Territory), that is able to tolerate extreme conditions, including high salinity. TsDHN-2 is a basic dehydrin from Thellungiella whose transcript increases over 10-fold in response to salinity treatment. Using RNA interference (RNAi) methodology, TsDHN-2 has been silenced and these lines were used in this study to investigate the role TsDHN-2 may play in the salt tolerance of Thellungiella. RNAi line 7-8 presented a 41% reduced expression of TsDHN-2 in comparison to wild-type (WT). Seed of this line showed a 15% germination rate compared to 40% in WT in the presence of 100 mM NaCl. Salinity stress experiments were performed by treating the RNAi lines and WT plants with 300 mM NaCl for up to two weeks. Line 7-8 exhibited a 6.2% greater decrease in photochemical efficiency of photosystem II (PSII) as estimated by the variable to maximal fluorescence ratio (Fv/Fm) and showed 5% greater phenotypic damage than WT when estimated visually. Concentrations of the compatible osmolyte proline increased in response to salt treatment by 3.4-fold in WT and 8.1-fold in line 7-8, suggesting this compound may be a marker for salinity tolerance. Collectively, these data support the notion that TsDHN-2 plays a role in the salinity tolerance mechanisms of Thellungiella.