Overexpression of a PIP1 Gene from Salicornia bigelovii in Tobacco Plants Improves Their Drought Tolerance

Aquaporin (AQP) proteins can transport water and other small molecules through cellular membranes and are one of the first targets of stress-induced signaling in plants. A number of AQP genes have been identified from glycophytes, and their functions have been studied. However, the reports on AQPs from halophytes and their precise role in abiotic stress response are still rare. In this study, we have identified a PIP1 subgroup AQP gene, designated SbPIP1, from the euhalophyte Salicornia bigelovii and characterized it by overexpressing in tobacco plants. SbPIP1 transcript was induced by cold, but suppressed by NaCl and polyethylene glycol (PEG). Transient expression of GFP (green fluorescent protein)-SbPIP fusion protein indicated its localization in the plasma membrane. Overexpression of SbPIP1 in tobacco (Nicotiana tabacum) plants increased their drought tolerance. Leaf protoplasts from transgenic tobacco plants absorbed water more quickly than those from wild type (WT) plants when they were put into hypotonic solution. In addition, the transgenic tobacco plants possessed higher relative water content (RWC) and proline content, but lower levels of malondialdehyde (MDA) and less ion leakage (IL) when compared with WT under the treatment of the different concentrations of PEG. Taken together, our results demonstrate that heterologous expression of SbPIP1 in tobacco plants confers them drought stress tolerance by reducing membrane injury and increasing the ability to retain water.