Overexpression of a wheat aquaporin gene, TaAQP8, enhances salt stress tolerance in transgenic tobacco.

Aquaporin (AQP) proteins have been shown to transport water and other small molecules through biological membranes, which is crucial for plants to combat salt stress. However, the precise role of AQP genes in salt stress response is not completely understood in plants. In this study, a PIP1 subgroup AQP gene, designated TaAQP8, was cloned and characterized from wheat. Transient expression of TaAQP8-green fluorescent protein (GFP) fusion protein revealed its localization in the plasma membrane. TaAQP8 exhibited water channel activity in Xenopus laevis oocytes. TaAQP8 transcript was induced by NaCl, ethylene and H(2)O(2). Further investigation showed that up-regulation of TaAQP8 under salt stress involves ethylene and H(2)O(2) signaling, with ethylene causing a positive effect and H(2)O(2) acting as a negative factor. Overexpression of TaAQP8 in tobacco increased root elongation compared with controls under salt stress. The roots of transgenic plants also retained a high K(+)/Na(+) ratio and Ca(2+) content, but reduced H(2)O(2) accumulation by an enhancement of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities under salt stress. Further investigation showed that whole seedlings from transgenic lines displayed higher SOD, CAT and POD activities, increased NtSOD and NtCAT transcript levels, and decreased H(2)O(2) accumulation and membrane injury under salt stress. Taken together, our results demonstrate that TaAQP8 confers salt stress tolerance not only by retaining high a K(+)/Na(+) ratio and Ca(2+) content, but also by reducing H(2)O(2) accumulation and membrane damage by enhancing the antioxidant system.