Populus euphratica Phospholipase D delta Increases Salt Tolerance by Regulating K+/Na+ and ROS Homeostasis in Arabidopsis

Phospholipase D alpha (PLD alpha), which produces signaling molecules phosphatidic acid (PA), has been shown to play a critical role in plants adapting to salt environments. However, it is unclear whether phospholipase D delta (PLD delta) can mediate the salt response in higher plants. PePLD delta was isolated from salt-resistant Populus euphratica and transferred to Arabidopsis thaliana to testify the salt tolerance of transgenic plants. The NaCl treatment (130 mM) reduced the root growth and wholeplant fresh weight of wild-type (WT) A. thaliana, vector controls (VC) and PePLD delta-overexpressed lines, although a less pronounced effect was observed in transgenic plants. Under salt treatment, PePLD delta-transgenic Arabidopsis exhibited lower electrolyte leakage, malondialdehyde content and H2O2 levels than WT and VC, resulting from the activated antioxidant enzymes and upregulated transcripts of genes encoding superoxide dismutase, ascorbic acid peroxidase and peroxidase. In addition, PePLD delta-overexpressed plants increased the transcription of genes encoding the plasma membrane Na+/H+ antiporter (AtSOS1) and H+-ATPase (AtAHA2), which enabled transgenic plants to proceed with Na+ extrusion and reduce K+ loss under salinity. The capacity to regulate reactive oxygen species (ROS) and K+/Na+ homeostasis was associated with the abundance of specific PA species in plants overexpressing PePLD delta. PePLD delta-transgenic plants retained a typically higher abundance of PA species, 34:2 (16:0-18:2), 34:3 (16:0-18:3), 36:4 (18:2-18:2), 36:5 (18:2-18:3) and 36:6 (18:3-18:3), under control and saline conditions. It is noteworthy that PA species 34:2 (16:0-18:2), 34:3 (16:0-18:3), 36:4 (18:2-18:2) and 36:5 (18:2-18:3) markedly increased in response to NaCl in transgenic plants. In conclusion, we suppose that PePLD delta-derived PA enhanced the salinity tolerance by regulating ROS and K+/Na+ homeostasis in Arabidopsis.