Rice Phospholipase Dα is Involved in Salt Tolerance by the Mediation of H+-ATPase Activity and Transcription

Phospholipase D alpha (PLD alpha) is involved in plant response to salt stress, but the mechanisms remain unclear. We investigated rice PLD alpha (OsPLD alpha) localization and its effect on tonoplast (TP) and plasma membrane (PM) H+-ATPase activity and transcription in response to NaCl. When rice suspension-cultured cells were treated with 100 mM NaCl, PLD alpha activity in cell extracts showed a transient activation with a threefold increase at 1 h. The amount of OsPLD alpha protein decreased slightly in the cytosolic fractions, whereas it increased significantly in the TP after NaCl treatment. OsPLD alpha 1 knockdown cells were developed using RNA interference (RNAi) methods. The increase in TP and PM H+-ATPase activity induced by NaCl was significantly inhibited in OsPLD alpha 1-RNAi cells. Knockdown of OsPLD alpha 1 prevented the NaCl-induced increase in the transcript level of OsVHA-A (encodes TP H+-ATPase) and OSA2 (encodes PM H+-ATPase), as well as OsNHX1 (encodes TP Na+/H+ antiporter). The cells died more in OsPLD alpha 1-RNAi mutant than in wild type when they were treated with NaCl. These results suggest that OsPLD alpha is involved in salt tolerance in rice through the mediation of H+-ATPase activity and transcription.