Phospholipase Dα3 is involved in the hyperosmotic response in Arabidopsis

Rapid activation of phospholipase D (PLD), which hydrolyzes membrane lipids to generate phosphatidic acid (PA), occurs under various hyperosmotic conditions, including salinity and water deficiency. The Arabidopsis thaliana PLD family has 12 members, and the function of PLD activation in hyperosmotic stress responses has remained elusive. Here, we show that knockout (KO) and overexpression (OE) of previously uncharacterized PLD alpha 3 alter plant response to salinity and water deficit. PLD alpha 3 uses multiple phospholipids as substrates with distinguishable preferences, and alterations of PLD alpha 3 result in changes in PA level and membrane lipid composition. PLD alpha 3-KO plants display increased sensitivities to salinity and water deficiency and also tend to induce abscisic acid-responsive genes more readily than wild-type plants, whereas PLD alpha 3-OE plants have decreased sensitivities. In addition, PLD alpha 3-KO plants flower later than wild-type plants in slightly dry conditions, whereas PLD alpha 3-OE plants flower earlier. These data suggest that PLD alpha 3 positively mediates plant responses to hyperosmotic stresses and that increased PLD alpha 3 expression and associated lipid changes promote root growth, flowering, and stress avoidance.