Multiple PLDs Required for High Salinity and Water Deficit Tolerance in Plants

Abstract

High salinity and drought have received much attention because they severely affect crop production worldwide. Analysis and comprehension of the plant's response to excessive salt and dehydration will aid in the development of stress-tolerant crop varieties. Signal transduction lies at the basis of the response to these stresses, and numerous signaling pathways have been implicated. Here, we provide further evidence for the involvement of phospholipase D (PLD) in the plant's response to high salinity and dehydration. A tomato (Lycopersicon esculentum) α-class PLD, LePLDα1, is transcriptionally up-regulated and activated in cell suspension cultures treated with salt. Gene silencing revealed that this PLD is indeed involved in the salt-induced phosphatidic acid production, but not exclusively. Genetically modified tomato plants with reduced LePLDα1 protein levels did not reveal altered salt tolerance. In Arabidopsis (Arabidopsis thaliana), both AtPLDα1 and AtPLDδ were found to be activated in response to salt stress. Moreover, pldα1 and pldδ single and double knock-out mutants exhibited enhanced sensitivity to high salinity stress in a plate assay. Furthermore, we show that both PLDs are activated upon dehydration and the knock-out mutants are hypersensitive to hyperosmotic stress, displaying strongly reduced growth.

Phospholipase D δ knock-out mutants are tolerant to severe drought stress

“…2 A proposed function for PLD during senescence and wounding is to breakdown membrane lipids, which generates high levels of PA and as a consequence a loss of membrane bilayer phase, leading to loss of cell membrane integrity. 3,4 In addition PLD has been shown to be involved in vesicular trafficking during polar cell-expansion, 5,6 and to be associated with the microtubules. 7 The PA produced by PLD has been proposed to be a membranous second messenger molecule.…”

“…16 PLDa and d classes have been linked to high salinity and water-deficit stress as well as to the stress hormone abscisic acid (ABA). 4,11,17 ABA regulates many aspects of plant development during environmental stresses, allowing the plant to cope and survive in adverse conditions, such as drought, low or high temperature, or high salinity.…”

Role of phosphatidic acid in plant galactolipid synthesis

“…An increase of PA from 1.2 to 11.5 nmol per mg of dry weight (9.6 fold increase) was reported in rosettes of preflowering Arabidopsis plants exposed to freezing [8]. Similarly, an increase of PA from 5 to 25 mol % of phospholipids (5 fold increase) was reported in leaves of tomato and Arabidopsis plants treated with high concentration of NaCl mimicking a drought stress [9] and an increase of PA from 0.5 to 4 mol % of total glycerolipids (8 fold increase) was detected in Arabidopsis cells at early steps of phosphate deprivation (Jouhet, personal communication).…”

Phospholipids

“…The double mutant, pldα1pldδ, was shown to be the most sensitive to salt stress compared with regardless of wild-type or single mutants. 22 By contrast, silencing of tomato (Lycopersicon esculentum) LePLDα1 did not render mutants any salt sensitivity. They showed the same root growth rate as wide-type plants.…”

“…9,10,[19][20][21][22] Phospholipase D (PLD), which can hydrolyze phospholipids into phosphatidic acid and head group, is involved in plant salt tolerance. Arabidopsis PLDα1 and PLDδ are proved to function cooperatively in high salinity.…”