Phospholipase Dα from sunflower (Helianthus annuus): cloning and functional characterization

D type phospholipases (PLD) are enzymes that hydrolyze the head group of phospholipids to produce phosphatidic acid. This activity is ubiquitous in plant tissues, and has been isolated and characterized from different species and organs. Several families of these proteins have been described in plants on the basis of their gene sequences (PLD α, β, γ, δ, ζ and ε). They have been shown to be involved in many metabolic events, such as response to abiotic stress, signal transduction, and membrane lipid turnover and degradation. In the present study, PLD activity was measured in the soluble fractions isolated from different organs of this plant. A PLD of α type was cloned from leaf cDNA that was responsible for most of this activity. The gene encoding this 810 aa protein was heterologously expressed in E. coli. This protein was not lethal for the eukaryotic host, although it altered its phospholipid profile. PLDα was purified to almost homogeneity by His-tag affinity chromatography, displaying an optimum pH of 6.5 and strong dependence on the presence of Ca2+ and SDS in the assay medium. The enzyme was active towards phosphatidylcholine, Phosphatidylethanolamine and phosphatidylglycerol. Furthermore, the HaPLDα gene was found to be expressed at high levels in leaf and stem tissues.