Phospholipase D (PLD) forms the major family of phospholipases that was first discovered and cloned in plants. In this report we have shown, for the first time, that C2 phosphatidylinositol-4,5-bisphosphate (PIP2)-dependent PLD(s) from 5 day hypocotyls of Brassica oleracea associated with plasma membrane is covalently modified-phosphorylated. Pre-incubation of the plasma membrane fraction with acid phosphatase resulted in concentration-dependent inhibition of PIP2-dependent PLD activity. Using matrix-assisted laser desorption/ionization time of flight mass spectrometry of tryptic in-gel digests, the BoPLDγ1,2 isoform was identified. Comparing the spectra of the proteins obtained from the plasma membrane fractions treated and non-treated with acid phosphatase, three peptides differing in the mass of the phosphate group (80 Da) were revealed: TMQMMYQTIYK, EVADGTVSVYNSPR and KASKSRGLGK which possess five potential Ser/Thr phosphorylation sites. Our findings suggest that a phosphorylation/dephosphorylation mechanism may be involved in the regulation of plant PIP2-dependent PLDγ activity.
