A plastidial lysophosphatidic acid acyltransferase from oilseed rape

The biosynthesis of phosphatidic acid, a key intermediate in the biosynthes is of lipids, is controlled by lysophosphatidic acid (LPA, or 1-acyl-glycer ol-3-P) acyltransferase (LPAAT, EC 2.3.1.51). We have isolated a cDNA encod ing a novel LPAAT by functional complementation of the Escherichia coli mut ant plsC with an immature embryo cDNA library of oilseed rape (Brassica nap us). Transformation of the acyltransferase-deficient E. coli strain JC201 w ith the cDNA sequence BAT2 alleviated the temperature-sensitive phenotype o f the plsC mutant and conferred a palmitoyl-coenzyme A-preferring acyltrans ferase activity to membrane fractions. The BAT2 cDNA encoded a protein of 3 51 amino acids with a predicted molecular mass of 38 kD and an isoelectric point of 9.7. Chloroplast-import experiments showed processing of a BAT2 pr ecursor protein to a mature protein of approximately 32 kD, which was local ized in the membrane fraction. BAT2 is encoded by a minimum of two genes th at may be expressed ubiquitously. These data are consistent with the identi ty of BAT2 as the plastidial enzyme of the prokaryotic glycerol-3-P pathway that uses a palmitoyl-ACP to produce phosphatidic acid with a prokaryotic- type acyl composition. The homologies between the deduced protein sequence of BAT2 with prokaryotic and eukaryotic microsomal LAP acytransferases sugg est that seed microsomal forms may have evolved from the plastidial enzyme.