Lyso-Phosphatidic Acid Acyl-Transferases: a link with intracellular protein transport in Arabidopsis root cells?

Phosphatidic acid (PA) and Lysophosphatidic acid acyltransferases (LPAATs) might be critical for the secretory pathway. Four extra-plastidial LPAATs (numbered 2,3,4 and 5) were identified in A. thaliana. These AtLPAATs, displaying an enzymatic activity specific for LPA to produce PA, are located in the endomembrane system. We focused on the putative role of the AtLPAATs 3, 4 and 5 in the secretory pathway of root cells through genetical (knock-out mutants), biochemical (activity inhibitor, lipid analyses) and imaging (live and immuno-confocal microscopies) approaches. Treating a lpaat4;lpaat5 double mutant with the LPAAT inhibitor CI976 showed a primary root growth decrease. The transport of the auxin transporter PIN2 was disturbed in this lpaat4;lpaat5 double mutant treated with CI976, but not that of H+-ATPases. The lpaat4;lpaat5 double mutant was sensitive to salt stress and the transport of the aquaporin PIP2;7 to the plasma membrane in the lpaat4;lpaat5 double mutant treated with CI976 was reduced. We measured the amounts of neo-synthesized PA in roots, and found a decrease in PA only in the lpaat4;lpaat5 double mutant treated with CI976, suggesting that the protein transport impairment was due to a critical PA concentration threshold. HighlightPhosphatidic acid produced by Lyso-Phosphatidic Acid Acyl-Transferases has an impact on the efficiency of the intracellular transport of some proteins in Arabidopsis thaliana root cells.