The signal molecule lysophosphatidylcholine in Eschscholzia californica is rapidly metabolized by reacylation

Abstract

In cultured cells of California poppy (Eschscholzia californica), lysophosphatidylcholine (LPC) triggers a signal path that finally induces alkaloid biosynthesis. LPC is transiently generated by elicitor-activated phospholipase A(2) of the plasma membrane. Externally added LPC is rapidly acylated by a membrane-bound enzyme that shows the highest specific activity in the purified plasma membrane. The fatty acid incorporated into the sn-2 position of LPC is preferentially linoleic (18:2), which is the most abundant acyl component in the PC species of Eschscholzia cells, but a minor component of the pool of free fatty acids. The fatty acid at the sn-1 position of LPC is less important for substrate specificity. The capacity of LPC acylation by intact cells or isolated plasma membranes by far exceeds the rate of LPC generation by activated phospholipase A(2) and is not limited by the availability of acyl donors. Metabolites other than phosphatidylcholine (PC) were not significantly produced from labeled LPC within 20 min, indicating that lysophospholipases are not significantly contributing to the short-time metabolism of LPC. It is concluded that reacylation to PC is the dominating process in the detoxication of LPC and ensures the transient character of its steady state concentrations, even at maximum phospholipase A(2) activities.

Phospholipases and the Network of Auxin Signal Transduction with ABP1 and TIR1 as Two Receptors: A Comprehensive and Provocative Model

“…Reacylation of lysolipid is quite active (Schwartze and Roos, 2008), which may explain why LPC accumulation is found only at high auxin concentrations. That PLA hydrolysis is followed by rapid conversion, e.g., to acyl-CoA of FFA or reacylation of lysolipids (Larsson et al, 2007; Schwartze and Roos, 2008), may be a necessary consequence because both FFA and lysolipids could be membrane-perturbing substances at higher concentrations. Reacylation also prevents an overshooting response to the signal.…”

“Self” and “Non-Self” in the Control of Phytoalexin Biosynthesis: Plant Phospholipases A2 with Alkaloid-Specific Molecular Fingerprints

“…(2) Lysophosphatidylcholine (LPC) produced by PLA2-catalyzed lipid hydrolysis acts as a second messenger by activating vacuolar H + /Na + antiporters. The LPC level in the cytoplasm peaks after elicitor contact (Viehweger et al, 2002) and is controlled by its PLA2-catalyzed generation and rapid enzymic reacylation (Schwartze and Roos, 2008). If added to permeabilized cells in low micromolar concentrations, LPC causes a Na + -dependent efflux of vacuolar protons, which is blocked by amiloride, an inhibitor of vacuolar sodium/proton antiporters ( Viehweger et al, 2002).…”

The Vacuolar Proton-Cation Exchanger EcNHX1 Generates pH Signals for the Expression of Secondary Metabolism in Eschscholzia californica

“…compartmentation and metabolism of LPC). Based on earlier results about the metabolism of LPC in E. californica cell cultures, it is likely that the LPC molecule itself, rather than a rapidly made metabolite, stimulates the Na + /H + antiporter: the only metabolite detectable after a 20-min feeding of radiolabeled LPC was phosphatidylcholine (made by reacylation; Schwartze and Roos, 2008). This compound does not stimulate the Na + /H + antiport activity, and the same holds true for potential degradation products such as lysophosphatidic acid, phosphorylcholine, and fatty acids (tested by Viehweger et al [2002]).…”

“…Prior to the pH shifts, the activation of a plasma membrane-localized phospholipase A2 (PLA2) is detectable in elicited cells, which gives rise to a transient peak of LPC in the cytoplasm (Roos et al, 1999;Viehweger et al, 2002Viehweger et al, , 2006Schwartze and Roos, 2008). In order to localize the interference of this molecule with the intracellular signal transfer, we established an osmotic procedure that permeabilized the plasma membrane for micromolecules less than 10 kD and left the tonoplast functionally intact, as confirmed by the vacuolar accumulation of pH probes, the ATP-or Figure 1.…”