At4g29530 is a phosphoethanolamine phosphatase homologous to PECP1 with a role in flowering time regulation.

Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the most abundant phospholipids in membranes. The biosynthesis of phospholipids occurs mainly via the Kennedy pathway. Recent studies have shown that through this pathway, choline (Cho) moieties are synthesized through the methylation of phosphoethanolamine (PEtn) to phosphocholine (PCho) by phospho-base N-methyltransferase. In Arabidopsis thaliana, the phosphoethanolamine/phosphocholine phosphatase1 (PECP1) is described as an enzyme that regulates the synthesis of PCho by decreasing the PEtn level during phosphate starvation to avoid the energy-consuming methylation step. By homology search, we identified a gene (At4g29530) encoding a putative PECP1 homolog from Arabidopsis with a currently unknown biological function in planta. We found that At4g29530 is not induced by phosphate starvation, and is mainly expressed in leaves and flowers. The analysis of null mutants and overexpression lines revealed that PEtn, rather than PCho, is the substrate in vivo, as in PECP1. Hydrophilic interaction chromatography-coupled mass spectrometry analysis of head group metabolites shows an increased PEtn level and decreased ethanolamine level in null mutants. At4g29530 null mutants have an early flowering phenotype, which is corroborated by a higher PC/PE ratio. Furthermore, we found an increased PCho level. The choline level was not changed, so the results corroborate that the PEtn-dependent pathway is the main route for the generation of Cho moieties. We assume that the PEtn-hydrolyzing enzyme participates in fine-tuning the metabolic pathway, and helps prevent the energy-consuming biosynthesis of PCho through the methylation pathway.

Pi starvation-dependent regulation of ethanolamine metabolism by phosphoethanolamine phosphatase PECP1 in Arabidopsis roots.

A universal plant response to phosphorus deprivation is the up-regulation of a diverse array of phosphatases. As reported recently, the AtPECP1 gene encodes a phosphatase with in vitro substrate specificity for phosphoethanolamine and phosphocholine. The putative substrates suggested that AtPECP1 is related to phospholipid metabolism; however, the biological function of AtPECP1 is as yet not understood. In addition, whereas lipid remodelling processes as part of the phosphorus starvation response have been extensively studied, knowledge of the polar head group metabolism and its regulation is lacking. We found that AtPECP1 is expressed in the cytosol and exerts by far its strongest activity in roots of phosphate-starved plants. We established a novel LC-MS/MS-based method for the quantitative and simultaneous measurement of the head group metabolites. The analysis of Atpecp1 null mutants and overexpression lines revealed that phosphoethanolamine, but not phosphocholine is the substrate of AtPECP1 in vivo. The impact on head group metabolite levels is greatest in roots of both loss-of-function and gain-of-function transgenic lines, indicating that the biological role of AtPECP1 is mainly restricted to roots. We suggest that phosphoethanolamine hydrolysis by AtPECP1 during Pi starvation is required to down-regulate the energy-consuming biosynthesis of phosphocholine through the methylation pathway.