Ethanolamide Oxylipins of Linolenic Acid Can Negatively Regulate Arabidopsis Seedling Development  

Abstract

N-Acylethanolamines (NAEs) are fatty-acid derivatives with potent biological activities in a wide range of eukaryotic organisms. Polyunsaturated NAEs are among the most abundant NAE types in seeds of Arabidopsis thaliana, and they can be metabolized by either fatty acid amide hydrolase (FAAH) or by lipoxygenase (LOX) to low levels during seedling establishment. Here, we identify and quantify endogenous oxylipin metabolites of N-linolenoylethanolamine (NAE 18:3) in Arabidopsis seedlings and show that their levels were higher in faah knockout seedlings. Quantification of oxylipin metabolites in lox mutants demonstrated altered partitioning of NAE 18:3 into 9-or 13-LOX pathways, and this was especially exaggerated when exogenous NAE was added to seedlings. When maintained at micromolar concentrations, NAE 18:3 specifically induced cotyledon bleaching of light-grown seedlings within a restricted stage of development. Comprehensive oxylipin profiling together with genetic and pharmacological interference with LOX activity suggested that both 9-hydroxy and 13-hydroxy linolenoylethanolamides, but not corresponding free fatty-acid metabolites, contributed to the reversible disruption of thylakoid membranes in chloroplasts of seedling cotyledons. We suggest that NAE oxylipins of linolenic acid represent a newly identified, endogenous set of bioactive compounds that may act in opposition to progression of normal seedling development and must be depleted for successful establishment.

A chemical genetic screen uncovers a small molecule enhancer of the N-acylethanolamine degrading enzyme, fatty acid amide hydrolase, in Arabidopsis

“…Thus far, only amidase 1 (AMI1) has been shown to hydrolyze NAE but its activity was more directed toward indole-3 acetamide and only exhibited low activity toward NAE30. Recently, alternative pathways for the metabolic fate of NAEs have been discovered including the malonylation of glucose-conjugated NAE 12:031 and lipoxygenase-mediated oxidation of polyunsaturated NAEs3233. It is not clear how these additional NAE metabolic pathways interact with FAAH-mediated NAE hydrolysis.…”

Changes in Retinal N‐Acylethanolamines and their Oxylipin Derivatives During the Development of Visual Impairment in a Mouse Model for Glaucoma

“…1. Chiral-phase HPLC of selected samples confirmed the enantiomeric nature of NAE oxylipins, as described previously [28]. …”

N‐Acylethanolamines: lipid metabolites with functions in plant growth and development

“…Most importantly, NAE levels in seeds decrease markedly with germination and seedling establishment (Chapman et al ., ; Kilaru et al ., ). As discussed below, there is accumulating evidence that this decrease in NAE levels is physiologically relevant for the embryo‐to‐seedling transition through interaction with abscisic acid (ABA) signaling pathways (Figure ; Teaster et al ., ; Keereetaweep et al ., ).…”

“…This figure has been reproduced from Keereetaweep et al . () with permission from the American Society of Plant Biologists ( www.plantcell.org).…”

“…Specific chlorophyll metabolites have not been identified or quantified in seedlings with increased NAE 18:3‐derived oxylipins. However, there are several characteristics of chloroplast disruption in this particular situation (Keereetaweep et al ., ) that may distinguish this seedling growth‐arrest from the general process of chlorophyll turnover. First, the effects are stage‐specific, i.e.…”