N-Acylethanolamines (NAEs), although are ubiquitous in plants and animals the occurrence of endocannabinoid ligands and the corresponding cannabinoid receptors was limited to mammals. Interestingly, bryophytes, unlike seed plants possess arachidonic acid (AA, 20:4) and eicosapentaenoic acid (EPA, 20:5), which are fatty acid precursors for endocannabinoid ligands. Here, we show that the moss Physcomitrella patens contains ~24 and 7 % of AA and EPA, respectively. Using selective lipidomic profiling, we identified polyunsaturated NAEs, including N-arachidonoyl ethanolamide (anandamide/AEA/NAE 20:4) and N-eicosapentaenoyl ethanolamide (EPEA) and also their corresponding N-acyl-phosphatidylethanolamine (NAPE) precursors in various developmental stages of Physcomitrella. Quantification of various NAPE and NAE species indicated the abundance of unsaturated species over saturated. In all haploid developmental stages analyzed, NAE 20:4 levels contributed to ~ 30 % (~ 26 ng mg-1 lipid) of the total NAE while NAE 20:5 remained as a minor component (~ 5 %; ~ 4.5 ng mg-1 lipid). Exogenous application of AEA, EPEA and their corresponding fatty acid precursors (AA and EPA, respectively) inhibited the growth of gametophytes and protonemata in a dose-dependent manner. AEA has shown the exclusive effect on the F-actin dynamics at the apex of protonemal cells, which was similar to the effect of abscisic acid (ABA) on protonemal growth inhibition. Additionally, we identified moss ortholog for NAPE-hydrolyzing phospholipase D (NAPE-PLD) enzyme that was responsive to exogenous ABA. Putative PpNAPE-PLD was expressed in E. coli for further characterization. Our data demonstrate the occurrence of evolutionarily conserved NAE metabolic pathway in the moss, with the occurrence of AEA and EPEA.

Classically, endogenous fatty acid ethanolamides and their derivatives that bind to the cannabinoid receptors and trigger a signalling pathway are referred to as endocannabinoids. Although derivatives of arachidonic acid, including arachidonylethanolamine or anandamide, are the known endogenous ligands for cannabinoid receptors, other fatty acid ethanolamides or N-acylethanolamines (NAE) that vary in carbon chain length and saturation occur ubiquitously in eukaryotic organisms and play an important role in their physiology and development. The metabolic pathway for NAEs is highly conserved among eukaryotes and well characterised in mammalian systems. Although NAE pathway is only partly elucidated in plants, significant progress has been made in the past 20 years in understanding the implications of the metabolism of saturated and unsaturated endocannabinoid-like molecules in plant development and growth. The latest advancements in the field of plant endocannabinoid research are reviewed. Key Concepts Endocannabinoids are endogenous ligands of cannabinoid receptors in mammalian systems. Endocannabinoids belong to a class of small bioactive lipid molecules that are derivatives of fatty acids including their ethanolamides, referred to as N-acylethanolamines. N-Acylethanolamines are ubiquitous and their metabolic pathway is highly conserved among eukaryotes. In higher plants, only 12–18C N-acylethanolamines have been identified and their metabolic pathway is partly elucidated. The endocannabinoid-like lipids play an important role in seed germination, seedling development, flowering and cellular organisation. In plants, N-acylethanolamines also participate in mediating responses to biotic and abiotic stress.