N-Acylethanolamine Signaling in Tobacco Is Mediated by a Membrane-Associated, High-Affinity Binding Protein

Abstract

N-Acylethanolamines (NAEs) are fatty acid derivatives found as minor constituents of animal and plant tissues, and their levels increase 10- to 50-fold in tobacco (Nicotiana tabacum) leaves treated with fungal elicitors. Infiltration of tobacco leaves with submicromolar to micromolar concentrations ofN-myristoylethanolamine (NAE 14:0) resulted in an increase in relative phenylalanine ammonia-lyase (PAL) transcript abundance within 8 h after infiltration, and this PAL activation was reduced after co-infiltration with cannabinoid receptor antagonists (AM 281 and SR 144528). A saturable, high-affinity specific binding activity for [3H]NAE 14:0 was identified in suspension-cultured tobacco cells and in microsomes from tobacco leaves (apparent K d of 74 and 35 nm,respectively); cannabinoid receptor antagonists reduced or eliminated specific [3H]NAE 14:0 binding, consistent with the physiological response. N-Oleoylethanolamine activatedPAL2 expression in leaves and diminished [3H]NAE 14:0 binding in microsomes, whereasN-linoleoylethanolamine did not activatePAL2 expression in leaves, and did not affect [3H]NAE 14:0 binding in microsomes. The nonionic detergent dodecylmaltoside solubilized functional [3H]NAE 14:0-binding activity from tobacco microsomal membranes. The dodecylmaltoside-solubilized NAE-binding activity retained similar, but not identical, binding properties to the NAE-binding protein(s) in intact tobacco microsomes. Additionally, high-affinity saturable NAE-binding proteins were identified in microsomes isolated from Arabidopsis and Medicago truncatula tissues, indicating the general prevalence of these binding proteins in plant membranes. We propose that plants possess an NAE-signaling pathway with functional similarities to the “endocannabinoid” pathway of animal systems and that this pathway, in part, participates in xylanase elicitor perception in tobacco.

The hrpN gene of Erwinia amylovora stimulates tobacco growth and enhances resistance to Botrytis cinerea

“…However, activation of defense-signaling cascades in plants is a consequence of sensing of the elicitor by specific plant receptors (Tripathy et al 2003). Since harpin-induced HR is a potentially useful tool for conferring pathogen-resistance on selected plants, transformation with harp genes has been used to engineer pathogen-resistance (Keller et al 1999;Peng et al 2004).…”

Molecular Identification of a Functional Homologue of the Mammalian Fatty Acid Amide Hydrolase in Arabidopsis thaliana

“…phenylalanine ammonia-lyase and PAL2 transcript abundance) in tobacco plants within hours of treatment in a manner similar to but independent of elicitor proteins (17). Mammalian cannabinoid receptor antagonists at concentrations equimolar to NAE blocked the activation of defense gene expression induced by either NAEs or by fungal elicitor proteins (16). A membrane-associated protein was identified in leaves of tobacco (and other plant species), which specifically bound to [ 3 H]NAE 14:0 with high affinity (K d in the low nanomolar range).…”

“…A membrane-associated protein was identified in leaves of tobacco (and other plant species), which specifically bound to [ 3 H]NAE 14:0 with high affinity (K d in the low nanomolar range). This NAE 14:0-binding protein was proposed to mediate the NAE activation of PAL2 expression in tobacco leaves, a conclusion that was based on the similarities between NAE binding properties in vitro and NAEinduced physiological responses in vivo, including experiments with cannabinoid receptor antagonists (16). Although some clear differences are evident between the emerging NAE signaling pathway in plants and the better characterized endocannabinoid signal pathway of animals, there appear to be some remarkable similarities in the formation and perception of bioactive acylethanolamides by these two diverse groups of multicellular organisms.…”

“…For example, NAE 14:0 appears to function as an endogenous modulator of pathogen elicitor signaling by plant cells (12,16). NAE 14:0 levels, quantified by gas-liquid chromatography-mass spectrometry, increased 10 -50-fold in leaves of tobacco plants that were treated for a few minutes with either xylanase or cryptogein elicitor proteins (17).…”

Phospholipids as Plant Growth Regulators

“…Additional enzyme studies showed that NAE could be metabolized to free fatty acids and ethanolamine (EA) by an amide hydrolase . In plants, NAPE-NAE metabolism is involved in PLD-mediated accumulation of NAE14:0 following elicitor perception, in NAE14:0 activation of phenylalanine ammonia lyase gene expression independent of pathogen elicitors, and in NAE14:0 reduction of pathogeninduced alkalinization (Tripathy et al 1999(Tripathy et al , 2003. These authors suggest that metabolism of NAPE and the specific accumulation of NAE14:0 is part of a transduction pathway that modulates cellular defence responses following perception of fungal elicitors.…”