N-Acylethanolamine metabolism interacts with abscisic acid signaling in Arabidopsis thaliana seedlings

Antibacterial Activity and Mechanism of Three Root Exudates from Mulberry Seedlings against Ralstonia pseudosolanacearum

Bacterial wilt is a significant soil-borne disease that poses a threat to mulberry production yield and quality of agricultural production worldwide. However, the disease resistance mechanisms dependent on root exudates are not well understood. In this present study, we investigated the antibacterial mechanisms of the main active substances (erucamide, oleamide, and camphor bromide) present in mulberry root exudates (MRE) against Ralstonia pseudosolanacearum (Rp), the causal agent of bacterial wilt. Our findings revealed that these three active substances inhibited the growth activity of Rp by affecting the cell morphology and extracellular polysaccharide content, as well as triggering a burst of reactive oxygen species. The active substances induced oxidative stress, leading to a decrease in Rp growth. Additionally, the expression levels of key genes in the hrp gene cluster (hrpB, hrpX, and hrpF) and other virulence-related genes (such as ripAW, ripAE, Rs5-4819, Rs5-4374, ace, egl3, and pehB) were significantly reduced upon treatment with the active substances. Further pathogenicity experiments demonstrated that root exudates (at a concentration of 1.5 mg·mL-1) delayed or slowed down the occurrence of bacterial wilt in mulberry. These findings provide valuable insight into the antimicrobial mechanisms of MRE against Rp and lay a theoretical foundation for the development and application of biocontrol agents to control mulberry bacterial wilt.

Lipidomics analysis reveals the effect of Sirex noctilio infestation on the lipid metabolism in Pinus radiata needles

The Sirex noctilio's climatic adaption and rapid proliferation have caused Pinus mortality worldwide. The infestation combines the early effect of female S. noctilio gland secretion and the spreading symbiotic fungus Amylostereum areolatum. 'Lipidomics' is the study of all non-water-soluble components of the metabolome. Most of these non-water-soluble compounds correspond to lipids which can provide information about a biological activity, an organelle, an organism, or a disease. Using HPLC-MS/MS based lipidomics, 122 lipids were identified in P. radiata needles during S. noctilio infestation. Phosphatidic acids, N-acylethanolamines, and phosphatidylinositol-ceramides accumulated in infested trees could suggest a high level of phospholipases activities. The phosphatidylcholines were the most down-regulated species during infection, which could also suggest that they may be used as a substrate for up-regulated lipids. The accumulation of very long-chain fatty acids and long-chain fatty acids during the infestation could imply the tree defense response to create a barrier in the drilled zone to avoid larvae development and fungus proliferation. Also, the growth arrest phase of the trees during the prolonged infestation suggests a resistance response, regulated by the accumulation of NAE, which potentially shifts the tree energy to respond to the infestation.

Two legume fatty acid amide hydrolase isoforms with distinct preferences for microbial- and plant-derived acylamides

Fatty acid amide hydrolase (FAAH) is a widely conserved amidase in eukaryotes, perhaps best known for inactivating N-acylethanolamine lipid mediators. However, FAAH enzymes hydrolyze a wide range of acylamide substrates. Analysis of FAAHs from multiple angiosperm species revealed two conserved phylogenetic groups that differed in key conserved residues in the substrate binding pocket. While the foundation group of plant FAAHs, designated FAAH1, has been studied at the structural and functional level in Arabidopsis thaliana, nothing is known about FAAH2 members. Here, we combined computational and biochemical approaches to compare the structural and enzymatic properties of two FAAH isoforms in the legume Medicago truncatula designated MtFAAH1 and MtFAAH2a. Differences in structural and physicochemical properties of the substrate binding pockets, predicted from homology modeling, molecular docking, and molecular dynamic simulation experiments, suggested that these two FAAH isoforms would exhibit differences in their amidohydrolase activity profiles. Indeed, kinetic studies of purified, recombinant MtFAAHs indicated a reciprocal preference for acylamide substrates with MtFAAH1 more efficiently utilizing long-chain acylamides, and MtFAAH2a more efficiently hydrolyzing short-chain and aromatic acylamides. This first report of the enzymatic behavior of two phylogenetically distinct plant FAAHs will provide a foundation for further investigations regarding FAAH isoforms in legumes and other plant species.

Fatty acid amide hydrolase and 9-lipoxygenase modulate cotton seedling growth by ethanolamide oxylipin levels

Polyunsaturated N-acylethanolamines (NAEs) can be hydrolyzed by fatty acid amide hydrolase (FAAH) or oxidized by lipoxygenase (LOX). In Arabidopsis (Arabidopsis thaliana), the 9-LOX product of linoleoylethanolamide, namely, 9-hydroxy linoleoylethanolamide (9-NAE-HOD), is reported to negatively regulate seedling development during secondary dormancy. In upland cotton (Gossypium hirsutum L.), six putative FAAH genes (from two diverged groups) and six potential 9-LOX genes are present; however, their involvement in 9-NAE-HOD metabolism and its regulation of seedling development remain unexplored. Here, we report that in cotton plants, two specific FAAH isoforms (GhFAAH Ib and GhFAAH IIb) are needed for hydrolysis of certain endogenous NAEs. Virus-induced gene silencing (VIGS) of either or both FAAHs led to reduced seedling growth and this coincided with reduced amidohydrolase activities and elevated quantities of endogenous 9-NAE-HOD. Transcripts of GhLOX21 were consistently elevated in FAAH-silenced tissues, and co-silencing of GhLOX21 and GhFAAH (Ib and/or IIb) led to reversal of seedling growth to normal levels (comparable with no silencing). This was concomitant with reductions in the levels of 9-NAE-HOD, but not of 13-NAE-HOD. Pharmacological experiments corroborated the genetic and biochemical evidence, demonstrating that direct application of 9-NAE-HOD, but not 13-NAE-HOD or their corresponding free fatty acid oxylipins, inhibited the growth of cotton seedlings. Additionally, VIGS of GhLOX21 in cotton lines overexpressing AtFAAH exhibited enhanced growth and no detectable 9-NAE-HOD. Altogether, we conclude that the growth of cotton seedlings involves fine-tuning of 9-NAE-HOD levels via FAAH-mediated hydrolysis and LOX-mediated production, expanding the mechanistic understanding of plant growth modulation by NAE oxylipins to a perennial crop species.

Plant N-acylethanolamines play a crucial role in defense and its variation in response to elevated CO2 and temperature in tomato

The ubiquitous lipid-derived molecules N-acylethanolamines (NAEs) have multiple immune functions in mammals, but their roles and mechanisms in plant defense response during changing environment remain largely unclear. Here, we found that exogenous NAE18:0 and NAE18:2 promoted defense against the necrotrophic pathogen Botrytis cinerea but suppressed defense to the hemi-biotrophic pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 in tomato. The knocking-down and overexpression function analysis of the pathogen-responsive NAE synthetic gene PHOSPHOLIPASE Dγ (PLDγ) and hydrolytic gene FATTY ACID AMID HYDROLASE 1 (FAAH1) revealed that the NAE pathway is crucial for plant defense response. Using exogenous applications and SA-abolished NahG plants, we unveiled the antagonistic relationship between NAE and SA in plant defense response. Elevated CO₂ and temperature significantly changed the NAE pathway in response to pathogens, while inhibition of the NAE pathway led to the alternation of environment-mediated defense variations against Pst DC3000 in tomato, indicating that NAE pathway is associated with plant defense variations in response to elevated CO₂ and temperature. The results herein reveal a new function of NAE in plant defense, and its involvement in environment-mediated defense variation in tomato. These findings shed light on the NAE-based plant defense, which may have relevance to crop disease management in future changing climate.

Plasma membrane proteomic changes of Arabidopsis DRP1E during cold acclimation in association with the enhancement of freezing tolerance

The freezing tolerance of plants that live in cold regions increases after exposure to low temperature, a process termed cold acclimation (CA). During CA, restructuring of the plasma membrane (PM) is important to enhance freezing tolerance. We have previously shown that the function of DYNAMIN-RELATED PROTEIN 1 E (DRP1E), which regulates endocytosis by pinching vesicles from the PM, is associated with the enhancement of freezing tolerance during CA in Arabidopsis. DRP1E is predicted to play a role in reconstituting the PM composition during CA. In this study, to test the validity of this hypothesis, we studied the changes in PM proteome patterns induced by drp1e mutation. In a detailed physiological analysis, after 3 days of CA, only young leaves showed significantly less increase in freezing tolerance in the mutant than in the wild type (WT). Using nano-liquid chromatography-tandem mass spectrometry, 496 PM proteins were identified. Among these proteins, 81 or 71 proteins were specifically altered in the WT or the mutant, respectively, in response to CA. Principal component analysis showed that the proteomic pattern differed between the WT and the mutant upon cold acclimation (CA), suggesting that DRP1E contributes to reconstruction of the PM during CA. Cluster analysis revealed that proteins that were significantly increased in the mutant after CA were biased toward glycosylphosphatidylinositol-anchored proteins, such as fasciclin-like arabinogalactan proteins. Thus, a primary target of DRP1E-associated PM reconstruction during CA is considered to be glycosylphosphatidylinositol-anchored proteins, which may be removed from the PM by DRP1E in young leaves after 3 days of CA.

Enhanced seedling growth by 3-n-pentadecylphenolethanolamide is mediated by fatty acid amide hydrolases in upland cotton (Gossypium hirsutum L.)

Fatty acid amide hydrolase (FAAH) is a conserved amidase that is known to modulate the levels of endogenous N-acylethanolamines (NAEs) in both plants and animals. The activity of FAAH is enhanced in vitro by synthetic phenoxyacylethanolamides resulting in greater hydrolysis of NAEs. Previously, 3-n-pentadecylphenolethanolamide (PDP-EA) was shown to exert positive effects on the development of Arabidopsis seedlings by enhancing Arabidopsis FAAH (AtFAAH) activity. However, there is little information regarding FAAH activity and the impact of PDP-EA in the development of seedlings of other plant species. Here, we examined the effects of PDP-EA on growth of upland cotton (Gossypium hirsutum L. cv Coker 312) seedlings including two lines of transgenic seedlings overexpressing AtFAAH. Independent transgenic events showed accelerated true-leaf emergence compared with non-transgenic controls. Exogenous applications of PDP-EA led to increases in overall seedling growth in AtFAAH transgenic lines. These enhanced-growth phenotypes coincided with elevated FAAH activities toward NAEs and NAE oxylipins. Conversely, the endogenous contents of NAEs and NAE-oxylipin species, especially linoleoylethanolamide and 9-hydroxy linoleoylethanolamide, were lower in PDP-EA treated seedlings than in controls. Further, transcripts for endogenous cotton FAAH genes were increased following PDP-EA exposure. Collectively, our data corroborate that the enhancement of FAAH enzyme activity by PDP-EA stimulates NAE-hydrolysis and that this results in enhanced growth in seedlings of a perennial crop species, extending the role of NAE metabolism in seedling development beyond the model annual plant species, Arabidopsis thaliana.

Duration of of Low-Temperature Storage, Clove Topping and Gibberellic Acid on Emergence, Yield and Yield Components of Garlic

Dormancy of freshly harvested garlic cloves does not allow early emergence, and preplanting garlic clove treatment is critical for more than one cycle of production in a year. This field experiment was conducted to assess the effect of treating cloves on emergence, growth, and yield of “Tseday” variety during the main cropping season of 2014/2015 and off-season of 2015/16 at Haramaya University. The experiment was arranged in a factorial combination of four (cold stored at 7°C for the duration of 10, 20, and 30 days and stored at room temperature 21°C for 30 days as control), two (whole and topped clove), and four GA3 treatment at concentration of 0, 125, 250, and 375 mg/l and distilled water treatment as second control laid out in randomized complete block design with three replications. The three main factors (clove type, cold storage duration, and GA3) and growing season showed significant influence on phenology, growth, bulb yield and yield components, and all size categories of cloves, while GA3 showed nonsignificant effect on days to emergence of cloves. Clove type interacted with cold storage duration and GA3, and cold storage duration interacted with GA3 significantly to influence all characters of the variety. In addition, the growing season also interacted with clove type and GA3 to influence all categories of clove size, bulb diameter, average bulb weight, and total bulb yield. The three main factors (clove type × cold storage duration × GA3) interaction significantly influenced all characteristics of the variety. However, 30 days of cold-stored and topped cloves reduced dormancy period and days to maturity by 18.84 and 19.50 days, respectively, and increased total bulb yield by 70.32% as compared to the control treatment. In addition, this treatment combination significantly increased most of the growth and bulb yield components, while the number and weight of small-sized cloves were decreased. Hence, it can be concluded that 30 days of cold storage and topping of cloves without soaking under GA3 could be recommended to enhance early emergence, good vegetative growth, and total bulb yield of the garlic variety both under rain-fed and irrigated conditions.

Beyond the Usual Suspects: Physiological Roles of the Arabidopsis Amidase Signature (AS) Superfamily Members in Plant Growth Processes and Stress Responses

The diversification of land plants largely relies on their ability to cope with constant environmental fluctuations, which negatively impact their reproductive fitness and trigger adaptive responses to biotic and abiotic stresses. In this limiting landscape, cumulative research attention has centred on deepening the roles of major phytohormones, mostly auxins, together with brassinosteroids, jasmonates, and abscisic acid, despite the signaling networks orchestrating the crosstalk among them are so far only poorly understood. Accordingly, this review focuses on the Arabidopsis Amidase Signature (AS) superfamily members, with the aim of highlighting the hitherto relatively underappreciated functions of AMIDASE1 (AMI1) and FATTY ACID AMIDE HYDROLASE (FAAH), as comparable coordinators of the growth-defense trade-off, by balancing auxin and ABA homeostasis through the conversion of their likely bioactive substrates, indole-3-acetamide and N-acylethanolamine.

Fatty acid export protein BnFAX6 functions in lipid synthesis and axillary bud growth in Brassica napus

Sugar is considered as the primary regulator of plant apical dominance, whereby the outgrowth of axillary buds is inhibited by the shoot tip. However, there are some deficiencies in this theory. Here, we reveal that Fatty Acid Export 6 (BnFAX6) functions in FA transport, and linoleic acid or its derivatives acts as a signaling molecule in regulating apical dominance of Brassica napus. BnFAX6 is responsible for mediating FA export from plastids. Overexpression of BnFAX6 in B. napus heightened the expression of genes involved in glycolysis and lipid biosynthesis, promoting the flow of photosynthetic products to the biosynthesis of FAs (including linoleic acid and its derivatives). Enhancing expression of BnFAX6 increased oil content in seeds and leaves and resulted in semi-dwarf and increased branching phenotypes with more siliques, contributing to increased yield per plant relative to wild-type. Furthermore, decapitation led to the rapid flow of the carbon from photosynthetic products to FA biosynthesis in axillary buds, consistent with the overexpression of BnFAX6 in B. napus. In addition, free FAs, especially linoleic acid, were rapidly transported from leaves to axillary buds. Increasing linoleic acid in axillary buds repressed expression of a key transcriptional regulator responsible for maintaining bud dormancy, resulting in bud outgrowth. Taken together, we uncovered that BnFAX6 mediating FA export from plastids functions in lipid biosynthesis and in axillary bud dormancy release, possibly through enhancing linoleic acid level in axillary buds of B. napus.

Lipid Signaling through G Proteins

N-Acylethanolamine (NAE) signaling has received considerable attention in vertebrates as part of the endocannabinoid signaling system, where anandamide acts as a ligand for G protein-coupled cannabinoid receptors. Recent studies indicate that G proteins also are required for some types of NAE signaling in plants. The genetic ablation of the Gβγ dimer or loss of the full set of extra-large G proteins strongly attenuated NAE-induced chloroplast responses in seedlings. Intriguing parallels and distinct differences have emerged between plants and animals in NAE signaling, despite the conserved use of these lipid mediators to modulate cellular processes. Here we compare similarities and differences and identify open questions in a fundamental lipid signaling pathway in eukaryotes with components that are both conserved and diverged in plants.

Endogenous indole-3-acetamide levels contribute to the crosstalk between auxin and abscisic acid, and trigger plant stress responses in Arabidopsis

The evolutionary success of plants relies to a large extent on their extraordinary ability to adapt to changes in their environment. These adaptations require that plants balance their growth with their stress responses. Plant hormones are crucial mediators orchestrating the underlying adaptive processes. However, whether and how the growth-related hormone auxin and the stress-related hormones jasmonic acid, salicylic acid, and abscisic acid (ABA) are coordinated remains largely elusive. Here, we analyse the physiological role of AMIDASE 1 (AMI1) in Arabidopsis plant growth and its possible connection to plant adaptations to abiotic stresses. AMI1 contributes to cellular auxin homeostasis by catalysing the conversion of indole-acetamide into the major plant auxin indole-3-acetic acid. Functional impairment of AMI1 increases the plant's stress status rendering mutant plants more susceptible to abiotic stresses. Transcriptomic analysis of ami1 mutants disclosed the reprogramming of a considerable number of stress-related genes, including jasmonic acid and ABA biosynthesis genes. The ami1 mutants exhibit only moderately repressed growth but an enhanced ABA accumulation, which suggests a role for AMI1 in the crosstalk between auxin and ABA. Altogether, our results suggest that AMI1 is involved in coordinating the trade-off between plant growth and stress responses, balancing auxin and ABA homeostasis.

Chemical Genetics to Uncover Mechanisms Underlying Lipid-Mediated Signaling Events in Plants

Like animals, plants use various lipids as signaling molecules to guide their growth and development. The focus of our work is on the N-acylethanolamine (NAE) group of lipid mediators, which have been shown to play important physiological roles in plants. However, mechanisms by which NAEs modulate plant function remain elusive. Chemical genetics has emerged as a potent tool to elucidate signaling pathways in plants, particularly those orchestrated by plant hormones. Like plant hormones, exogenous application of NAEs elicits distinct plant growth phenotypes that can serve as biological readouts for chemical genetic screens. For example, N-lauroylethanolamide (NAE 12:0) inhibits seedling development in the model plant Arabidopsis thaliana. Thus, a library of small synthetic chemical compounds can be rapidly screened for their ability to reverse the inhibitory effect of NAE 12:0 on seedling development. Chemicals identified through such screens could be potential agonists/antagonists of NAE receptors or signaling pathways and therefore serve as additional tools for understanding NAE function in plants. In this chapter, we describe general protocols for NAE 12:0-based chemical genetic screens in Arabidopsis. Although such screens were designed primarily for NAE 12:0, they could potentially be applied for similar work with other NAE species or plant lipid mediators.

Seedling Chloroplast Responses Induced by N-Linolenoylethanolamine Require Intact G-Protein Complexes

In animals, several long-chain N-acylethanolamines (NAEs) have been identified as endocannabinoids and are autocrine signals that operate through cell surface G-protein-coupled cannabinoid receptors. Despite the occurrence of NAEs in land plants, including nonvascular plants, their precise signaling properties and molecular targets are not well defined. Here we show that the activity of N-linolenoylethanolamine (NAE 18:3) requires an intact G-protein complex. Specifically, genetic ablation of the Gβγ dimer or loss of the full set of atypical Gα subunits strongly attenuates an NAE-18:3-induced degreening of cotyledons in Arabidopsis (Arabidopsis thaliana) seedlings. This effect involves, at least in part, transcriptional regulation of chlorophyll biosynthesis and catabolism genes. In addition, there is feedforward transcriptional control of G-protein signaling components and G-protein interactors. These results are consistent with NAE 18:3 being a lipid signaling molecule in plants with a requirement for G-proteins to mediate signal transduction, a situation similar, but not identical, to the action of NAE endocannabinoids in animal systems.

Lipophilic signals lead to organ-specific gene expression changes in Arabidopsis seedlings

In plants, N-acylethanolamines (NAEs) are most abundant in desiccated seeds and their levels decline during germination and early seedling establishment. However, endogenous NAE levels rise in seedlings when ABA or environmental stress is applied, and this results in an inhibition of further seedling development. When the most abundant, polyunsaturated NAEs of linoleic acid (18:2) and linolenic acid (18:3) were exogenously applied, seedling development was affected in an organ-specific manner. NAE 18:2 primarily affected primary root elongation and NAE 18:3 primarily affected cotyledon greening and expansion and overall seedling growth. The molecular components and signaling mechanisms involved in this pathway are not well understood. In addition, the bifurcating nature of this pathway provides a unique system in which to study the spatial aspects and interaction of these lipid-specific and organ-targeted signaling pathways. Using whole transcriptome sequencing (RNA-seq) and differential expression analysis, we identified early (1-3 hr) transcriptional changes induced by the exogenous treatment of NAE 18:2 and NAE 18:3 in cotyledons, roots, and seedlings. These two treatments led to a significant enrichment in ABA-response and chitin-response genes in organs where the treatments led to changes in development. In Arabidopsis seedlings, NAE 18:2 treatment led to the repression of genes involved in cell wall biogenesis and organization in roots and seedlings. In addition, cotyledons, roots, and seedlings treated with NAE 18:3 also showed a decrease in transcripts that encode proteins involved in growth processes. NAE 18:3 also led to changes in the abundance of transcripts involved in the modulation of chlorophyll biosynthesis and catabolism in cotyledons. Overall, NAE 18:2 and NAE 18:3 treatment led to lipid-type and organ-specific gene expression changes that include overlapping and non-overlapping gene sets. These data will provide future, rich opportunities to examine the genetic pathways involved in transducing early signals into downstream physiological changes in seedling growth.

Abscisic acid-dependent histone demethylation during postgermination growth arrest in Arabidopsis

After germination, seedlings undergo growth arrest in response to unfavourable conditions, a critical adaptation enabling plants to survive harsh environments. The plant hormone abscisic acid (ABA) plays a key role in this arrest. To arrest growth, ABA-dependent transcription factors change gene expression patterns in a flexible and reversible manner. Although the control of gene expression has important roles in growth arrest, the epigenetic mechanisms in the response to ABA are not fully understood. Here, we show that the histone demethylases JUMONJI-C domain-containing protein 30 (JMJ30) and JMJ32 control ABA-mediated growth arrest in Arabidopsis thaliana. During the postgermination stage (2-3 days after germination), the ABA-dependent transcription factor ABA-insensitive3 (ABI3) activates the expression of JMJ30 in response to ABA. JMJ30 then removes a repressive histone mark, H3 lysine 27 trimethylation (H3K27me3), from the SNF1-related protein kinase 2.8 (SnRK2.8) promoter, and hence activates SnRK2.8 expression. SnRK2.8 encodes a kinase that activates ABI3 and is responsible for JMJ30- and JMJ32-mediated growth arrest. A feed-forward loop involving the ABI3 transcription factor, JMJ histone demethylases, and the SnRK2.8 kinase fine-tunes ABA-dependent growth arrest in the postgermination phase. Our findings highlight the importance of the histone demethylases in mediating adaptation of plants to the environment.

Population genomics demystifies the defoliation phenotype in the plant pathogen Verticillium dahliae

Verticillium dahliae is a broad host-range pathogen that causes vascular wilts in plants. Interactions between three hosts and specific V. dahliae genotypes result in severe defoliation. The underlying mechanisms of defoliation are unresolved. Genome resequencing, gene deletion and complementation, gene expression analysis, sequence divergence, defoliating phenotype identification, virulence analysis, and quantification of V. dahliae secondary metabolites were performed. Population genomics previously revealed that G-LSR2 was horizontally transferred from the fungus Fusarium oxysporum f. sp. vasinfectum to V. dahliae and is exclusively found in the genomes of defoliating (D) strains. Deletion of seven genes within G-LSR2, designated as VdDf genes, produced the nondefoliation phenotype on cotton, olive, and okra but complementation of two genes restored the defoliation phenotype. Genes VdDf5 and VdDf6 associated with defoliation shared homology with polyketide synthases involved in secondary metabolism, whereas VdDf7 shared homology with proteins involved in the biosynthesis of N-lauroylethanolamine (N-acylethanolamine (NAE) 12:0), a compound that induces defoliation. NAE overbiosynthesis by D strains also appears to disrupt NAE metabolism in cotton by inducing overexpression of fatty acid amide hydrolase. The VdDfs modulate the synthesis and overproduction of secondary metabolites, such as NAE 12:0, that cause defoliation either by altering abscisic acid sensitivity, hormone disruption, or sensitivity to the pathogen.

Food Authentication: Small-Molecule Profiling as a Tool for the Geographic Discrimination of German White Asparagus

For the first time, a non-targeted metabolomics approach by means of ultraperformance liquid chromatography coupled to electrospray quadruple time-of-flight mass spectrometry was chosen for the discrimination of geographical origins of white asparagus samples ( Asparagus officinalis). Over a period of four harvesting periods (4 years), approximately 400 asparagus samples were measured. Initially, four different liquid chromatography-mass spectrometry methods were used to detect as many metabolites as possible and to assess which method is most suitable. The most relevant marker compounds were linked to the influence of different plant stress parameters and climate effects. Some of the samples were also analyzed by isotope-ratio mass spectrometry (IRMS), which is the current gold standard for the discrimination of the geographical origin of asparagus. In summary, the analysis of the metabolome was proven to be quite suitable to determine the geographical origin of asparagus and seems to provide better interpretable results than IRMS studies.

Unraveling the metabolic response of Brassica oleracea exposed to Xanthomonas campestris pv. campestris

BACKGROUND

Brassica crops together with cereals represent the basis of world supplies. Due to their importance, the production losses caused by Xanthomonas campestris pv. campestris (Xcc) infection represent a high economic impact. Understanding molecular and biochemical mechanisms of plants is essential to develop resistant crops with durable protection against diseases. In this regard, metabolomics has emerged as a valuable technology to provide an overview of the biological status of a plant exposed to a disease. This study investigated the dynamic changes in the metabolic profile of Brassica oleracea plants during an Xcc infection from leaves collected at five different days post infection using a mass spectrometry approach.

RESULTS

Results showed that Xcc infection causes dynamic changes in the metabolome of B. oleracea. Moreover, induction/repression pattern of the metabolites implicated in the response follows a complex dynamics during infection progression, indicating a complex temporal response. Specific metabolic pathways such as alkaloids, coumarins or sphingolipids are postulated as promising key role candidates in the infection response.

CONCLUSION

This work tries to decipher the changes produced on Brassica crops metabolome under Xcc infection and represents a step forward in the understanding of B. oleracea-Xcc interaction. © 2018 Society of Chemical Industry.

N,N-dimethyl hexadecylamine and related amines regulate root morphogenesis via jasmonic acid signaling in Arabidopsis thaliana

Plant growth-promoting rhizobacteria are natural inhabitants of roots, colonize diverse monocot and dicot species, and affect several functional traits such as root architecture, adaptation to adverse environments, and protect plants from pathogens. N,N-dimethyl-hexadecylamine (C16-DMA) is a rhizobacterial amino lipid that modulates the postembryonic development of several plants, likely as part of volatile blends. In this work, we evaluated the bioactivity of C16-DMA and other related N,N-dimethyl-amines with varied length and found that inhibition of primary root growth was related to the length of the acyl chain. C16-DMA inhibited primary root growth affecting cell division and elongation, while promoting lateral root formation and root hair growth and density in Arabidopsis thaliana (Arabidopsis) wild-type (WT) seedlings. Interestingly, C16-DMA induced the expression of the jasmonic acid (JA)-responsive gene marker pLOX2:uidA, while JA-related mutants jar1, coi1-1, and myc2 affected on JA biosynthesis and perception, respectively, are compromised in C16-DMA responses. Comparison of auxin-regulated gene expression, root architectural changes in WT, and auxin-related mutants aux1-7, tir1/afb2/afb3, and arf7-1/arf19-1 to C16-DMA shows that the C16-DMA effects occur independently of auxin signaling. Together, these results reveal a novel class of aminolipids modulating root organogenesis via crosstalk with the JA signaling pathway.

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

N-Acylethanolamines (NAEs) are a group of fatty acid amides that play signaling roles in diverse physiological processes in eukaryotes. Fatty acid amide hydrolase (FAAH) degrades NAE into ethanolamine and free fatty acid to terminate its signaling function. In animals, chemical inhibitors of FAAH have been used for therapeutic treatment of pain and as tools to probe deeper into biochemical properties of FAAH. In a chemical genetic screen for small molecules that dampened the inhibitory effect of N-lauroylethanolamine (NAE 12:0) on Arabidopsis thaliana seedling growth, we identified 6-(2-methoxyphenyl)-1,3-dimethyl-5-phenyl-1H-pyrrolo[3,4-d]pyrimidine-2,4(3 H,6 H)-dione (or MDPD). MDPD alleviated the growth inhibitory effects of NAE 12:0, in part by enhancing the enzymatic activity of Arabidopsis FAAH (AtFAAH). In vitro, biochemical assays showed that MDPD enhanced the apparent V_max of AtFAAH but did not alter the affinity of AtFAAH for its NAE substrates. Structural analogs of MDPD did not affect AtFAAH activity or dampen the inhibitory effect of NAE 12:0 on seedling growth indicating that MDPD is a specific synthetic chemical activator of AtFAAH. Collectively, our study demonstrates the feasibility of using an unbiased chemical genetic approach to identify new pharmacological tools for manipulating FAAH- and NAE-mediated physiological processes in plants.

Malonylation of Glucosylated N-Lauroylethanolamine: A NEW PATHWAY THAT DETERMINES N-ACYLETHANOLAMINE METABOLIC FATE IN PLANTS

N-Acylethanolamines (NAEs) are bioactive fatty acid derivatives present in trace amounts in many eukaryotes. Although NAEs have signaling and physiological roles in animals, little is known about their metabolic fate in plants. Our previous microarray analyses showed that inhibition of Arabidopsis thaliana seedling growth by exogenous N-lauroylethanolamine (NAE 12:0) was accompanied by the differential expression of multiple genes encoding small molecule-modifying enzymes. We focused on the gene At5g39050, which encodes a phenolic glucoside malonyltransferase 1 (PMAT1), to better understand the biological significance of NAE 12:0-induced gene expression changes. PMAT1 expression was induced 3-5-fold by exogenous NAE 12:0. PMAT1 knockouts (pmat1) had reduced sensitivity to the growth-inhibitory effects of NAE 12:0 compared with wild type leading to the hypothesis that PMAT1 might be a previously uncharacterized regulator of NAE metabolism in plants. To test this hypothesis, metabolic profiling of wild-type and pmat1 seedlings treated with NAE 12:0 was conducted. Wild-type seedlings treated with NAE 12:0 accumulated glucosylated and malonylated forms of this NAE species, and structures were confirmed using nuclear magnetic resonance (NMR) spectroscopy. By contrast, only the peak corresponding to NAE 12:0-glucoside was detected in pmat1 Recombinant PMAT1 catalyzed the reaction converting NAE 12:0-glucoside to NAE 12:0-mono- or -dimalonylglucosides providing direct evidence that this enzyme is involved in NAE 12:0-glucose malonylation. Taken together, our results indicate that glucosylation of NAE 12:0 by a yet to be determined glucosyltransferase and its subsequent malonylation by PMAT1 could represent a mechanism for modulating the biological activities of NAEs in plants.

Quantification and enzyme targets of fatty acid amides from duckweed root exudates involved in the stimulation of denitrification

Fatty acid amides from plant root exudates, such as oleamide and erucamide, have the ability to participate in strong plant-microbe interactions, stimulating nitrogen metabolism in rhizospheric bacteria. However, mechanisms of secretion of such fatty acid amides, and the nature of their stimulatory activities on microbial metabolism, have not been examined. In the present study, collection, pre-treatment, and determination methods of oleamide and erucamide in duckweed root exudates are compared. The detection limits of oleamide and erucamide by gas chromatography (GC) (10.3ngmL(-1) and 16.1ngmL(-1), respectively) are shown to be much lower than those by liquid chromatography (LC) (1.7 and 5.0μgmL(-1), respectively). Quantitative GC analysis yielded five times larger amounts of oleamide and erucamide in root exudates of Spirodela polyrrhiza when using a continuous collection method (50.20±4.32 and 76.79±13.92μgkg(-1) FW day(-1)), compared to static collection (10.88±0.66 and 15.27±0.58μgkg(-1) FW day(-1)). Furthermore, fatty acid amide secretion was significantly enhanced under elevated nitrogen conditions (>300mgL(-1)), and was negatively correlated with the relative growth rate of duckweed. Mechanistic assays were conducted to show that erucamide stimulates nitrogen removal by enhancing denitrification, targeting two key denitrifying enzymes, nitrate and nitrite reductases, in bacteria. Our findings significantly contribute to our understanding of the regulation of nitrogen dynamics by plant root exudates in natural ecosystems.

Lipid signalling in plant responses to abiotic stress

Lipids are one of the major components of biological membranes including the plasma membrane, which is the interface between the cell and the environment. It has become clear that membrane lipids also serve as substrates for the generation of numerous signalling lipids such as phosphatidic acid, phosphoinositides, sphingolipids, lysophospholipids, oxylipins, N-acylethanolamines, free fatty acids and others. The enzymatic production and metabolism of these signalling molecules are tightly regulated and can rapidly be activated upon abiotic stress signals. Abiotic stress like water deficit and temperature stress triggers lipid-dependent signalling cascades, which control the expression of gene clusters and activate plant adaptation processes. Signalling lipids are able to recruit protein targets transiently to the membrane and thus affect conformation and activity of intracellular proteins and metabolites. In plants, knowledge is still scarce of lipid signalling targets and their physiological consequences. This review focuses on the generation of signalling lipids and their involvement in response to abiotic stress. We describe lipid-binding proteins in the context of changing environmental conditions and compare different approaches to determine lipid-protein interactions, crucial for deciphering the signalling cascades.

Growth inhibition and possible mechanism of oleamide against the toxin-producing cyanobacterium Microcystis aeruginosa NIES-843

Oleamide, a fatty acid derivative, shows inhibitory effect against the bloom-forming cyanobacterium Microcystis aeruginosa. The EC50 of oleamide on the growth of M. aeruginosa NIES-843 was 8.60 ± 1.20 mg/L. In order to elucidate the possible mechanism of toxicity of oleamide against M. aeruginosa, chlorophyll fluorescence transient, cellular ultrastructure, fatty acids composition and the transcription of the mcyB gene involved in microcystins synthesis were studied. The results of chlorophyll fluorescence transient showed that oleamide could destruct the electron accepting side of the photosystem II of M. aeruginosa NIES-843. Cellular ultrastructure examination indicated that the destruction of fatty acid constituents, the distortion of thylakoid membrane and the loss of integrity of cell membrane were associated with oleamide treatment and concentration. The damage of cellular membrane increased the release of microcystins from intact cells into the medium. Results presented in this study provide new information on the possible mechanisms involved and potential utilization of oleamide as an algicide in cyanobacterial bloom control.

Lipoxygenase-derived 9-hydro(pero)xides of linoleoylethanolamide interact with ABA signaling to arrest root development during Arabidopsis seedling establishment

Ethanolamide-conjugated fatty acid derivatives, also known as N-acylethanolamines (NAEs), occur at low levels (μg per g) in desiccated seeds, and endogenous amounts decline rapidly with seedling growth. Linoleoylethanolamide (NAE18:2) is the most abundant of these NAEs in seeds of almost all plants, including Arabidopsis thaliana. In Arabidopsis, NAE18:2 may be oxidized by lipoxygenase (LOX) or hydrolyzed by fatty acid amide hydrolase (FAAH) during normal seedling establishment, and this contributes to the normal progression of NAE depletion that is coincident with the depletion of abscisic acid (ABA). Here we provide biochemical, genetic and pharmacological evidence that a specific 9-LOX metabolite of NAE18:2 [9-hydro(pero)xy linoleoylethanolamide (9-NAE-H(P)OD)] has a potent negative influence on seedling root elongation, and acts synergistically with ABA to modulate the transition from embryo to seedling growth. Genetic analyses using mutants in ABA synthesis (aba1 and aba2), perception (pyr1, pyl1, pyl2, pyl4, pyl5 and pyl8) or transcriptional activation (abi3-1) indicated that arrest of root growth by 9-NAE-H(P)OD requires an intact ABA signaling pathway, and probably operates to increase ABA synthesis as part of a positive feedback loop to modulate seedling establishment in response to adverse environmental conditions. These results identify a specific, bioactive ethanolamide oxylipin metabolite of NAE18:2, different from those of ethanolamide-conjugated linolenic acid (NAE18:3), as well as a molecular explanation for its inhibitory action, emphasizing the oxidative metabolism of NAEs as an important feature of seedling development.

Effects of synthetic alkamides on Arabidopsis fatty acid amide hydrolase activity and plant development

Alkamides and N-acylethanolamines (NAEs) are bioactive, amide-linked lipids that influence plant development. Alkamides are restricted to several families of higher plants and some fungi, whereas NAEs are widespread signaling molecules in both plants and animals. Fatty acid amide hydrolase (FAAH) has been described as a key contributor to NAE hydrolysis; however, no enzyme has been associated with alkamide degradation in plants. Herein reported is synthesis of 12 compounds structurally similar to a naturally occurring alkamide (N-isobutyl-(2E,6Z,8E)decatrienamide or affinin) with different acyl compositions more similar to plant NAEs and various amino alkyl head groups. These "hybrid" synthetic alkamides were tested for activity toward recombinant Arabidopsis FAAH and for their effects on plant development (i.e., cotyledon expansion and primary root length). A substantial increase in FAAH activity was discovered toward NAEs in vitro in the presence of some of these synthetic alkamides, such as N-ethyllauroylamide (4). This "enhancement" effect was found to be due, at least in part, to relief from product inhibition of FAAH by ethanolamine, and not due to an alteration in the oligomerization state of the FAAH enzyme. For several of these alkamides, an inhibition of seedling growth was observed with greater results in FAAH knockouts and less in FAAH over-expressing plants, suggesting that these alkamides could be hydrolyzed by FAAH in planta. The tight regulation of NAE levels in vivo appears to be important for proper seedling establishment, and as such, some of these synthetic alkamides may be useful pharmacological tools to manipulate the effects of NAEs in situ.

Roles of lipids as signaling molecules and mitigators during stress response in plants

Lipids are the major constituents of biological membranes that can sense extracellular conditions. Lipid-mediated signaling occurs in response to various environmental stresses, such as temperature change, salinity, drought and pathogen attack. Lysophospholipid, fatty acid, phosphatidic acid, diacylglycerol, inositol phosphate, oxylipins, sphingolipid, and N-acylethanolamine have all been proposed to function as signaling lipids. Studies on these stress-inducible lipid species have demonstrated that each lipid class has specific biological relevance, biosynthetic mechanisms and signaling cascades, which activate defense reactions at the transcriptional level. In addition to their roles in signaling, lipids also function as stress mitigators to reduce the intensity of stressors. To mitigate particular stresses, enhanced syntheses of unique lipids that accumulate in trace quantities under normal growth conditions are often observed under stressed conditions. The accumulation of oligogalactolipids and glucuronosyldiacylglycerol has recently been found to mitigate freezing and nutrition-depletion stresses, respectively, during lipid remodeling. In addition, wax, cutin and suberin, which are not constituents of the lipid bilayer, but are components derived from lipids, contribute to the reduction of drought stress and tissue injury. These features indicate that lipid-mediated defenses against environmental stress contributes to plant survival.

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

Twenty years ago, N-acylethanolamines (NAEs) were considered by many lipid chemists to be biological 'artifacts' of tissue damage, and were, at best, thought to be minor lipohilic constituents of various organisms. However, that changed dramatically in 1993, when anandamide, an NAE of arachidonic acid (N-arachidonylethanolamine), was shown to bind to the human cannabinoid receptor (CB1) and activate intracellular signal cascades in mammalian neurons. Now NAEs of various types have been identified in diverse multicellular organisms, in which they display profound biological effects. Although targets of NAEs are still being uncovered, and probably vary among eukaryotic species, there appears to be remarkable conservation of the machinery that metabolizes these bioactive fatty acid conjugates of ethanolamine. This review focuses on the metabolism and functions of NAEs in higher plants, with specific reference to the formation, hydrolysis and oxidation of these potent lipid mediators. The discussion centers mostly on early seedling growth and development, for which NAE metabolism has received the most attention, but also considers other areas of plant development in which NAE metabolism has been implicated. Where appropriate, we indicate cross-kingdom conservation in NAE metabolic pathways and metabolites, and suggest areas where opportunities for further investigation appear most pressing.

Synthesis of phenoxyacyl-ethanolamides and their effects on fatty acid amide hydrolase activity

N-Acylethanolamines (NAEs) are involved in numerous biological activities in plant and animal systems. The metabolism of these lipids by fatty acid amide hydrolase (FAAH) is a key regulatory point in NAE signaling activity. Several active site-directed inhibitors of FAAH have been identified, but few compounds have been described that enhance FAAH activity. Here we synthesized two sets of phenoxyacyl-ethanolamides from natural products, 3-n-pentadecylphenolethanolamide and cardanolethanolamide, with structural similarity to NAEs and characterized their effects on the hydrolytic activity of FAAH. Both compounds increased the apparent Vmax of recombinant FAAH proteins from both plant (Arabidopsis) and mammalian (Rattus) sources. These NAE-like compounds appeared to act by reducing the negative feedback regulation of FAAH activity by free ethanolamine. Both compounds added to seedlings relieved, in part, the negative growth effects of exogenous NAE12:0. Cardanolethanolamide reduced neuronal viability and exacerbated oxidative stress-mediated cell death in primary cultured neurons at nanomolar concentrations. This was reversed by FAAH inhibitors or exogenous NAE substrate. Collectively, our data suggest that these phenoxyacyl-ethanolamides act to enhance the activity of FAAH and may stimulate the turnover of NAEs in vivo. Hence, these compounds might be useful pharmacological tools for manipulating FAAH-mediated regulation of NAE signaling in plants or animals.

Ethanolamide oxylipins of linolenic acid can negatively regulate Arabidopsis seedling development

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.

Analysis of fatty acid amide hydrolase activity in plants

N-Acylethanolamines (NAEs) are fatty acid derivatives amide-linked to ethanolamine. NAEs vary in chain lengths and numbers of double bonds and generally reflect the fatty acids found in membrane lipids in the tissues in which they reside. NAEs are present naturally in trace amounts and occur in a wide range of organisms including plants, animals, and microbes. Some NAE types are known to be involved in the endocannabinoid signaling system of vertebrates, and in plants they may play important regulatory roles in several physiological processes, such as root growth, seedling development, stress responses, and pathogen interactions. The biological effects of NAEs are terminated through their hydrolysis into the ethanolamine and free fatty acid by a membrane enzyme known as the fatty acid amide hydrolase (FAAH). Thus, FAAH represents an important target to better understand the function of these lipid mediators in numerous cellular processes. FAAH has been extensively characterized in mammalian and plant systems, and they share a conserved Ser-Ser-Lys catalytic mechanism. Here we describe procedures and experimental conditions to assay and characterize recombinant and endogenous FAAH enzymatic activity derived from plant tissues.

N-Acylated phospholipid metabolism and seedling growth: insights from lipidomics studies in Arabidopsis

N-Acylphosphatidylethanolamines (NAPEs) are precursors of endogenous bioactive lipids, N-acylethanolamines (NAEs). NAPEs, which occur as a minor membrane lipid, are hydrolyzed in a single enzymatic step catalyzed by a type of phospholipase D (PLD) to generate fatty acid ethanolamides. Although, the occurrence of NAPE is widespread in the plant kingdom, the physiological roles remain under appreciated due to the lack of sensitive tools to quantify the pathway metabolites. In Kilaru et al. (2012, Planta, DOI 10.1007/s00425-012-1669-z), comprehensive mass spectrometry (MS)-based methods were developed to gain a clearer understanding of the complex network of metabolites that participate in NAE metabolic pathway. This targeted lipidomics approach allowed insights to be drawn into the implications of altered NAE levels on NAPE content and composition, and the overall regulation of PLD-mediated hydrolysis in Arabidopsis. Based on these results, we point out here the important need for the identification of the precise isoform(s) of PLD in plants that is (are) involved in the regulated hydrolysis of NAPE and formation of NAE lipid mediators in vivo.

Lipidomic analysis of N-acylphosphatidylethanolamine molecular species in Arabidopsis suggests feedback regulation by N-acylethanolamines

N-Acylphosphatidylethanolamine (NAPE) and its hydrolysis product, N-acylethanolamine (NAE), are minor but ubiquitous lipids in multicellular eukaryotes. Various physiological processes are severely affected by altering the expression of fatty acid amide hydrolase (FAAH), an NAE-hydrolyzing enzyme. To determine the effect of altered FAAH activity on NAPE molecular species composition, NAE metabolism, and general membrane lipid metabolism, quantitative profiles of NAPEs, NAEs, galactolipids, and major and minor phospholipids for FAAH mutants of Arabidopsis were determined. The NAPE molecular species content was dramatically affected by reduced FAAH activity and elevated NAE content in faah knockouts, increasing by as much as 36-fold, far more than the NAE content, suggesting negative feedback regulation of phospholipase D-mediated NAPE hydrolysis by NAE. The N-acyl composition of NAPE remained similar to that of NAE, suggesting that the NAPE precursor pool largely determines NAE composition. Exogenous NAE 12:0 treatment elevated endogenous polyunsaturated NAE and NAPE levels in seedlings; NAE levels were increased more in faah knockouts than in wild-type or FAAH overexpressors. Treated seedlings with elevated NAE and NAPE levels showed impaired growth and reduced galactolipid synthesis by the "prokaryotic" (i.e., plastidic), but not the "eukaryotic" (i.e., extraplastidic), pathway. Overall, our data provide new insights into the regulation of NAPE-NAE metabolism and coordination of membrane lipid metabolism and seedling development.

N-Acylethanolamines and related compounds: aspects of metabolism and functions

N-Acylethanolamines (NAE) are fatty acid derivates that are linked with an ethanolamine group via an amide bond. NAE can be characterized as lipid mediators in the plant and animal kingdoms owing to the diverse functions throughout the eukaryotic domain. The functions of NAE have been widely investigated in animal tissues in part due to their abilities to interact with the cannabinoid receptors, vanilloid receptors or peroxisome proliferator activated receptors. However, the interest of studying the functions of these lipids in plants is progressively becoming more apparent. The number of publications about the functions related to NAE and to structural analogs (homoserine lactone and alkamides) is greatly increasing, showing the importance of these lipids in various plant physiological processes. This review sheds light on their role in different processes such as seedling development, plant pathogen interaction, phospholipase D alpha inhibition and senescence of cut flowers, and underlines the interaction between NAE and NAE-related molecules with plant hormone signaling. The different metabolic pathways promoting the synthesis and degradation of NAE are also discussed, in particular the oxygenation of polyunsaturated N-acylethanolamines, which leads to NAE-oxylipins, a new family of bioactive lipids.

Overexpression of Fatty Acid Amide Hydrolase Induces Early Flowering in Arabidopsis thaliana

N-acylethanolamines (NAEs) are bioactive lipids derived from the hydrolysis of the membrane phospholipid N-acylphosphatidylethanolamine (NAPE). In animal systems this reaction is part of the "endocannabinoid" signaling pathway, which regulates a variety of physiological processes. The signaling function of NAE is terminated by fatty acid amide hydrolase (FAAH), which hydrolyzes NAE to ethanolamine and free fatty acid. Our previous work in Arabidopsis thaliana showed that overexpression of AtFAAH (At5g64440) lowered endogenous levels of NAEs in seeds, consistent with its role in NAE signal termination. Reduced NAE levels were accompanied by an accelerated growth phenotype, increased sensitivity to abscisic acid (ABA), enhanced susceptibility to bacterial pathogens, and early flowering. Here we investigated the nature of the early flowering phenotype of AtFAAH overexpression. AtFAAH overexpressors flowered several days earlier than wild type and AtFAAH knockouts under both non-inductive short day (SD) and inductive long day (LD) conditions. Microarray analysis revealed that the FLOWERING LOCUS T (FT) gene, which plays a major role in regulating flowering time, and one target MADS box transcription factor, SEPATALLA3 (SEP3), were elevated in AtFAAH overexpressors. Furthermore, AtFAAH overexpressors, with the early flowering phenotype had lower endogenous NAE levels in leaves compared to wild type prior to flowering. Exogenous application of NAE 12:0, which was reduced by up to 30% in AtFAAH overexpressors, delayed the onset of flowering in wild type plants. We conclude that the early flowering phenotype of AtFAAH overexpressors is, in part, explained by elevated FT gene expression resulting from the enhanced NAE hydrolase activity of AtFAAH, suggesting that NAE metabolism may participate in floral signaling pathways.

Alkamides activate jasmonic acid biosynthesis and signaling pathways and confer resistance to Botrytis cinerea in Arabidopsis thaliana

Alkamides are fatty acid amides of wide distribution in plants, structurally related to N-acyl-L-homoserine lactones (AHLs) from Gram-negative bacteria and to N- acylethanolamines (NAEs) from plants and mammals. Global analysis of gene expression changes in Arabidopsis thaliana in response to N-isobutyl decanamide, the most highly active alkamide identified to date, revealed an overrepresentation of defense-responsive transcriptional networks. In particular, genes encoding enzymes for jasmonic acid (JA) biosynthesis increased their expression, which occurred in parallel with JA, nitric oxide (NO) and H₂O₂ accumulation. The activity of the alkamide to confer resistance against the necrotizing fungus Botrytis cinerea was tested by inoculating Arabidopsis detached leaves with conidiospores and evaluating disease symptoms and fungal proliferation. N-isobutyl decanamide application significantly reduced necrosis caused by the pathogen and inhibited fungal proliferation. Arabidopsis mutants jar1 and coi1 altered in JA signaling and a MAP kinase mutant (mpk6), unlike salicylic acid- (SA) related mutant eds16/sid2-1, were unable to defend from fungal attack even when N-isobutyl decanamide was supplied, indicating that alkamides could modulate some necrotrophic-associated defense responses through JA-dependent and MPK6-regulated signaling pathways. Our results suggest a role of alkamides in plant immunity induction.

N-acylethanolamine (NAE) inhibits growth in Arabidopsis thaliana seedlings via ABI3-dependent and -independent pathways

N-acylethanolamines (NAEs) are lipid metabolites derived from the hydrolysis of the membrane phospholipid N-acylphosphatidylethanolamine (NAPE). Recent work in Arabidopsis thaliana seedlings showed that combined treatments of NAE 12:0 and ABA inhibited seedling growth synergistically, suggesting low levels of NAE could potentiate the action of ABA. Here we examined the interplay between compound concentrations, growth inhibition and mutant genotypes with impaired sensitivities to these regulators. NAE 12:0 and ABA both induced dose-dependent increases in transcript levels of ABI3, and two ABI3 responsive genes, AtHVA22B and RD29B. Interestingly, even in the absence of growth inhibition, RD29B transcripts were elevated by ABA but not NAE treatment outside the sensitive window for ABA/NAE treatment, indicating some differences in the regulation of growth and the modulation of gene expression by these two compounds. Also noteworthy, the growth of ABA insensitive mutant (abi 3-1) seedlings was inhibited at higher concentrations of NAE 12:0 but not ABA, suggesting that NAE may act to inhibit early seedling establishment by both ABI3-dependent and ABI3-independent pathways. Collectively our results reinforce the concept that NAE12:0 interacts with ABA signaling in seedling establishment, but also points to a complexity in this interaction that modulates the sensitivity of young seedlings to phytohormone-mediated growth arrest.

Lipoxygenase-mediated oxidation of polyunsaturated N-acylethanolamines in Arabidopsis

N-acylethanolamines (NAEs) are bioactive fatty acid derivatives that occur in all eukaryotes. In plants, NAEs have potent negative growth-regulating properties, and fatty acid amide hydrolase (FAAH)-mediated hydrolysis is a primary catabolic pathway that operates during seedling establishment to deplete these compounds. Alternatively, polyunsaturated (PU)-NAEs may serve as substrates for lipid oxidation. In Arabidopsis, PU-NAEs (NAE 18:2 and NAE 18:3) were the most abundant NAE species in seeds, and their levels were depleted during seedling growth even in FAAH tDNA knock-out plants. Therefore, we hypothesized that lipoxygenase (LOX) participated in the metabolism of PU-NAEs through the formation of NAE-oxylipins. Comprehensive chromatographic and mass spectrometric methods were developed to identify NAE hydroperoxides and -hydroxides. Recombinant Arabidopsis LOX enzymes expressed in Escherichia coli utilized NAE 18:2 and NAE 18:3 as substrates with AtLOX1 and AtLOX5 exhibiting 9-LOX activity and AtLOX2, AtLOX3, AtLOX4, and AtLOX6 showing predominantly 13-LOX activity. Feeding experiments with exogenous PU-NAEs showed they were converted to hydroxide metabolites indicating that indeed Arabidopsis seedlings had the capacity for LOX-mediated metabolism of PU-NAEs in planta. Detectable levels of endogenous NAE-oxylipin metabolites were identified in FAAH fatty acid amide hydrolase seedlings but not in wild-type or FAAH overexpressors, suggesting that NAE hydroxide pools normally do not accumulate unless flux through hydrolysis is substantially reduced. These data suggest that Arabidopsis LOXs indeed compete with FAAH to metabolize PU-NAEs during seedling establishment. Identification of endogenous amide-conjugated oxylipins suggests potential significance of these metabolites in vivo, and FAAH mutants may offer opportunities to address this in the future.

Disruption of the Arabidopsis CGI-58 homologue produces Chanarin-Dorfman-like lipid droplet accumulation in plants

CGI-58 is the defective gene in the human neutral lipid storage disease called Chanarin-Dorfman syndrome. This disorder causes intracellular lipid droplets to accumulate in nonadipose tissues, such as skin and blood cells. Here, disruption of the homologous CGI-58 gene in Arabidopsis thaliana resulted in the accumulation of neutral lipid droplets in mature leaves. Mass spectroscopy of isolated lipid droplets from cgi-58 loss-of-function mutants showed they contain triacylglycerols with common leaf-specific fatty acids. Leaves of mature cgi-58 plants exhibited a marked increase in absolute triacylglycerol levels, more than 10-fold higher than in wild-type plants. Lipid levels in the oil-storing seeds of cgi-58 loss-of-function plants were unchanged, and unlike mutations in β-oxidation, the cgi-58 seeds germinated and grew normally, requiring no rescue with sucrose. We conclude that the participation of CGI-58 in neutral lipid homeostasis of nonfat-storing tissues is similar, although not identical, between plant and animal species. This unique insight may have implications for designing a new generation of technologies that enhance the neutral lipid content and composition of crop plants.

Modulation of redox homeostasis under suboptimal conditions by Arabidopsis nudix hydrolase 7

BACKGROUND

Nudix hydrolases play a key role in maintaining cellular homeostasis by hydrolyzing various nuceloside diphosphate derivatives and capped mRNAs. Several independent studies have demonstrated that Arabidopsis nudix hydrolase 7 (AtNUDT7) hydrolyzes NADH and ADP-ribose. Loss of function Atnudt7-1 mutant plants (SALK_046441) exhibit stunted growth, higher levels of reactive oxygen species, enhanced resistance to pathogens. However, using the same T-DNA line, two other groups reported that mutant plants do not exhibit any visible phenotypes. In this study we analyze plausible factors that account for differences in the observed phenotypes in Atnudt7. Secondly, we evaluate the biochemical and molecular consequences of increased NADH levels due to loss of function of AtNUDT7 in Arabidopsis.

RESULTS

We identified a novel conditional phenotype of Atnudt7-1 knockout plants that was contingent upon nutrient composition of potting mix. In nutrient-rich Metro-Mix, there were no phenotypic differences between mutant and wild-type (WT) plants. In the nutrient-poor mix (12 parts vermiculite: 3 parts Redi-earth and 1 part sand), mutant plants showed the characteristic stunted phenotype. Compared with WT plants, levels of glutathione, NAD+, NADH, and in turn NADH:NAD+ ratio were higher in Atnudt7-1 plants growing in 12:3:1 potting mix. Infiltrating NADH and ADP-ribose into WT leaves was sufficient to induce AtNUDT7 protein. Constitutive over-expression of AtNudt7 did not alter NADH levels or resistance to pathogens. Transcriptome analysis identified nearly 700 genes differentially expressed in the Atnudt7-1 mutant compared to WT plants grown in 12:3:1 potting mix. In the Atnudt7-1 mutant, genes associated with defense response, proteolytic activities, and systemic acquired resistance were upregulated, while gene ontologies for transcription and phytohormone signaling were downregulated.

CONCLUSIONS

Based on these observations, we conclude that the differences observed in growth phenotypes of the Atnudt7-1 knockout mutants can be due to differences in the nutrient composition of potting mix. Our data suggests AtNUDT7 plays an important role in maintaining redox homeostasis, particularly for maintaining NADH:NAD+ balance for normal growth and development. During stress conditions, rapid induction of AtNUDT7 is important for regulating the activation of stress/defense signaling and cell death pathways.

Lauroylethanolamide is a potent competitive inhibitor of lipoxygenase activity

The lipoxygenase (LOX) pathway was proposed to compete with hydrolysis and be partly responsible for the metabolism of polyunsaturated N-acylethanolamines (PU-NAEs). Treatment of Arabidopsis seedlings with lauroylethanolamide (NAE 12:0) resulted in elevated levels of PU-NAE species, and this was most pronounced in plants with reduced NAE hydrolase activity. Enzyme activity assays revealed that NAE 12:0 inhibited LOX-mediated oxidation of PU lipid substrates in a dose-dependent and competitive manner. NAE 12:0 was 10-20 times more potent an inhibitor of LOX activities than lauric acid (FFA 12:0). Furthermore, treatment of intact Arabidopsis seedlings with NAE 12:0 (but not FFA 12:0) substantially blocked the wound-induced formation of jasmonic acid (JA), suggesting that NAE 12:0 may be used in planta to manipulate oxylipin metabolism.

The RY/Sph element mediates transcriptional repression of maturation genes from late maturation to early seedling growth

In orthodox seeds, the transcriptional activator ABI3 regulates two major stages in embryo maturation: a mid-maturation (MAT) stage leading to accumulation of storage compounds, and a late maturation (LEA) stage leading to quiescence and desiccation tolerance. Our aim was to elucidate mechanisms for transcriptional shutdown of MAT genes during late maturation, to better understand phase transition between MAT and LEA stages. Using transgenic and transient approaches in Nicotiana, we examined activities of two ABI3-dependent reporter genes driven by multimeric RY and abscisic acid response elements (ABREs) from a Brassica napus napin gene, termed RY and ABRE, where the RY reporter requires ABI3 DNA binding. Expression of RY peaks during mid-maturation and drops during late maturation, mimicking the MAT gene program, and in Arabidopsis thaliana RY elements are over-represented in MAT, but not in LEA, genes. The ABI3 transactivation of RY is inhibited by staurosporine, by a PP2C phosphatase, and by a repressor of maturation genes, VAL1/HSI2. The RY element mediates repression of MAT genes, and we propose that transcriptional shutdown of the MAT program during late maturation involves inhibition of ABI3 DNA binding by dephosphorylation. Later, during seedling growth, VAL1/HSI2 family repressors silence MAT genes by binding RY elements.

Mutations in Arabidopsis fatty acid amide hydrolase reveal that catalytic activity influences growth but not sensitivity to abscisic acid or pathogens

Fatty acid amide hydrolase (FAAH) terminates the endocannabinoid signaling pathway that regulates numerous neurobehavioral processes in animals by hydrolyzing N-acylethanolamines (NAEs). Recently, an Arabidopsis FAAH homologue (AtFAAH) was identified, and several studies, especially those using AtFAAH overexpressing and knock-out lines, have suggested an in vivo role for FAAH in the catabolism of NAEs in plants. We previously reported that overexpression of AtFAAH in Arabidopsis resulted in accelerated seedling growth, and in seedlings that were insensitive to exogenous NAEs but hypersensitive to abscisic acid (ABA) and hypersusceptible to nonhost pathogens. Here we show that whereas the enhanced growth and NAE tolerance of the AtFAAH overexpressing seedlings depend on the catalytic activity of AtFAAH, hypersensitivity to ABA and hypersusceptibility to nonhost pathogens are independent of its enzymatic activity. Five amino acids known to be critical for rat FAAH activity are also conserved in AtFAAH (Lys-205, Ser-281, Ser-282, Ser-305, and Arg-307). Site-directed mutation of each of these conserved residues in AtFAAH abolished its hydrolytic activity when expressed in Escherichia coli, supporting a common catalytic mechanism in animal and plant FAAH enzymes. Overexpression of these inactive AtFAAH mutants in Arabidopsis showed no growth enhancement and no NAE tolerance, but still rendered the seedlings hypersensitive to ABA and hypersusceptible to nonhost pathogens to a degree similar to the overexpression of the native AtFAAH. Taken together, our findings suggest that the AtFAAH influences plant growth and interacts with ABA signaling and plant defense through distinctly different mechanisms.

Highlights of recent progress in plant lipid research

Raw fossil material reserves are not inexhaustible and as prices continue to raise it is necessary to find new sources of alternative and renewable energy. Oils from oleaginous field crops (sunflower and rape) with properties close to those of fossil fuel could constitute an alternative source of energy for the production of raw materials. This is the context in which the 18th International Symposium on Plant lipids (ISPL) was held in Bordeaux from 20th to 25th July 2008 at "La Cité Mondiale". The 18th ISPL gathered 270 researchers from 33 countries. Sixty nine oral communications and 136 posters were presented during the 12 sessions of the Symposium. The sessions have covered all the different aspects of the Plant Lipid field including: Surface lipids: suberin, cutin and waxes, Fatty acids, Glycerolipids, Plant lipids as renewable sources of energy, Seed oils and bioengineering of metabolic pathways, Lipid catabolism, Models for lipid studies: lower plants, micro-organisms and others, Modifications of proteins by lipids, Sphingolipids, sterols and isoprenoids, Lipid signaling and plant stress responses, Lipid trafficking and membrane dynamics, New methods and technologies: functional lipidomics, fluxome, modelling. During the ISPL 2008 Bordeaux, important and new information was reported in the different fields. A selection of these results is presented here.

Overexpression of a fatty acid amide hydrolase compromises innate immunity in Arabidopsis

N-acylethanolamines are a group of lipid mediators that accumulate under a variety of neurological and pathological conditions in mammals. N-acylethanolamine signaling is terminated by the action of diverse hydrolases, among which fatty acid amide hydrolase (FAAH) has been well characterized. Here, we show that transgenic Arabidopsis lines overexpressing an AtFAAH are more susceptible to the bacterial pathogens Pseudomonas syringae pv. tomato and P. syringae pv. maculicola. AtFAAH overexpressors also were highly susceptible to non-host pathogens P. syringae pv. syringae and P. syringae pv. tabaci. AtFAAH overexpressors had lower amounts of jasmonic acid, abscisic acid and both free and conjugated salicylic acid (SA), compared with the wild-type. Gene expression studies revealed that transcripts of a number of plant defense genes, as well as genes involved in SA biosynthesis and signaling, were lower in AtFAAH overexpressors than wild-type plants. Our data suggest that FAAH overexpression alters phytohormone accumulation and signaling which in turn compromises innate immunity to bacterial pathogens.

Cytokinin receptors are involved in alkamide regulation of root and shoot development in Arabidopsis

Alkamides and N-acilethanolamides are a class of lipid compounds related to animal endocannabinoids of wide distribution in plants. We investigated the structural features required for alkamides to regulate plant development by comparing the root responses of Arabidopsis (Arabidopsis thaliana) seedlings to a range of natural and synthetic compounds. The length of the acyl chain and the amide moiety were found to play a crucial role in their biological activity. From the different compounds tested, N-isobutyl decanamide, a small saturated alkamide, was found to be the most active in regulating primary root growth and lateral root formation. Proliferative-promoting activity of alkamide treatment was evidenced by formation of callus-like structures in primary roots, ectopic blades along petioles of rosette leaves, and disorganized tumorous tissue originating from the leaf lamina. Ectopic organ formation by N-isobutyl decanamide treatment was related to altered expression of the cell division marker CycB1:uidA and an enhanced expression of the cytokinin-inducible marker ARR5:uidA both in roots and in shoots. The involvement of cytokinins in mediating the observed activity of alkamides was tested using Arabidopsis mutants lacking one, two, or three of the putative cytokinin receptors CRE1, AHK2, and AHK3. The triple cytokinin receptor mutant was insensitive to N-isobutyl decanamide treatment, showing absence of callus-like structures in roots, the lack of lateral root proliferation, and absence of ectopic outgrowths in leaves under elevated levels of this alkamide. Taken together our results suggest that alkamides and N-acylethanolamides may belong to a class of endogenous signaling compounds that interact with a cytokinin-signaling pathway to control meristematic activity and differentiation processes during plant development.