Apparent Role of Phosphatidylcholine in the Metabolism of Petroselinic Acid in Developing Umbelliferae Endosperm

Apiaceae Family an Important Source of Petroselinic Fatty Acid: Abundance, Biosynthesis, Chemistry, and Biological Proprieties

Petroselinic fatty acid (PeFA) is considered a rare fatty acid and one of the most important fatty acids in the Apiaceae family. Its content varies depending on plant species, geographical origin, extraction method, ripeness, etc. Indeed, reported levels of petroselinic fatty acid range from 10.4 to 75.6% (in anise seed oil), 1 to 81.9% (in coriander seed oil), 28.5 to 57.6% (in caraway seed oil), 49.4 to 75.6% (in celery seed oil), 41.3 to 61.8% (in caraway seed oil), 79.9 to 87.2% (in dill seed oil), 43.1 to 81.9% (in fennel seed oil), and 35 to 75.1% (parsley seed oil). In this review, we also show current knowledge about genes encoding biosynthesis, from the desaturation of 16:0-ACP to petroselinic acid stored in triacylglycerol in the seeds. Furthermore, petroselinic acid is not related to the synthesis of ABA. PeFA was successfully isolated from Apiaceae family plant seeds in order to study their reactivity and biological activities. Several investigations showed that this fatty acid has a wide range of biological potentials, including antidiabetic, antibacterial, and antifungal activities. In cosmetics, PeFA alone or in association with other active compounds has interesting applications as an anti-inflammatory agent for the treatment of skin, hair, and nail disorders.

Do betaine lipids replace phosphatidylcholine as fatty acid editing hubs in microalgae?

Acyl editing refers to a deacylation and reacylation cycle on a lipid, which allows for fatty acid desaturation and modification prior to being removed and incorporated into other pools. Acyl editing is an important determinant of glycerolipid synthesis and has been well-characterized in land plants, thus this review begins with an overview of acyl editing in plants. Much less is known about acyl editing in algae, including the extent to which acyl editing impacts lipid synthesis and on which lipid substrate(s) it occurs. This review compares what is known about acyl editing on its major hub phosphatidylcholine (PC) in land plants with the evidence for acyl editing of betaine lipids such as diacylglyceryltrimethylhomoserine (DGTS), the structural analog that replaces PC in several species of microalgae. In land plants, PC is also known to be a major source of fatty acids and diacylglycerol (DAG) for synthesis of the neutral lipid triacylglycerol (TAG). We review the evidence that DGTS contributes substantially to TAG accumulation in algae as a source of fatty acids, but not as a precursor to DAG. We conclude with evidence of acyl editing on other membrane lipid substrates in plants and algae apart from PC or DGTS, and discuss future analyses to elucidate the role of DGTS and other betaine lipids in acyl editing in microalgae.

Divergent evolution of extreme production of variant plant monounsaturated fatty acids

The dietary and oleochemical value of vegetable oils is determined by their component fatty acids. Double bonds or “unsaturation” in fatty acids are critical for vegetable oil functionality. Seeds containing vegetable oils with extremely high levels of a single fatty acid have provided insights into enzyme-substrate recognition and metabolic plasticity and genes for biotechnological improvement of oilseeds. We report the discovery of species with seed oils containing >90% of an unusual monounsaturated fatty acid. We identified the variant enzyme that produces this fatty acid and elucidated its three-dimensional structure. We used this information to develop enzymes that produce nonnaturally occurring monounsaturated fatty acids and sourced genes from these species to engineer oilseeds and bacteria for modified fatty acid compositions.

Metabolic extremes provide opportunities to understand enzymatic and metabolic plasticity and biotechnological tools for novel biomaterial production. We discovered that seed oils of many Thunbergia species contain up to 92% of the unusual monounsaturated petroselinic acid (18:1Δ6), one of the highest reported levels for a single fatty acid in plants. Supporting the biosynthetic origin of petroselinic acid, we identified a Δ6-stearoyl-acyl carrier protein (18:0-ACP) desaturase from Thunbergia laurifolia, closely related to a previously identified Δ6-palmitoyl-ACP desaturase that produces sapienic acid (16:1Δ6)-rich oils in Thunbergia alata seeds. Guided by a T. laurifolia desaturase crystal structure obtained in this study, enzyme mutagenesis identified key amino acids for functional divergence of Δ6 desaturases from the archetypal Δ9-18:0-ACP desaturase and mutations that result in nonnative enzyme regiospecificity. Furthermore, we demonstrate the utility of the T. laurifolia desaturase for the production of unusual monounsaturated fatty acids in engineered plant and bacterial hosts. Through stepwise metabolic engineering, we provide evidence that divergent evolution of extreme petroselinic acid and sapienic acid production arises from biosynthetic and metabolic functional specialization and enhanced expression of specific enzymes to accommodate metabolism of atypical substrates.

Transcriptome Analysis Reveals Candidate Genes for Petroselinic Acid Biosynthesis in Fruits of Coriandrum sativum L

Petroselinic acid (18:1Δ⁶), a monounsaturated cis Δ-6 fatty acid, has many prospective applications in functional foods and for the nutraceutical and pharmaceutical industries. Up to 80% of petroselinic acid has been found in the oil from fruits of coriander (Coriandrum sativum L.), which make it an ideal source for investigating the biosynthesis of petroselinic acid. A coriander acyl-acyl carrier protein desaturase was identified to be involved in its biosynthesis more than two decades ago, but since then little further progress in this area has been reported. In this study, the fatty acid profiles of coriander fruits at six developmental stages were analyzed. Fruit samples from three developmental stages with rapid accumulation of petroselinic acid were used for RNA sequencing using the Illumina Hiseq4000 platform. The transcriptome analysis presented 93 323 nonredundant unigenes and 8545 differentially expressed genes. Functional annotation and combined gene expression data revealed candidate genes potentially involved in petroselinic acid biosynthesis and its incorporation into triacylglycerols. Tissue-specific examination of q-PCR validation further suggested that ACPD1/3, KAS I-1, FATB-1/3, and DGAT2 may be highly involved. Bioinformatic analysis of CsFATB and CsDGAT2 identified their putative key amino acids or functional motifs. These results provide a molecular foundation for petroselinic acid biosynthesis in coriander fruit and facilitate its genetic engineering in other hosts.

Identification of Key Genes Involved in Embryo Development and Differential Oil Accumulation in Two Contrasting Maize Genotypes

Maize is an important oil seed crop and a major food crop in different parts of the world. Since maize has relatively lower seed oil content as compared to other oil crops, efforts are continuing to improve its oil content percentage. In this study, we analyzed two contrasting maize genotypes with differential oil accumulation percentages. High oil-content (HOC) maize had 11% oil content while low oil-content (LOC) maize had significantly lower oil content (5.4%). Transmission electron microscopy revealed a higher accumulation of oil bodies in the HOC maize embryo as compared to LOC maize. Comparative RNA-sequencing analysis at different developmental stages of the seed embryos identified 739 genes that are constantly differentially expressed (DEGs) at all the six developmental stages from 15 days after pollination (DAP) to 40 DAP. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis identified fatty acid metabolism and fatty acid biosynthesis as the most enriched biological pathways contributed by these DEGs. Notably, transcriptional changes are more intense at the early stages of embryo development as compared to later stages. In addition, pathways related to oil biosynthesis and their corresponding genes were more enriched at 30 DAP, which seems to be the key stage for oil accumulation. The study also identified 33 key DEGs involved in fatty acid and triacylglycerols biosynthesis, most of which were up-regulated in HOC, that may shape the differential oil contents in the two contrasting maize. Notably, we discovered that both acyl-CoA-dependent and acyl-CoA-independent processes are essential for the high oil accumulation in maize embryo.

Seed Transcriptomics Analysis in Camellia oleifera Uncovers Genes Associated with Oil Content and Fatty Acid Composition

Camellia oleifera is a major tree species for producing edible oil. Its seed oil is well known for the high level of oleic acids; however, little is known regarding the molecular mechanism of lipid biosynthesis in C. oleifera. Here, we measured the oil contents and fatty acid (FA) compositions at four developmental stages and investigated the global gene expression profiles through transcriptomics sequencing. We identified differentially-expressed genes (DEGs) among the developmental stages and found that the distribution of numbers of DEGs was associated with the accumulation pattern of seed oil. Gene Ontology (GO) enrichment analysis revealed some critical biological processes related to oil accumulation, including lipid metabolism and phosphatidylcholine metabolism. Furthermore, we investigated the expression patterns of lipid biosynthesis genes. We showed that most of the genes were identified with single or multiple copies, and some had correlated profiles along oil accumulation. We proposed that the higher levels of stearoyl-ACP desaturases (SADs) coupled with lower activities of fatty acid desaturase 2 (FAD2) might be responsive to the boost of oleic acid at the late stage of C. oleifera seeds’ development. This work presents a comprehensive transcriptomics study of C. oleifera seeds and uncovers valuable DEGs that are associated with the seed oil accumulation.

Understanding the control of acyl flux through the lipid metabolic network of plant oil biosynthesis

Plant oil biosynthesis involves a complex metabolic network with multiple subcellular compartments, parallel pathways, cycles, and pathways that have a dual function to produce essential membrane lipids and triacylglycerol. Modern molecular biology techniques provide tools to alter plant oil compositions through bioengineering, however with few exceptions the final composition of triacylglycerol cannot be predicted. One reason for limited success in oilseed bioengineering is the inadequate understanding of how to control the flux of fatty acids through various fatty acid modification, and triacylglycerol assembly pathways of the lipid metabolic network. This review focuses on the mechanisms of acyl flux through the lipid metabolic network, and highlights where uncertainty resides in our understanding of seed oil biosynthesis. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner.

Tracking the metabolic pulse of plant lipid production with isotopic labeling and flux analyses: Past, present and future

Metabolism is comprised of networks of chemical transformations, organized into integrated biochemical pathways that are the basis of cellular operation, and function to sustain life. Metabolism, and thus life, is not static. The rate of metabolites transitioning through biochemical pathways (i.e., flux) determines cellular phenotypes, and is constantly changing in response to genetic or environmental perturbations. Each change evokes a response in metabolic pathway flow, and the quantification of fluxes under varied conditions helps to elucidate major and minor routes, and regulatory aspects of metabolism. To measure fluxes requires experimental methods that assess the movements and transformations of metabolites without creating artifacts. Isotopic labeling fills this role and is a long-standing experimental approach to identify pathways and quantify their metabolic relevance in different tissues or under different conditions. The application of labeling techniques to plant science is however far from reaching it potential. In light of advances in genetics and molecular biology that provide a means to alter metabolism, and given recent improvements in instrumentation, computational tools and available isotopes, the use of isotopic labeling to probe metabolism is becoming more and more powerful. We review the principal analytical methods for isotopic labeling with a focus on seminal studies of pathways and fluxes in lipid metabolism and carbon partitioning through central metabolism. Central carbon metabolic steps are directly linked to lipid production by serving to generate the precursors for fatty acid biosynthesis and lipid assembly. Additionally some of the ideas for labeling techniques that may be most applicable for lipid metabolism in the future were originally developed to investigate other aspects of central metabolism. We conclude by describing recent advances that will play an important future role in quantifying flux and metabolic operation in plant tissues.

Biochemical pathways in seed oil synthesis

Oil produced in plant seeds is utilized as a major source of calories for human nutrition, as feedstocks for non-food uses such as soaps and polymers, and can serve as a high-energy biofuel. The biochemical pathways leading to oil (triacylglycerol) synthesis in seeds involve multiple subcellular organelles, requiring extensive lipid trafficking. Phosphatidylcholine plays a central role in these pathways as a substrate for acyl modifications and likely as a carrier for the trafficking of acyl groups between organelles and membrane subdomains. Although much has been clarified regarding the enzymes and pathways responsible for acyl-group flux, there are still major gaps in our understanding. These include the identity of several key enzymes, how flux between alternative pathways is controlled and the specialized cell biology leading to biogenesis of oil bodies that store up to 80% of carbon in seeds.

The significance of different diacylgycerol synthesis pathways on plant oil composition and bioengineering

The unique properties of vegetable oils from different plants utilized for food, industrial feedstocks, and fuel is dependent on the fatty acid (FA) composition of triacylglycerol (TAG). Plants can use two main pathways to produce diacylglycerol (DAG), the immediate precursor molecule to TAG synthesis: (1) De novo DAG synthesis, and (2) conversion of the membrane lipid phosphatidylcholine (PC) to DAG. The FA esterified to PC are also the substrate for FA modification (e.g., desaturation, hydroxylation, etc.), such that the FA composition of PC-derived DAG can be substantially different than that of de novo DAG. Since DAG provides two of the three FA in TAG, the relative flux of TAG synthesis from de novo DAG or PC-derived DAG can greatly affect the final oil FA composition. Here we review how the fluxes through these two alternate pathways of DAG/TAG synthesis are determined and present evidence that suggests which pathway is utilized in different plants. Additionally, we present examples of how the endogenous DAG synthesis pathway in a transgenic host plant can produce bottlenecks for engineering of plant oil FA composition, and discuss alternative strategies to overcome these bottlenecks to produce crop plants with designer vegetable oil compositions.

High-value oils from plants

The seed oils of domesticated oilseed crops are major agricultural commodities that are used primarily for nutritional applications, but in recent years there has been increasing use of these oils for production of biofuels and chemical feedstocks. This is being driven in part by the rapidly rising costs of petroleum, increased concern about the environmental impact of using fossil oil, and the need to develop renewable domestic sources of fuel and industrial raw materials. There is also a need to develop sustainable sources of nutritionally important fatty acids such as those that are typically derived from fish oil. Plant oils can provide renewable sources of high-value fatty acids for both the chemical and health-related industries. The value and application of an oil are determined largely by its fatty acid composition, and while most vegetable oils contain just five basic fatty acid structures, there is a rich diversity of fatty acids present in nature, many of which have potential usage in industry. In this review, we describe several areas where plant oils can have a significant impact on the emerging bioeconomy and the types of fatty acids that are required in these various applications. We also outline the current understanding of the underlying biochemical and molecular mechanisms of seed oil production, and the challenges and potential in translating this knowledge into the rational design and engineering of crop plants to produce high-value oils in plant seeds.

Optical manipulation reveals strong attracting forces at membrane contact sites between endoplasmic reticulum and chloroplasts

Eukaryote cells depend on membrane lipid trafficking from biogenic membranes, like the endoplasmic reticulum (ER), to other membranes in the cell. Two major routes for membrane lipid transport are recognized: vesicular trafficking and lipid transfer at zones of close contact between membranes. Specific ER regions involved in such membrane contact sites (MCSs) have been isolated, and lipid transfer at MCSs as well as protein-protein interactions between the partaking membranes have been demonstrated (reviewed by Holthuis, J. C. M., and Levine, T. P. (2005) Nat. Rev. 6, 209-220). Here we present the first demonstration of the physical association between membranes involved in MCSs: by using optical imaging and manipulation, strong attracting forces between ER and chloroplasts are revealed. We used Arabidopsis thaliana expressing green fluorescent protein in the ER lumen and observed leaf protoplasts by confocal microscopy. The ER network was evident, with ER branch end points apparently localized at chloroplast surfaces. After rupture of a protoplast using a laser scalpel, the cell content was released. ER fragments remained attached to the released chloroplasts and could be stretched out by optical tweezers. The applied force, 400 pN, could not drag a chloroplast free from its attached ER, which could reflect protein-protein interactions at the ER-chloroplast MCSs. As chloroplasts rely on import of ER-synthesized lipids, we propose that lipid transfer occurs at these MCSs. We suggest that lipid transfer at the MCSs also occurs in the opposite direction, for example to channel plastid-synthesized acyl groups to supply substrates for ER-localized synthesis of membrane and storage lipids.

Arabidopsis genes involved in acyl lipid metabolism. A 2003 census of the candidates, a study of the distribution of expressed sequence tags in organs, and a web-based database

The genome of Arabidopsis has been searched for sequences of genes involved in acyl lipid metabolism. Over 600 encoded proteins have been identified, cataloged, and classified according to predicted function, subcellular location, and alternative splicing. At least one-third of these proteins were previously annotated as "unknown function" or with functions unrelated to acyl lipid metabolism; therefore, this study has improved the annotation of over 200 genes. In particular, annotation of the lipolytic enzyme group (at least 110 members total) has been improved by the critical examination of the biochemical literature and the sequences of the numerous proteins annotated as "lipases." In addition, expressed sequence tag (EST) data have been surveyed, and more than 3,700 ESTs associated with the genes were cataloged. Statistical analysis of the number of ESTs associated with specific cDNA libraries has allowed calculation of probabilities of differential expression between different organs. More than 130 genes have been identified with a statistical probability > 0.95 of preferential expression in seed, leaf, root, or flower. All the data are available as a Web-based database, the Arabidopsis Lipid Gene database (http://www.plantbiology.msu.edu/lipids/genesurvey/index.htm). The combination of the data of the Lipid Gene Catalog and the EST analysis can be used to gain insights into differential expression of gene family members and sets of pathway-specific genes, which in turn will guide studies to understand specific functions of individual genes.

Metabolic engineering of fatty acid biosynthesis in plants

Fatty acids are the most abundant form of reduced carbon chains available from nature and have diverse uses ranging from food to industrial feedstocks. Plants represent a significant renewable source of fatty acids because many species accumulate them in the form of triacylglycerol as major storage components in seeds. With the advent of plant transformation technology, metabolic engineering of oilseed fatty acids has become possible and transgenic plant oils represent some of the first successes in design of modified plant products. Directed gene down-regulation strategies have enabled the specific tailoring of common fatty acids in several oilseed crops. In addition, transfer of novel fatty acid biosynthetic genes from noncommercial plants has allowed the production of novel oil compositions in oilseed crops. These and future endeavors aim to produce seeds higher in oil content as well as new oils that are more stable, are healthier for humans, and can serve as a renewable source of industrial commodities. Large-scale new industrial uses of engineered plant oils are on the horizon but will require a better understanding of factors that limit the accumulation of unusual fatty acid structures in seeds.

An unusual seed-specific 3-ketoacyl-ACP synthase associated with the biosynthesis of petroselinic acid in coriander

Petroselinic acid (18:1 delta6) is the major component of the seed oil of Umbelliferae species such as coriander (Coriandrum sativum) as well as Araliaceae and Garryaceae species. This unusual fatty acid is synthesized in plastids by the delta4 desaturation of palmitoyl-acyl carrier protein (16:0-ACP) and subsequent elongation of delta4-hexadecenoyl (16:1 delta4)-ACP. To characterize the enzymatic nature of the elongation reaction, an in vitro assay was developed with 16:1 delta4-ACP and 16:0-ACP as substrates. Extracts from developing coriander seeds elongated 16:1 delta4-ACP in a competitive assay at rates ten-fold greater than that with 16:0-ACP. In contrast, extracts from castor seeds, which do not synthesize petroselinic acid, displayed a strong preference for the elongation of 16:0-ACP rather than 16:1 A4-ACP. In addition, the elongation of 16:1 A4-ACP and 16:0-ACP by coriander seed extracts was strongly inhibited by cerulenin at concentrations as low as 10 microM. This finding suggested that the elongation of 16:1 A4-ACP and 16:0-ACP in coriander seed is catalyzed by a 3-ketoacyl-ACP synthase (KAS) 1-type enzyme(s), rather than a KAS II-type activity that is typically associated with 16:0-ACP elongation. Consistent with this, a cDNA for a diverged form of KAS I was isolated from a cDNA library prepared from developing coriander seed. Using a variety of heterologous probing techniques, no KAS II-type cDNAs could be identified in this library. Multiple alignment of KAS amino acid sequences indicated that, although the polypeptide corresponding to the coriander cDNA is more closely related to KAS I. its active site motif deviates from those found in both KAS I and KAS II enzymes. Also suggestive of a possible role in petroselinic acid synthesis, antibodies raised to the recombinant protein recognize an abundant 45 kDa polypeptide in coriander endosperm that is not detected in coriander leaves. These antibodies also recognize a major band of similar size in developing seeds of English ivy (Hedera helix), an Araliaceae species that also accumulates petroselinic acid in a seed-specific manner.

VARIATIONS IN THE BIOSYNTHESIS OF SEED-STORAGE LIPIDS

In many plants lipids represent up to 80% of dry weight of storage tissues. In seeds, lipids accumulate as triacylglycerols (TAGs), which are formed by an extension of the membrane-lipid biosynthetic pathway common to all plant tissues. In contrast to the conserved fatty acid (FA) composition of membrane lipids, the observed divergence in seed oil acyl chains among different species is very high. The acyl groups of seed TAGs can vary in their chain length (from 8 to 24) as well as in their degree of unsaturation. In addition to methylene-interrupted double bonds, many seeds contain TAGs that have unusual functional groups in their FAs, such as hydroxyl, oxirane, or acetylene groups. All of the major steps in the biosynthetic pathway to TAG are now known and sequence information for genes encoding most of the enzymes involved is available. Here we present the current knowledge of the metabolic mechanisms involved in the divergence from the membrane-lipid biosynthetic pathway during storage lipid formation.

All fatty acids are not equal: discrimination in plant membrane lipids

Plant membrane lipids are primarily composed of 16-carbon and 18-carbon fatty acids containing up to three double bonds. By contrast, the seed oils of many plant species contain fatty acids with significantly different structures. These unusual fatty acids sometimes accumulate to >90% of the total fatty acid content in the seed triacylglycerols, but are generally excluded from the membrane lipids of the plant, including those of the seed. The reasons for their exclusion and the mechanisms by which this is achieved are not completely understood. Here we discuss recent research that has given new insights into how plants prevent the accumulation of unusual fatty acids in membrane lipids, and how strict this censorship of membrane composition is. We also describe a transgenic experiment that resulted in an excessive buildup of unusual fatty acids in cellular membranes, and clearly illustrated that the control of membrane lipid composition is essential for normal plant growth and development.

The biosynthesis of erucic acid in developing embryos of brassica rapa

The prevailing hypothesis on the biosynthesis of erucic acid in developing seeds is that oleic acid, produced in the plastid, is activated to oleoyl-coenzyme A (CoA) for malonyl-CoA-dependent elongation to erucic acid in the cytosol. Several in vivo-labeling experiments designed to probe and extend this hypothesis are reported here. To examine whether newly synthesized oleic acid is directly elongated to erucic acid in developing seeds of Brassica rapa L., embryos were labeled with [14C]acetate, and the ratio of radioactivity of carbon atoms C-5 to C-22 (de novo fatty acid synthesis portion) to carbon atoms C-1 to C-4 (elongated portion) of erucic acid was monitored with time. If newly synthesized 18:1 (oleate) immediately becomes a substrate for elongation to erucic acid, this ratio would be expected to remain constant with incubation time. However, if erucic acid is produced from a pool of preexisting oleic acid, the ratio of 14C in the 4 elongation carbons to 14C in the methyl-terminal 18 carbons would be expected to decrease with time. This labeling ratio decreased with time and, therefore, suggests the existence of an intermediate pool of 18:1, which contributes at least part of the oleoyl precursor for the production of erucic acid. The addition of 2-[3-chloro-5-(trifluromethyl)-2-pyridinyloxyphenoxy] propanoic acid, which inhibits the homodimeric acetyl-CoA carboxylase, severely inhibited the synthesis of [14C]erucic acid, indicating that essentially all malonyl-CoA for elongation of 18:1 to erucate was produced by homodimeric acetyl-CoA carboxylase. Both light and 2-[3-chloro-5-(trifluromethyl)-2-pyridinyloxyphenoxy]-propanoic acid increased the accumulation of [14C]18:1 and the parallel accumulation of [14C]phosphatidylcholine. Taken together, these results show an additional level of complexity in the biosynthesis of erucic acid.

Phosphatidate phosphatases of mammals, yeast, and higher plants

Phosphatidate phosphatase (EC 3.1.3.4) catalyzes the hydrolysis of phosphatidate to yield sn-1,2-diacylglycerol and inorganic phosphate. In mammalian systems, forms of phosphatidate phosphatase involved in glycerolipid synthesis and signal transduction have been identified. Forms of the enzyme involved in signal transduction have been purified and partially characterized. In yeast, phosphatidate phosphatases associated with the endoplasmic reticulum and mitochondria have also been purified and partially characterized. Information on phosphatidate phosphatases from mammals and yeast is useful in characterizing the enzyme from plant systems. This review examines progress on the characterization of phosphatidate phosphatases from mammals, yeast, and higher plants. The purification and characterization of the phosphatidate phosphatase involved in glycerolipid synthesis in developing oilseeds may lead to the identification of the encoding gene. Increasing our understanding of the enzymes of lipid synthesis in developing seeds will aid in the development of biotechnological strategies for seed oil modification.

Intracellular Levels of Free Linolenic and Linoleic Acids Increase in Tomato Leaves in Response to Wounding

An intracellular signaling pathway for activating plant defense genes against attacking herbivores and pathogens is mediated by a lipid-based signal transduction cascade. In this pathway, linolenic acid (18:3) is proposed to be liberated from cell membranes and is converted to cyclopentanones that are involved in transcriptional regulation of defense genes, analogously to prostaglandin synthesis and function in animals. Levels of 18:3 and linoleic acid in tomato (Lycopersicon esculentum) leaves increased within 1 h when the leaves were wounded with a hemostat across the main vein to simulate herbivore attacks. The increase correlated with the time course of accumulation of jasmonic acid, a cyclopentanone product of 18:3, that had previously been shown to increase in leaves in response both to wounding and to elicitors of plant defense genes. One hour after wounding, at least a 15-fold excess of 18:3 was found over that required to account for the levels of newly synthesized jasmonic acid. The free fatty acids in both control and wounded leaves accounted for less than 0.25% of the total fatty acids. However, the total lipid contents of the leaves remained relatively unchanged up to 8 h after wounding, indicating that extensive loss of lipids did not occur, although a gradual decrease in polar lipids was observed, mainly in monogalactosyl diacylglycerol of chloroplast lipids. The data support a role for lipid release as a key step in the signaling events that activate defense genes in tomato leaves in response to wounding by attacking herbivores.

Modification of the fatty acid composition of Escherichia coli by coexpression of a plant acyl-acyl carrier protein desaturase and ferredoxin

Expression of a plant delta 6-palmitoyl (16:0)-acyl carrier protein desaturase in Escherichia coli resulted in the accumulation of the novel monounsaturated fatty acids delta 6-hexadecenoic acid (16:1 delta 6) and delta 8-octadecenoic acid. Amounts of 16:1 delta 6 accumulated by E. coli were increased more than twofold by the expression of a plant ferredoxin together with the delta 6-16:0-acyl carrier protein desaturase.