Resolution and purification of an aldehyde-generating and an alcohol-generating fatty acyl-CoA reductase from pea leaves (Pisum sativum L.)

Morphology and chemical composition of Taiwan oil millet (Eccoilopus formosanus) epicuticular wax

MAIN CONCLUSION

Taiwan oil millet has two types of epicuticular wax: platelet wax composed primarily of octacosanol and filament wax constituted essentially by the singular compound of octacosanoic acid. Taiwan oil millet (TOM-Eccoilopus formosanus) is an orphan crop cultivated by the Taiwan indigenous people. It has conspicuous white powder covering its leaf sheath indicating abundant epicuticular waxes, that may contribute to its resilience. Here, we characterized the epicuticular wax secretion in TOM leaf blade and leaf sheath using various microscopy techniques, as well as gas chromatography to determine its composition. Two kinds of waxes, platelet and filaments, were secreted in both the leaf blades and sheaths. The platelet wax is secreted ubiquitously by epidermal cells, whereas the filament wax is secreted by a specific cell called epidermal cork cells. The newly developed filament waxes were markedly re-synthesized by the epidermal cork cells through papillae protrusions on the external periclinal cell wall. Ultrastructural images of cork cell revealed the presence of cortical endoplasmic reticulum (ER) tubules along the periphery of plasma membrane (PM) and ER-PM contact sites (EPCS). The predominant wax component was a C28 primary alcohol in leaf blade, and a C28 free fatty acid in the leaf sheath, pseudopetiole and midrib. The wax morphology present in distinct plant organs corresponds to the specific chemical composition: platelet wax composed of alcohols exists mainly in the leaf blade, whereas filament wax constituted mainly by the singular compound C28 free fatty acids is present abundantly in leaf sheath. Our study clarifies the filament wax composition in relation to a previous study in sorghum. Both platelet and filament waxes comprise a protection barrier for TOM.

Study on molecular mechanism of volatiles variation during Bupleurum scorzonerifolium root development based on metabolome and transcriptome analysis

Bupleurum scorzonerifolium Willd. is a medicinal herb. Its root has a high content of volatile oil (BSVO), which shows a variety of biological activities. Currently, BSVO in the injectable form is used for treating fever in humans and livestock. The yield and quality of volatile oils depends on the developmental stages of plants. However, the changes in BSVO yield and quality during root development in Bupleurum scorzonerifolium and the underlying molecular regulatory mechanisms remain unclear. This knowledge gap is limiting the improvement in the quality of BSVO. In the present study, B. scorzonerifolium root was collected at germinative, vegetative, florescence, fruiting and defoliating stages. The yield of BSVO, metabolic profile of volatile components and transcriptome of root samples at various developmental stages were comprehensively determined and compared. BSVO continuously accumulated from the germinative to fruiting stages, and its level slightly decreased from the fruiting to defoliating stages. A total of 82 volatile components were detected from B. scorzonerifolium root, of which 22 volatiles were identified as differentially accumulated metabolites (DAMs) during the root development. Of these volatiles, fatty acids and their derivatives accounted for the largest proportion. The contents of most major volatiles were highest at the fruiting stage. A large number of differentially expressed genes (DEGs) were detected during B. scorzonerifolium root development, of which 65 DEGs encoded various enzymes and transcription factors regulating the biosynthesis of fatty acids and their derivatives. In further analysis, 42 DEGs were identified to be significantly correlated with DAMs, and these DEGs may be the key genes for the biosynthesis of volatiles. To the best of our knowledge, this is the first study to comprehensively report the changes in the composition and content of volatiles and underlying mechanism during B. scorzonerifolium root development. This study provided important reference for future studies to determine the harvest time of B. scorzonerifolium roots and improve the quality of BSVO.

The Plant Fatty Acyl Reductases

Fatty acyl reductase (FAR) is a crucial enzyme that catalyzes the NADPH-dependent reduction of fatty acyl-CoA or acyl-ACP substrates to primary fatty alcohols, which in turn acts as intermediate metabolites or metabolic end products to participate in the formation of plant extracellular lipid protective barriers (e.g., cuticular wax, sporopollenin, suberin, and taproot wax). FARs are widely present across plant evolution processes and play conserved roles during lipid synthesis. In this review, we provide a comprehensive view of FAR family enzymes, including phylogenetic analysis, conserved structural domains, substrate specificity, subcellular localization, tissue-specific expression patterns, their varied functions in lipid biosynthesis, and the regulation mechanism of FAR activity. Finally, we pose several questions to be addressed, such as the roles of FARs in tryphine, the interactions between transcription factors (TFs) and FARs in various environments, and the identification of post-transcriptional, translational, and post-translational regulators.

bHLH010/089 Transcription Factors Control Pollen Wall Development via Specific Transcriptional and Metabolic Networks in Arabidopsis thaliana

The pollen wall is a specialized extracellular cell wall that protects male gametophytes from various environmental stresses and facilitates pollination. Here, we reported that bHLH010 and bHLH089 together are required for the development of the pollen wall by regulating their specific downstream transcriptional and metabolic networks. Both the exine and intine structures of bhlh010 bhlh089 pollen grains were severely defective. Further untargeted metabolomic and transcriptomic analyses revealed that the accumulation of pollen wall morphogenesis-related metabolites, including polysaccharides, glyceryl derivatives, and flavonols, were significantly changed, and the expression of such metabolic enzyme-encoding genes and transporter-encoding genes related to pollen wall morphogenesis was downregulated in bhlh010 bhlh089 mutants. Among these downstream target genes, CSLB03 is a novel target with no biological function being reported yet. We found that bHLH010 interacted with the two E-box sequences at the promoter of CSLB03 and directly activated the expression of CSLB03. The cslb03 mutant alleles showed bhlh010 bhlh089–like pollen developmental defects, with most of the pollen grains exhibiting defective pollen wall structures.

The production of wax esters in transgenic plants: towards a sustainable source of bio-lubricants

Wax esters are high-value compounds used as feedstocks for the production of lubricants, pharmaceuticals, and cosmetics. Currently, they are produced mostly from fossil reserves using chemical synthesis, but this cannot meet increasing demand and has a negative environmental impact. Natural wax esters are also obtained from Simmondsia chinensis (jojoba) but comparably in very low amounts and expensively. Therefore, metabolic engineering of plants, especially of the seed storage lipid metabolism of oil crops, represents an attractive strategy for renewable, sustainable, and environmentally friendly production of wax esters tailored to industrial applications. Utilization of wax ester-synthesizing enzymes with defined specificities and modulation of the acyl-CoA pools by various genetic engineering approaches can lead to obtaining wax esters with desired compositions and properties. However, obtaining high amounts of wax esters is still challenging due to their negative impact on seed germination and yield. In this review, we describe recent progress in establishing non-food-plant platforms for wax ester production and discuss their advantages and limitations as well as future prospects.

Machine learning-guided acyl-ACP reductase engineering for improved in vivo fatty alcohol production

Alcohol-forming fatty acyl reductases (FARs) catalyze the reduction of thioesters to alcohols and are key enzymes for microbial production of fatty alcohols. Many metabolic engineering strategies utilize FARs to produce fatty alcohols from intracellular acyl-CoA and acyl-ACP pools; however, enzyme activity, especially on acyl-ACPs, remains a significant bottleneck to high-flux production. Here, we engineer FARs with enhanced activity on acyl-ACP substrates by implementing a machine learning (ML)-driven approach to iteratively search the protein fitness landscape. Over the course of ten design-test-learn rounds, we engineer enzymes that produce over twofold more fatty alcohols than the starting natural sequences. We characterize the top sequence and show that it has an enhanced catalytic rate on palmitoyl-ACP. Finally, we analyze the sequence-function data to identify features, like the net charge near the substrate-binding site, that correlate with in vivo activity. This work demonstrates the power of ML to navigate the fitness landscape of traditionally difficult-to-engineer proteins.

Transcriptional Changes of Cell Wall Organization Genes and Soluble Carbohydrate Alteration during Leaf Blade Development of Rice Seedlings

Plant cell walls have two constituent parts with different components and developmental stages. Much of the mystery concerning the mechanisms of synthesis, decomposition, modification, and so forth, has been resolved using omics and microscopic techniques. However, it still remains to be determined how cell wall development progresses over time after leaf emergence. Our focus in the present study was to expand our knowledge of the molecular mechanisms associated with cell wall synthesis in rice leaf blade during three distinct stages (sink, sink-to-source transition, and source). The RNA-seq, quantitative reverse transcription PCR (qRT-PCR) and carbohydrate concentrations were evaluated using developing fifth leaf blades harvested at different time points. The results revealed that some of the essential genes for the primary cell wall (PCW) were highly upregulated in the sink-to-source transition compared to the sink stage, whereas those essential to the secondary cell wall (SCW) displayed relatively higher levels (p < 0.05) during the source stage. The concentrations of soluble carbohydrates differed via type rather than stage; we observed higher monosaccharides during the sink stage and higher di- and oligo-saccharides during the sink-to-source transition and source stages. In conclusion, our findings suggest that the transcriptional regulation of plant cell wall biosynthesis genes are both synchronistic with and independent of, and directly and indirectly governed by, the abundance of soluble carbohydrates in the developing leaf blade, and, finally, raffinose is likely to play a transport role comparable to sucrose.

Biosynthesis of Fatty Alcohols in Engineered Microbial Cell Factories: Advances and Limitations

Concerns about climate change and environmental destruction have led to interest in technologies that can replace fossil fuels and petrochemicals with compounds derived from sustainable sources that have lower environmental impact. Fatty alcohols produced by chemical synthesis from ethylene or by chemical conversion of plant oils have a large range of industrial applications. These chemicals can be synthesized through biological routes but their free forms are produced in trace amounts naturally. This review focuses on how genetic engineering of endogenous fatty acid metabolism and heterologous expression of fatty alcohol producing enzymes have come together resulting in the current state of the field for production of fatty alcohols by microbial cell factories. We provide an overview of endogenous fatty acid synthesis, enzymatic methods of conversion to fatty alcohols and review the research to date on microbial fatty alcohol production. The primary focus is on work performed in the model microorganisms, Escherichia coli and Saccharomyces cerevisiae but advances made with cyanobacteria and oleaginous yeasts are also considered. The limitations to production of fatty alcohols by microbial cell factories are detailed along with consideration to potential research directions that may aid in achieving viable commercial scale production of fatty alcohols from renewable feedstock.

Yarrowia lipolytica as a Metabolic Engineering Platform for the Production of Very-Long-Chain Wax Esters

The oleaginous yeast Yarrowia lipolytica is an attractive cell factory platform strain and can be used for sustainable production of high-value oleochemical products. Wax esters (WEs) have a good lubricating property and are usually used as a base for the production of advanced lubricants and emollient oils. In this study, we reported the metabolic engineering of Y. lipolytica to heterologously biosynthesize high-content very-long-chain fatty acids (VLCFAs) and fatty alcohols and efficiently esterify them to obtain very-long-chain WEs. Co-expression of fatty acid elongases from different sources in Y. lipolytica could yield VLCFAs with carbon chain lengths up to 24. Combining with optimization of the central metabolic modules could further enhance the biosynthesis of VLCFAs. Furthermore, through the screening of heterologous fatty acyl reductases (FARs), we enabled high-level production of fatty alcohols. Genomic integration and heterologous expression of wax synthase (WS) and FAR in a VLCFA-producing Y. lipolytica strain yielded 95-650 mg/L WEs with carbon chain lengths from 32 to 44. Scaled-up fermentation in 5 L laboratory bioreactors significantly increased the production of WEs to 2.0 g/L, the highest content so far in yeasts. This study contributes to the further efficient biosynthesis of VLCFAs and their derivatives.

Ten fatty acyl-CoA reductase family genes were essential for the survival of the destructive rice pest, Nilaparvata lugens

BACKGROUND

Fatty alcohols are the precursors of sex pheromone components, wax esters and hydrocarbons in insects. Fatty acyl-CoA reductases (FARs) are important enzymes required for the reduction of fatty alcohol and thereby contribute to the production of cuticular hydrocarbon (CHC).

RESULTS

Based on bioinformatics analyses we identified 17 FAR genes in the brown planthopper, Nilaparvata lugens. RNA interference against these genes demonstrated that ten NlFAR genes were essential for the survival of N. lugens. For instance, knockdown of NlFAR5, 6, 11 or 15 was lethal and caused a slender body shape, while the old cuticles of the respective animals remained attached to the abdomen or failed to split open from the nota. Knockdown of NlFAR9 resulted in a phenotype, with a smooth body surface and a decrease in CHC amounts. Similarly, CHC deficiency in N. lugens resulted in increased adhesion of water droplets and secreted honeydew to the insect surface and the inability of N. lugens to survive in paddy fields with varying humidity. Knockdown of NlFAR1, 4, 5, 6, 8, 9, 11 and 13 additionally resulted in female adult infertility.

CONCLUSION

The present study illustrates the structural and functional differences of FAR family genes and provides potential targets for RNA interference-based rice planthopper management. © 2020 Society of Chemical Industry.

MYB41, MYB107, and MYC2 promote ABA-mediated primary fatty alcohol accumulation via activation of AchnFAR in wound suberization in kiwifruit

Wound damage triggers the accumulation of abscisic acid (ABA), which induces the expression of a large number of genes involved in wound suberization in plants. Fatty acyl-CoA reductase (FAR) catalyzes the generation of primary fatty alcohols by the reduction of fatty acids in suberin biosynthesis. However, the regulatory effects of transcription factors (TFs) on AchnFAR in response to ABA are unexplored. In this study, kiwifruit AchnFAR displayed a biological function analogous to that of FAR in transiently overexpressed tobacco (Nicotiana benthamiana) leaves. The positive role of TFs, including AchnMYB41, AchnMYB107, and AchnMYC2, in the regulation of AchnFAR was identified. The three TFs could individually bind to the AchnFAR promoter to activate gene transcription in yeast one-hybrid and dual-luciferase assays. Transient overexpression of TFs in tobacco leaves resulted in the upregulation of aliphatic synthesis genes (including FAR) and the increase in aliphatics, including primary alcohols, α,ω-diacids, ω-hydroxyacids, and fatty acids. Moreover, exogenous ABA treatment elevated TF-mediated AchnFAR expression and the accumulation of primary alcohols. Conversely, fluridone, an inhibitor of ABA biosynthesis, suppressed the expression of AchnFAR and TF genes and reduced the formation of primary alcohols. The results indicate that AchnMYB41, AchnMYB107, and AchnMYC2 activate AchnFAR transcription to promote ABA-mediated primary alcohol formation in wound suberization in kiwifruit.

Biotechnological potential of insect fatty acid-modifying enzymes

There are more than one million described insect species. This species richness is reflected in the diversity of insect metabolic processes. In particular, biosynthesis of secondary metabolites, such as defensive compounds and chemical signals, encompasses an extraordinarily wide range of chemicals that are generally unparalleled among natural products from other organisms. Insect genomes, transcriptomes and proteomes thus offer a valuable resource for discovery of novel enzymes with potential for biotechnological applications. Here, we focus on fatty acid (FA) metabolism-related enzymes, notably the fatty acyl desaturases and fatty acyl reductases involved in the biosynthesis of FA-derived pheromones. Research on insect pheromone-biosynthetic enzymes, which exhibit diverse enzymatic properties, has the potential to broaden the understanding of enzyme specificity determinants and contribute to engineering of enzymes with desired properties for biotechnological production of FA derivatives. Additionally, the application of such pheromone-biosynthetic enzymes represents an environmentally friendly and economic alternative to the chemical synthesis of pheromones that are used in insect pest management strategies.

Effects of Lucilia sericata on wound healing in streptozotocin-induced diabetic rats and analysis of its secretome at the proteome level

The use of Lucilia sericata larvae on the healing of wounds in diabetics has been reported. However, the role of the excretion/secretion (ES) products of the larvae in treatment of diabetic wounds remains unknown. This study investigated whether application of the ES products of L. sericata on the wound surface could improve the impaired wound healing in streptozotocin-induced diabetic rats. Additional analysis was performed to understand proteome content of L. sericata secretome to understand ES contribution at the molecular level. For this purpose, full-thickness skin wounds were created on the backs of diabetic and control rats. A study was conducted to assess the levels of the ES-induced collagen I/III expression and to assay nuclear factor κB (NF-κB) (p65) activity in wound biopsies and ES-treated wounds of diabetic rat skin in comparison to the controls. The expression levels of collagen I/III and NF-κB (p65) activity were determined at days 3, 7, and 14 after wounding using immunohistological analyses and enzyme-linked immunosorbent assay technique. The results indicated that treatment with the ES extract increased collagen I expressions of the wound control and diabetic tissue. But the increase in collagen I expression in the controls was higher than the one in the diabetics. NF-κB (p65) activity was also increased in diabetic wounds compared to the controls, whereas it was decreased in third and seventh days upon ES treatment. The results indicated that ES products of L. sericata may enhance the process of wound healing by influencing phases such as inflammation, NF-κB (p65) activity, collagen synthesis, and wound contraction. These findings may provide new insights into understanding of therapeutic potential of ES in wound healing in diabetics.

Preen oil and bird fitness: a critical review of the evidence

The uropygial gland is a holocrine complex exclusive to birds that produces an oleaginous secretion (preen oil) whose function is still debated. Herein, I examine critically the evidence for the many hypotheses of potential functions of this gland. The main conclusion is that our understanding of this gland is still in its infancy. Even for functions that are considered valid by most researchers, real evidence is scarce. Although it seems clear that preen oil contributes to plumage maintenance, we do not know whether this is due to a role in reducing mechanical abrasion or in reducing feather degradation by keratinophilic organisms. Evidence for a function against pathogenic bacteria is mixed, as preen oil has been demonstrated to act against bacteria in vitro, but not in vivo. Nor is it clear whether preen oil can combat pathogenic bacteria on eggshells to improve hatching success. Studies on the effect of preen oil against dermatophytes are very scarce and there is no evidence of a function against chewing lice. It seems clear, however, that preen oil improves waterproofing, but it is unclear whether this acts by creating a hydrophobic layer or simply by improving plumage structure. Several hypotheses proposed for the function of preen oil have been poorly studied, such as reduction of drag in flight. Similarly, we do not know whether preen oil functions as repellent against predators or parasites, makes birds unpalatable, or functions to camouflage birds with ambient odours. On the other hand, a growing body of work shows the important implications of volatiles in preen oil with regard to social communication in birds. Moreover, preen oil clearly alters plumage colouration. Finally, studies examining the impact of preen oil on fitness are lacking, and the costs or limitations of preen-oil production also remain poorly known. The uropygial gland appears to have several non-mutually exclusive functions in birds, and thus is likely to be subject to several selective pressures. Therefore, future studies should consider how the inevitable trade-offs among different functions drive the evolution of uropygial gland secretions.

Wax Ester Fermentation and Its Application for Biofuel Production

In Euglena cells under anaerobic conditions, paramylon, the storage polysaccharide, is promptly degraded and converted to wax esters. The wax esters synthesized are composed of saturated fatty acids and alcohols with chain lengths of 10-18, and the major constituents are myristic acid and myristyl alcohol. Since the anaerobic cells gain ATP through the conversion of paramylon to wax esters, the phenomenon is named "wax ester fermentation". The wax ester fermentation is quite unique in that the end products, i.e. wax esters, have relatively high molecular weights, are insoluble in water, and accumulate in the cells, in contrast to the common fermentation end products such as lactic acid and ethanol.A unique metabolic pathway involved in the wax ester fermentation is the mitochondrial fatty acid synthetic system. In this system, fatty acid are synthesized by the reversal of β-oxidation with an exception that trans-2-enoyl-CoA reductase functions instead of acyl-CoA dehydrogenase. Therefore, acetyl-CoA is directly used as a C₂ donor in this fatty acid synthesis, and the conversion of acetyl-CoA to malonyl-CoA, which requires ATP, is not necessary. Consequently, the mitochondrial fatty acid synthetic system makes possible the net gain of ATP through the synthesis of wax esters from paramylon. In addition, acetyl-CoA is provided in the anaerobic cells from pyruvate by the action of a unique enzyme, oxygen sensitive pyruvate:NADP⁺ oxidoreductase, instead of the common pyruvate dehydrogenase multienzyme complex.Wax esters produced by anaerobic Euglena are promising biofuels because myristic acid (C_14:0) in contrast to other algal produced fatty acids, such as palmitic acid (C_16:0) and stearic acid (C_18:0), has a low freezing point making it suitable as a drop-in jet fuel. To improve wax ester production, the molecular mechanisms by which wax ester fermentation is regulated in response to aerobic and anaerobic conditions have been gradually elucidated by identifying individual genes related to the wax ester fermentation metabolic pathway and by comprehensive gene/protein expression analysis. In addition, expression of the cyanobacterial Calvin cycle fructose-1,6-bisphosphatase/sedohepturose-1,7-bisphosphatase, in Euglena provided photosynthesis resulting in increased paramylon accumulation enhancing wax ester production. This chapter will discuss the biochemistry of the wax ester fermentation, recent advances in our understanding of the regulation of the wax ester fermentation and genetic engineering approaches to increase production of wax esters for biofuels.

W3 Is a New Wax Locus That Is Essential for Biosynthesis of β-Diketone, Development of Glaucousness, and Reduction of Cuticle Permeability in Common Wheat

The cuticle plays important roles in plant development, growth and defense against biotic and abiotic attacks. Crystallized epicuticular wax, the outermost layer of cuticle, is visible as white-bluish glaucousness. In crops like barley and wheat, glaucousness is trait of adaption to the dry and hot cultivation conditions, and hentriacontane-14,16-dione (β-diketone) and its hydroxy derivatives are the major and unique components of cuticular wax in the upper parts of adult plants. But their biosynthetic pathway and physiological role largely remain unknown. In the present research, we identified a novel wax mutant in wheat cultivar Bobwhite. The mutation is not allelic to the known wax production gene loci W1 and W2, and designated as W3 accordingly. Genetic analysis localized W3 on chromosome arm 2BS. The w3 mutation reduced 99% of β-diketones, which account for 63.3% of the total wax load of the wild-type. W3 is necessary for β-diketone synthesis, but has a different effect on β-diketone hydroxylation because the hydroxy-β-diketones to β-diketone ratio increased 11-fold in the w3 mutant. Loss of β-diketones caused failure to form glaucousness and significant increase of cuticle permeability in terms of water loss and chlorophyll efflux in the w3 mutant. Transcription of 23 cuticle genes from five functional groups was altered in the w3 mutant, 19 down-regulated and four up-regulated, suggesting a possibility that W3 encodes a transcription regulator coordinating expression of cuticle genes. Biosynthesis of β-diketones in wheat and their implications in glaucousness formation and drought and heat tolerance were discussed.

Molecular Characterization of TaFAR1 Involved in Primary Alcohol Biosynthesis of Cuticular Wax in Hexaploid Wheat

Cuticular waxes are complex mixtures of very long chain (VLC) fatty acids and their derivatives in which primary alcohols are the most abundant components in the leaf surface of common wheat (Triticum aestivum L.). However, the genes involved in primary alcohol biosynthesis in wheat are still largely unknown. Here we identified, via a homology-based approach, the TaFAR1 gene belonging to the fatty acyl-CoA reductases (FARs) from wheat. Heterologous expression of TaFAR1 in yeast (Saccharomyces cerevisiae) and in the Arabidopsis (Arabidopsis thaliana) cer4-3 mutant afforded production of C22 primary alcohol and C22-C24 primary alcohols, respectively, and transgenic expression of TaFAR1 in tomato (Solanum lycopersicum) cv MicroTom leaves and fruits resulted in the accumulation of C26-C30 primary alcohols and C30-C34 primary alcohols, respectively. The TaFAR1 protein was localized to the endoplasmic reticulum (ER) in rice (Oryza sativa L.) leaf protoplasts. Moreover, the TaFAR1 expression pattern across various organs correlated with the levels of primary alcohols accumulating in corresponding waxes, and with the presence of platelet-shaped epicuticular wax crystals formed by primary alcohols. A nullisomic-tetrasomic wheat line lacking TaFAR1 had significantly reduced levels of primary alcohols in its leaf blade and anther wax. TaFAR1 was located on chromosome 4AL and appeared to be highly conserved, with only one haplotype among 32 wheat cultivars. Finally, TaFAR1 expression was induced by drought and cold stress in an ABA-dependent manner. Taken together, our results show that TaFAR1 is an active enzyme forming primary alcohols destined for the wheat cuticle.

FAR5, a fatty acyl-coenzyme A reductase, is involved in primary alcohol biosynthesis of the leaf blade cuticular wax in wheat (Triticum aestivum L.)

A waxy cuticle that serves as a protective barrier against non-stomatal water loss and environmental damage coats the aerial surfaces of land plants. It comprises a cutin polymer matrix and waxes. Cuticular waxes are complex mixtures of very long chain fatty acids (VLCFAs) and their derivatives. Results show that primary alcohols are the major components of bread wheat (Triticum aestivum L.) leaf blade cuticular waxes. Here, the characterization of TaFAR5 from wheat cv Xinong 2718, which is allelic to TAA1b, an anther-specific gene, is reported. Evidence is presented for a new function for TaFAR5 in the biosynthesis of primary alcohols of leaf blade cuticular wax in wheat. Expression of TaFAR5 cDNA in yeast (Saccharomyces cerevisiae) led to production of C22:0 primary alcohol. The transgenic expression of TaFAR5 in tomato (Solanum lycopersicum) cv MicroTom leaves resulted in the accumulation of C26:0, C28:0, and C30:0 primary alcohols. TaFAR5 encodes an alcohol-forming fatty acyl-coenzyme A reductase (FAR). Expression analysis revealed that TaFAR5 was expressed at high levels in the leaf blades, anthers, pistils, and seeds. Fully functional green fluorescent protein-tagged TaFAR5 protein was localized to the endoplasmic reticulum (ER), the site of primary alcohol biosynthesis. SDS-PAGE analysis indicated that the TaFAR5 protein possessed a molecular mass of 58.4kDa, and it was also shown that TaFAR5 transcript levels were regulated in response to drought, cold, and abscisic acid (ABA). Overall, these data suggest that TaFAR5 plays an important role in the synthesis of primary alcohols in wheat leaf blade.

Enhanced production of fatty alcohols by engineering the TAGs synthesis pathway in Saccharomyces cerevisiae

The production of fatty acid-derived chemicals has received a great deal of attention in recent years. In yeast cells, the main storage forms of fatty acids are TAGs. However, the conversion of TAGs into fatty acid derivatives suffers from a practical standpoint. Herein, a more direct strategy was applied to accumulate cellular fatty acyl-CoAs in Saccharomyces cerevisiae, which are the activated forms of fatty acids and used as important precursors for various converting enzymes. The dga1 gene was deleted to block the fatty acyl-CoAs dependent pathway of TAGs synthesis and a significant decrease in lipid content was observed. The FAR gene was cloned and overexpressed in the wild type strain and gene disrupted strain, to convert the fatty acyl-CoAs to the corresponding fatty acid derivatives. The metabolic engineered pathway resulted in enhanced production of fatty alcohols. Compared with the wild type strain with overexpressed FAR gene, the yield of fatty alcohols in the Δdga1 strain with FAR was dramatically increased: the intracellular fatty alcohols increased from 26 mg/L to 45 mg/L, while the extracellular fatty alcohols increased from 2.2 mg/L to 4.3 mg/L. By optimizing the culture medium with increased carbon concentration and limited nitrogen concentration, the fatty alcohols yield in the Δdga1 strain with FAR was further increased to 84 mg/L in cells and 14 mg/L secreted in broth. The results in this study demonstrated the feasibility of using the designed strategy to solve the bottleneck in utilizing TAGs for fatty acid derivatives production.

Improved production of fatty alcohols in cyanobacteria by metabolic engineering

BACKGROUND

Fatty alcohols are widely used in industrial chemicals. The biosynthetic pathways for fatty alcohols are diverse and widely existing in nature. They display a high capacity to produce fatty alcohols by the metabolic engineering of different microbe hosts. Direct recycling of carbon dioxide to fatty alcohols can be achieved by introducing a fatty alcohol-producing pathway into photosynthetic cyanobacteria. According to our precious reports, a relatively low yield of fatty alcohols was obtained in the genetically engineered cyanobacterium Synechocystis sp. PCC 6803.

RESULTS

The photosynthetic production of fatty alcohols in Synechocystis sp. PCC 6803 was improved through heterologously expressing fatty acyl-Coenzyme A (acyl-CoA) reductase gene maqu_2220 from the marine bacterium Marinobacter aquaeolei VT8. Maqu_2220 has been proved to catalyze both the four-electron reduction of fatty acyl-CoA or acyl-Acyl Carrier Protein (acyl-ACP) and the two-electron reduction of fatty aldehyde to fatty alcohol. The knockout of the aldehyde-deformylating oxygenase gene (sll0208) efficiently blocked the hydrocarbon accumulation and redirected the carbon flux into the fatty alcohol-producing pathway. By knocking-out both sll0208 and sll0209 (encoding an acyl-ACP reductase), the productivity of fatty alcohols was further increased to 2.87 mg/g dry weight.

CONCLUSIONS

The highest yield of fatty alcohols was achieved in cyanobacteria by expressing the prokaryotic fatty acyl-CoA reductase Maqu_2220 and knocking-out the two key genes (sll0208 and sll0209) that are involved in the alka(e)ne biosynthesis pathway. Maqu_2220 was demonstrated as a robust enzyme for producing fatty alcohols in cyanobacteria. The production of fatty alcohols could be significantly increased by blocking the hydrocarbon biosynthesis pathway.

Fine mapping and metabolic and physiological characterization of the glume glaucousness inhibitor locus Iw3 derived from wild wheat

This research provided the first view of metabolic and physiological effect of a tissue-specific glaucousness inhibitor in wheat and laid foundation for map-based cloning of the Iw3 locus. Cuticular wax constitutes the outermost layer of plant skin, and its composition greatly impacts plant appearance and plant-environment interaction. Epicuticular wax in the upper part of adult wheat plants can form the glaucousness, which is associated with drought tolerance. In this research, we characterized a glume-specific glaucousness inhibitor, Iw3, by fine mapping, physiological, and molecular approaches. Iw3 inhibits glaucousness formation by altering wax composition. Compared to the wild type, Iw3 eliminated β-diketone, reduced 47 % primary alcohols, but increased aldehyde 400-fold and alkanes fivefold, which led to 30 % reduction of total glume wax load. Loss of the glaucousness increased cuticle permeability, suggesting an important role in drought sensitivity. Genetically, the glaucousness-inhibiting effect by Iw3 is partially dominant in a dosage-dependent manner. We localized the Iw3 locus within a 0.13-cM interval delimited by marker loci Xpsp3000 and XWL3096. Of the 53 wax genes assayed, we detected transcription changes in nine genes by Iw3, downregulation of Cer4-1 and upregulation of other five Cer4 and three KCS homologs. All these results provided initial insights into Iw3-mediated regulation of wax metabolism and paved way for in-depth characterization of the Iw3 locus and the glaucousness-related β-diketone pathway.

Fatty acids from pool lipids as possible precursors of the male marking pheromone in bumblebees

Triacylglycerols (TGs) stored in the fat bodies of bumblebee males have a species-specific composition. The striking structural similarities between TG fatty acids (FAs) and components of the male marking pheromone in certain species led to the hypothesis that FAs may serve as precursors in pheromone biosynthesis. Here, we analysed TGs from B.ruderatus, B. bohemicus, and B. campestris. Nonadec-9-ene and icos-15-en-1-ol are the main components of B. ruderatus labial gland secretion, forming up to 92% of the gland extract. The corresponding icos-11-enic and icos-15-enic acids were found in TGs at levels higher than usual for bumblebee species. We found similar relationships in B. campestris and B. bohemicus. These results suggest that FAs might be precursors of aliphatic compounds in the male pheromones. Furthermore, we report for the first time the pheromone structure of B. ruderatus males.

Metabolic engineering of Saccharomyces cerevisiae for production of fatty acid-derived biofuels and chemicals

As the serious effects of global climate change become apparent and access to fossil fuels becomes more limited, metabolic engineers and synthetic biologists are looking towards greener sources for transportation fuels. In recent years, microbial production of high-energy fuels by economically efficient bioprocesses has emerged as an attractive alternative to the traditional production of transportation fuels. Here, we engineered the budding yeast Saccharomyces cerevisiae to produce fatty acid-derived biofuels and chemicals from simple sugars. Specifically, we overexpressed all three fatty acid biosynthesis genes, namely acetyl-CoA carboxylase (ACC1), fatty acid synthase 1 (FAS1) and fatty acid synthase 2 (FAS2), in S. cerevisiae. When coupled to triacylglycerol (TAG) production, the engineered strain accumulated lipid to more than 17% of its dry cell weight, a four-fold improvement over the control strain. Understanding that TAG cannot be used directly as fuels, we also engineered S. cerevisiae to produce drop-in fuels and chemicals. Altering the terminal "converting enzyme" in the engineered strain led to the production of free fatty acids at a titer of approximately 400 mg/L, fatty alcohols at approximately 100mg/L and fatty acid ethyl esters (biodiesel) at approximately 5 mg/L directly from simple sugars. We envision that our approach will provide a scalable, controllable and economic route to this important class of chemicals.

Production of propane and other short-chain alkanes by structure-based engineering of ligand specificity in aldehyde-deformylating oxygenase

Biocatalytic propane production: structure-based engineering of aldehyde-deformylating oxygenase improves specificity for short- and medium-chain-length aldehydes and enhances the propane generation in whole-cell biotransformations. This presents new opportunities for developing biocatalytic modules for the production of volatile "drop-in" biofuels.

Fatty alcohol production in engineered E. coli expressing Marinobacter fatty acyl-CoA reductases

Although successful production of fatty alcohols in metabolically engineered Escherichia coli with heterologous expression of fatty acyl-CoA reductase has been reported, low biosynthetic efficiency is still a hurdle to be overcome. In this study, we examined the characteristics of two fatty acyl-CoA reductases encoded by Maqu_2220 and Maqu_2507 genes from Marinobacter aquaeolei VT8 on fatty alcohol production in E. coli. Fatty alcohols with diversified carbon chain length were obtained by co-expressing Maqu_2220 with different carbon chain length-specific acyl-ACP thioesterases. Both fatty acyl-CoA reductases displayed broad substrate specificities for C12-C18 fatty acyl chains in vivo. The optimized mutant strain of E. coli carrying the modified tesA gene and fadD gene from E. coli and Maqu_2220 gene from Marinobacter aquaeolei VT8 produced fatty alcohols at a remarkable level of 1.725 g/L under the fermentation condition.

Acyl-lipid metabolism

Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables.

Genetic interactions underlying the biosynthesis and inhibition of β-diketones in wheat and their impact on glaucousness and cuticle permeability

Cuticular wax composition greatly impacts plant responses to dehydration. Two parallel pathways exist in Triticeae for manipulating wax composition: the acyl elongation, reduction, and decarbonylation pathway that is active at the vegetative stage and yields primary alcohols and alkanes, and the β-diketone pathway that predominates at the reproductive stage and synthesizes β-diketones. Variation in glaucousness during the reproductive stage of wheat is mainly controlled by the wax production genes, W1 and W2, and wax inhibitor genes, Iw1 and Iw2. Little is known about the metabolic and physiological effects of the genetic interactions among these genes and their roles in shifting wax composition during plant development. We characterized the effect of W1, W2, Iw1, and Iw2 and analyzed their interaction using a set of six near-isogenic lines (NILs) by metabolic, molecular and physiological approaches. Loss of functional alleles of both W genes or the presence of either Iw gene depletes β-diketones and results in the nonglaucous phenotype. Elimination of β-diketones is compensated for by an increase in aldehydes and primary alcohols in the Iw NILs. Accordingly, transcription of CER4-6, which encodes an alcohol-forming fatty acyl-CoA reductase, was elevated 120-fold in iw1Iw2. CER4-6 was transcribed at much higher levels in seedlings than in adult plants, and showed little difference between the glaucous and nonglaucous NILs, suggesting that Iw2 counteracts the developmental repression of CER4-6 at the reproductive stage. While W1 and W2 redundantly function in β-diketone biosynthesis, a combination of both functional alleles led to the β-diketone hydroxylation. Consistent with this, transcription of MAH1-9, which encodes a mid-chain alkane hydroxylase, increased seven-fold only in W1W2. In parallel with the hydroxyl-β-diketone production patterns, glaucousness was intensified and cuticle permeability was reduced significantly in W1W2 compared to the other NILs. This suggests that both W1 and W2 are required for enhancing drought tolerance.

Wax ester synthesis is required for Mycobacterium tuberculosis to enter in vitro dormancy

Mycobacterium tuberculosis (Mtb) is known to produce wax esters (WE) when subjected to stress. However, nothing is known about the enzymes involved in biosynthesis of WE and their role in mycobacterial dormancy. We report that two putative Mtb fatty acyl-CoA reductase genes (fcr) expressed in E. coli display catalytic reduction of fatty acyl-CoA to fatty aldehyde and fatty alcohol. Both enzymes (FCR1/Rv3391) and FCR2/Rv1543) showed a requirement for NADPH as the reductant, a preference for oleoyl-CoA over saturated fatty acyl-CoA and were inhibited by thiol-directed reagents. We generated Mtb gene-knockout mutants for each reductase. Metabolic incorporation of( 14)C-oleate into fatty alcohols and WE was severely diminished in the mutants under dormancy-inducing stress conditions that are thought to be encountered by the pathogen in the host. The fatty acyl-CoA reductase activity in cell lysates of the mutants under nitric oxide stress was significantly reduced when compared with the wild type. Complementation restored the lost activity completely in the Δfcr1 mutant and partially in the Δfcr2 mutant. WE synthesis was inhibited in both Δfcr mutants. The Δfcr mutants exhibited faster growth rates, an increased uptake of (14)C-glycerol suggesting increased permeability of the cell wall, increased metabolic activity levels and impaired phenotypic antibiotic tolerance under dormancy-inducing combined multiple stress conditions. Complementation of the mutants did not restore the development of antibiotic tolerance to wild-type levels. Transcript analysis of Δfcr mutants showed upregulation of genes involved in energy generation and transcription, indicating the inability of the mutants to become dormant. Our results indicate that the fcr1 and fcr2 gene products are involved in WE synthesis under in vitro dormancy-inducing conditions and that WE play a critical role in reaching a dormant state. Drugs targeted against the Mtb reductases may inhibit its ability to go into dormancy and therefore increase susceptibility of Mtb to currently used antibiotics thereby enhancing clearance of the pathogen from patients.

Arabidopsis cuticular waxes: advances in synthesis, export and regulation

Cuticular waxes and cutin form the cuticle, a hydrophobic layer covering the aerial surfaces of land plants and acting as a protective barrier against environmental stresses. Very-long-chain fatty acid derived compounds that compose the cuticular waxes are produced in the endoplasmic reticulum of epidermal cells before being exported to the environmental face of the epidermis. Twenty years of genetic studies on Arabidopsis thaliana have led to the molecular characterization of enzymes catalyzing major steps in fatty acid elongation and wax biosynthesis. Although transporters required for wax export from the plasma membrane have been identified, intracellular and extracellular traffic remains largely unknown. In accordance with its major function in producing an active waterproof barrier, wax metabolism is up-regulated at the transcriptional level in response to water deficiency. However its developmental regulation is still poorly described. Here, we discuss the present knowledge of wax functions, biosynthesis and transport as well as the regulation of these processes.

Biochemical characterization of a chloroplast localized fatty acid reductase from Arabidopsis thaliana

Primary long-chain fatty alcohols are present in a variety of phyla. In eukaryotes, the production of fatty alcohols is catalyzed by fatty acyl-CoA reductase (FAR) enzymes that convert fatty acyl-CoAs or acyl-ACPs into fatty alcohols. Here, we report on the biochemical properties of a purified plant FAR, Arabidopsis FAR6 (AtFAR6). In vitro assays show that the enzyme preferentially uses 16 carbon acyl-chains as substrates and produces predominantly fatty alcohols. Free fatty acids and fatty aldehyde intermediates can be released from the enzyme, in particular with suboptimal chain lengths and concentrations of the substrates. Both acyl-CoA and acyl-ACP could serve as substrates. Transient expression experiments in Nicotiana tabacum showed that AtFAR6 is a chloroplast localized FAR. In addition, expression of full length AtFAR6 in Nicotiana benthamiana leaves resulted in the production of C16:0-alcohol within this organelle. Finally, a GUS reporter gene fusion with the AtFAR6 promoter showed that the AtFAR6 gene is expressed in various tissues of the plant with a distinct pattern compared to that of other Arabidopsis FARs, suggesting specialized functions in planta.

Plant fatty acyl reductases: enzymes generating fatty alcohols for protective layers with potential for industrial applications

Primary fatty alcohols are found throughout the biological world, either in free form or in a combined state. They are common components of plant surface lipids (i.e. cutin, suberin, sporopollenin, and associated waxes) and their absence can significantly perturb these essential barriers. Fatty alcohols and/or derived compounds are also likely to have direct functions in plant biotic and abiotic interactions. An evolutionarily related set of alcohol-forming fatty acyl reductases (FARs) is present in all kingdoms of life. Plant microsomal and plastid-associated FAR enzymes have been characterized, acting on acyl-coenzymeA (acyl-CoA) or acyl-acyl carrier protein (acyl-ACP) substrates, respectively. FARs have distinct substrate specificities both with regard to chain length and chain saturation. Fatty alcohols and wax esters, which are a combination of fatty alcohol and fatty acid, have a variety of commercial applications. The expression of FARs with desired specificities in transgenic microbes or oilseed crops would provide a novel means of obtaining these valuable compounds. In the present review, we report on recent progress in characterizing plant FAR enzymes and in understanding the biological roles of primary fatty alcohols, as well as describe the biotechnological production and industrial uses of fatty alcohols.

Optimization of fatty alcohol biosynthesis pathway for selectively enhanced production of C12/14 and C16/18 fatty alcohols in engineered Escherichia coli

BACKGROUND

With the increasing stress from oil price and environmental pollution, aroused attention has been paid to the microbial production of chemicals from renewable sources. The C12/14 and C16/18 alcohols are important feedstocks for the production of surfactants and detergents, which are widely used in the most respected consumer detergents, cleaning products and personal care products worldwide. Though bioproduction of fatty alcohols has been carried out in engineered E. coli, several key problems have not been solved in earlier studies, such as the quite low production of C16/18 alcohol, the lack of optimization of the fatty alcohol biosynthesis pathway, and the uncharacterized performance of the engineered strains in scaled-up system.

RESULTS

We improved the fatty alcohol production by systematically optimizing the fatty alcohol biosynthesis pathway, mainly targeting three key steps from fatty acyl-acyl carrier proteins (ACPs) to fatty alcohols, which are sequentially catalyzed by thioesterase, acyl-coenzyme A (CoA) synthase and fatty acyl-CoA reductase. By coexpression of thioesterase gene BTE, acyl-CoA synthase gene fadD and fatty acyl-CoA reductase gene acr1, 210.1 mg/L C12/14 alcohol was obtained. A further optimization of expression level of BTE, fadD and acr1 increased the C12/14 alcohol production to 449.2 mg/L, accounting for 75.0% of the total fatty alcohol production (598.6 mg/L). In addition, by coexpression of thioesterase gene 'tesA, acyl-CoA synthase gene fadD and fatty acyl-CoA reductase gene FAR, 101.5 mg/L C16/18 alcohol was obtained, with C16/18 alcohol accounting for 89.2% of the total fatty alcohol production.

CONCLUSIONS

To our knowledge, this is the first report on selective production of C12/14 and C16/18 alcohols by microbial fermentation. This work achieved high-specificity production of both C12/14 and C16/18 alcohols. The encouraging 598.6 mg/L of fatty alcohols represents the highest titer reported so far. In addition, the 101.5 mg/L 89.2% C16/18 alcohol suggests an important breakthrough in C16/18 alcohol production. A more detailed optimization of the expression level of fatty alcohol biosynthesis pathway may contribute to a further improvement of fatty alcohol production.

Molecular and functional analysis of three fatty acyl-CoA reductases with distinct substrate specificities in copepod Calanus finmarchicus

The marine copepod Calanus finmarchicus constitutes the substantial amount of biomass in the Arctic and Northern seas. It is unique in that this small crustacean accumulates a high level of wax esters as carbon storage which is mainly comprised of 20:1n-9 and 22:1n-11 alcohols (Alc) linked with various kinds of fatty acids, including n-3 polyunsaturated fatty acids. The absence of 20:1n-9 Alc and 22:1n-11 Alc in diatoms and dinoflagellates, the primary food sources of copepods, suggests the existence of de novo biosynthesis of fatty alcohols in C. finmarchinus. Here, we report identification of three genes, CfFAR1, CfFAR2, and CfFAR3, coding for fatty acyl-CoA reductases involved in the conversion of various fatty acyl-CoAs to their corresponding alcohols. Functional characterization of these genes in yeast indicated that CfFAR1 could use a wide range of saturated fatty acids from C18 to C26 as substrates, CfFAR2 had a narrow range of substrates with only very-long-chain saturated fatty acid 24:0 and 26:0, while CfFAR3 was active towards both saturated (16:0 and 18:0) and unsaturated (18:1 and 20:1) fatty acids producing corresponding alcohols. This finding suggested that these three fatty acyl-CoA reductases are likely responsible for de novo synthesis of a series of fatty alcohol moieties of wax esters in C. finmarchicus.

Fatty acyl-CoA reductases of birds

Background

Birds clean and lubricate their feathers with waxes that are produced in the uropygial gland, a holocrine gland located on their back above the tail. The type and the composition of the secreted wax esters are dependent on the bird species, for instance the wax ester secretion of goose contains branched-chain fatty acids and unbranched fatty alcohols, whereas that of barn owl contains fatty acids and alcohols both of which are branched. Alcohol-forming fatty acyl-CoA reductases (FAR) catalyze the reduction of activated acyl groups to fatty alcohols that can be esterified with acyl-CoA thioesters forming wax esters.

Results

cDNA sequences encoding fatty acyl-CoA reductases were cloned from the uropygial glands of barn owl (Tyto alba), domestic chicken (Gallus gallus domesticus) and domestic goose (Anser anser domesticus). Heterologous expression in Saccharomyces cerevisiae showed that they encode membrane associated enzymes which catalyze a NADPH dependent reduction of acyl-CoA thioesters to fatty alcohols. By feeding studies of transgenic yeast cultures and in vitro enzyme assays with membrane fractions of transgenic yeast cells two groups of isozymes with different properties were identified, termed FAR1 and FAR2. The FAR1 group mainly synthesized 1-hexadecanol and accepted substrates in the range between 14 and 18 carbon atoms, whereas the FAR2 group preferred stearoyl-CoA and accepted substrates between 16 and 20 carbon atoms. Expression studies with tissues of domestic chicken indicated that FAR transcripts were not restricted to the uropygial gland.

Conclusion

The data of our study suggest that the identified and characterized avian FAR isozymes, FAR1 and FAR2, can be involved in wax ester biosynthesis and in other pathways like ether lipid synthesis.

Oxygen-independent alkane formation by non-heme iron-dependent cyanobacterial aldehyde decarbonylase: investigation of kinetics and requirement for an external electron donor

Cyanobacterial aldehyde decarbonylase (cAD) is, structurally, a member of the di-iron carboxylate family of oxygenases. We previously reported that cAD from Prochlorococcus marinus catalyzes the unusual hydrolysis of aldehydes to produce alkanes and formate in a reaction that requires an external reducing system but does not require oxygen [Das et al. (2011) Angew. Chem. 50, 7148-7152]. Here we demonstrate that cADs from divergent cyanobacterial classes, including the enzyme from N. puntiformes that was reported to be oxygen dependent, catalyze aldehyde decarbonylation at a much faster rate under anaerobic conditions and that the oxygen in formate derives from water. The very low activity (<1 turnover/h) of cAD appears to result from inhibition by the ferredoxin reducing system used in the assay and the low solubility of the substrate. Replacing ferredoxin with the electron mediator phenazine methosulfate allowed the enzyme to function with various chemical reductants, with NADH giving the highest activity. NADH is not consumed during turnover, in accord with the proposed catalytic role for the reducing system in the reaction. With octadecanal, a burst phase of product formation, k(prod) = 3.4 ± 0.5 min(-1), is observed, indicating that chemistry is not rate-determining under the conditions of the assay. With the more soluble substrate, heptanal, k(cat) = 0.17 ± 0.01 min(-1) and no burst phase is observed, suggesting that a chemical step is limiting in the reaction of this substrate.

Characterization of a fatty acyl-CoA reductase from Marinobacter aquaeolei VT8: a bacterial enzyme catalyzing the reduction of fatty acyl-CoA to fatty alcohol

Fatty alcohols are of interest as a renewable feedstock to replace petroleum compounds used as fuels, in cosmetics, and in pharmaceuticals. One biological approach to the production of fatty alcohols involves the sequential action of two bacterial enzymes: (i) reduction of a fatty acyl-CoA to the corresponding fatty aldehyde catalyzed by a fatty acyl-CoA reductase, followed by (ii) reduction of the fatty aldehyde to the corresponding fatty alcohol catalyzed by a fatty aldehyde reductase. Here, we identify, purify, and characterize a novel bacterial enzyme from Marinobacter aquaeolei VT8 that catalyzes the reduction of fatty acyl-CoA by four electrons to the corresponding fatty alcohol, eliminating the need for a separate fatty aldehyde reductase. The enzyme is shown to reduce fatty acyl-CoAs ranging from C8:0 to C20:4 to the corresponding fatty alcohols, with the highest rate found for palmitoyl-CoA (C16:0). The dependence of the rate of reduction of palmitoyl-CoA on substrate concentration was cooperative, with an apparent K(m) ~ 4 μM, V(max) ~ 200 nmol NADP(+) min(-1) (mg protein)(-1), and n ~ 3. The enzyme also reduced a range of fatty aldehydes with decanal having the highest activity. The substrate cis-11-hexadecenal was reduced in a cooperative manner with an apparent K(m) of ~50 μM, V(max) of ~8 μmol NADP(+) min(-1) (mg protein)(-1), and n ~ 2.

The positional sterile (ps) mutation affects cuticular transpiration and wax biosynthesis of tomato fruits

Cuticular waxes are known to play a pivotal role in limiting transpirational water loss across primary plant surfaces. The astomatous tomato fruit is an ideal model system that permits the functional characterization of intact cuticular membranes and therefore allows direct correlation of their permeance for water with their qualitative and quantitative composition. The recessive positional sterile (ps) mutation, which occurred spontaneously in tomato (Solanum lycopersicum L.), is characterized by floral organ fusion and positional sterility. Because of a striking phenotypical similarity with the lecer6 wax mutant of tomato, which is defective in very-long-chain fatty acid elongation, ps mutant fruits were analyzed for their cuticular wax and cutin composition. We also examined their cuticular permeance for water following the developmental course of fruit ripening. Wild type and ps mutant fruits showed considerable differences in their cuticular permeance for water, while exhibiting similar quantitative wax accumulation. The ps mutant fruits showed a five- to eightfold increase in water loss per unit time and surface area when compared to the corresponding wild type fruits. The cuticular waxes of ps mutant fruits were characterized by an almost complete absence of n-alkanes and aldehydes, with a concomitant increase in triterpenoids and sterol derivatives. We also noted the occurrence of alkyl esters not present in the wild type. Quantitative and qualitative cutin monomer composition remained largely unaffected. The significant differences in the cuticular wax composition of ps mutant fruits induced a distinct increase of cuticular water permeance. The fruit wax compositional phenotype indicates the ps mutation is responsible for effectively blocking the decarbonylation pathway of wax biosynthesis in epidermal cells of tomato fruits.

Gene expression profile analysis of tobacco leaf trichomes

BACKGROUND

Leaf trichomes of Nicotiana tabacum are distinguished by their large size, high density, and superior secretion ability. They contribute to plant defense response against biotic and abiotic stress, and also influence leaf aroma and smoke flavor. However, there is limited genomic information about trichomes of this non-model plant species.

RESULTS

We have characterized Nicotiana tabacum leaf trichome gene expression using two approaches. In the first, a trichome cDNA library was randomly sequenced, and 2831 unique genes were obtained. The most highly abundant transcript was ribulose bisphosphate carboxylase (RuBisCO). Among the related sequences, most encoded enzymes involved in primary metabolism. Secondary metabolism related genes, such as isoprenoid and flavonoid biosynthesis-related, were also identified. In the second approach, a cDNA microarray prepared from these 2831 clones was used to compare gene expression levels in trichome and leaf. There were 438 differentially expressed genes between trichome and leaves-minus-trichomes. Of these, 207 highly expressed genes in tobacco trichomes were enriched in second metabolic processes, defense responses, and the metabolism regulation categories. The expression of selected unigenes was confirmed by semi-quantitative RT-PCR analysis, some of which were specifically expressed in trichomes.

CONCLUSION

The expression feature of leaf trichomes in Nicotiana tabacum indicates their metabolic activity and potential importance in stress resistance. Sequences predominantly expressed in trichomes will facilitate gene-mining and metabolism control of plant trichome.

The reductase domain in a Type I fatty acid synthase from the apicomplexan Cryptosporidium parvum: restricted substrate preference towards very long chain fatty acyl thioesters

Background

The apicomplexan Cryptosporidium parvum genome possesses a 25-kb intronless open reading frame (ORF) that predicts a multifunctional Type I fatty acid synthase (CpFAS1) with at least 21 enzymatic domains. Although the architecture of CpFAS1 resembles those of bacterial polyketide synthases (PKSs), this megasynthase is predicted to function as a fatty acyl elongase as our earlier studies have indicated that the N-terminal loading unit (acyl-[ACP] ligase) prefers using intermediate to long chain fatty acids as substrates, and each of the three internal elongation modules contains a complete set of enzymes to produce a saturated fatty acyl chain. Although the activities of almost all domains were confirmed using recombinant proteins, that of the C-terminal reductase domain (CpFAS1-R) was yet undetermined. In fact, there were no published studies to report the kinetic features of any reductase domains in bacterial PKSs using purified recombinant or native proteins.

Results

In the present study, the identity of CpFAS1-R as a reductase is confirmed by in silico analysis on sequence similarity and characteristic motifs. Phylogenetic analysis based on the R-domains supports a previous notion on the bacterial origin of apicomplexan Type I FAS/PKS genes. We also developed a novel assay using fatty acyl-CoAs as substrates, and determined that CpFAS1-R could only utilize very long chain fatty acyl-CoAs as substrates (i.e., with activity on C26 > C24 > C22 > C20, but no activity on C18 and C16). It was capable of using both NADPH and NADH as electron donors, but prefers NADPH to NADH. The activity of CpFAS1-R displayed allosteric kinetics towards C26 hexacosanoyl CoA as a substrate (h = 2.0; V_max = 32.8 nmol min^-1 mg^-1 protein; and K₅₀ = 0.91 mM).

Conclusions

We have confirmed the activity of CpFAS1-R by directly assaying its substrate preference and kinetic parameters, which is for the first time for a Type I FAS, PKS or non-ribosomal peptide synthase (NRPS) reductase domain. The restricted substrate preference towards very long chain fatty acyl thioesters may be an important feature for this megasynthase to avoid the release of product(s) with undesired lengths.

Three Arabidopsis fatty acyl-coenzyme A reductases, FAR1, FAR4, and FAR5, generate primary fatty alcohols associated with suberin deposition

Suberin is a protective hydrophobic barrier consisting of phenolics, glycerol, and a variety of fatty acid derivatives, including C18:0-C22:0 primary fatty alcohols. An eight-member gene family encoding alcohol-forming fatty acyl-coenzyme A reductases (FARs) has been identified in Arabidopsis (Arabidopsis thaliana). Promoter-driven expression of the beta-glucuronidase reporter gene indicated that three of these genes, FAR1(At5g22500), FAR4(At3g44540), and FAR5(At3g44550), are expressed in root endodermal cells. The three genes were transcriptionally induced by wounding and salt stress. These patterns of gene expression coincide with known sites of suberin deposition. We then characterized a set of mutants with T-DNA insertions in FAR1, FAR4, or FAR5 and found that the suberin compositions of roots and seed coats were modified in each far mutant. Specifically, C18:0-OH was reduced in far5-1, C20:0-OH was reduced in far4-1, and C22:0-OH was reduced in far1-1. We also analyzed the composition of polymer-bound lipids of leaves before and after wounding and found that the basal levels of C18:0-C22:0 primary alcohols in wild-type leaves were increased by wounding. In contrast, C18:0-OH and C22:0-OH were not increased by wounding in far5-1 and far1-1 mutants, respectively. Heterologous expression of FAR1, FAR4, and FAR5 in yeast confirmed that they are indeed active alcohol-forming FARs with distinct, but overlapping, chain length specificities ranging from C18:0 to C24:0. Altogether, these results indicate that Arabidopsis FAR1, FAR4, and FAR5 generate the fatty alcohols found in root, seed coat, and wound-induced leaf tissue.

Acyl-lipid metabolism

Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables.

Genetic engineering of algae for enhanced biofuel production

There are currently intensive global research efforts aimed at increasing and modifying the accumulation of lipids, alcohols, hydrocarbons, polysaccharides, and other energy storage compounds in photosynthetic organisms, yeast, and bacteria through genetic engineering. Many improvements have been realized, including increased lipid and carbohydrate production, improved H(2) yields, and the diversion of central metabolic intermediates into fungible biofuels. Photosynthetic microorganisms are attracting considerable interest within these efforts due to their relatively high photosynthetic conversion efficiencies, diverse metabolic capabilities, superior growth rates, and ability to store or secrete energy-rich hydrocarbons. Relative to cyanobacteria, eukaryotic microalgae possess several unique metabolic attributes of relevance to biofuel production, including the accumulation of significant quantities of triacylglycerol; the synthesis of storage starch (amylopectin and amylose), which is similar to that found in higher plants; and the ability to efficiently couple photosynthetic electron transport to H(2) production. Although the application of genetic engineering to improve energy production phenotypes in eukaryotic microalgae is in its infancy, significant advances in the development of genetic manipulation tools have recently been achieved with microalgal model systems and are being used to manipulate central carbon metabolism in these organisms. It is likely that many of these advances can be extended to industrially relevant organisms. This review is focused on potential avenues of genetic engineering that may be undertaken in order to improve microalgae as a biofuel platform for the production of biohydrogen, starch-derived alcohols, diesel fuel surrogates, and/or alkanes.

A novel in vitro multiple-stress dormancy model for Mycobacterium tuberculosis generates a lipid-loaded, drug-tolerant, dormant pathogen

BACKGROUND

Mycobacterium tuberculosis (Mtb) becomes dormant and phenotypically drug resistant when it encounters multiple stresses within the host. Inability of currently available drugs to kill latent Mtb is a major impediment to curing and possibly eradicating tuberculosis (TB). Most in vitro dormancy models, using single stress factors, fail to generate a truly dormant Mtb population. An in vitro model that generates truly dormant Mtb cells is needed to elucidate the metabolic requirements that allow Mtb to successfully go through dormancy, identify new drug targets, and to screen drug candidates to discover novel drugs that can kill dormant pathogen.

METHODOLOGY/PRINCIPAL FINDINGS

We developed a novel in vitro multiple-stress dormancy model for Mtb by applying combined stresses of low oxygen (5%), high CO(2) (10%), low nutrient (10% Dubos medium) and acidic pH (5.0), conditions Mtb is thought to encounter in the host. Under this condition, Mtb stopped replicating, lost acid-fastness, accumulated triacylglycerol (TG) and wax ester (WE), and concomitantly acquired phenotypic antibiotic-resistance. Putative neutral lipid biosynthetic genes were up-regulated. These genes may serve as potential targets for new antilatency drugs. The triacylglycerol synthase1 (tgs1) deletion mutant, with impaired ability to accumulate TG, exhibited a lesser degree of antibiotic tolerance and complementation restored antibiotic tolerance. Transcriptome analysis with microarray revealed the achievement of dormant state showing repression of energy generation, transcription and translation machineries and induction of stress-responsive genes. We adapted this model for drug screening using the Alamar Blue dye to quantify the antibiotic tolerant dormant cells.

CONCLUSIONS/SIGNIFICANCE

The new in vitro multiple stress dormancy model efficiently generates Mtb cells meeting all criteria of dormancy, and this method is adaptable to high-throughput screening for drugs that can kill dormant Mtb. A critical link between storage-lipid accumulation and development of phenotypic drug-resistance in Mtb was established. Storage lipid biosynthetic genes may be appropriate targets for novel drugs that can kill latent Mtb.

Functional expression of five Arabidopsis fatty acyl-CoA reductase genes in Escherichia coli

Very long chain primary alcohols are significant components in cuticle waxes of plants. Fatty acyl-CoA reductases (FARs) catalyze the formation of a fatty alcohol from an acyl-CoA. The Arabidopsis (Arabidopsis thaliana) genome contains eight genes homologous to FAR genes from jojoba (Simmondsia chinensis), silk moth, wheat and mouse. Expression of six Arabidopsis FAR homologs in Escherichia coli resulted in production of alcohols from endogenous E. coli fatty acids by five of these genes, confirming that they encode for FAR enzymes. Only a truncated splicing version of the sixth gene was found, and this gene yielded a protein with no FAR activity. The five functional FAR enzymes yielded distinctly different compositions of fatty alcohols when expressed in E. coli, indicating that the different enzymes may be involved in the production of different types of alcohols in plant cells.

[Progress in the study on genes encoding enzymes involved in biosynthesis of very long chain fatty acids and cuticular wax in plants]

Very long chain fatty acids (VLCFAs) play a comprehensive role in organisms. They are essential biological components in seed storage triacylglycerols (TAGs), membrane lipids, and sphingolipids. They also serve as precursors of wax layer compounds. The cuticle covers the aerial surface of land plants, which consists of cutin and wax. The wax, including amorphous intracuticular wax embedded in cutin polymer and epicuticular wax crystalloids that cover the outer plant surface, plays crucial roles in plant growth and development, and adaptation to environment. Biosynthesis of VLCFAs is catalyzed by the fatty acyl-CoA elongase, a membrane-bound enzymatic complex containing 3-ketoacyl-CoA synthase (KCS), 3-ketoacyl-CoA reductase (KCR), 3-hydroxacyl-CoA dehydratase (HCD), and trans-2, 3-enoyl-CoA reductase (ECR). Very long chain fatty acid wax precursors flux into cuticular wax biosynthetic pathways through acyl reduction and decarbonylation, and then are converted to all kinds of wax components. This article reviews the functions of VLCFAs and cuticular wax, and the recent progress in cloning and characterization of genes encoding enzymes involved in catalyzing VLCFAs and cuticular wax biosynthesis. The problems existing in researches of wax genes are also discussed.

Biosynthesis and function of polyacetylenes and allied natural products

Polyacetylenic natural products are a substantial class of often unstable compounds containing a unique carbon-carbon triple bond functionality, that are intriguing for their wide variety of biochemical and ecological functions, economic potential, and surprising mode of biosynthesis. Isotopic tracer experiments between 1960 and 1990 demonstrated that the majority of these compounds are derived from fatty acid and polyketide precursors. During the past decade, research into the metabolism of polyacetylenes has swiftly advanced, driven by the cloning of the first genes responsible for polyacetylene biosynthesis in plants, moss, fungi, and actinomycetes and the initial characterization of the gene products. The current state of knowledge of the biochemistry and molecular genetics of polyacetylenic secondary metabolic pathways will be presented together with an up-to-date survey of new terrestrial and marine natural products, their known biological activities, and a discussion of their likely metabolic origins.

Plant surface lipid biosynthetic pathways and their utility for metabolic engineering of waxes and hydrocarbon biofuels

Due to their unique physical properties, waxes are high-value materials that are used in a variety of industrial applications. They are generated by chemical synthesis, extracted from fossil sources, or harvested from a small number of plant and animal species. As a result, the diversity of chemical structures in commercial waxes is low and so are their yields. These limitations can be overcome by engineering of wax biosynthetic pathways in the seeds of high-yielding oil crops to produce designer waxes for specific industrial end uses. In this review, we first summarize the current knowledge regarding the genes and enzymes generating the chemical diversity of cuticular waxes that accumulate at the surfaces of primary plant organs. We then consider the potential of cuticle biosynthetic genes for biotechnological wax production, focusing on selected examples of wax ester chain lengths and isomers. Finally, we discuss the genes/enzymes of cuticular alkane biosynthesis and their potential in future metabolic engineering of plants for the production of renewable hydrocarbon fuels.

Sealing plant surfaces: cuticular wax formation by epidermal cells

The vital importance of plant surface wax in protecting tissue from environmental stresses is reflected in the huge commitment of epidermal cells to cuticle formation. During cuticle deposition, a massive flux of lipids occurs from the sites of lipid synthesis in the plastid and the endoplasmic reticulum to the plant surface. Recent genetic studies in Arabidopsis have improved our understanding of fatty acid elongation and of the subsequent modification of the elongated products into primary alcohols, wax esters, secondary alcohols, and ketones, shedding light on the enzymes involved in these pathways. In contrast, the biosynthesis of alkanes is still poorly understood, as are the mechanisms of wax transport from the site of biosynthesis to the cuticle. Currently, nothing is known about wax trafficking from the endoplasmic reticulum to the plasma membrane, or about translocation through the cell wall to the cuticle. However, a first breakthrough toward an understanding of wax export recently came with the discovery of ATP binding cassette (ABC) transporters that are involved in releasing wax from the plasma membrane into the apoplast. An overview of our present knowledge of wax biosynthesis and transport and the regulation of these processes during cuticle assembly is presented, including the evidence for coordination of cutin polyester and wax production.