The Yeast ATF1 Acetyltransferase Efficiently Acetylates Insect Pheromone Alcohols: Implications for the Biological Production of Moth Pheromones

Mechanisms of production and control of acetate esters in yeasts

Acetate esters, such as isoamyl acetate and ethyl acetate, are major aroma components of alcoholic beverages. They are produced through synthesis from acetyl CoA and the corresponding alcohol by alcohol acetyltransferase (AATase) with specific control of reaction factors, including unsaturated fatty acids and precursors, the percentage of nitrogen, and oxygen. However, the mechanisms by which these specific reaction factors affect acetate ester production remain largely unknown. The cellular mechanisms underlying the effects of these factors on acetate ester production were examined by purifying AATase from yeast, characterizing it, and cloning the ATF gene encoding AATase from sake yeast and bottom-fermenting yeast. Genetic and biochemical studies suggested that the decrease in acetate production with the addition of oxygen and unsaturated fatty acids was due to a decrease in enzyme synthesis resulting from transcriptional repression of the ATF1 gene, which is responsible for most of the AATase activity. Furthermore, these results suggest that expression of the ATF1 gene is intricately regulated by a number of transcriptional regulatory genes such as ROX1 and RAP1. Based on these results, the mechanism of ester regulation by oxygen, unsaturated fatty acids and precursors, and ratio of nitrogen source are becoming clearer from a molecular biological point of view. The physiological significance of ester production by yeast is then discussed. In this review, we summarize the studies on AATase, ATF gene, regulation of ester production, and physiological significance of acetate ester.

Diversity and sex differences in rectal gland volatiles of Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae)

Rectal gland volatiles are key mediators of sexual interactions in tephritid fruit flies. We used solid-phase microextraction (SPME) plus gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID) to substantially expand rectal gland chemical characterisation of the Queensland fruit fly (Bactrocera tryoni (Diptera: Tephritidae); Qfly). The SPME GC-MS analysis identified 24 of the 30 compounds previously recorded from Qfly rectal glands, plus another 21 compounds that had not previously been reported. A few amides and fatty acid esters dominated the chromatograms of males and females respectively, but we also found other esters, alcohols and aldehydes and a ketone. The GC-FID analyses also revealed over 150 others, as yet unidentified, volatiles, generally in lesser amounts. The GC-FID analyses also showed 49 and 12 compounds were male- and female-specific, respectively, both in single sex (virgin) and mixed sex (mostly mated) groups. Another ten compounds were male-specific among virgins but undetected in mixed sex groups, and 29 were undetected in virgins but male-specific in mixed sex groups. The corresponding figures for females were four and zero, respectively. Most short retention time peaks (including a ketone and an ester) were male-specific, whereas most female-biased peaks (including five fatty acid esters) had long retention times. Our results indicate previously unsuspected diversity of rectal gland volatiles that might have pheromone functions in males, but far fewer in females.

Acyl-CoA:diacylglycerol acyltransferase: Properties, physiological roles, metabolic engineering and intentional control

Acyl-CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the last reaction in the acyl-CoA-dependent biosynthesis of triacylglycerol (TAG). DGAT activity resides mainly in membrane-bound DGAT1 and DGAT2 in eukaryotes and bifunctional wax ester synthase-diacylglycerol acyltransferase (WSD) in bacteria, which are all membrane-bound proteins but exhibit no sequence homology to each other. Recent studies also identified other DGAT enzymes such as the soluble DGAT3 and diacylglycerol acetyltransferase (EaDAcT), as well as enzymes with DGAT activities including defective in cuticular ridges (DCR) and steryl and phytyl ester synthases (PESs). This review comprehensively discusses research advances on DGATs in prokaryotes and eukaryotes with a focus on their biochemical properties, physiological roles, and biotechnological and therapeutic applications. The review begins with a discussion of DGAT assay methods, followed by a systematic discussion of TAG biosynthesis and the properties and physiological role of DGATs. Thereafter, the review discusses the three-dimensional structure and insights into mechanism of action of human DGAT1, and the modeled DGAT1 from Brassica napus. The review then examines metabolic engineering strategies involving manipulation of DGAT, followed by a discussion of its therapeutic applications. DGAT in relation to improvement of livestock traits is also discussed along with DGATs in various other eukaryotic organisms.

Bioproduction of (Z,E)-9,12-tetradecadienyl acetate (ZETA), the major pheromone component of Plodia, Ephestia, and Spodoptera species in yeast

BACKGROUND

(Z,E)-9,12-tetradecadienyl acetate (ZETA, Z9,E12-14:OAc) is a major sex pheromone component for many stored-product moth species. This pheromone is used worldwide for mating disruption, detection, monitoring, and mass trapping in raw and processed food storage facilities. In this study, we demonstrate the biological production of ZETA pheromone by engineered yeast Saccharomyces cerevisiae.

RESULTS

We mined the pheromone gland transcriptome data of the almond moth, Ephestia (Cadra) cautella (Walker), to trace a novel E12 fatty acyl desaturase and expressed candidates heterologously in yeast and Sf9 systems. Furthermore, we demonstrated a tailor-made ZETA pheromone bioproduction in yeast through metabolic engineering using this E12 desaturase, in combination with three genes from various sources coding for a Z9 desaturase, a fatty acyl reductase, and an acetyltransferase, respectively. Electrophysiological assays (gas chromatography coupled to an electroantennographic detector) proved that the transgenic yeast-produced ZETA pheromone component elicits distinct antennal responses.

CONCLUSION

The reconstructed biosynthetic pathway in yeast efficiently produces ZETA pheromone, leaves an undetectable level of biosynthetic intermediates, and paves the way for the economically competitive high-demand ZETA pheromone's bioproduction technology for high-value storage pest control.

Production of Volatile Moth Sex Pheromones in Transgenic Nicotiana benthamiana Plants

Plant-based bioproduction of insect sex pheromones has been proposed as an innovative strategy to increase the sustainability of pest control in agriculture. Here, we describe the engineering of transgenic plants producing (Z)-11-hexadecenol (Z11-16OH) and (Z)-11-hexadecenyl acetate (Z11-16OAc), two main volatile components in many Lepidoptera sex pheromone blends. We assembled multigene DNA constructs encoding the pheromone biosynthetic pathway and stably transformed them into Nicotiana benthamiana plants. The constructs contained the Amyelois transitella AtrΔ11 desaturase gene, the Helicoverpa armigera fatty acyl reductase HarFAR gene, and the Euonymus alatus diacylglycerol acetyltransferase EaDAct gene in different configurations. All the pheromone-producing plants showed dwarf phenotypes, the severity of which correlated with pheromone levels. All but one of the recovered lines produced high levels of Z11-16OH, but very low levels of Z11-16OAc, probably as a result of recurrent truncations at the level of the EaDAct gene. Only one plant line (SxPv1.2) was recovered that harboured an intact pheromone pathway and which produced moderate levels of Z11-16OAc (11.8 μg g-1 FW) and high levels of Z11-16OH (111.4 μg g-1). Z11-16OAc production was accompanied in SxPv1.2 by a partial recovery of the dwarf phenotype. SxPv1.2 was used to estimate the rates of volatile pheromone release, which resulted in 8.48 ng g-1 FW per day for Z11-16OH and 9.44 ng g-1 FW per day for Z11-16OAc. Our results suggest that pheromone release acts as a limiting factor in pheromone biodispenser strategies and establish a roadmap for biotechnological improvements.

Latest Developments in Insect Sex Pheromone Research and Its Application in Agricultural Pest Management

Since the first identification of the silkworm moth sex pheromone in 1959, significant research has been reported on identifying and unravelling the sex pheromone mechanisms of hundreds of insect species. In the past two decades, the number of research studies on new insect pheromones, pheromone biosynthesis, mode of action, peripheral olfactory and neural mechanisms, and their practical applications in Integrated Pest Management has increased dramatically. An interdisciplinary approach that uses the advances and new techniques in analytical chemistry, chemical ecology, neurophysiology, genetics, and evolutionary and molecular biology has helped us to better understand the pheromone perception mechanisms and its practical application in agricultural pest management. In this review, we present the most recent developments in pheromone research and its application in the past two decades.

Biotechnological production of the European corn borer sex pheromone in the yeast Yarrowia lipolytica

The European corn borer (ECB) Ostrinia nubilalis is a widespread pest of cereals, particularly maize. Mating disruption with the sex pheromone is a potentially attractive method for managing this pest; however, chemical synthesis of pheromones requires expensive starting materials and catalysts and generates hazardous waste. The goal of this study was to develop a biotechnological method for the production of ECB sex pheromone. Our approach was to engineer the oleaginous yeast Yarrowia lipolytica to produce (Z)-11-tetradecenol (Z11-14:OH), which can then be chemically acetylated to (Z)-11-tetradecenyl acetate (Z11-14:OAc), the main pheromone component of the Z-race of O. nubilalis. First, a C14 platform strain with increased biosynthesis of myristoyl-CoA was obtained by introducing a point mutation into the α-subunit of fatty acid synthase, replacing isoleucine 1220 with phenylalanine (Fas2p^I1220F ). The intracellular accumulation of myristic acid increased 8.4-fold. Next, fatty acyl-CoA desaturases (FAD) and fatty acyl-CoA reductases (FAR) from nine different species of Lepidoptera were screened in the C14 platform strain, individually and in combinations. A titer of 29.2 ± 1.6 mg L^-1  Z11-14:OH was reached in small-scale cultivation with an optimal combination of a FAD (Lbo_PPTQ) from Lobesia botrana and FAR (HarFAR) from Helicoverpa armigera. When the second copies of FAD and FAR genes were introduced, the titer improved 2.1-fold. The native FAS1 gene's overexpression led to a further 1.5-fold titer increase, reaching 93.9 ± 11.7 mg L^-1  in small-scale cultivation. When the same engineered strain was cultivated in controlled 1 L bioreactors in fed-batch mode, 188.1 ± 13.4 mg L^-1  of Z11-14:OH was obtained. Fatty alcohols were extracted from the biomass and chemically acetylated to obtain Z11-14:OAc. Electroantennogram experiments showed that males of the Z-race of O. nubilalis were responsive to biologically-derived pheromone blend. Behavioral bioassays in a wind tunnel revealed attraction of male O. nubilalis, although full precopulatory behavior was observed less often than for the chemically synthesized pheromone blend. The study paves the way for the production of ECB pheromone by fermentation.

The genetic architecture of larval aggregation behavior in Drosophila

Many insect species exhibit basal social behaviors such as aggregation, which play important roles in their feeding and mating ecologies. However, the evolutionary, genetic, and physiological mechanisms that regulate insect aggregation remain unknown for most species. Here, we used natural populations of Drosophila melanogaster to identify the genetic architecture that drives larval aggregation feeding behavior. By using quantitative and reverse genetic approaches, we have identified a complex neurogenetic network that plays a role in regulating the decision of larvae to feed in either solitude or as a group. Results from single gene, RNAi-knockdown experiments show that several of the identified genes represent key nodes in the genetic network that determines the level of aggregation while feeding. Furthermore, we show that a single non-coding variant in the gene CG14205, a putative acyltransferase, is associated with both decreased mRNA expression and increased aggregate formation, which suggests that it has a specific role in inhibiting aggregation behavior. Our results identify, for the first time, the genetic components which interact to regulate naturally occurring levels of aggregation in D. melanogaster larvae.

Production of Long Chain Fatty Alcohols Found in Bumblebee Pheromones by Yarrowia lipolytica

Fatty alcohols (FA-OH) are aliphatic unbranched primary alcohols with a chain of four or more carbon atoms. Besides potential industrial applications, fatty alcohols have important biological functions as well. In nature, fatty alcohols are produced as a part of a mixture of pheromones in several insect species, such as moths, termites, bees, wasps, etc. In addition, FA-OHs have a potential for agricultural applications, for example, they may be used as a suitable substitute for commercial insecticides. The insecticides have several drawbacks associated with their preparation, and they exert a negative impact on the environment. Currently, pheromone components are prepared mainly through the catalytic hydrogenation of plant oils and petrochemicals, which is an unsustainable, ecologically unfriendly, and highly expensive process. The biotechnological production of the pheromone components using engineered microbial strains and through the expression of the enzymes participating in the biosynthesis of these components is a promising approach that ensures ecological sustenance as well. The present study was aimed at evaluating the production of FA-OHs in the oleaginous yeast, Yarrowia lipolytica, with different lengths of fatty-acyl chains by expressing the fatty acyl-CoA reductase (FAR) BlapFAR4 from B. lapidarius, producing C16:0-OH, C16:1Δ⁹-OH, and lower quantities of both C14:0-OH and C18:1Δ⁹-OH, and BlucFAR1 from B. lucorum, producing FA-OHs with a chain length of 18-26 carbon atoms, in this yeast. Among the different novel Y. lipolytica strains used in the present study, the best results were obtained with JMY7086, which carried several lipid metabolism modifications and expressed the BlucFAR1 gene under the control of a strong constitutive promoter 8UAS-pTEF. JMY7086 produced only saturated fatty alcohols with chain lengths from 18 to 24 carbon atoms. The highest titer and accumulation achieved were 166.6 mg/L and 15.6 mg/g DCW of fatty alcohols, respectively. Unlike JMY7086, the BlapFAR4-expressing strain JMY7090 produced only 16 carbon atom-long FA-OHs with a titer of 14.6 mg/L.

Functional identification of fatty acyl reductases in female pheromone gland and tarsi of the corn earworm, Helicoverpa zea

Most moths utilize sex pheromones released by the female to attract a mate. Females produce the sex pheromone in the pheromone gland in a biosynthetic pathway which consists of several key enzymes. Fatty acyl-CoA reductase is one of the key enzymes, which catalyzes the conversion of fatty acyl-CoA to the corresponding alcohol, playing an important role in producing the final proportion of each pheromone component. In Helicoverpa zea, (Z)-11-hexadecenal is the major sex pheromone component in female pheromone glands and previously a large amount of hexadecanal was also found in female and male tarsi. In our previous study, we compared the transcriptome between pheromone glands and tarsi and found 20 fatty acyl-CoA reductases in both tissues. In this study, we functionally characterized four FARs which were expressed at high levels according to the transcriptome of pheromone glands and tarsi. Fatty acyl-CoA reductase 1 was homologous to other moth pheromone gland specific fatty acyl-CoA reductases, and it was also present in male tarsi. Functional expression in yeast cells indicates that only fatty acyl-CoA reductase 1 was able to produce fatty alcohols. In addition, a decreased mRNA level of fatty acyl-CoA reductase 1 in female pheromone glands and male tarsi by RNAi knockdown caused a significant decrease in the production of (Z)-11-hexadecenal in pheromone glands and hexadecanal in male tarsi. This study is the first to demonstrate the direct function of a fatty acyl-CoA reductase in male tarsi and also confirms its role in sex pheromone biosynthesis in H. zea.

Schizosaccharomyces pombe can Reduce Acetic Acid Produced by Baijiu Spontaneous Fermentation Microbiota

The spontaneous fermentation of alcoholic beverage is a bioprocess donated by microbiota with complex stress environments. Among various microbes, non-Saccharomyces yeasts have high stress tolerance and significantly affect the taste and quality of products in process. Although many researchers have focused on the influence of acid stress, the mechanism of non-Saccharomyces yeasts to tolerant stress remains unclear in microbiota. To bridge the gap, we constructed in situ and in vitro studies to explore the reduction pathway of acetic acid in non-Saccharomyces yeasts. In this study, we found Schizosaccharomyces pombe has special capacities to resist 10 g/L acetic acid in laboratory cultures and decrease the average concentration of acetic acid from 9.62 to 6.55 g/kg fermented grains in Chinese Maotai-flavor liquor (Baijiu) production. Moreover, Schi. pombe promoted metabolic level of mevalonate pathway (high expressions of gene ACCAT1, HMGCS1, and HMGCR1) to degrade a high concentration of acetic acid. Meanwhile, Schi. pombe also improved the concentration of mevalonic acid that is the precursor of terpenes to enhance the taste and quality of Baijiu. Overall, the synchronicity of reduction and generation in Schi. pombe advances the current knowledge to guide more suitable strategies for mechanism studies of non-Saccharomyces yeasts in fermented industries of alcoholic beverages.

The molecular biology of fruity and floral aromas in beer and other alcoholic beverages

Aroma compounds provide attractiveness and variety to alcoholic beverages. We discuss the molecular biology of a major subset of beer aroma volatiles, fruity and floral compounds, originating from raw materials (malt and hops), or formed by yeast during fermentation. We introduce aroma perception, describe the most aroma-active, fruity and floral compounds in fruits and their presence and origin in beer. They are classified into categories based on their functional groups and biosynthesis pathways: (1) higher alcohols and esters, (2) polyfunctional thiols, (3) lactones and furanones, and (4) terpenoids. Yeast and hops are the main sources of fruity and flowery aroma compounds in beer. For yeast, the focus is on higher alcohols and esters, and particularly the complex regulation of the alcohol acetyl transferase ATF1 gene. We discuss the release of polyfunctional thiols and monoterpenoids from cysteine- and glutathione-S-conjugated compounds and glucosides, respectively, the primary biological functions of the yeast enzymes involved, their mode of action and mechanisms of regulation that control aroma compound production. Furthermore, we discuss biochemistry and genetics of terpenoid production and formation of non-volatile precursors in Humulus lupulus (hops). Insight in these pathways provides a toolbox for creating innovative products with a diversity of pleasant aromas.

Identification of the pheromone biosynthesis genes from the sex pheromone gland transcriptome of the diamondback moth, Plutella xylostella

The diamondback moth was estimated to increase costs to the global agricultural economy as the global area increase of Brassica vegetable crops and oilseed rape. Sex pheromones traps are outstanding tools available in Integrated Pest Management for many years and provides an effective approach for DBM population monitoring and control. The ratio of two major sex pheromone compounds shows geographical variations. However, the limitation of our information in the DBM pheromone biosynthesis dampens our understanding of the ratio diversity of pheromone compounds. Here, we constructed a transcriptomic library from the DBM pheromone gland and identified genes putatively involved in the fatty acid biosynthesis, pheromones functional group transfer, and β-oxidation enzymes. In addition, odorant binding protein, chemosensory protein and pheromone binding protein genes encoded in the pheromone gland transcriptome, suggest that female DBM moths may receive odors or pheromone compounds via their pheromone gland and ovipositor system. Tissue expression profiles further revealed that two ALR, three DES and one FAR5 genes were pheromone gland tissue biased, while some chemoreception genes expressed extensively in PG, pupa, antenna and legs tissues. Finally, the candidate genes from large-scale transcriptome information may be useful for characterizing a presumed biosynthetic pathway of the DBM sex pheromone.

Membrane topology and identification of key residues of EaDAcT, a plant MBOAT with unusual substrate specificity

Euonymus alatus diacylglycerol acetyltransferase (EaDAcT) catalyzes the transfer of an acetyl group from acetyl-CoA to the sn-3 position of diacylglycerol to form 3-acetyl-1,2-diacyl-sn-glycerol (acetyl-TAG). EaDAcT belongs to a small, plant-specific subfamily of the membrane bound O-acyltransferases (MBOAT) that acylate different lipid substrates. Sucrose gradient density centrifugation revealed that EaDAcT colocalizes to the same fractions as an endoplasmic reticulum (ER)-specific marker. By mapping the membrane topology of EaDAcT, we obtained an experimentally determined topology model for a plant MBOAT. The EaDAcT model contains four transmembrane domains (TMDs), with both the N- and C-termini orientated toward the lumen of the ER. In addition, there is a large cytoplasmic loop between the first and second TMDs, with the MBOAT signature region of the protein embedded in the third TMD close to the interface between the membrane and the cytoplasm. During topology mapping, we discovered two cysteine residues (C187 and C293) located on opposite sides of the membrane that are important for enzyme activity. In order to identify additional amino acid residues important for acetyltransferase activity, we isolated and characterized acetyltransferases from other acetyl-TAG-producing plants. Among them, the acetyltransferase from Euonymus fortunei possessed the highest activity in vivo and in vitro. Mutagenesis of conserved amino acids revealed that S253, H257, D258 and V263 are essential for EaDAcT activity. Alteration of residues unique to the acetyltransferases did not alter the unique acyl donor specificity of EaDAcT, suggesting that multiple amino acids are important for substrate recognition.

Plant volatile-mediated signalling and its application in agriculture: successes and challenges

856 I. 856 II. 857 III. 858 IV. 859 V. 860 VI. 862 VII. 863 VIII. 864 IX. 866 866 References 866 SUMMARY: The mediation of volatile secondary metabolites in signalling between plants and other organisms has long been seen as presenting opportunities for sustainable crop protection. Initially, exploitation of interactions between plants and other organisms, particularly insect pests, foundered because of difficulties in delivering, sustainably, the signal systems for crop protection. We now have mounting and, in some cases, clear practical evidence for successful delivery by companion cropping or next-generation genetic modification (GM). At the same time, the type of plant signalling being exploited has expanded to signalling from plants to organisms antagonistic to pests, and to plant stress-induced, or primed, plant-to-plant signalling for defence and growth stimulation.

Defining the extreme substrate specificity of Euonymus alatus diacylglycerol acetyltransferase, an unusual membrane-bound O-acyltransferase

The membrane-bound O-acyltransferase Euonymus alatus diacylglycerol acetyltransferase (EaDAcT) preferentially uses acetyl-CoA to acetylate sn-1,2 DAGs but other acyl-donor and acyl-acceptor substrates can be used with low efficiency.

Euonymus alatus diacylglycerol acetyltransferase (EaDAcT) synthesizes the unusually structured 3-acetyl-1,2-diacylglycerols (acetyl-TAG) found in the seeds of a few plant species. A member of the membrane-bound O-acyltransferase (MBOAT) family, EaDAcT transfers the acetyl group from acetyl-CoA to sn-1,2-diacylglycerol (DAG) to produce acetyl-TAG. In vitro assays demonstrated that the enzyme is also able to utilize butyryl-CoA and hexanoyl-CoA as acyl donors, though with much less efficiency compared with acetyl-CoA. Acyl-CoAs longer than eight carbons were not used by EaDAcT. This extreme substrate specificity of EaDAcT distinguishes it from all other MBOATs which typically catalyze the transfer of much longer acyl groups. In vitro selectivity experiments revealed that EaDAcT preferentially acetylated DAG molecules containing more double bonds over those with less. However, the enzyme was also able to acetylate saturated DAG containing medium chain fatty acids, albeit with less efficiency. Interestingly, EaDAcT could only acetylate the free hydroxyl group of sn-1,2-DAG but not the available hydroxyl groups in sn-1,3-DAG or in monoacylglycerols (MAG). Consistent with its similarity to the jojoba wax synthase, EaDAcT could acetylate fatty alcohols in vitro to produce alkyl acetates. Likewise, when coexpressed in yeast with a fatty acyl-CoA reductase capable of producing fatty alcohols, EaDAcT synthesized alkyl acetates although the efficiency of production was low. This improved understanding of EaDAcT specificity confirms that the enzyme preferentially utilizes acetyl-CoA to acetylate sn-1,2-DAGs and will be helpful in engineering the production of acetyl-TAG with improved functionality in transgenic plants.