Functional characterisation of two Δ12-desaturases demonstrates targeted production of linoleic acid as pheromone precursor in Nasonia

The bioconversion of dietary α-linolenic acid to eicosapentaenoic acid in Bombyx mori

n-3 Long-chain polyunsaturated fatty acids (n-3 LC-PUFAs), including eicosapentaenoic acid (EPA), are essential multifunctional nutrients in animals. Microorganisms such as microalgae are known to be n-3 LC-PUFA producers in aquatic environments. Various aquatic invertebrates, including Harpacticoida copepods, and a few terrestrial invertebrates, such as the nematode Caenorhabditis elegans, possess n-3 LC-PUFA biosynthetic enzymes. However, the capacity for n-3 LC-PUFA biosynthesis and the underlying molecular mechanisms in terrestrial insects are largely unclear. In this study, we investigated the fatty acid biosynthetic pathway in the silkworm Bombyx mori and found that EPA was present in silkworms throughout their development. Stable isotope tracing revealed that dietary α-linolenic acid (ALA) was metabolized to EPA in silkworm larvae. These results indicated that silkworms synthesize EPA from ALA. Given that EPA is enriched in the central nervous system, we propose that EPA confers optimal neuronal functions, similar to docosahexaenoic acid, in the mammalian nervous system.

Fatty Acid Origin of Insect Pheromones

Pheromones are utilized to a great extent in insects. Many of these pheromones are biosynthesized through a pathway involving fatty acids. This chapter will provide examples where the biosynthetic pathways of fatty acid-derived pheromones have been studied in detail. These include pheromones from Lepidoptera, Coleoptera, and Hymenoptera. Many species of Lepidoptera utilize fatty acids as precursors to pheromones with a functional group that include aldehydes, alcohols, and acetate esters. In addition, the biosynthesis of hydrocarbons will be briefly examined because many insects utilize hydrocarbons or modified hydrocarbons as pheromones.

A Horizontally Transferred Plant Fatty Acid Desaturase Gene Steers Whitefly Reproduction

Polyunsaturated fatty acids (PUFAs) are essential nutrients for all living organisms. PUFA synthesis is mediated by Δ12 desaturases in plants and microorganisms, whereas animals usually obtain PUFAs through their diet. The whitefly Bemisia tabaci is an extremely polyphagous agricultural pest that feeds on phloem sap of many plants that do not always provide them with sufficient PUFAs. Here, a plant-derived Δ12 desaturase gene family BtFAD2 is characterized in B. tabaci and it shows that the BtFAD2-9 gene enables the pest to synthesize PUFAs, thereby significantly enhancing its fecundity. The role of BtFAD2-9 in reproduction is further confirmed by transferring the gene to Drosophila melanogaster, which also increases the fruit fly's reproduction. These findings reveal an extraordinary evolutionary scenario whereby a phytophagous insect acquired a family of plant genes that enables it to synthesize essential nutrients, thereby lessening its nutritional dependency and allowing it to feed and reproduce on many host plants.

The collembolan Sinella dubiosa produces eicosapentaenoic acid

n-3 polyunsaturated fatty acids (n-3 PUFAs), including eicosapentaenoic acid (EPA), are essential nutrients for vertebrate development and physiology. Microorganisms, such as microalgae, produce n-3 PUFAs that are transferred to higher predators in the aquatic food web. However, recent studies have demonstrated that various aquatic invertebrates possess the biosynthetic enzymes required for n-3 PUFA production, raising the possibility that n-3 PUFAs are also produced in certain aquatic invertebrates. In contrast to aquatic invertebrates, it remains unclear whether and how PUFAs are produced in terrestrial invertebrates, including collembolans, one of the most widespread microarthropods in soil ecosystems. In this study, we investigated the biosynthetic capacity of n-3 PUFAs in litter-dwelling Collembola, Sinella dubiosa. We detected EPA in Sinella dubiosa reared on Brewer's yeast, which produced only saturated and monounsaturated fatty acids. Furthermore, metabolic analysis using isotope-labeled fatty acids revealed that oleic, linolenic, and arachidonic acids were metabolized to EPA in Sinella dubiosa. Given that collembolans are food for predatory arthropods and their nutrients are transferred to higher predatory vertebrates in the soil food web, we propose that Collembola serve as an EPA source in soil ecosystems.

Examination of gammarid transcriptomes reveals a widespread occurrence of key metabolic genes from epibiont bdelloid rotifers in freshwater species

Previous data revealed the unexpected presence of genes encoding for long-chain polyunsaturated fatty acid (LC-PUFA) biosynthetic enzymes in transcriptomes from freshwater gammarids but not in marine species, even though closely related species were compared. This study aimed to clarify the origin and occurrence of selected LC-PUFA biosynthesis gene markers across all published gammarid transcriptomes. Through systematic searches, we confirmed the widespread occurrence of sequences from seven elongases and desaturases involved in LC-PUFA biosynthesis, in transcriptomes from freshwater gammarids but not marine species, and clarified that such occurrence is independent from the gammarid species and geographical origin. The phylogenetic analysis established that the retrieved elongase and desaturase sequences were closely related to bdelloid rotifers, confirming that multiple transcriptomes from freshwater gammarids contain contaminating rotifers' genetic material. Using the Adineta steineri genome, we investigated the genomic location and exon-intron organization of the elongase and desaturase genes, establishing they are all genome-anchored and, importantly, identifying instances of horizontal gene transfer. Finally, we provide compelling evidence demonstrating Bdelloidea desaturases and elongases enable these organisms to perform all the reactions for de novo biosynthesis of PUFA and, from them, LC-PUFA, an advantageous trait when considering the low abundance of these essential nutrients in freshwater environments.

Characterization of male-biased fatty acid desaturase in the jewel wasp Nasonia vitripennis and its role in pheromone production

Linoleic acid is the material for biosynthesis of sex attracting and blocking (postmating) pheromones in Nasonia vitripennis, it is synthesized from oleic acid by a male-biased fatty acid desaturase (SCD5a). In this study, we developed a specific antibody and further characterized the expression patterns of SCD5a in males at different mating stages by western blot. SCD5a was mainly expressed in male heads rather than in abdomens. Along with the aging process (from Day 1 to Day 3), SCD5a increased significantly. Compared with virgin males, mated males showed higher levels of SCD5a. Likewise, abdomen dipping frequency, during which males release attracting pheromone, increased with age and mating. Moreover, real-time quantitative PCR revealed that genes responsible for the first three steps of attracting pheromone biosynthesis were more highly expressed in head than in abdomen, but the final gene for transformation of attracting pheromone was more highly expressed in abdomen than in head. These results suggest that linoleic acid for biosynthesis of attracting pheromones may also originate from the head rather than only synthesized at the rectal vesicles.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

De novo biosynthesis of linoleic acid is widespread in parasitic wasps

Linoleic acid (C18:2^∆9,12 , LA) is an important metabolite with numerous essential functions for growth, health, and reproduction of organisms. It has long been assumed that animals lack ∆12-desaturases, the enzymes needed to produce LA from oleic acid (C18:1^∆9 , OA). There is, however, increasing evidence that this is not generally true for invertebrates. In the insect order Hymenoptera, LA biosynthesis has been shown for only two parasitic wasp species of the so-called "Nasonia group," but it is unknown whether members of other taxa are also capable of synthesizing LA. Here, we demonstrate LA biosynthesis in 13 out of 14 species from six families of parasitic wasps by gas chromatography-mass spectrometry analysis using two different stable isotope labeling techniques. Females of the studied species converted topically applied fully ¹³ C-labeled OA into LA and/or produced labeled LA after feeding on fully ¹³ C-labeled α- d-glucose. These results indicate that ∆12-desaturases are widespread in parasitic Hymenoptera and confirm previous studies demonstrating that these insects are capable of synthesizing fatty acids de novo.

Parasitic wasps do not lack lipogenesis

Fatty acids are crucial primary metabolites for virtually all creatures on earth. Most organisms thus do not rely exclusively on a nutritional supply containing fatty acids, but have the ability to synthesize fatty acids and triacylglycerides de novo from carbohydrates in a process called lipogenesis. The ubiquity of lipogenesis has been questioned by a series of studies reporting that many parasitic wasps (parasitoids) do not accumulate lipid mass despite having unlimited access to sugar. This has been interpreted as an evolutionary metabolic trait loss in parasitoids. Here, we demonstrate de novo biosynthesis of fatty acids from 13C-labelled α-d-glucose in 13 species of parasitoids from seven families. We furthermore show in the model organism Nasonia vitripennis that lipogenesis occurs even when lipid reserves are still intact, but relative 13C-incorporation rates increase in females with widely depleted fat reserves. We therefore conclude that the presumed 'lack of lipogenesis' in parasitoids needs to be re-evaluated.

A complete enzymatic capacity for biosynthesis of docosahexaenoic acid (DHA, 22 : 6n-3) exists in the marine Harpacticoida copepod Tigriopus californicus

The long-standing paradigm establishing that global production of Omega-3 (n–3) long-chain polyunsaturated fatty acids (LC-PUFA) derived almost exclusively from marine single-cell organisms, was recently challenged by the discovery that multiple invertebrates possess methyl-end (or ωx) desaturases, critical enzymes enabling the biosynthesis of n–3 LC-PUFA. However, the question of whether animals with ωx desaturases have complete n–3 LC-PUFA biosynthetic pathways and hence can contribute to the production of these compounds in marine ecosystems remained unanswered. In the present study, we investigated the complete enzymatic complement involved in the n–3 LC-PUFA biosynthesis in Tigriopus californicus, an intertidal harpacticoid copepod. A total of two ωx desaturases, five front-end desaturases and six fatty acyl elongases were successfully isolated and functionally characterized. The T. californicus ωx desaturases enable the de novo biosynthesis of C₁₈ PUFA such as linoleic and α-linolenic acids, as well as several n–3 LC-PUFA from n–6 substrates. Functions demonstrated in front-end desaturases and fatty acyl elongases unveiled various routes through which T. californicus can biosynthesize the physiologically important arachidonic and eicosapentaenoic acids. Moreover, T. californicus possess a Δ4 desaturase, enabling the biosynthesis of docosahexaenoic acid via the ‘Δ4 pathway’. In conclusion, harpacticoid copepods such as T. californicus have complete n–3 LC-PUFA biosynthetic pathways and such capacity illustrates major roles of these invertebrates in the provision of essential fatty acids to upper trophic levels.

Acetone application for administration of bioactive substances has no negative effects on longevity, fitness, and sexual communication in a parasitic wasp

Administration of defined amounts of bioactive substances is a perseverative problem in physiological studies on insects. Apart from feeding and injection, topical application of solutions of the chemicals is most commonly used for this purpose. The solvents used should be non-toxic and have least possible effects on the studied parameters. Acetone is widely used for administration of chemical substances to insects, but possible side-effects of acetone application on fitness and behavioral parameters have been rarely investigated. Here we study the effects of acetone application (207 nl) on fitness and sexual communication in the parasitic wasp Nasonia giraulti Darling. Application of acetone had neither negative effects on longevity nor on offspring number and offspring sex ratio of treated wasps. Treatment of females hampered courtship and mating of N. giraulti couples neither directly after application nor one day after. Male sex pheromone titers were not influenced by acetone treatment. Three application examples demonstrate that topical acetone application is capable of bringing active amounts of insect hormones, neuromodulators, and biosynthetic precursors even in tiny insects. We advocate the use of acetone as a convenient, conservative, and broadly applicable vehicle for studying the effects of bioactive substances in insects.

Unique fatty acid desaturase capacities uncovered in Hediste diversicolor illustrate the roles of aquatic invertebrates in trophic upgrading

Omega-3 (ω3 or n-3) long-chain polyunsaturated fatty acids (PUFA), including eicosapentaenoic acid and docosahexaenoic acid (DHA), play physiologically important roles in vertebrates. These compounds have long been believed to have originated almost exclusively from aquatic (mostly marine) single-cell organisms. Yet, a recent study has discovered that many invertebrates possess a type of enzymes called methyl-end desaturases (ωx) that enables them to endogenously produce n-3 long-chain PUFA and could make a significant contribution to production of these compounds in the marine environment. Polychaetes are major components of benthic fauna and thus important to maintain a robust food web as a recycler of organic matter and a prey item for higher trophic level species like fish. In the present study, we investigated the ωx enzymes from the common ragworm, Hediste diversicolor, a common inhabitant in sedimentary littoral ecosystems of the North Atlantic. Functional assays of the H. diversicolor ωx demonstrated unique desaturation capacities. An ω3 desaturase mediated the conversion of n-6 fatty acid substrates into their corresponding n-3 products including DHA. A further enzyme possessed unique regioselectivities combining both ω6 and ω3 desaturase activities. These results illustrate that the long-chain PUFA biosynthetic enzymatic machinery of aquatic invertebrates such as polychaetes is highly diverse and clarify that invertebrates can be major contributors to fatty acid trophic upgrading in aquatic food webs. This article is part of the theme issue 'The next horizons for lipids as 'trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

De novo biosynthesis of fatty acids from α-D-glucose in parasitoid wasps of the Nasonia group

Fatty acids are indispensable primary metabolites for virtually any organism on earth and thus enzymatic machinery enabling de novo production of fatty acids from carbohydrates is highly conserved. A series of studies has questioned the ubiquity of lipogenesis in parasitoid wasps suggesting that the vast majority of species have lost the ability to synthesize fatty acids de novo. One such species is Nasonia vitripennis, which, like the congeneric species N. giraulti and N. longicornis, uses a fatty acid-derived male sex pheromone for sexual communication. Here we demonstrate by feeding fully ¹³C-labeled α-D-glucose and analyzing insect-derived fatty acid methyl esters and the male sex pheromone by coupled gas chromatography/mass spectrometry that both males and females of N. vitripennis as well as N. giraulti and N. longicornis are capable of synthesizing fatty acids de novo. We furthermore show by a proteomics approach that predicted fatty acid synthase, ATP-citrate synthase, and acetyl-CoA carboxylase, key enzymes of lipogenesis, are expressed in the male pheromone gland of N. vitripennis and N. giraulti. Labeling experiments with Urolepis rufipes, a closely related species producing a male sex pheromone independently of fatty acids via the mevalonate pathway, revealed that both sexes are likewise able to synthesize fatty acids de novo. We conclude that the parasitoid wasp species studied here, irrespective of the biosynthetic origin of their sex pheromones, are capable of responding flexibly to lipid shortage during their adult life by keeping enzymatic machinery for lipogenesis running.