Transcriptional analysis of the pheromone gland of the turnip moth, Agrotis segetum (Noctuidae), reveals candidate genes involved in pheromone production

Sex pheromone biosynthesis in the sugarcane borer Diatraea saccharalis: paving the way for biotechnological production

BACKGROUND

The sugarcane borer Diatraea saccharalis (Lepidoptera) is a key pest on sugarcane and other grasses in the Americas. Biological control as well as insecticide treatments are used for pest management, but economic losses are still significant. The use of female sex pheromones for mating disruption or mass trapping in pest management could be established for this species, provided that economical production of pheromone is available.

RESULTS

Combining in vivo labelling studies, differential expression analysis of transcriptome data and functional characterisation of insect genes in a yeast expression system, we reveal the biosynthetic pathway and identify the desaturase and reductase enzymes involved in the biosynthesis of the main pheromone component (9Z,11E)-hexadecadienal, and minor components hexadecanal, (9Z)-hexadecenal and (11Z)-hexadecenal. We next demonstrate heterologous production of the corresponding alcohols of the pheromone components, by expressing multiple steps of the biosynthetic pathway in yeast.

CONCLUSION

Elucidation of the genetic basis of sex pheromone biosynthesis in D. saccharalis, and heterologous expression in yeast, paves the way for biotechnological production of the pheromone compounds needed for pheromone-based pest management of this species. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Transcriptome analysis identifies candidate genes in the biosynthetic pathway of sex pheromones from a zygaenid moth, Achelura yunnanensis (Lepidoptera: Zygaenidae)

In most moth species, sex pheromones responsible for mating and communication of both sexes are primarily produced by the pheromone glands (PGs) of female moths. Although the PG transcriptomes and pheromone production related genes from 24 moth species have been characterized, studies on the related information remain unknown in the Zygaenidae family. Here, we sequenced the PG transcriptome of a zygaenid moth, Achelura yunnanensis. Such the sequencing resulted in the yields of 47,632,610 clean reads that were assembled into 54,297 unigenes, coupled with RNA sequencing data from 12 other tissues. Based on the transcriptome, a total of 191 genes encoding pheromone biosynthesis and degradation enzymes were identified, 161 of which were predicted to have full-length sequences. A comparative analysis among 24 moth species of nine families indicated that the numbers of the genes were variable, ranging from 14 in two Grapholita species to 191 in A. yunnanensis. Phylogenetic analysis in parallel with the expression data highlighted some key genes, including three △9 and four △11 desaturases, four fatty acyl-CoA reductases (FARs) clustering in the pgFAR clade, and three significantly antennae-enriched aldehyde oxidases. An extensive tissue- and sex- expression profile revealed a broad distribution of the genes, in which 128 relatives were detected in the PGs and 127 in the antennae. This study reports, for the first time, the gene repertoires associated with the pheromone production in Zygaenidae, and provides a valuable resource for exploring putative roles of the PG-enriched genes in A. yunnanensis.

Transcriptome and microbiome analyses of the mechanisms underlying antibiotic-mediated inhibition of larval development of the saprophagous insect Musca domestica (Diptera: Muscidae)

Antibiotics are designed to treat bacterial infections in humans and animals; however, the overuse of various antibiotics and consequent contamination in the environment can have adverse effects on aquatic, soil, and saprophytic organisms. The house fly, an important decomposer in ecosystems, has been used for bioconversion of human and animal waste. Vermireactors have been used to remove antibiotics from waste for pollution control, but the effects of antibiotics on fly larvae are unclear. In the present work, we aimed to reveal the mechanism underlying the effects of antibiotics on larval growth in house flies at the transcriptome and microbiome levels and the relationships between genes and the microbiota. Observation of house flies after antibiotic exposure showed that gentamicin sulfate and levofloxacin hydrochloride inhibited larval development to a greater extent than amoxicillin. Transcriptome analysis revealed that biological pathways related to protein synthesis and the metabolism of fatty acids, pentose, and glucuronate were significantly enriched in flies exposed to gentamicin sulfate and levofloxacin hydrochloride. Crucial genes in these pathways were identified as candidates for future study. Microbiome analysis revealed three key bacteria that were closely correlated with gentamicin sulfate and levofloxacin hydrochloride exposure. The correlation network between the differentially expressed genes and bacteria identified an important microbic effector, Pseudomonas and its associated genes. This work will improve the knowledge about the mechanism underlying the effects of antibiotics on the larval development of house flies in the environment and provide guidance for improving the application of house fly bioconversion.

Pheromone biosynthetic pathway and chemoreception proteins in sex pheromone gland of Eogystia hippophaecolus

The moth Eogystia hippophaecolus (Hua et al.) is a major threat to sea buckthorn plantations in China. Specific and highly efficient artificial sex pheromone traps have been developed and used to control this pest species. However, the biosynthesis of sex pheromones Z7-14: Ac and E3-14:Ac remains poorly understood. We investigated the female pheromone gland transcriptome of E. hippophaecolus and identified two pheromone biosynthesis-activating neuropeptides (PBANs), two pheromone biosynthesis-activating neuropeptide receptors (PBANrs), five acetyl-CoA carboxylases (ACCs), six fatty acid synthases (FASs), 16 Acyl-CoA desaturases (DESs), 26 reductases (REDs), 13 acetyltransferases (ACTs), one fatty acid transport protein (FATP), one acyl-CoA-binding protein (ACBP), and five elongation of very long-chain fatty acid proteins (ELOs) in pheromone biosynthesis pathways. Additionally, we identified 11 odorant-degrading enzymes (ODEs) and 16 odorant-binding proteins (OBPs), 14 chemosensory proteins (CSPs), two sensory neuron membrane proteins (SNMPs), three odorant receptors (ORs), seven ionotropic receptors (IRs), and six gustatory receptors (GRs). 77 unigenes involved in female pheromone biosynthesis, 31 chemoreception proteins and 11 odorant degradation enzymes were identified, which provided insight into the regulation of the pheromone components and pheromone recognition in the sex pheromone gland, and knowledge pertinent to new integrated pest management strategy of interference pheromone biosynthesis and recognition.

Comparative transcriptomics of the pheromone glands provides new insights into the differentiation of sex pheromone between two host populations of Chilo suppressalis

Reproductive isolation between different host populations is often based on intraspecific sex pheromone differences. The mechanisms underlying these differences have not been thoroughly elucidated to date. Previous studies suggested that Chilo suppressalis has differentiated into rice and water-oat host populations, and these two populations manifest clear differences in sex pheromone titer and mating rhythm. Hence, this moth is an ideal model to investigate the endogenous mechanisms of intraspecific reproductive isolation. Here, we identified a series of putative genes associated with sex pheromone biosynthesis based on the C. suppressalis pheromone gland transcriptome data. Transcripts of most genes were at higher level in the rice population. Then we obtained 11 pivotal differentially expressed genes (DEGs). The expression levels of these DEGs exhibited a distinct increase in the rice population. Moreover, we also observed the expression rhythm of these DEGs is discrepant between two host populations. Our study offers a new understanding to elucidate the mechanisms of intraspecific reproductive isolation.

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.

Expressional divergences of two desaturase genes determine the opposite ratios of two sex pheromone components in Helicoverpa armigera and Helicoverpa assulta

The sympatric closely related species Helicoverpa armigera and Helicoverpa assulta use 97:3 and 7:93 of (Z)-11-hexadecenal and (Z)-9-hexadecenal, respectively, as their sex pheromone to find/locate correct sex mates. Moreover, (Z)-11-hexadecenyl alcohol and (Z)-9-hexadecenyl alcohol are more abundant in the pheromone gland of H. assulta than in that of H. armigera. To clarify the molecular basis of these differences, we sequenced the pheromone gland transcriptomes of the two species and compared the expression patterns of the candidate enzyme genes involved in the pheromone biosynthetic pathways by FPKM values and quantitative RT-PCR analysis. We found that the desaturase gene LPAQ expressed about 70 times higher in H. armigera than in H. assulta, whereas another desaturase gene NPVE expressed about 60 times higher in H. assulta than in H. armigera. We also observed significantly higher expression of the fatty acyl reductase (FAR) gene FAR1 and the aldehyde reductase (AR) gene AR3 in H. assulta than in H. armigera. Examination of the pheromone glands of the backcross offspring of their hybrids to H. assulta showed a positive linear correlation between the expression level of LPAQ and the amount of Z11-16:Ald and between the expression level of NPVE and the amount of Z9-16:Ald in the pheromone glands. Taken together, these data demonstrate that the expressional divergences of LPAQ and NPVE determine the opposite sex pheromone component ratios in the two species and the divergent expression of FAR1 and AR3 may account for the greater accumulation of alcohols in the pheromone gland of H. assulta.

The Genetic Basis of Pheromone Evolution in Moths

Moth sexual pheromones are widely studied as a fine-tuned system of intraspecific sexual communication that reinforces interspecific reproductive isolation. However, their evolution poses a dilemma: How can the female pheromone and male preference simultaneously change to create a new pattern of species-specific attraction? Solving this puzzle requires us to identify the genes underlying intraspecific variation in signals and responses and to understand the evolutionary mechanisms responsible for their interspecific divergence. Candidate gene approaches and functional analyses have yielded insights into large families of biosynthetic enzymes and pheromone receptors, although the factors controlling their expression remain largely unexplored. Intra- and interspecific crosses have provided tantalizing evidence of regulatory genes, although, to date, mapping resolution has been insufficient to identify them. Recent advances in high-throughput genome and transcriptome sequencing, together with established techniques, have great potential to help scientists identify the specific genetic changes underlying divergence and resolve the mystery of how moth sexual communication systems evolve.

Analysis of the Agrotis segetum pheromone gland transcriptome in the light of sex pheromone biosynthesis

BACKGROUND

Moths rely heavily on pheromone communication for mate finding. The pheromone components of most moths are modified from the products of normal fatty acid metabolism by a set of tissue-specific enzymes. The turnip moth, Agrotis segetum uses a series of homologous fatty-alcohol acetate esters ((Z)-5-decenyl, (Z)-7-dodecenyl, and (Z)-9 tetradecenyl acetate) as its sex pheromone components. The ratio of the components differs between populations, making this species an interesting subject for studies of the enzymes involved in the biosynthetic pathway and their influence on sex pheromone variation.

RESULTS

Illumina sequencing and comparative analysis of the transcriptomes of the pheromone gland and abdominal epidermal tissue, enabled us to identify genes coding for putative key enzymes involved in the pheromone biosynthetic pathway, such as fatty acid synthase, β-oxidation enzymes, fatty-acyl desaturases (FAD), fatty-acyl reductases (FAR), and acetyltransferases. We functionally assayed the previously identified ∆11-desaturase [GenBank: ES583599, JX679209] and FAR [GenBank: JX679210] and candidate acetyltransferases (34 genes) by heterologous expression in yeast. The functional assay confirmed that the ∆11-desaturase interacts with palmitate and produces (Z)-11-hexadecenoate, which is the common unsaturated precursor of three homologous pheromone component acetates produced by subsequent chain-shortening, reduction and acetylation. Much lower, but still visible, activity on 14C and 12C saturated acids may account for minor pheromone compounds previously observed in the pheromone gland. The FAR characterized can operate on various unsaturated fatty acids that are the immediate acyl precursors of the different A. segetum pheromone components. None of the putative acetyltransferases that we expressed heterologously did acetylate any of the fatty alcohols tested as substrates.

CONCLUSIONS

The massive sequencing technology generates enormous amounts of candidate genes potentially involved in pheromone biosynthesis but testing their function by heterologous expression or gene silencing is a bottleneck. We confirmed the function of a previously identified desaturase gene and a fatty-acyl reductase gene by heterologous expression, but the acetyltransferase postulated to be involved in pheromone biosynthesis remains illusive, in spite of 34 candidates being assayed. We also generated lists of gene candidates that may be useful for characterizing the acetyl-CoA carboxylase, fatty acid synthetase and β-oxidation enzymes.

Genes involved in sex pheromone biosynthesis of Ephestia cautella, an important food storage pest, are determined by transcriptome sequencing

BACKGROUND

Insects use pheromones, chemical signals that underlie all animal behaviors, for communication and for attracting mates. Synthetic pheromones are widely used in pest control strategies because they are environmentally safe. The production of insect pheromones in transgenic plants, which could be more economical and effective in producing isomerically pure compounds, has recently been successfully demonstrated. This research requires information regarding the pheromone biosynthetic pathways and the characterization of pheromone biosynthetic enzymes (PBEs). We used Illumina sequencing to characterize the pheromone gland (PG) transcriptome of the Pyralid moth, Ephestia cautella, a destructive storage pest, to reveal putative candidate genes involved in pheromone biosynthesis, release, transport and degradation.

RESULTS

We isolated the E. cautella pheromone compound as (Z,E)-9,12-tetradecadienyl acetate, and the major pheromone precursors 16:acyl, 14:acyl, E14-16:acyl, E12-14:acyl and Z9,E12-14:acyl. Based on the abundance of precursors, two possible pheromone biosynthetic pathways are proposed. Both pathways initiate from C16:acyl-CoA, with one involving ∆14 and ∆9 desaturation to generate Z9,E12-14:acyl, and the other involving the chain shortening of C16:acyl-CoA to C14:acyl-CoA, followed by ∆12 and ∆9 desaturation to generate Z9,E12-14:acyl-CoA. Then, a final reduction and acetylation generates Z9,E12-14:OAc. Illumina sequencing yielded 83,792 transcripts, and we obtained a PG transcriptome of ~49.5 Mb. A total of 191 PBE transcripts, which included pheromone biosynthesis activating neuropeptides, fatty acid transport proteins, acetyl-CoA carboxylases, fatty acid synthases, desaturases, β-oxidation enzymes, fatty acyl-CoA reductases (FARs) and fatty acetyltransferases (FATs), were selected from the dataset. A comparison of the E. cautella transcriptome data with three other Lepidoptera PG datasets revealed that 45% of the sequences were shared. Phylogenetic trees were constructed for desaturases, FARs and FATs, and transcripts that clustered with the ∆14, ∆12 and ∆9 desaturases, PG-specific FARs and potential candidate FATs, respectively, were identified. Transcripts encoding putative pheromone degrading enzymes, and candidate pheromone carrier and receptor proteins expressed in the E. cautella PG, were also identified.

CONCLUSIONS

Our study provides important background information on the enzymes involved in pheromone biosynthesis. This information will be useful for the in vitro production of E. cautella sex pheromones and may provide potential targets for disrupting the pheromone-based communication system of E. cautella to prevent infestations.

Large number of putative chemoreception and pheromone biosynthesis genes revealed by analyzing transcriptome from ovipositor-pheromone glands of Chilo suppressalis

The chemoreception role of moth ovipositor has long been suggested, but its molecular mechanism is mostly unknown. By transcriptomic analysis of the female ovipositor-pheromone glands (OV-PG) of Chilo suppressalis, we obtained 31 putative chemoreception genes (9 OBPs, 10 CSPs, 2 ORs, 1 SNMP, 8 CXEs and 1 AOX), in addition to 32 genes related to sex pheromone biosynthesis (1 FAS, 6 Dess, 10 FARs, 2 ACOs, 1 ACC, 4 FATPs, 3 ACBPs and 5 ELOs). Tissue expression profiles further revealed that CsupCSP2 and CsupCSP10 were OV-PG biased, while most chemoreception genes were highly and preferably expressed in antennae. This suggests that OV-PG employs mostly the same chemoreception proteins as in antennae, although the physiological roles of these proteins might be different in OV-PG. Of the 32 pheromone biosynthesis related genes, CsupDes4, CsupDes5 and CsupFAR2 are strongly OV-PG biased, and clustered with functionally validated genes from other moths, strongly indicating their involvement in specific step of the pheromone biosynthesis. Our study for the first time identified a large number of putative chemoreception genes, and provided an important basis for exploring the chemoreception mechanisms of OV-PG in C. suppressalis, as well as other moth species.

Putative pathway of sex pheromone biosynthesis and degradation by expression patterns of genes identified from female pheromone gland and adult antenna of Sesamia inferens (Walker)

The general pathway of biosynthesis and degradation for Type-I sex pheromones in moths is well established, but some genes involved in this pathway remain to be characterized. The purple stem borer, Sesamia inferens, employs a pheromone blend containing components with three different terminal functional groups (Z11-16:OAc, Z11-16:OH, and Z11-16:Ald) of Type-I sex pheromones. Thus, it provides a good model to study the diversity of genes involved in pheromone biosynthesis and degradation pathways. By analyzing previously obtained transcriptomic data of the sex pheromone glands and antennae, we identified 73 novel genes that are possibly related to pheromone biosynthesis (46 genes) or degradation (27 genes). Gene expression patterns and phylogenetic analysis revealed that one desaturase (SinfDes4), one fatty acid reductase (SinfFAR2), and one fatty acid xtransport protein (SinfFATP1) genes were predominantly expressed in pheromone glands, and clustered with genes involved in pheromone synthesis in other moth species. Ten genes including five carboxylesterases (SinfCXE10, 13, 14, 18, and 20), three aldehyde oxidases (SinfAOX1, 2 and 3), and two alcohol dehydrogenases (SinfAD1 and 3) were expressed specifically or predominantly in antennae, and could be candidate genes involved in pheromone degradation. SinfAD1 and 3 are the first reported alcohol dehydrogenase genes with antennae-biased expression. Based on these results we propose a pathway involving these potential enzyme-encoding gene candidates in sex pheromone biosynthesis and degradation in S. inferens. This study provides robust background information for further elucidation of the genetic basis of sex pheromone biosynthesis and degradation, and ultimately provides potential targets to disrupt sexual communication in S. inferens for control purposes.

Molecular evidence of RNA editing in Bombyx chemosensory protein family

Chemosensory proteins (CSPs) are small scavenger proteins that are mainly known as transporters of pheromone/odor molecules at the periphery of sensory neurons in the insect antennae and in the producing cells from the moth female pheromone gland. Sequencing cDNAs of RNA encoding CSPs in the antennae, legs, head, pheromone gland and wings from five single individual adult females of the silkworm moth Bombyx mori showed that they differed from genomic sequences by subtle nucleotide replacement (RDD). Both intronless and intronic CSP genes expressed RDDs, although in different rates. Most interestingly, in our study the degree of RDDs in CSP genes were found to be tissue-specific. The proportion of CSP-RDDs was found to be significantly much higher in the pheromone gland. In addition, Western blot analysis of proteins in different tissues showed existence of multiple CSP protein variant chains particularly found in the pheromone gland. Peptide sequencing demonstrated the occurrence of a pleiad of protein variants for most of all BmorCSPs from the pheromone gland. Our findings show that RNA editing is an important feature in the expression of CSPs and that a high variety of RDDs is found to expand drastically thus altering the repertoire of CSP proteins in a tissue-specific manner.

A moth pheromone brewery: production of (Z)-11-hexadecenol by heterologous co-expression of two biosynthetic genes from a noctuid moth in a yeast cell factory

BACKGROUND

Moths (Lepidoptera) are highly dependent on chemical communication to find a mate. Compared to conventional unselective insecticides, synthetic pheromones have successfully served to lure male moths as a specific and environmentally friendly way to control important pest species. However, the chemical synthesis and purification of the sex pheromone components in large amounts is a difficult and costly task. The repertoire of enzymes involved in moth pheromone biosynthesis in insecta can be seen as a library of specific catalysts that can be used to facilitate the synthesis of a particular chemical component. In this study, we present a novel approach to effectively aid in the preparation of semi-synthetic pheromone components using an engineered vector co-expressing two key biosynthetic enzymes in a simple yeast cell factory.

RESULTS

We first identified and functionally characterized a ∆11 Fatty-Acyl Desaturase and a Fatty-Acyl Reductase from the Turnip moth, Agrotis segetum. The ∆11-desaturase produced predominantly Z11-16:acyl, a common pheromone component precursor, from the abundant yeast palmitic acid and the FAR transformed a series of saturated and unsaturated fatty acids into their corresponding alcohols which may serve as pheromone components in many moth species. Secondly, when we co-expressed the genes in the Brewer's yeast Saccharomyces cerevisiae, a set of long-chain fatty acids and alcohols that are not naturally occurring in yeast were produced from inherent yeast fatty acids, and the presence of (Z)-11-hexadecenol (Z11-16:OH), demonstrated that both heterologous enzymes were active in concert. A 100 ml batch yeast culture produced on average 19.5 μg Z11-16:OH. Finally, we demonstrated that oxidized extracts from the yeast cells containing (Z)-11-hexadecenal and other aldehyde pheromone compounds elicited specific electrophysiological activity from male antennae of the Tobacco budworm, Heliothis virescens, supporting the idea that genes from different species can be used as a molecular toolbox to produce pheromone components or pheromone component precursors of potential use for control of a variety of moths.

CONCLUSIONS

This study is a first proof-of-principle that it is possible to "brew" biologically active moth pheromone components through in vitro co-expression of pheromone biosynthetic enzymes, without having to provide supplementary precursors. Substrates present in the yeast alone appear to be sufficient.

Identification of genes expressed in the sex pheromone gland of the black cutworm Agrotis ipsilon with putative roles in sex pheromone biosynthesis and transport

Background

One of the challenges in insect chemical ecology is to understand how insect pheromones are synthesised, detected and degraded. Genome wide survey by comparative sequencing and gene specific expression profiling provide rich resources for this challenge. A. ipsilon is a destructive pest of many crops and further characterization of the genes involved in pheromone biosynthesis and transport could offer potential targets for disruption of their chemical communication and for crop protection.

Results

Here we report 454 next-generation sequencing of the A. ipsilon pheromone gland transcriptome, identification and expression profiling of genes putatively involved in pheromone production, transport and degradation. A total of 23473 unigenes were obtained from the transcriptome analysis, 86% of which were A. ipsilon specific. 42 transcripts encoded enzymes putatively involved in pheromone biosynthesis, of which 15 were specifically, or mainly, expressed in the pheromone glands at 5 to 120-fold higher levels than in the body. Two transcripts encoding for a fatty acid synthase and a desaturase were highly abundant in the transcriptome and expressed more than 40-fold higher in the glands than in the body. The transcripts encoding for 2 acetyl-CoA carboxylases, 1 fatty acid synthase, 2 desaturases, 3 acyl-CoA reductases, 2 alcohol oxidases, 2 aldehyde reductases and 3 acetyltransferases were expressed at a significantly higher level in the pheromone glands than in the body. 17 esterase transcripts were not gland-specific and 7 of these were expressed highly in the antennae. Seven transcripts encoding odorant binding proteins (OBPs) and 8 encoding chemosensory proteins (CSPs) were identified. Two CSP transcripts (AipsCSP2, AipsCSP8) were highly abundant in the pheromone gland transcriptome and this was confirmed by qRT-PCR. One OBP (AipsOBP6) were pheromone gland-enriched and three OBPs (AipsOBP1, AipsOBP2 and AipsOBP4) were antennal-enriched. Based on these studies we proposed possible A. ipsilon biosynthesis pathways for major and minor sex pheromone components.

Conclusions

Our study identified genes potentially involved in sex pheromone biosynthesis and transport in A. ipsilon. The identified genes are likely to play essential roles in sex pheromone production, transport and degradation and could serve as targets to interfere with pheromone release. The identification of highly expressed CSPs and OBPs in the pheromone gland suggests that they may play a role in the binding, transport and release of sex pheromones during sex pheromone production in A. ipsilon and other Lepidoptera insects.

Transcriptome exploration of the sex pheromone gland of Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae)

BACKGROUND

Molecules involved in pheromone biosynthesis may represent alternative targets for insect population control. This may be particularly useful in managing the reproduction of Lutzomyia longipalpis, the main vector of the protozoan parasite Leishmania infantum in Latin America. Besides the chemical identity of the major components of the L. longipalpis sex pheromone, there is no information regarding the molecular biology behind its production. To understand this process, obtaining information on which genes are expressed in the pheromone gland is essential.

METHODS

In this study we used a transcriptomic approach to explore the pheromone gland and adjacent abdominal tergites in order to obtain substantial general sequence information. We used a laboratory-reared L. longipalpis (one spot, 9-Methyl GermacreneB) population, captured in Lapinha Cave, state of Minas Gerais, Brazil for this analysis.

RESULTS

From a total of 3,547 cDNA clones, 2,502 high quality sequences from the pheromone gland and adjacent tissues were obtained and assembled into 1,387 contigs. Through blast searches of public databases, a group of transcripts encoding proteins potentially involved in the production of terpenoid precursors were identified in the 4th abdominal tergite, the segment containing the pheromone gland. Among them, protein-coding transcripts for four enzymes of the mevalonate pathway such as 3-hydroxyl-3-methyl glutaryl CoA reductase, phosphomevalonate kinase, diphosphomevalonate descarboxylase, and isopentenyl pyrophosphate isomerase were identified. Moreover, transcripts coding for farnesyl diphosphate synthase and NADP+ dependent farnesol dehydrogenase were also found in the same tergite. Additionally, genes potentially involved in pheromone transportation were identified from the three abdominal tergites analyzed.

CONCLUSION

This study constitutes the first transcriptomic analysis exploring the repertoire of genes expressed in the tissue containing the L. longipalpis pheromone gland as well as the flanking tissues. Using a comparative approach, a set of molecules potentially present in the mevalonate pathway emerge as interesting subjects for further study regarding their association to pheromone biosynthesis. The sequences presented here may be used as a reference set for future research on pheromone production or other characteristics of pheromone communication in this insect. Moreover, some matches for transcripts of unknown function may provide fertile ground of an in-depth study of pheromone-gland specific molecules.

Functional flexibility as a prelude to signal diversity?: Role of a fatty acyl reductase in moth pheromone evolution

Sex pheromones are the hallmark of reproductive behavior in moths. Mature females perform the task of mate signaling and release bouquets of odors that attract conspecific males at long range. The pheromone chemistry follows a relatively minimal design but still the combinatorial action of a handful of specialized pheromone production enzymes has resulted in remarkably diverse sexual signals that subtly vary in structure and in number and ratio of components. In a recent article,1 we showed that a single reductase gene (pgFAR) enables the conversion of key biosynthetic fatty-acyl precursors into fatty alcohols, the immediate precursors of the multi-component pheromone in small ermine moths (Lepidoptera: Yponomeutidae). In the light of the widespread usage of multi-component pheromone blends across Lepidoptera, it is likely that the pgFAR biochemical flexibility is a regular feature of the moth pheromone machinery and polyvalent reductase genes are emerging as pivots to promote phenotypic transitions in moth mating signals. In addition, the small ermine moth pgFAR nevertheless contributes to regulating the ratio among components. Here we show that the pgFAR substrate specificity is actually counterbalancing the inherent chain-length preference of an upstream desaturase with Δ11-activity and that the enzymes together modulate the final blend ratio between the Z11-16:OH, Z11-14:OH and E11-14:OH compounds before the final acetylation.

Transcriptome analysis of the sex pheromone gland of the noctuid moth Heliothis virescens

BACKGROUND

The chemical components of sex pheromones have been determined for more than a thousand moth species, but so far only a handful of genes encoding enzymes responsible for the biosynthesis of these compounds have been identified. For understanding the evolution of moth sexual communication, it is essential to know which genes are involved in the production of specific pheromone components and what controls the variation in their relative frequencies in the pheromone blend. We used a transcriptomic approach to characterize the pheromone gland of the Noctuid moth Heliothis virescens, an important agricultural pest, in order to obtain substantial general sequence information and to identify a range of candidate genes involved in the pheromone biosynthetic pathway.

RESULTS

To facilitate identifying sets of genes involved in a broad range of processes and to capture rare transcripts, we developed our majority of ESTs from a normalized cDNA library of Heliothis virescens pheromone glands (PG). Combining these with a non-normalized library yielded a total of 17,233 ESTs, which assembled into 2,082 contigs and 6,228 singletons. Using BLAST searches of the NR and Swissprot databases we were able to identify a large number of putative unique gene elements (unigenes), which we compared to those derived from previous transcriptomic surveys of the larval stage of Heliothis virescens. The distribution of unigenes among GO Biological Process functional groups shows an overall similarity between PG and larval transcriptomes, but with distinct enrichment of specific pathways in the PG. In addition, we identified a large number of candidate genes in the pheromone biosynthetic pathways.

CONCLUSION

These data constitute one of the first large-scale EST-projects for Noctuidae, a much-needed resource for exploring these pest species. Our analysis shows a surprisingly complex transcriptome and we identified a large number of potential pheromone biosynthetic pathway and immune-related genes that can be applied to population and systematic studies of Heliothis virescens and other Noctuidae.

Molecular cloning, expression profile and 5' regulatory region analysis of two chemosensory protein genes from the diamondback moth, Plutella xylostella

Chemosensory proteins play an important role in transporting chemical compounds to their receptors on dendrite membranes. In this study, two full-length cDNA codings for chemosensory proteins of Plutella xylostella (Lepidoptera: Plutellidae) were obtained by RACE-PCR. PxylCSP3 and Pxyl-CSP4, with GenBank accession numbers ABM92663 and ABM92664, respectively, were cloned and sequenced. The gene sequences both consisted of three exons and two introns. RT-PCR analysis showed that Pxyl-CSP3 and Pxyl-CSP4 had different expression patterns in the examined developmental stages, but were expressed in all larval stages. Phylogenetic analysis indicated that lepidopteran insects consist of three branches, and Pxyl-CSP3 and Pxyl-CSP4 belong to different branches. The 5'regulatory regions of Pxyl-CSP3 and Pxyl-CSP4 were isolated and analyzed, and the results consist of not only the core promoter sequences (TATA-box), but also several transcriptional elements (BR-C Z4, Hb, Dfd, CF2-II, etc.). This study provides clues to better understanding the various physiological functions of CSPs in P. xylostella and other insects.

Global transcriptional analysis of pheromone biosynthesis-related genes in the female turnip moth, Agrotis segetum (Noctuidae) using a custom-made cDNA microarray

Using a custom-made cDNA microarray, global transcriptional analyses were conducted to identify genes differentially regulated in the pheromone gland as compared to the remaining insect tissue of the moth Agrotis segetum (Noctuidae). A two-fold or larger difference in relative expression levels was found for 227 of 864 genes investigated comparing the two tissues. Unexpectedly, an antennal binding protein homologue, containing a pheromone-binding/general odorant-binding protein PFAM domain, was expressed at a 56-fold higher level in the pheromone gland. Relatively higher expression levels in the pheromone gland were also found for other gene representatives putatively encoding odorant-binding proteins and chemosensory proteins, as well as a number of gene representatives putatively encoding proteins involved in juvenile hormone interactions. The largest relative up-regulation (84-fold) in the pheromone gland was found for a gene encoding a Delta11-desaturase homologue implicated in desaturation of pheromone precursors. For three gene representatives, the expression patterns were independently verified by quantitative real-time PCR (qPCR). Additionally the expression pattern in the pheromone gland for the Delta11-desaturase homologue was shown by qPCR to follow the previously known pattern of pheromone production in female A. segetum, both with respect to age and circadian rhythm, whereas the expression of a Delta9-desaturase and a chemosensory protein homologue did not share this pattern.