Identification of genes expressed in the sex pheromone gland of the black cutworm Agrotis ipsilon with putative roles in sex pheromone biosynthesis and transport
© Gu et al.; licensee BioMed Central Ltd. 2013
Received: 6 February 2013
Accepted: 13 September 2013
Published: 22 September 2013
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.
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.
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.
Lepidoptera sex pheromones are primarily C10-C18 long straight chain unsaturated alcohols, aldehydes or acetate esters , biosynthesised and released mainly from pheromone glands located between the 8th and 9th abdominal segments of the female moths. Usually the females use a mixture of compounds in a unique ratio to attract conspecific males . The extremely high specificity and sensitivity of species-specific pheromones make them potential biological control agents for population monitoring, mass trapping and reducing pesticide use in integrated pest management (IPM) programs [3–5]. Further use of pheromones in such strategies would be aided by an understanding of the pathways involved in pheromone biosynthesis and transport.
Most sex pheromone blends of Lepidoptera insects are synthesised de novo via modified fatty acid biosynthesis pathways [2, 6, 7] and gland-specific enzymes are involved in desaturation, chain shortening, reduction and acetylation [1, 2]. Different species use different combinations of these reactions to produce unique species-specific pheromone blends. The first step is the synthesis of saturated fatty acid precursors malonyl-CoA from acetyl-CoA by acetyl-CoA carboxylase (ACC) and fatty acid synthetase (FAS) [8, 9]. Labeling studies conducted with acetate indicated that malonyl-CoA and NADPH are used by FAS to produce mainly saturated stearic acid (18:0) and palmitic acid (16:0) with 18 and 16 carbon atoms and no double bonds, respectively, as precursors [10–12]. Modification of the fatty acid chain includes the introduction of a double bond by desaturases specific to pheromone biosynthesis followed by chain shortening using specific β–oxidation enzymes [13, 14]. So far, several types of desaturases have been extensively studied through gene characterization and expression analysis, including Δ5 , Δ9 [16, 17], Δ10 , Δ11 [19, 20], and Δ14  desaturases. Once unsaturated pheromone precursor with a specific chain-length is produced, the carboxyl carbon is modified to form one of functional groups (aldehyde, alcohol or acetate ester). These modifications require the enzymes fatty acid reductase to produce the alcohols from the fatty acyl precursor , which in some species may be oxidized to aldehydes serving as pheromone components , and to acetate esters (OAc) by acetyltransferase . Recently, a few members of the reductase gene family have been discovered and functionally characterized in several Lepidoptera species, including Ostrinia scapulalis, Heliothis virescens, Heliothis subflexa, Helicoverpa armigera, Helicoverpa assulta, Ostrinia nubilalis, Yponomeuta evonymellus (L.), Yponomeuta padellus (L.) and Yponomeuta rorellus (Hübner) . A number of pheromone gland-specific enzymes have been identified and their essential functions in pheromone production demonstrated in vitro as well as in vivo. For example, using RNA interference, Matsumoto and colleagues showed that two pheromone gland-specific enzymes (acyl-CoA desaturase and a fatty-acyl reductase) are responsible for pheromone production in the silk moth Bombyx mori[29–31].
After production and release of the sex pheromone components by female moths the males detect the pheromone and respond for mating. It is commonly accepted that pheromone molecules are captured and transported to the pheromone receptors on the dendrites of pheromone-sensitive neurons by olfactory binding proteins, including odorant binding proteins (OBPs) and chemosensory proteins (CSPs) [32–34]. Pheromone binding proteins (PBPs) bind to sex pheromone components and classified into a subclass of OBPs . After activation of the pheromone receptors the olfactory signals must be degraded rapidly to prevent from prolonged neuronal excitation . This may involve pheromone degrading enzymes (PDEs) capable of degrading the pheromone molecules .
The black cutworm Agrotis ipsilon is a destructive polyphagous insect pest of many crops and for a strain from China the female sex pheromone blend comprises five main acetate components: (Z)-11-hexadecenyl acetate (Z11-16:OAc), (Z)-9-tetradecenyl acetate (Z9-14:OAc), (Z)-7-dodecenyl acetate (Z7-12:OAc), (Z)-8-dodecenyl acetate (Z8-12:OAc) and (Z)-5-decenyl acetate (Z5-10:OAc) . These components indicate the involvement of different desaturases and ß-oxidases during the sex pheromone biosynthesis. However, the genes/proteins and their specific function in mediating A. ipsilon pheromone production, transport and degradation have not been characterized. Over the last few years, the next generation sequencing such as 454 pyrosequencing technique provides an easy and effective method for the discovery of novel genes. In present study, using the Roche GS FLX Titanium sequencing platform, we report a genetic database of the genes expressed in the pheromone glands of A. ipsilon and the identification of genes with putative roles in pheromone biosynthesis, degradation and transport as well as their tissue expression profiles.
Results and discussion
454 sequencing and unigene assembly
Sequencing of a cDNA library prepared from mRNAs of the pheromone glands of A. ipsilon gave a total of 631,425 raw reads with an average length of 517 base pairs (bp). After trimming adaptor sequences and removing low quality sequences, 629,273 clean reads remained with an average length of 496 bp. The size distribution of the clean reads is shown in Additional file 1. The sequences of all reads have been deposited in the NCBI SRA database with the accession number SRX189143.
Summary of A. ipsilon pheromone gland unigene sequences and assembly
Average length (bp)
Analysis of the transcripts from the A. ipsilon pheromone gland
Gene Ontology of the genes expressed in the A. ipsilon pheromone gland
The 23,473 assembled transcripts were annotated into different functional groups according to Gene Ontology (GO) analysis. Some transcripts were annotated into more than one GO category. Of the 22,473 transcripts, 7,546 (32%) could be assigned to a GO category (Additional file 3). The “cellular process” and “metabolic process” GO categories were most abundantly represented with 4,056 (17.3%) and 3,361 (14.3%) transcripts, respectively, within the biological process GO ontology. In the “cellular components” GO ontology the transcripts were mainly distributed in cell (18.8%) (4,415 transcripts) and cell part (17.6%) (4,133 transcripts). The GO analysis also showed that in the molecular function ontology 3,271 transcripts (13.9%) were annotated as having binding functions and 3,484 (14.8%) to have catalytic activity.
Comparative analysis of transcripts in Lepidoptera pheromone glands
In order to compare the A. ipsilon pheromone gland transcriptome with those from other Lepidoptera and to identify A. ipsilon transcripts with potential involvement in sex pheromone production and transport we downloaded the pheromone gland ESTs of three other Lepidoptera A. segetum, B. mori and H. virescens from the dbEST database of NCBI and previously published pheromone gland transcriptome of H. virescens. After assembling these ESTs we obtained 925 unigenes from A. segetum, 3943 from B. mori and 8202 from H. virescens with an average length of 384 bp, 692 bp and 474 bp, respectively. These are much lower numbers than that obtained by the current study through the 454 sequencing of the A. ipisilon pheromone gland, demonstrating that our pheromone gland transcriptome is currently the largest transcriptome resource for an insect pheromone gland.
Transcript abundance in the A. ipsilon pheromone gland
The most prevalent mRNAs in A. ipsilon sex pheromone gland
No. of Reads
C-type lectin 5
translation elongation factor 2
heat shock e protein 70
elongation factor 1 alpha
myosin regulatory light chain 2
fatty acid synthase
Candidate genes in the A. ipsilon pheromone gland with putative functions in pheromone production, transport and degradation
Putative pheromone biosynthesis related genes in the A. ipsilon pheromone gland
No. of Reads
Acetyl CoA Carboxylase
Fatty acid synthase
fatty acid synthase
acyl-CoA delta 9 desaturase
acyl-CoA delta 11 desaturase
acyl-CoA desaturase HassNPVE
Fatty acyl reductase
fatty-acyl CoA reductase 6
putative fatty acyl-CoA reductase
putative fatty acyl-CoA reductase
putative fatty acyl-CoA reductase
fatty-acyl CoA reductase 3
fatty-acyl CoA reductase 6
fatty-acyl CoA reductase 4
fatty-acyl CoA reductase 5
fatty-acyl CoA reductase 6
putative fatty acyl-CoA reductase
No. of Reads
Putative alcohol dehydrogenase
Putative alcohol dehydrogenase
Putative alcohol dehydrogenase
Putative alcohol dehydrogenase
putative aldo-ketosereductase 1
aldehyde reductase 1
putative acetyl transferase
putative acetyl-CoA acetyltransferase
Candidate esterase genes likely involved in A. ipsilon pheromone degradation
No. of reads
antennal esterase CXE2
antennal esterase CXE3
antennal esterase CXE4
antennal esterase CXE5
antennal esterase CXE6
antennal esterase CXE7
antennal esterase CXE8
antennal esterase CXE9
antennal esterase CXE10
antennal esterase CXE11
antennal esterase CXE12
antennal esterase CXE13
antennal esterase CXE14
antennal esterase CXE15
antennal esterase CXE16
antennal esterase CXE20
Candidate olfactory genes involved in A. ipsilon pheromone reception
No. of reads
chemosensory protein 2
chemosensory protein 2
Odorant binding proteins
odorant binding protein
pheromone binding protein 4
odorant-binding protein 19
antennal binding protein
odorant binding protein
odorant binding protein
odorant binding protein 3
Receptor for the pheromone biosynthesis activating neuropeptide (PBAN)
PBAN is released from the suboesophagal ganglion in the brain and goes to the hemolymph, where it binds to the PBAN receptor in the membrane of the pheromone gland and triggers the pheromone production [42, 43]. Although there was no PBAN receptor found in the pheromone gland transcriptome of H. virescens we found one transcript (Unigene_3821) encoding a protein highly homologous to PBAN receptor isoform B. It has very low abundance in the A. ipsilon transcriptome (31 RPKM) but high amino acid identity of 97% to H. virescens PBAN receptor in GenBank (Protein IDs: ABU93813) .
Acetyl-CoA carboxylase (ACC)
Fatty acid synthase (FAS)
FAS has been shown to catalyse the conversion of malonyl-CoA and NADPH to produce saturated fatty acids . We identified one putative FAS transcript (FAS-JX989151) in the A. ipsilon pheromone gland (Table 3), containing an ORF of 7176 bp and encoding a FAS with 57% amino acid identity to the FAS of T. castaneum (Protein ID: XP_970417). The RT-PCR and qRT-PCR revealed that FAS-JX989151 is highly expressed in the pheromone gland (40-fold higher than in the body, Figure 5 and Figure 6) and also has a high abundance (343 RPKM) in the transcriptome (Figure 3).
Fatty acyl-CoA reductase (FAR)
Once a specific Δ11 and possibly Δ12 double bond is introduced into fatty acid precursors to form a fatty acyl-CoA precursor, the chain of the precursors is then shortened sequentially by ß–oxidation to form different shorter chain fatty acyl-CoA precursors . These precursors are further reduced individually by fatty acyl reductase (FAR) to form corresponding fatty alcohols [26, 28, 51]. In the A. ipsilon pheromone gland transcriptome there are 13 transcripts homologous to putative FAR genes (Table 3). Among them, 5 transcripts encode proteins with 59%-80% amino acid identity to the fatty-acyl CoA reductases of Ostrinia nubilalis (Protein IDs: ADI82776, ADI82777, ADI82778 and ADI82779). Other FAR transcripts are homologous to the fatty acyl-CoA reductase from a wide range of insect species including H. virescens, N. vitripennis, Danaus plexippus, Bombus terrestris and Apis mellifera with amino acid identities of about 60% (Table 3). The RT-PCR and qRT-PCR results indicated that three transcripts (FAR-JX989157, FAR-JX989162 and FAR-JX989164) are highly expressed in the pheromone gland (Figure 5 and Figure 6). The other ten transcripts seem equally expressed in the pheromone gland and the body or highly expressed in the body. All FAR transcripts except two (FAR-JX989157 and FAR-JX989159) have low abundance (from 81 and 16 RPKM) in the pheromone gland transcriptome (Figure 3).
Alcohol oxidase/dehydrogenase (AOX)
Fatty alcohols can be used as pheromone components in many moth species, and they are also pheromone intermediates to produce aldehyde pheromones by the alcohol oxidases [52, 53]. In the A. ipsilon PG 5 homologous genes of alcohol oxidase/dehydrogenase were identified, the BLASTx results revealed three unigenes (AOX-KC007341, AOX-KC007342 and AOX-KC007344) are with the amino acid identity of 43%, 55% and 64%, respectively, to a putative alcohol dehydrogenase of D. plexippus (Protein ID: EHJ70611), and one unigene (AOX-KC007345) are homologous to another putative alcohol dehydrogenase of D. plexippus (Protein ID: EHJ73729 ) with the amino acid identity of 68%. AOX-KC007343 showed 78% amino acid identity with the alcohol dehydrogenase of H. virescens (Protein ID: ACX53694). The RT-PCR and qRT-PCR results indicated that AOX-KC007341 and AOX-KC007343 showed a higher expressed level in the PG than in the body (Figure 5 and Figure 6).
Aldehyde reductase (AR)
Aldehyde reductases are members of the aldo-ketoreductase superfamily and could be used to reduce long-chain acyl-CoA to form alcohol intermediates . In the A. ipsilon pheromone gland we identified 11 transcripts with homology to the aldo-ketoreductases of Papilio dardanus, B. mori, H. armigera, D. plexippus, Culex quinquefasciatus, H. virescens and Papilio xuthus (Table 3). The derived protein sequences of these 11 transcripts show 53%-88% amino acid identity with their homologs in other insects. The RT-PCR and qRT-PCR results indicated that AR-KC007350 and AR-KC007351 are mainly expressed in the pheromone gland, while the other 9 putative aldehyde reductase transcripts have equal expression levels between the pheromone gland and the body or a higher expression level in the body (Figure 5 and Figure 6). All aldehyde reductase transcripts are present at low abundance (from 67 to 10 RPKM) in the pheromone gland transcriptome (Figure 3). The involvement of aldehyde reductase in sex pheromone biosynthesis has not been demonstrated in moth species.
The fatty acid alcohols are used as pheromone components in many moth species. In A. ipsilon whose sex pheromone blends comprise only acetates, they are intermediates and acetylated to pheromone components as acetate esters by actyltransferases . In the A. ipsilon pheromone gland transcriptome 5 acetyltransferase homologous transcripts were identified (Table 3), 3 of them (ATF-KC007357, ATF-KC007360 and ATF-KC007361) encode proteins that are homologous to the acetyltransferase of D. plexippus (Protein IDs: EHJ65205, EHJ65977 and EHJ68573) with relatively high amino acid identities (<70%), one (ATF-KC007358) encodes a protein with 90% amino acid identity to H. virescens acetyltransferase (Protein ID: ACX53812) and one (ATF-KC007359) encodes a protein with 86% amino acid identity with the acetyltransferase of B. mori (Protein ID: NP_001182381). The RT-PCR and qRT-PCR revealed that three transcripts (ATF-KC007358, ATF-KC007360 and ATF-KC007357) are mainly expressed in the pheromone gland (Figure 5 and Figure 6) and have a relative high abundance of 195, 155 and 71 RPKM, respectively in the pheromone gland transcriptome (Figure 3).
Genes encoding candidate pheromone degrading enzymes in the A. ipsilon pheromone gland
Genes encoding candidate pheromone carrier proteins in the A. ipsilon pheromone gland
Moth sex pheromones are synthesised and protected from degradation until being released from the female pheromone gland and it has been proposed that OBPs and CSPs could participate in this process. In this study we have identified transcripts of 7 OBPs and 8 CSPs from the A. ipsilon pheromone gland (Table 5), all of these have the typical insect OBP sequence motif C1-X15-39-C2-X3-C3-X21-44-C4-X7-12-C5-X8-C6 [35, 64] or CSP sequence motif C1-X6-8-C2-X16-21-C3-X2-C4. One CSP transcript, AipsCSP2 seems to be gland-specific and has an extremely high expression level (<100 folds) in the pheromone glands compared with the antennae and body and a relative high abundance in the pheromone gland transcriptome. AipsCSP8 shows a higher expression level in the pheromone gland (10-fold higher than in body) (Figure 9) and is extremely abundant with 1,364 RPKM in the pheromone gland transcriptome (Figure 4).
The black cutworm A. ipsilon is a destructive pest of many crops [66, 67] and mainly controlled by chemical pesticides, which has led to the development of resistance to various compounds . Our study provides information and resource to identify and facilitate functional studies of genes responsible for pheromone production, transport and degradation at the molecular level both in vivo and in vitro.
By deep sequencing of the A. ipsilon sex pheromone gland transcriptome, we have identified 42 transcripts encoding enzymes putative involved in pheromone production. This is the first study reporting the key enzyme ∆11-desaturase involved in A. ipsilon sex pheromone biosynthesis. One new transcript (DES-JX989154) encoding a desaturase is highly abundant in the transcriptome and highly expressed in the pheromone gland, suggesting this desaturase encoded by DES-JX989154 or other newly identified transcripts (DES-JX989155 and DES-JX989156) may play important roles in A. ipsilon sex pheromone biosynthesis. They may contribute in the introducing a double bond at C11 and C12 positions of the saturated fatty acid precursor palmitic acid for the production of pheromone precursors. Further studies are needed to confirm the substrates and the products thus the involvement of these desaturases and other newly identified genes such as those encoding for aldehyde reductases and acetyltransferases in A. ipsilon sex pheromone biosynthesis. Two of the CSPs are highly abundant transcripts (AipsCSP2 and AipsCSP8) with 100- and 10-fold higher transcription level, respectively than in the body. Furthermore AipsCSP2 and AipsOBP6 are pheromone gland-specific and –enriched, respectively (Figure 9 and Figure 10). This suggests a functional role of the PG-enriched CSPs and OBPs in sex pheromone transport and release. It is clear that during perireceptor event after pheromones and odorants enter the sensillun lymph that the antennae-specific odorant binding proteins (OBPs) capture these hydrophobic pheromone and odorant and deliver them to the membrane-bound olfactory receptors (ORs) . Further study of these PG-expressed OBPs, especially their binding to sex pheromone components is needed to confirm its function.
The A. ipsilon colony has been reared in our laboratory (State Key Laboratory for Biology of Plant Diseases and Insect Pests, Chinese Academy of Agricultural Sciences, Beijing, China) since 2006 with field-collected moths introduced each summer to prevent inbreeding effects. The larvae were reared on an artificial diet comprising wheat germ, casein and sucrose as the main components. The colony was kept at 24°C with 75% relative humidity and a 14h:10h light:dark photoperiod. Pupae were sexed and kept separately in hyaline plastic cups before emergence. Adult moths were given 20% honey solution after emergence.
Pheromone gland dissection
The pheromone gland plus associated ovipositor valves and parts of the terminal abdominal segments were dissected with fine scissors  from the rest of the body parts refereed as ‘body’ which comprises of heads, thoraxes, legs, wings and abdomens (without the pheromone glands). The calling behavior of female A. ipsilon moths begins on the first night after eclosion and increases sharply, peaking on the third night . So in order to cover all genes involved in pheromone biosynthesis, four glands of 1-day-old females, four glands of 2-day-old females and ten glands of 3-day-old females were dissected during the second half of the scotophase, which is reported to be the calling period of this moth [69–71]. The eighteen glands were mixed in one RNase-free centrifuge tube for total RNA extraction and frozen in liquid nitrogen until further processing.
RNA extraction and cDNA library construction
Total RNA was extracted using TRIzol regent (Invitrogen, Carlsbad, CA, USA) according to the manufacturer’s protocol. The quantity of RNA was determined using a Nanodrop spectrophotometer (Thermo Scientific, Wilmington, DE, USA) and 1.1% agarose gel electrophoresis. About 500 ng mRNA was further purified from 50 μg total RNA using the polyATtract mRNA isolation system III (Promega, Madison, WI, USA). The mRNA was then sheared into about 800 nucleotides using a RNA fragmentation solution (Autolab, Beijing, China) at 70°C for 30 sec, and then cleaned and condensed using RNeasyMinElute RNA Cleaning Up kit (Qiagen, Valencia, CA, USA). The mRNA was used as a template for first-strand cDNA synthesis using N6 random primers and MMLV reverse transcriptase (TaKaRa, Dalian, China) and the second strands were synthesized using Secondary Strand cDNA synthesis enzyme mixtures (Autolab, Beijing, China). cDNAs with appropriate length were purified with the QIAquick PCR Purification kit (Qiagen, Valencia, CA, USA) and eluted with 10 μl Elution Buffer. After blunt ending and the addition of a poly-A tail at the 3’ end according to the Roche’s Rapid Library Preparing protocols (Roche, USA), the purified cDNAs were linked to GS-FLX sequencing Adaptors (Roche, USA). Finally, the cDNAs shorter than 500 bp were removed using Ampure Beads according to the manufactures’ instruction (Beckman, USA) before the preparation of the cDNA library.
Pyrosequencing of the cDNA library was performed by Beijing Autolab Biotechnology Company using a 454 GS-FLX sequencer (Roche, IN, USA). All sequencing reads were deposited into the Short Read Archive (SRA) of the National Center for Biotechnology Information (NCBI) under the accession number SRX189143.
Sequence analysis and assembly
Base calling of the raw 454 reads in SFF files was carried out using the python script sff_extract.py developed by COMAV (http://bioinf.comav.upv.es). All raw reads were then processed to remove low quality and adaptor sequences using programs tagdust , LUCY  and SeqClean  with default parameters. The resulting sequences were then screened against the NCBI UniVec database (http://www.ncbi.nlm.nih.gov/VecScreen/UniVec.html) to remove possible vector sequence contamination. Cleaned reads shorter than 60 bases were discarded because they are likely to be sequencing artifacts .
Two steps were taken to assemble the clean reads. First MIRA3  was used with the assembly settings of minimum sequence overlap of 30 bp and minimum percentage overlap identity of 80%. Then CAP3 was used with assembly parameters of overlap length cutoff <30 and overlap percent identity cutoff <90% . The resulting contigs and singletons of more than 100 bases were retained as unigenes and annotated as described below.
Homology searches and functional classification
Following the assembly, homology searches of all unigenes were performed using BLASTx and BLASTn programs against the GenBank non-redundant protein (nr) and nucleotide sequence (nt) database at NCBI . Matches with an E-value less than 1.0E-5 were considered significant . Gene names were assigned to each unigene based on the best BLASTx hit with the highest score value.
Gene Ontology terms were assigned by Blast2GO  through BLASTx program with an E-value less than 1.0E-5. Then, WEGO  software was used for assignment of each GO ID to the related ontology entries. The longest open reading frame (ORF) of each unigene was determined by an ORF finder tool (http://www.ncbi.nlm.nih.gov/gorf/gorf.html).
Pheromone gland ESTs from other insects
The H. virescens pheromone gland ESTs (14112 with accession number: GR958232-GR972305, GT067784-GT067747) , the A. segetum pheromone gland ESTs (2286 with accession number: ES582156-ES584441)  and the B. mori pheromone gland ESTs (10501 with accession number: BP184340-BP182009; AV404455-AV403746; DC552314-DC544856) were downloaded from the dbEST database at NCBI (http://www.ncbi.nlm.nih.gov/nucest) and saved as fasta files. All the EST sequences were assembled using the CAP3 program with the same parameters as used in the A. ipsilon assembly. The comparative analyses of A. ipsilon, H. virescens, B. mori and A. segetum pheromone gland unigenes were performed based on the Best Bidirectional Hits results (reciprocal BLASTn, E-value less than 1.0E-6).
Identification of candidate genes associated with moth pheromone biosynthesis
Some putative genes and enzymes have been reported previously as being involved in moth sex pheromone production. We focused our research on the target genes: (1) Acetyl-CoA carboxylase; (2) Fatty acid synthase; (3) Desaturase; (4) Fatty acyl reductase; (5) Alcohol oxidase; (6) Aldehyde reductase; (7) Acetyltransferase.
Identification of putative genes involved in pheromone degradation
Since the sex pheromone blend of A. Ipsilon is comprised of acetate esters (Z)-7-dodecenyl acetate (Z7-12:Ac) (40.5%), (Z)-9-tetradecenyl acetate (Z9-14:Ac) (13.2%), (Z)-11-hexadecenyl acetate (Z11-16:Ac) (14.9%), (Z)-8-dodecenyl acetate (Z8-12:Ac) (17.2%) and (Z)-5-decenyl acetate (Z5-10:Ac) (14.3%) , esterases may play a major role in pheromone degradation. Therefore, we performed BLASTx and BLASTn searches to identify candidate esterase genes in the A. ipsilon pheromone gland NGS dataset.
Identification of putative genes involved in pheromone transport
Genes encoding odorant binding proteins (OBPs) and chemosensory proteins (CSPs) were identified using the “OBP sequence motif” C1-X15-39-C2-X3-C3-X21-44-C4-X7-12-C5-X8-C6  and the “CSP sequence motif” C1-X6-8-C2-X16-21-C3-X2-C4, . Candidate olfactory receptors (ORs), ionotropic receptors (IRs), sensory neuron membrane proteins (SNMPs) genes were identified by BLASTx and BLASTn searches.
The putative N-terminal signal peptides and most likely cleavage sites were predicted by the SignalP V3.0 program  (http://www.cbs.dtu.dk/services/SignalP/). Sequence alignments were done with ClustalX 1.83  with default gap penalty parameters of gap opening 10 and extension 0.2.
RT-PCR and qRT-PCR
The cDNAs from female pheromone glands and other body parts (mixture of heads, thoraxes, legs, wings and abdomens (without the pheromone glands)) were synthesized using PrimeScript RT Reagent with gDNA Eraser (TaKaRa, Dalian, China). 200 ng cDNA was used as RT-PCR and qRT-PCR templates. Specific primer pairs for RT-PCR analysis were designed with Primer 3 (http://frodo.wi.mit.edu/) or Primer Premier 5 (see Additional file 4). To test the integrity of the cDNA templates, a pair of control primers for the β-actin (GenBank Acc. JQ822245) of A. ipsilon was used. The PCR cycling profile was: 95°C for 2 min, followed by 35 cycles of 95°C for 30 sec, 60°C for 30 sec, 72°C for 1 min and a final extension for 10 min at 72°C. PCR products were separated in 1.2% agarose gels and stained with ethidium bromide. Each reaction was done at least six times with three biological replicates.
qRT-PCR analysis was conducted using the ABI 7500 Real-Time PCR System (Applied Biosystems, Carlsbad, CA). The primers were designed by Beacon Designer 7.90 (PREMIER Biosoft International) (see Additional file 5). Two reference genes, β-actin (GenBank Acc. JQ822245) and ribosomal protein S3 (GenBank Acc. JQ822246) were used for normalizing expression of the target gene and correcting for sample-to-sample variation. qRT-PCRs were done in a 25 μl reaction containing 12.5 μl of Platinum SYBR Green qPCR SuperMix-UDG (Invitrogen, Shanghai, China), 0.5 μl of each primer (10 pmol/ μl), 0.5 μl of Rox Reference Dye, 1 μl of sample cDNA (200 ng/μl), 10 μl of sterilized H2O. The cycling parameters were: 50°C for 2 min, 95°C for 2 min, followed by 40 cycles of 95°C for 15 sec and 60°C for 30 sec. Then, the PCR products were heated to 95°C for 15 sec, cooled to 60°C for 1 min and heated to 95°C for 30 sec and cooled to 60°C for 15 sec to measure the dissociation curves. Negative controls, without either template or transcriptase, were included in each experiment. To check reproducibility, each qRT-PCR reaction for each sample was carried out in three technical replicates and three biological replicates.
qRT-PCR data analysis
Relative quantification was performed using the comparative 2-ΔΔCt method . All data were normalized to endogenous β-actin or ribosomal protein S3 levels from the same individual samples. In the analysis of the relative fold change in different tissues, the body sample was taken as the calibrator. Thus, the relative fold change in different tissues was assessed by comparing the expression level of each target gene in other tissues to that in the body part. The results are presented as the mean of the fold change in three biological samples. The comparative analyses of each OBP, CSP and CXE gene among different tissues were determined with one-way nested analysis of variance (ANOVA), followed by a Tukey’s honestly significance difference (HSD) test using SPSS Statistics 18.0 (SPSS Inc., Chicago, IL, USA). The comparative analyses of each putative pheromone biosynthesis gene between pheromone gland (PG) and body part were determined with paired t-test. When applicable, values were presented as mean ± SE.
Odorant binding protein
Expressed sequenced tag
Sensory neuron membrane protein
Next generation sequencing
Polymerase chain reaction
Pheromone degrading enzyme
Pheromone binding protein
Pheromone biosynthesis activating neuropeptide
Fatty acid synthetase
Fatty acyl-CoA reductase
OAc: (Z)-7-dodecenyl acetate
OAc: (Z)-9-tetradecenyl acetate
OAc: (Z)-11-hexadecenyl acetate
OAc: (Z)-5-decenyl acetate
OAc: (Z)-8-dodecenyl acetate
Olfactory receptor neuron.
This work was supported by the China National “973” Basic Research Program (2012CB114104) and the National Natural Science Foundation of China (31071694, 31171858 and 31272048). JJ Zhou and YJ Zhang acknowledge financial support from the Royal Society, UK for the international joint project between China and UK (31111130203; JP100849) and BBSRC International Partnering Award (BB/J020281). Rothamsted Research receives grant-aided support from the Biotechnology and Biological Sciences Research Council of the United Kingdom. The authors thank Ms. RN Yang, XY Qi and W Wang for their contributions in the insect rearing and the RT-PCR experiment.
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