BackgroundA large number of insect chemosensory genes from different gene subfamilies have been identified and annotated, but their functional diversity and complexity are largely unknown. A systemic examination of expression patterns in chemosensory organs could provide important information.Methodology/Principal FindingsWe identified 92 putative chemosensory genes by analysing the transcriptome of the antennae and female sex pheromone gland of the purple stem borer Sesamia inferens, among them 87 are novel in this species, including 24 transcripts encoding for odorant binding proteins (OBPs), 24 for chemosensory proteins (CSPs), 2 for sensory neuron membrane proteins (SNMPs), 39 for odorant receptors (ORs) and 3 for ionotropic receptors (IRs). The transcriptome analyses were validated and quantified with a detailed global expression profiling by Reverse Transcription-PCR for all 92 transcripts and by Quantitative Real Time RT-PCR for selected 16 ones. Among the chemosensory gene subfamilies, CSP transcripts are most widely and evenly expressed in different tissues and stages, OBP transcripts showed a clear antenna bias and most of OR transcripts are only detected in adult antennae. Our results also revealed that some OR transcripts, such as the transcripts of SNMP2 and 2 IRs were expressed in non-chemosensory tissues, and some CSP transcripts were antenna-biased expression. Furthermore, no chemosensory transcript is specific to female sex pheromone gland and very few are found in the heads.ConclusionOur study revealed that there are a large number of chemosensory genes expressed in S. inferens, and some of them displayed unusual expression profile in non-chemosensory tissues. The identification of a large set of putative chemosensory genes of each subfamily from a single insect species, together with their different expression profiles provide further information in understanding the functions of these chemosensory genes in S. inferens as well as other insects.

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.

Pheromones are environmentally friendly alternatives to traditional pesticides for pest control. They are widely applied for insect monitoring, mating disruption and mass trapping. Nicotiana benthamiana and N. tabacum are potential green biomass production platforms of moth sex pheromones. Using these two Nicotiana species as plant factories, we expressed biosynthetic genes of plant and insect origin in leaf tissue. Moth sex pheromone precursors (E)-11-tetradecenoic acid, (Z)-11-tetradecenoic acid and (Z)-11-hexadecenoic acid were produced by introducing the acyl-ACP thioesterases CpuFatB1 from Cuphea pulcherrima or CpaFatB2 from C. palustris and the fatty acyl desaturases Ave∆11 from Argyrotaenia velutinana, CpaE11 from Choristoneura parallela or Atr∆11 from Amyelois transitella, under the control of CaMV-35S promoter. Among the Nicotiana spp. transformants, the best line produced (Z)-11-hexadecenoic acid at 17.6% of total fatty acids in leaves, during flowering stage, corresponding to 335 µg of (Z)-11-hexadecenoic acid per gram of fresh leaf. The (Z)-11-hexadecenoic acid production lines from N. benthamiana were selected for further propagation to obtain homozygous lines. In the N. benthamiana T2 generation, the production quantity of (Z)-11-hexadecenoic acid was stable. Our study demonstrates the feasibility of stable transformation of N. benthamiana for production of moth pheromone precursors in vegetative tissue.

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.

The beet armyworm, Spodoptera exigua , uses ( Z , E )-9,12-tetradecadienyl acetate as the major component of its sex pheromone. Previous isotope-labeling experiments demonstrated an unusual ∆12 desaturase activity involved in the biosynthesis of this compound; however, the putative ∆12 desaturase gene has not been reported to date. In the present study, we confirmed this ∆12 desaturation pathway by in vivo labeling experiments, and characterized candidate desaturase genes in a yeast heterologous expression system. We demonstrated that a pheromone gland-specific desaturase, SexiDes5, uses palmitic acid and the subsequently chain-shortened product ( Z )-9-tetradecenoic acid as substrates to produce ( Z )-11-hexadecenoic and ( Z , E )-9,12-tetradecadienoic acids, respectively. In addition, the homologous desaturase SlitDes5 from the congeneric Spodoptera litura had analogous functions. Electronic supplementary material The online version of this article (10.1007/s10886-019-01067-3) contains supplementary material, which is available to authorized users.