Molecular identification of a pancreatic lipase-like gene involved in sex pheromone biosynthesis of Bombyx mori

Lipases and carboxylesterases affect moth sex pheromone compounds involved in interspecific mate recognition

Moth sex pheromones are a classical model for studying sexual selection. Females typically produce a species-specific pheromone blend that attracts males. Revealing the enzymes involved in the interspecific variation in blend composition is key for understanding the evolution of these sexual communication systems. The nature of the enzymes involved in the variation of acetate esters, which are prominent compounds in moth pheromone blends, remains unclear. We identify enzymes involved in acetate degradation using two closely related moth species: Heliothis (Chloridea) subflexa and H. (C.) virescens, which have different quantities of acetate esters in their sex pheromone. Through comparative transcriptomic analyses and CRISPR/Cas9 knockouts, we show that two lipases and two esterases from H. virescens reduce the levels of pheromone acetate esters when expressed in H. subflexa females. Together, our results show that lipases and carboxylesterases are involved in tuning Lepidoptera pheromones composition.

Diapause-Linked Gene Expression Pattern and Related Candidate Duplicated Genes of the Mountain Butterfly Parnassius glacialis (Lepidoptera: Papilionidae) Revealed by Comprehensive Transcriptome Profiling

The mountain butterfly Parnassius glacialis is a representative species of the genus Parnassius, which probably originated in the high-altitude Qinhai–Tibet Plateau in the Miocene and later dispersed eastward into relatively low-altitude regions of central to eastern China. However, little is known about the molecular mechanisms underlying the long-term evolutionary adaptation to heterogeneous environmental conditions of this butterfly species. In this study, we obtained the high-throughput RNA-Seq data from twenty-four adult individuals in eight localities, covering nearly all known distributional areas in China, and firstly identified the diapause-linked gene expression pattern that is likely to correlate with local adaptation in adult P. glacialis populations. Secondly, we found a series of pathways responsible for hormone biosynthesis, energy metabolism and immune defense that also exhibited unique enrichment patterns in each group that are probably related to habitat-specific adaptability. Furthermore, we also identified a suite of duplicated genes (including two transposable elements) that are mostly co-expressed to promote the plastic responses to different environmental conditions. Together, these findings can help us to better understand this species’ successful colonization to distinct geographic areas from the western to eastern areas of China, and also provide us with some insights into the evolution of diapause in mountain Parnassius butterfly species.

Genome-wide identification of lipases in silkworm (Bombyx mori) and their spatio-temporal expression in larval midgut

Lipases play crucial roles in food digestion by degrading dietary lipids into free fatty acids and glycerols. The domesticated silkworm (Bombyx mori) has been widely used as an important Lepidopteran model for decades. However, little is known about the lipase gene family in the silkworm, especially their hydrolytic activities as digestive enzymes. In this study, a total of 38 lipase genes were identified in the silkworm genome. Phylogenetic analysis indicated that they were divided into three major groups. Twelve lipases were confirmed to be expressed in the midgut at both transcriptional and translational levels. They were grouped into the same gene cluster, suggesting that they could have similar physiological functions. Quantitative real-time PCR (qRT-PCR) analyses indicated that lipases were mainly expressed in anterior and middle midgut regions, and their expression levels varied greatly along the length of midgut. A majority of lipases were down-regulated in the midgut when larvae stopped feeding. However, a unique lipase gene (Bmlip10583) showed low expression level during feeding stage, but it was significantly up-regulated during the larvae-pupae transition. These results demonstrated that expression of silkworm lipases was spatially and temporally regulated in the midgut during larval development. Taken together, our results provide a fundamental research of the lipase gene family in the silkworm.

A Novel Digestive Proteinase Lipase Member H-A in Bombyx mori Contributes to Digestive Juice Antiviral Activity Against B. mori Nucleopolyhedrovirus

Previous studies have revealed that some proteins in Bombyx mori larvae digestive juice show antiviral activity. Here, based on the label-free proteomics data, BmLipase member H-A (BmLHA) was identified as being involved in the response to BmNPV infection in B. mori larvae digestive juice. In the present study, a gene encoding the BmLHA protein in B. mori was characterized. The protein has an open reading fragment of 999 bp, encoding a predicted 332 amino acid residue-protein with a molecular weight of approximately 35.9 kDa. The phylogenetic analysis revealed that BmLHA shares a close genetic distance with Papilio xuthus Lipase member H-A. BmLHA was highly expressed in the middle part of the B. mori gut, and the expression level increased with instar rising in larvae. There was higher expression of BmLHA in A35 than in P50 strains, and it was upregulated in both A35 and P50 strains, following BmNPV infection. The expression level of VP39 decreased significantly in appropriate recombinant-BmLHA-treated groups compared with the PBS-treated group in B. mori larvae and BmN cells. Meanwhile, overexpression of BmLHA significantly reduced the infectivity of BmNPV in BmN cells. These results indicated that BmLHA did not have digestive function but had anti-BmNPV activity. Taken together, our work provides valuable data for the clarification of the molecular characterization BmLHA and supplements research on proteins of anti-BmNPV activity in B. mori.

Biotechnological potential of insect fatty acid-modifying enzymes

There are more than one million described insect species. This species richness is reflected in the diversity of insect metabolic processes. In particular, biosynthesis of secondary metabolites, such as defensive compounds and chemical signals, encompasses an extraordinarily wide range of chemicals that are generally unparalleled among natural products from other organisms. Insect genomes, transcriptomes and proteomes thus offer a valuable resource for discovery of novel enzymes with potential for biotechnological applications. Here, we focus on fatty acid (FA) metabolism-related enzymes, notably the fatty acyl desaturases and fatty acyl reductases involved in the biosynthesis of FA-derived pheromones. Research on insect pheromone-biosynthetic enzymes, which exhibit diverse enzymatic properties, has the potential to broaden the understanding of enzyme specificity determinants and contribute to engineering of enzymes with desired properties for biotechnological production of FA derivatives. Additionally, the application of such pheromone-biosynthetic enzymes represents an environmentally friendly and economic alternative to the chemical synthesis of pheromones that are used in insect pest management strategies.

Host miRNAs are involved in hormonal regulation of HaSNPV-triggered climbing behaviour in Helicoverpa armigera

Baculoviruses manipulate host climbing behaviour to ensure that the hosts die at elevated positions on host plants to facilitate virus proliferation and transmission, which is a process referred to as tree-top disease. However, the detailed molecular mechanism underlying tree-top disease has not been elucidated. Using transcriptome analysis, we showed that two hormone signals, juvenile hormone (JH) and 20-hydroxyecdysone (20E), are key components involved in HaSNPV-induced tree-top disease in Helicoverpa armigera larvae. RNAi-mediated knockdown and exogenous hormone treatment assays demonstrated that 20E inhibits virus-induced tree-top disease, while JH mediates tree-top disease behaviour. Knockdown of BrZ2, a downstream signal of JH and 20E, promoted HaSNPV-induced tree-top disease. We also found that two miRNAs target BrZ2 and are involved in the cross-talk regulation between 20E and JH manipulating HaSNPV replication, time to death and HaSNPV-induced tree-top disease.

Regulation of pheromone biosynthesis in moths

Female moths release sex pheromones for attracting males from a distance. Most moths are nocturnal so there is a periodicity to the release of sex pheromone. The temporal release of sex pheromone in most moths is regulated by calling behavior and by the biosynthesis of sex pheromone. In most moths, biosynthesis occurs in the pheromone gland and is controlled by the neuropeptide PBAN (pheromone biosynthesis activating neuropeptide). PBAN is produced in the subesophageal ganglion and released into circulation where it travels to the pheromone gland to activate pheromone biosynthesis. The G-protein coupled receptor that binds PBAN has been identified as well as aspects of signal transduction to activate the biosynthetic pathway. This review will highlight recent advances in the study of regulation of pheromone biosynthesis in moths.

Exploring complex pheromone biosynthetic processes in the bumblebee male labial gland by RNA sequencing

Male marking pheromones (MPs) are used by the majority of bumblebee species (Hymenoptera: Apidae), including a commercially important greenhouse pollinator, the buff-tailed bumblebee (Bombus terrestris), to attract conspecific females. MP biosynthetic processes in the cephalic part of the bumblebee male labial gland (LG) are of extraordinary complexity, involving enzymes of fatty acid and isoprenoid biosynthesis, which jointly produce more than 50 compounds. We employed a differential transcriptomic approach to identify candidate genes involved in MP biosynthesis by sequencing Bombus terrestris LG and fat body (FB) transcriptomes. We identified 12 454 abundantly expressed gene products (reads per kilobase of exon model per million mapped reads value > 1) that had significant hits in the GenBank nonredundant database. Of these, 876 were upregulated in the LG (> 4-fold difference). We identified more than 140 candidate genes potentially involved in MP biosynthesis, including esterases, fatty acid reductases, lipases, enzymes involved in limited fatty acid chain shortening, neuropeptide receptors and enzymes involved in biosynthesis of triacylglycerols, isoprenoids and fatty acids. For selected candidates, we confirmed their abundant expression in LG using quantitative real-time reverse transcription-PCR (qRT-PCR). Our study shows that the Bombus terrestris LG transcriptome reflects both fatty acid and isoprenoid MP biosynthetic processes and identifies rational gene targets for future studies to disentangle the molecular basis of MP biosynthesis. Additionally, LG and FB transcriptomes enrich the available transcriptomic resources for Bombus terrestris.

Identification of a thioredoxin peroxidase gene involved in resistance to nucleopolyhedrovirus infection in Helicoverpa armigera with RNA interference

Thioredoxin peroxidases (Tpxs) play a crucial role in protection against oxidative damage in several insect species. However, studies on the characteristics and functions of Tpxs in Helicoverpa armigera are lacking. In this study, a novel 2-Cys Tpx gene from H. armigera (HaTpx) was identified. Sequence analysis revealed that HaTpx is highly conserved and shares two catalysis regions (VCP) with other insect species. HaTpx mRNA was found to be expressed in an age-dependent manner and was ubiquitous in all tissues examined. Hormone treatment showed that the expression of HaTpx is clearly induced by 20-hydroxyecdysone but repressed by Juvenile hormone. Additionally, extreme temperature, ultraviolet light, mechanical injury, Escherichia coli, Metarhizium anisopliae, nucleopolyhedrovirus (NPV) infection, and H2O2 treatment markedly induced HaTpx gene expression. Reactive oxygen species (ROS) levels in hemocytes and MDA concentrations in the hemolymph after NPV infection were evaluated, and the results indicated that NPV infection causes excessive ROS generation. After knockdown of HaTpx by RNA interference, the expression of three antioxidant genes (Cu/ZnSOD, Trx, and TrxR) was increased, whereas two antioxidant genes (CAT and GPX) showed decreased expression. Moreover, the susceptibility of H. armigera to NPV infection increased after HaTpx knockdown. These results indicated that HaTpx contributes to the susceptibility of H. armigera to NPV, and the results also provide a theoretical basis for a novel strategy for developing new chemicals and microbial pesticides that target HaTpx gene for controlling H. armigera.

Glycerol-3-phosphate O-acyltransferase is required for PBAN-induced sex pheromone biosynthesis in Bombyx mori

Female moths employ their own pheromone blends as a communicational medium in mating behavior. The biosynthesis and release of sex pheromone in female moths are regulated by pheromone biosynthesis activating neuropeptide (PBAN) and the corresponding action of PBAN has been well elucidated in Bombyx mori. However, very little is known about the molecular mechanism regarding the biosynthesis of sex pheromone precursor. In this study, quantitative proteomics was utilized to comprehensively elucidate the expression dynamics of pheromone glands (PGs) during development. Proteomic analysis revealed a serial of differentially expressed sex pheromone biosynthesis-associated proteins at the different time points of B. mori development. Most interestingly B. mori glycerol-3-phosphate O-acyltransferase (BmGPAT) was found to be expressed during the key periods of sex pheromone biosynthesis. RNAi knockdown of BmGPAT confirmed the important function of this protein in the biosynthesis of sex pheromone precursor, triacylglcerol (TAG), and subsequently PBAN-induced production of sex pheromone, bombykol. Behavioral analysis showed that RNAi knockdown of GPAT significantly impaired the ability of females to attract males. Our findings indicate that GPAT acts to regulate the biosynthesis of sex pheromone precursor, TAG, thus influencing PBAN-induced sex pheromone production and subsequent mating behavior.

Identification of differentially expressed genes in the pheromone glands of mated and virgin Bombyx mori by digital gene expression profiling

Background

Mating decreases female receptivity and terminates sex pheromone production in moths. Although significant progress has been made in elucidating the mating-regulated inactivation of pheromone biosynthesis-activating neuropeptide (PBAN) secretion, little is known about the mating induced gene expression profiles in pheromone glands (PGs). In this study, the associated genes involved in Bombyx mori mating were identified through digital gene expression (DGE) profiling and subsequent RNA interference (RNAi) to elucidate the molecular mechanisms underlying the mating-regulated gene expression in PGs.

Results

Eight DGE libraries were constructed from the PGs of mated and virgin females: 1 h mating (M1)/virgin (V1) PGs, 3 h mating (M3)/virgin (V3) PGs, 24 h mating (M24)/virgin (V24) PGs and 48 h mating (M48)/virgin (V48) PGs (M48 and V48). These libraries were used to investigate the gene expression profiles affected by mating. DGE profiling revealed a series of genes showing differential expression in each set of mated and virgin female samples, including immune-associated genes, sex pheromone synthesis-associated genes, juvenile hormone (JH) signal-associated genes, etc. Most interestingly, JH signal was found to be activated by mating. Application of the JH mimics, methoprene to the newly-emerged virgin females leaded to the significant reduction of sex pheromone production. RNAi-mediated knockdown of putative JH receptor gene, Methoprene tolerant 1 (Met1), in female pupa resulted in a significant decrease in sex pheromone production in mature females, suggesting the importance of JH in sex pheromone synthesis.

Conclusion

A series of differentially expressed genes in PGs in response to mating was identified. This study improves our understanding of the role of JH signaling on the mating-elicited termination of sex pheromone production.