Seminal fluid protein genes of the brown planthopper, Nilaparvata lugens

The evolution and functional divergence of 10 Apolipoprotein D-like genes in Nilaparvata lugens

Apolipoprotein D (ApoD), a member of the lipocalin superfamily of proteins, is involved in lipid transport and stress resistance. Whereas only a single copy of the ApoD gene is found in humans and some other vertebrates, there are typically several ApoD-like genes in insects. To date, there have been relatively few studies that have examined the evolution and functional differentiation of ApoD-like genes in insects, particularly hemi-metabolous insects. In this study, we identified 10 ApoD-like genes (NlApoD1-10) with distinct spatiotemporal expression patterns in Nilaparvata lugens (BPH), which is an important pest of rice. NlApoD1-10 were found to be distributed on 3 chromosomes in a tandem array of NlApoD1/2, NlApoD3-5, and NlApoD7/8, and show sequence and gene structural divergence in the coding regions, indicating that multiple gene duplication events occurred during evolution. Phylogenetic analysis revealed that NlApoD1-10 can be clustered into 5 clades, with NlApoD3-5 and NlApoD7/8 potentially evolving exclusively in the Delphacidae family. Functional screening using an RNA interference approach revealed that only NlApoD2 was essential for BPH development and survival, whereas NlApoD4/5 are highly expressed in testes, and might play roles in reproduction. Moreover, stress response analysis revealed that NlApoD3-5/9, NlApoD3-5, and NlApoD9 were up-regulated after treatment with lipopolysaccharide, H2 O2 , and ultraviolet-C, respectively, indicating their potential roles in stress resistance.

Proteome Analysis of Male Accessory Gland Secretions in the Diamondback Moth, Plutella xylostella (Lepidoptera: Plutellidae)

In insects, male accessory gland proteins (ACPs) are important reproductive proteins secreted by male accessory glands (MAGs) of the internal male reproductive system. During mating, ACPs are transferred along with sperms inside female bodies and have a significant impact on the post-mating physiology changes of the females. Under sexual selection pressures, the ACPs exhibit remarkably rapid and divergent evolution and vary from species to species. The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a major insect pest of cruciferous vegetables worldwide. Mating has a profound impact on the females' behavior and physiology in this species. It is still unclear what the ACPs are in this species. In this study, two different proteomic methods were used to identify ACPs in P. xylostella. The proteins of MAGs were compared immediately before and after mating by using a tandem mass tags (TMT) quantitative proteomic analysis. The proteomes of copulatory bursas (CB) in mated females shortly after mating were also analyzed by the shotgun LC-MS/MS technique. In total, we identified 123 putative secreted ACPs. Comparing P. xylostella with other four insect ACPs, trypsins were the only ACPs detected in all insect species. We also identified some new insect ACPs, including proteins with chitin binding Peritrophin-A domain, PMP-22/ EMP/ MP20/ Claudin tight junction domain-containing protein, netrin-1, type II inositol 1,4,5-trisphosphate 5-phosphatase, two spaetzles, allatostatin-CC, and cuticular protein. This is the first time that ACPs have been identified and analyzed in P. xylostella. Our results have provided an important list of putative secreted ACPs, and have set the stage for further exploration of the functions of these putative proteins in P. xylostella reproduction.

Octopamine signaling is involved in the female postmating state in Nilaparvata lugens Stål (Hemiptera: Delphacidae)

Mating triggers physiological and behavioral changes in female insects. In many species, females experience postmating behavioral and physiological changes that define a post-mated state. These changes are comprised of several conditions, including long-term refractoriness to re-mating and increased production and laying of eggs. Here, we report that mating led to several changes in brown planthopper (BPH) females, including increased octopamine (OA), cAMP concentrations, and activities of several enzymes. Mating also led to changes in the expression of several genes acting in female physiology, including those in the cAMP/PKA signal transduction pathway. OA injections into virgin females led to similar changes. RNAi silencing of the gene encoding tyramine β-hydroxylase, involved in the final step in OA synthesis, led to decreased expression of these genes, and reduced the cAMP/PKA signaling. At the whole-organism level, the RNAi treatments led to reduced fecundity, body weights, and longevity. RNAi silencing of genes acting in OA signaling led to truncated ovarian development, egg maturation, and ovarian vitellogenin (Vg) uptake. The impact of these decreases is also registered at the population level, seen as decreased population growth. We infer that OA signaling modulates the postmating state in female BPH and possibly other hemipterans.

Identification of putative abdominal vibration-related genes through transcriptome analyses in the brown planthopper (Nilaparvata lugens)

The sexually mature female brown planthoppers (BPHs) send out abdominal vibration (AV) signals through the rice so that the males can obtain intraspecific, gender, and localization information to prepare for mating. Destroying vibration signals is an alternative biological method for pest control. However, the regulatory mechanism of AV in female BPHs remains elusive, which presents an obstacle to pest control. We observed that before mating female BHPs emitted abdominal vibration signals that disappeared immediately after mating and reappeared after 6 days. Therefore, ovarian and brain samples of female BPHs from Unmated-6h⁺ (with AV), Mated-6h^- (without AV) and Mated-6d⁺ (with AV) individuals were collected for transcript analyses. By transcriptional sequencing analyses, 33 candidate genes that might involve in the regulation of female AV were obtained. After selecting 4 candidate genes of them for verification by RNA interference (RNAi), it was found that interference of juvenile hormone binding protein (JHBP) could greatly reduce the probability and frequency of AV for female BPHs. In general, this study identified AV-related candidate genes in female BPHs through transcriptome analyses and provided an important basis for future research on pest control in BPHs.

Transcriptome Analysis of Ophraella communa Male Reproductive Tract in Indirect Response to Elevated CO2 and Heat Wave

Increase in atmospheric CO₂ directly affects the insect physiology and behavior, and indirectly affects the herbivorous insects by affecting their hosts. The increase in atmospheric CO₂ is accompanied by an increase in temperature and heat waves. Ophraella communa LeSage is a natural enemy of Ambrosia artemisiifolia (common ragweed). The development and reproduction of this beetle is weakened upon eating common ragweed grown under stress conditions. As female behavior and physiology alter after mating, the reproductive tract of males is likely to modulate reproduction and development in this species. Herein, the transcriptional profiles of testes and accessory glands from male O. communa individuals feeding on common ragweed under conditions of high CO₂ concentration and heat waves and that grown under ambient CO₂ concentration were compared. Differentially expressed genes (DEGs) were identified between the same tissues from beetles fed on common ragweed grown under different stress conditions. There were 3, 2, 3, 1and 5 genes related to decomposition and transport of macromolecular substances, host location, stress response, reproduction, and poisonous food-utilization. No expected response was observed in the male reproductive tract, but some of the identified DEGs might control the development of the population. The results presented here should be helpful in guiding future studies on deciphering the indirect response of other organs to high CO₂ concentration and heat waves, as well as the functions of seminal fluid proteins in O. communa.

Proteomic analysis of Laodelphax striatellus gonads reveals proteins that may manipulate host reproduction by Wolbachia

Wolbachia are intracellular bacteria that manipulate host reproduction by several mechanisms including cytoplasmic incompatibility (CI). However, the underlying mechanisms of Wolbachia-induced CI are not entirely clear. Here, we monitored the Wolbachia distribution in the male gonads of the small brown planthopper (Laodelphax striatellus, SBPH) at different development stages, and investigated the influence of Wolbachia on male gonads by a quantitative proteomic analysis. A total of 276 differentially expressed proteins were identified, with the majority of them participating in metabolism, modification, and reproduction. Knocking down the expression of outer dense fiber protein (ODFP) and venom allergen 5-like (VA5L) showed decreased egg reproduction, and these two genes might be responsible for Wolbachia improved fecundity in infected L. striatellus; whereas knocking down the expression of cytosol amino-peptidase-like (CAL) significantly decreased the egg hatch rate in Wolbachia-uninfected L. striatellus, but not in the Wolbachia-infected one. Considering that the mRNA/protein level of CAL was downregulated by Wolbachia infection and dsCAL treatment closely mimicked Wolbachia-induced CI, we presumed that CAL might be one of the factors determining the CI phenotype.

Male Selenoprotein F-Like (SPF-L) Influences Female Reproduction and Population Growth in Nilaparvata lugens (Hemiptera: Delphacidae)

Selenoproteins serve in anti-oxidant and cellular redox functions in almost all organisms. A recent study characterized a selenoprotein F-like (SPF-L) in the brown plant hopper’s (BPH), Nilaparvata lugens, male accessory glands (MAGs), raised the question of whether the SPF-L is associated with female fecundity. In this study, SPF-L mRNA was found to be enriched in the internal reproductive organ (IRO) of virgin males, also expressed relatively stably in virgin males and females, and dietary dsSPF-L-treatments led to reduced MAG protein and Arginine content. Knockdown of NlSPF-L in unmated males did not influence juvenile hormone (JH) III and ecdysteroid titers, however, dsSPF-L-treated mated males had increased JH III titer, and reduced ecdysteroid titer compared to controls. After mating with dsSPF-L-treated males, female partners had reduced fat body and ovary soluble proteins and JH III tier and vitellogenin (Vg) mRNA levels, but no alterations in ecdysteroid titer, body weight or longevity. The experimental females had prolonged pre-oviposition periods and they laid fewer eggs, which suffered reduced hatching rates and population growth index (PGI). Such mating also led to impaired IRO development in males and females, which was confirmed by immunofluorescence staining. We infer that SPF-L affects reproductive success of males and their partners.

A targeted in situ hybridization screen identifies putative seminal fluid proteins in a simultaneously hermaphroditic flatworm

BACKGROUND

Along with sperm, in many taxa ejaculates also contain large numbers of seminal fluid proteins (SFPs). SFPs and sperm are transferred to the mating partner, where they are thought to play key roles in mediating post-mating sexual selection. They modulate the partner's behavior and physiology in ways that influence the reproductive success of both partners, thus potentially leading to sexual conflict. Despite the presumed general functional and evolutionary significance of SFPs, their identification and characterization has to date focused on just a few animal groups, predominantly insects and mammals. Moreover, until now seminal fluid profiling has mainly focused on species with separate sexes. Here we report a comprehensive screen for putative SFPs in the simultaneously hermaphroditic flatworm Macrostomum lignano.

RESULTS

Based on existing transcriptomic data, we selected 150 transcripts known to be (a) predominantly expressed in the tail region of the worms, where the seminal fluid-producing prostate gland cells are located, and (b) differentially expressed in social environments differing in sperm competition level, strongly implying that they represent a phenotypically plastic aspect of male reproductive allocation in this species. For these SFP candidates, we then performed whole-mount in situ hybridization (ISH) experiments to characterize tissue-specific expression. In total, we identified 98 transcripts that exhibited prostate-specific expression, 76 of which we found to be expressed exclusively in the prostate gland cells; additional sites of expression for the remaining 22 included the testis or other gland cells. Bioinformatics analyses of the prostate-limited candidates revealed that at least 64 are predicted to be secretory proteins, making these especially strong candidates to be SFPs that are transferred during copulation.

CONCLUSIONS

Our study represents a first comprehensive analysis using a combination of transcriptomic and ISH screen data to identify SFPs based on transcript expression in seminal fluid-producing tissues. We thereby extend the range of taxa for which seminal fluid has been characterized to a flatworm species with a sequenced genome and for which several methods such as antibody staining, transgenesis and RNA interference have been established. Our data provide a basis for testing the functional and evolutionary significance of SFPs.

Seminal plasma proteomes and sperm fertility

During ejaculation, the spermatozoa are transported by the seminal plasma, a fluid resulting from secretions originating mainly from the prostate and the seminal vesicles in mammals. The interaction of the seminal plasma with spermatozoa induces binding of seminal proteins onto the sperm surface and membrane remodeling potentially impacting the sperm transport, survival and fertilizing ability in the female genital tract. The seminal plasma also contains peptides and proteins involved in the inflammatory and immune response of the female tract. Therefore the seminal plasma proteome has been investigated in a large range of taxa, including mammals, birds, fishes and insect species. The association of the seminal plasma with semen preservation or fertility identified proteic markers of seminal plasma function in domestic species. This review summarizes the current knowledge in seminal plasma proteomes and proteic markers of sperm preservation in animal species.