Transcriptome Sequencing Analysis and Functional Identification of Sex Differentiation Genes from the Mosquito Parasitic Nematode, Romanomermis wuchangensis

Regulatory roles of Bxy-laf-1 in reproductive behaviour of Bursaphelenchus xylophilus

Bursaphelenchus xylophilu is a worldwide quarantine nematode, causing huge economic losses and ecological disasters in many countries. The sex ratio of B. xylophilus plays an important role in the nematode infestation. The laf-1-related genes are highly conserved in animals, playing crucial roles in sex determination. Therefore, we investigated the expression pattern and biological function of its orthologue, Bxy-laf-1 in B. xylophilus. Bxy-laf-1 has two typical conserved DNA-binding domains, DEAD and Helicase C. The real-time quantitative PCR data revealed that Bxy-laf-1 expression was required throughout the entire life of B. xylophilus, with the maximum expression in the J2 stage and the lowest expression in the adult stage. mRNA in situ hybridization showed that Bxy-laf-1 is mainly located in the cephalopharynx and reproductive organs of B. xylophilus. RNA interference (RNAi) indicated that the head swing frequency was dramatically decreased. The RNA interference results displayed that a significant reduction in motility was observed in the hatched larvae. The female to male sex ratio was also decreased in the F0 and F1 generations, but recovered in the F2 generation. The tail of female adults with eggs in the belly appeared deformities. This phenomenon appeared in the F0 and F1 generations, but recovered in the F2 generation. Bxy-laf-1 is a typical sex-determination gene with distinct expression patterns in males and females. As demonstrated in other species, the sex ratio was altered after knocking down Bxy-laf-1 expression. The results of this study contribute to our understanding of the molecular processes of Bxy-laf-1 in B. xylophilus, which may provide clues about how to control pine wilt disease by inhibiting ontogenic growth and reducing nematode fertility.

Steroid hormone 20-hydroxyecdysone promotes CTL1-mediated cellular immunity in Helicoverpa armigera

Mermithid nematodes, such as Ovomermis sinensis, are used as biological control agents against many insect pests, including cotton bollworm (Helicoverpa armigera). However, given the host's robust immune system, the infection rate of O. sinensis is low, thus restricting its widespread use. To understand the host defense mechanisms against mermithid nematodes, we identified and characterized a protein involved in the recognition of O. sinensis, the potential O. sinensis-binding protein C-type lectin 1 (HaCTL1a and/or HaCTL1b), which was eluted from the surface of O. sinensis after incubation with H. armigera plasma. HaCTL1b is homologous to the previously reported HaCTL1a protein. HaCTL1 was predominantly expressed in hemocytes and was induced by the steroid hormone 20-hydroxyecdysone through ecdysone receptor (HaEcR) or ultraspiracle (HaUSP), or both. Binding assays confirmed the interactions of the HaCTL1 proteins with O. sinensis but not with Romanomermis wuchangensis, a parasitic nematode of mosquito. Moreover, the HaCTL1 proteins were secreted into the hemocoel and promoted hemocyte-mediated encapsulation and phagocytosis. A knockdown of HaEcR and/or HaUSP resulted in compromised encapsulation and phagocytosis. Thus, HaCTL1 appears to modulate cellular immunity in the defense against parasitic nematodes, and the 20-hydroxyecdysone-HaEcR-HaUSP complex is involved in regulating the process.

The role of mab-3 in spermatogenesis and ontogenesis of pinewood nematode, Bursaphelenchus xylophilus

BACKGROUND

Bursaphelenchus xylophilus is one of the most destructive invasive species, causing extensive economic losses worldwide. The sex ratio of female to male of B. xylophilus plays an important role in the nematode infestation. However, little is known about the processes of its sex determination. The double sex/mab-3-related family of transcription factors are highly conserved in animals, playing crucial roles in sex determination, spermatogenesis and ontogenesis. We therefore investigated its orthologue, Bxy-mab-3, in B. xylophilus.

RESULTS

Bxy-mab-3 has two typical conserved DNA-binding domains. It was observed in J2 (the second-stage of juveniles), J3, J4 and male adults (specifically on the spicules), but not in eggs or female adults via mRNA in situ hybridization. RNA-Seq indicated significantly higher expression in males. RNAi showed that the body size and sperm size of male adults were markedly smaller than those of the controls. Meanwhile, almost all the RNAi-treated males failed to mate with the normal females, even 26.34% of interfered males did not produce sperm. However, RNAi of Bxy-mab-3 had no effect on the sex ratio of B. xylophilus.

CONCLUSION

Bxy-mab-3 is indispensable for spermatogenesis, ontogenesis and mating behavior. It is a typical sex-determination gene with differential expression in males and females. However, knocking down Bxy-mab-3 expression could not alter the sex ratio as seen in other species. Our findings contribute towards a better understanding of the molecular events of Bxy-mab-3 in B. xylophilus, which provides promising hints for control of pine wilt disease by blocking ontogenesis and decreasing nematode fecundity.

Identification and tissue expression profiling of candidate UDP-glycosyltransferase genes expressed in Holotrichia parallela motschulsky antennae

It is difficult to control Holotrichia parallela Motschulsky with chemical insecticides due to the larvae's soil-living habit, thus the pest has caused great economic losses in agriculture. In addition, uridine diphosphate-glycosyltransferases (UGTs) catalyze the glycosylation process of a variety of small lipophilic molecules with sugars to produce water-soluble glycosides, and play multiple roles in detoxification, endobiotic modulation, and sequestration in an insect. Some UGTs were found specifically expressed in antennae of Drosophila melanogaster and Spodoptera littoralis, and glucurono-conjugated odorants could not elicit any olfactory signals, suggesting that the UGTs may play roles in odorant inactivation by biotransformation. In the current study, we performed a genome-wide analysis of the candidate UGT family in the dark black chafer, H. parallela. Based on a UGT gene signature and the similarity of these genes to UGT homologs from other organisms, 20 putative H. parallela UGT genes were identified. Bioinformatics analysis was used to predict sequence and structural features of H. parallela UGT proteins, and revealed important domains and residues involved in sugar donor binding and catalysis by comparison with human UGT2B7. Phylogenetic analysis of these 20 UGT protein sequences revealed eight major groups, including both order-specific and conserved groups, which are common to more than one order. Of these 20 UGT genes, HparUGT1265-1, HparUGT3119, and HparUGT8312 were highly (>100-fold change) expressed in antennae, suggesting a possible role in olfactory tissue, and most likely in odorant inactivation and olfactory processing. The remaining UGT genes were expressed in all tissues (head, thorax, abdomen, leg, and wing), indicating that these UGTs likely have different biological functions. This study provides the fundamental basis for determining the function of UGTs in a highly specialized olfactory organ, the H. parallela antenna.

Cloning and expression analysis of the DEAD-box/RNA helicase Oslaf-1 in Ovomermis sinensis

Ovomermis sinensis is a potentially-valuable nematode for controlling insect pests. The parasitic stage of the nematode absorbs nutrients in its host’s hemolymph to maintain its growth development and then kills the host when it emerges. At present, little known about its reproductive development, particularly the responsible molecular mechanism. More detailed research on the genes of reproductive development will not only help us understand the mechanisms underlying sex differentiation in the nematode, but would also be valuable for successfully cultivating them in vitro and using them for biocontrol. In this study, we used the homology cloning method to clone the full-length cDNA of a DEAD-box family gene (Oslaf-1) from O. sinensis. Then, using qRT-PCR technology to detect the expression pattern of the Oslaf-1 gene at different development stages and tissues, the gene was found to be highly expressed in the post-parasitic stage (P < 0.01) and ovarian (P < 0.05) of O. sinensis. Western blot analysis showed the same result that the gene is associated with gonadal development and function, but is not gonad-specific. In situ hybridization further demonstrated that the gene is widely expressed in early embryos and is mainly distributed in the gonadal area. However, the signal was mainly concentrated in the reproductive primordia in pre-parasitic juveniles. RNA interference (RNAi) studies revealed that the sex ratio of O. sinensis soaked in dsRNA of Oslaf-1 was not statistically different than the gfp dsRNA treated groups. Our results suggest that Oslaf-1 may play a vital role in the reproductive systems of the nematode. In addition, we speculate that the Oslaf-1 gene plays an important role during embryonic development and that it occurs and develops in the gonads of pre-parasitic juveniles of O. sinensis.