De Novo Transcriptome Identifies Olfactory Genes in Diachasmimorpha longicaudata (Ashmead)

Abstract

Diachasmimoorpha longicaudata (Ashmead, D. longicaudata) (Hymenoptera: Braconidae) is a solitary species of parasitoid wasp and widely used in integrated pest management (IPM) programs as a biological control agent in order to suppress tephritid fruit flies of economic importance. Although many studies have investigated the behaviors in the detection of their hosts, little is known of the molecular information of their chemosensory system. We assembled the first transcriptome of D. longgicaudata using transcriptome sequencing and identified 162,621 unigenes for the Ashmead insects in response to fruit flies fed with different fruits (guava, mango, and carambola). We annotated these transcripts on both the gene and protein levels by aligning them to databases (e.g., NR, NT, KEGG, GO, PFAM, UniProt/SwissProt) and prediction software (e.g., SignalP, RNAMMER, TMHMM Sever). CPC2 and MIREAP were used to predict the potential noncoding RNAs and microRNAs, respectively. Based on these annotations, we found 43, 69, 60, 689, 26 and 14 transcripts encoding odorant-binding protein (OBP), chemosensory proteins (CSPs), gustatory receptor (GR), odorant receptor (OR), odorant ionotropic receptor (IR), and sensory neuron membrane protein (SNMP), respectively. Sequence analysis identified the conserved six Cys in OBP sequences and phylogenetic analysis further supported the identification of OBPs and CSPs. Furthermore, 9 OBPs, 13 CSPs, 3 GRs, 4IRs, 25 ORs, and 4 SNMPs were differentially expressed in the insects in response to fruit flies with different scents. These results support that the olfactory genes of the parasitoid wasps were specifically expressed in response to their hosts with different scents. Our findings improve our understanding of the behaviors of insects in the detection of their hosts on the molecular level. More importantly, it provides a valuable resource for D. longicaudata research and will benefit the IPM programs and other researchers in this filed.

Keywords: Ashmead; Diachasmimorpha longicaudata; chemosensory protein; odorant-binding protein; olfactory protein; parasitoid wasps; transcriptome.

Figure 1

Overview of the assembled Ashmead transcriptome and annotation. (A) Length distribution of the assembled Ashmead transcriptome. (B) Number of transcripts and likely proteins aligned to different databases. (C) Number of the transcripts aligned to other species in the NR mapping results. (D) GO annotation for the assembled Ashmead transcriptome. (E) KEGG pathway annotation for the assembled Ashmead transcriptome. (F) KOG annotation for the assembled transcriptome.

Figure 2

Expression levels of olfactory transcripts in the Ashmead insects. (A) Number of transcripts identified in the insects stimulated by three fruits. (B) Heat maps of the expression levels of OBP, CSP, and OR transcripts. (C) Heat maps showing the expression levels of transcripts encoding GRs, IRs, and SNMPs in the Ashmead insects.

Figure 3

Phylogenetic trees for OBPs (A) and CSPs (B). Ashmead proteins are highlighted in red, the percentage represents the bootstrap value, and the scale bar represents the evolutionary distance.

Figure 4

Differentially expressed transcripts in the parasitoid wasps of fruit flies fed with different fruits. (A) Number of differentially expressed transcripts in the insects in response to two fruit scents. (B) Venn diagram of up- (upper panel) and downregulated (lower panel) transcripts identified in C and M, compared to G. (C) A heat map showed the differential expression of 9 OBPs, 13 CSPs, 3 GRs, 4IRs, 25 ORs, and 4 SNMPs in the parasitoid wasps of fruit flies fed with different fruits.