Identification and expression analysis of putative chemoreception genes from Cyrtorhinus lividipennis (Hemiptera: Miridae) antennal transcriptome

Abstract

Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae) is an important egg predator of planthoppers which are destructive rice pests. The chemosensory genes in the mirid antennae play important roles in mating and prey-seeking behaviors. To gain a better understanding of the olfaction of C. lividipennis, we sequenced the antennal transcriptomes of the predator to identify the key olfaction genes. We identified 18 odorant binding proteins (OBPs), 12 chemosensory proteins (CSPs), 1 Niemann-Pick C2 protein (NPC2), 15 odorant receptors (ORs), 6 ionotropic receptors (IRs), 3 gustatory receptors (GRs) and 3 sensory neuron membrane proteins (SNMPs). Quantitative real-time PCR results showed that the relative transcript levels of three ClivORs (ClivOR6, 7 and 14) in the female antennae were 3 to 6 folds higher than that in the male antennae, indicating these genes were more related to oviposition site selection. The relative transcript levels of ClivCSP8 and ClivOR11 were 2.6 and 2.7 times higher in the male antennae than that of the female, respectively, indicating that these genes might be involved in mate searching. Moreover, the responses of dsorco treated predators to volatiles emitted from infested rice were significantly reduced, indicating these volatiles might serve as crucial cues in the host searching of C. lividipennis.

Figure 1

Species distribution of the C. lividipennis antennal transcriptome unigenes based on the results of BLASTX search. Different colors represent different species.

Figure 2

Gene ontology classifications of C. lividipennis antennal transcriptome unigenes. The left y-axis denote the number of genes in the category.

Figure 3

Phylogenetic analysis of ORs from five hemipteran insects. Cliv, Cyrtorhinus lividipennis; Aluc, Apolygus lucorum; Mper, Myzus persicae; Apis, Acyrthosiphon pisum; Nlug, Nilaparvata lugens.

Figure 4

Sex-specific expression of C. lividipennis chemoreception genes. (A) The female-dominantly expressed olfactory genes. (B) The male-dominantly expressed olfactory genes. Gene expression patterns in antennae were normalized relative to legs (male and female mixture). Data were presented as the mean of three replicates (n = 3) ± SE. Different lower cases indicate significant differences (p < 0.05). FA: female antennae, MA: male antennae, L: legs.

Figure 5

Responses to different odor sources by C. lividipennis after dsRNA silencing treatment. (A) Relative transcript accumulation of orco after RNAi were quantified by qRT-PCR. (B) Responses of C. lividipennis to different odor sources after dsGFP and dsorco treatment. Infested plants, healthy plants denote volatiles emitted by gravid female-damaged rice seedlings and healthy rice seedlings respectively. *, **, and n.s. refereed to the difference between two treatments (dsGFP and dsorco) is significant (p < 0.05), highly significant (p < 0.01), and not significant (p > 0.05) (t-test), respectively.

Figure 6

The H-shaped olfactometer used for exploring the responses of C. lividipennis to odors after dsRNA treatment. (A) Release hole. (B) The area that mirids respond to the left odor source. (C) The area that mirids do not respond. (D) The area that respond to the right odor source.