Molecular characterizations and expression profiles of transient receptor potential channels in the brown planthopper, Nilaparvata lugens

Identification of amino acid residues that are crucial for afidopyropen binding to the TRPV channel of Myzus persicae (Sulzer)

Afidopyropen is highly effective against sucking insects, including the Myzus persicae, that modulates the transient receptor potential vanilloid (TRPV) channel. However, the action mechanisms of afidopyropen to the TRPV channel remain unknown. In this study, the genes encoding the Nanchung (MpNan) and Inactive (MpIav) subunits of the TRPV channel of M. persicae (MpTRPV) were cloned, and their spatiotemporal expression profiles were investigated. Then, MpTRPV was functionally expressed in Xenopus laevis oocytes, and the AA residues crucial for afidopyropen binding were identified using the two-electrode voltage clamp (TEVC) technique. The results showed that both MpNan and MpIav exhibited the highest expression in the antennae and were most abundant in the 4th instar nymphs and adults. Knockdown of these two genes by RNAi greatly increased the toxicity of afidopyropen to the aphids. Moreover, the AA residues involved in afidopyropen binding to MpNan were predicted and L412 was further identified as the key residue for binding by TEVC analysis. The results also showed that afdopyropen and pymetrozine share the same binding site. These findings lay a foundation not only for exploring the mechanisms of pest target resistance to afidopyropen and pymetrozine but also for developing new insecticides targeting the TRPV channels of pests.

miR-252 targeting temperature receptor CcTRPM to mediate the transition from summer-form to winter-form of Cacopsylla chinensis

Temperature determines the geographical distribution of organisms and affects the outbreak and damage of pests. Insects seasonal polyphenism is a successful strategy adopted by some species to adapt the changeable external environment. Cacopsylla chinensis (Yang & Li) showed two seasonal morphotypes, summer-form and winter-form, with significant differences in morphological characteristics. Low temperature is the key environmental factor to induce its transition from summer-form to winter-form. However, the detailed molecular mechanism remains unknown. Here, we firstly confirmed that low temperature of 10 °C induced the transition from summer-form to winter-form by affecting the cuticle thickness and chitin content. Subsequently, we demonstrated that CcTRPM functions as a temperature receptor to regulate this transition. In addition, miR-252 was identified to mediate the expression of CcTRPM to involve in this morphological transition. Finally, we found CcTre1 and CcCHS1, two rate-limiting enzymes of insect chitin biosyntheis, act as the critical down-stream signal of CcTRPM in mediating this behavioral transition. Taken together, our results revealed that a signal transduction cascade mediates the seasonal polyphenism in C. chinensis. These findings not only lay a solid foundation for fully clarifying the ecological adaptation mechanism of C. chinensis outbreak, but also broaden our understanding about insect polymorphism.

Reverse genetic study reveals the molecular targets of chordotonal organ TRPV channel modulators

Insecticides have been widely used for the control of insect pests that have a significant impact on agriculture and human health. A better understanding of insecticide targets is needed for effective insecticide design and resistance management. Pymetrozine, afidopyropen and flonicamid are reported to target on proteins that located on insect chordotonal organs, resulting in the disruption of insect coordination and the inhibition of feeding. In this study, we systematically examined the susceptibility of six Drosophila melanogaster mutants (five transient receptor potential channels and one mechanoreceptor) to three commercially used insecticides, in order to identify the receptor subunits critical to the insect's response to insecticides. Our results showed that iav1, nan36aand wtrw1 mutants exhibited significantly reduced susceptibility to pymetrozine and afidopyropen, but not to flonicamid. The number of eggs produced by the three mutant females were significantly less than that of the w1118 strain. Meanwhile, the longevity of all male mutants and females of nan36a and wtrw1 mutants was significantly shorter than that of the w1118 strain as the control. However, we observed no gravitaxis defects in wtrw1 mutants and the anti-gravitaxis of wtrw1 mutants was abolished by pymetrozine. Behavioral assays using thermogenetic tools further confirmed the bioassay results and supported the idea that Nan as a TRPV subfamily member located in Drosophila chordotonal neurons, acting as a target of pymetrozine, which interferes with Drosophila and causes motor deficits with gravitaxis defects. Taken together, this study elucidates the interactions of pymetrozine and afidopyropen with TRPV channels, Nan and Iav, and TRPA channel, Wtrw. Our research provides another evidence that pymetrozine and afidopyropen might target on nan, iav and wtrw channels and provides insights into the development of sustainable pest management strategies.

Genome-Wide Characterization and Gene Expression Analysis of TRP Channel Superfamily Genes in the Migratory Locust, Locusta migratoria

The TRP channel superfamily was widely found in multiple species. They were involved in many extrasensory perceptions and were important for adapting to the environment. The migratory locust was one of the worldwide agricultural pests due to huge damage. In this study, we identified 13 TRP superfamily genes in the locust genome. The number of LmTRP superfamily genes was consistent with most insects. The phylogenetic tree showed that LmTRP superfamily genes could be divided into seven subfamilies. The conserved motifs and domains analysis documented that LmTRP superfamily genes contained unique characteristics of the TRP superfamily. The expression profiles in different organs identified LmTRP superfamily genes in the head and antennae, which were involved in sensory function. The expression pattern of different life phases also demonstrated that LmTRP superfamily genes were mainly expressed in third-instar nymphs and male adults. Our findings could contribute to a better understanding of the TRP channel superfamily gene and provide potential targets for insect control.

Mining Lygus hesperus (western tarnished plant bug) transcriptomic data for transient receptor potential channels: Expression profiling and functional characterization of a Painless homolog

The transient receptor potential (TRP) family of cation channels are evolutionarily conserved proteins with critical roles in sensory physiology. Despite extensive studies in model species, knowledge of TRP channel functional diversity and physiological impact remains limited in many non-model insect species. To assess the TRP channel repertoire in a non-model agriculture pest species (Lygus hesperus), publicly available transcriptomic datasets were mined for potential homologs. Among the transcripts identified, 30 are predicted to encompass complete open reading frames that encode proteins representing each of the seven TRP channel subfamilies. Although no homologs were identified for the Pyrexia and Brivido channels, the TRP complement in L. hesperus exceeded the 13-16 channels reported in most insects. This diversity appears to be driven by a combination of alternative splicing, which impacted members of six subfamilies, and gene expansion of the TRPP subfamily. To validate the in silico data and provide more detailed analyses of L. hesperus TRP functionality, the putative Painless homolog was selected for more in depth analysis and its functional role in thermosensation examined in vitro. RT-PCR expression profiling revealed near ubiquitous expression of the Painless transcript throughout nymphal and adult development. Electrophysiological data generated using a Xenopus oocyte recombinant expression system indicated activation parameters for L. hesperus Painless homolog that are consistent with a role in noxious heat (40°-45 °C) thermosensation.

TRPA1-mediated repellency behavior in the red flour beetle Tribolium castaneum

The sensory perception of irritant chemicals results in escape and repellency behavioral patterns in insects. Transient receptor potential channels are cation channels that function as sensor proteins for several types of signals, such as light, sound, temperature, taste, as well as chemical and physical stimuli; among these, the TRPA channel is widely conserved and activated by irritant chemicals. Certain plant-derived essential oils (EOs), produced by secondary metabolism, are mixtures of volatile compounds, which are used as repellents because they contain environmentally sustainable ingredients. Citronellal, which is present in citronella EO from Cymbopogon species, is a potentially viable insect repellent; however, the repellency capability against coleopteran beetles remains limited. We investigated the citronellal-derived repellency behavior for the red flour beetle Tribolium castaneum, in which TcTRPA1 and odorant receptor co-receptor (Orco) expressions were mediated by RNA interference. Area-preference tests showed dose-dependent repellency behavior for citronellal; additionally, both TcTRPA1 and TcOrco double-strand RNA (dsRNA) micro-injection showed clear TcTRPA1 and TcOrco transcript reductions, and only TcTRPA1 dsRNA treatment significantly impaired repellency behavior. The relative expression level of the TcTRPA1 transcripts, evaluated by quantitative reverse-transcription PCR (qRT-PCR), revealed dominant expression in the antennae, indicating the antennae-expressed TcTRPA1-mediated repellency behavior.