The temporal-spatial expression and functional analysis of three gustatory receptor genes in Solenopsis invicta using sweet and bitter compounds

The insect gustatory system participates in identifying potential food sources and avoiding toxic compounds.During this process,gustatory receptors(GRs)recognize feeding stimulant and deterrent compounds.However,the GRs involved in recognizing stimulant and deterrent compounds in the red imported fire ant,Solenopsis invicta,remain unknown.Therefore,we conducted a study on the genes SinvGR1,SinvGR32b,and SinvGR28a to investigate the roles of GRs in detecting feeding stimulant and deterrent compounds.In this current study,we found that sucrose and fructose are feeding stimulants and the bitter compound quinine is a feeding deterrent.The fire ant workers showed significant behavior changes to avoid the bitter taste in feeding stimulant compounds.Reverse transcription quantitative real-time polymerase chain reaction results from developmental stages showed that the SinvGR1,SinvGR32b,and SinvGR28a genes were highly expressed in fire ant workers.Tissue-specific expression profiles indicated that SinvGR1,SinvGR32b,and SinvGR28a were specifically expressed in the antennae and foreleg tarsi of workers,whereas SinvGR32b gene transcripts were also highly accumulated in the male antennae.Furthermore,the silencing of SinvGRI or SinvGR32b alone and the co-silencing of both genes disrupted worker stimulation and feeding on sucrose and fructose.The results also showed that SinvGR28a is required for avoiding quinine,as workers with knockdown of the SinvGR28a gene failed to avoid and fed on quinine.This study first identified stimulant and deterrent compounds of fire ant workers and then the GRs involved in the taste recognition of these compounds.This study could provide potential target gustatory genes for the control of the fire ant.

Identification and expression profiles of gustatory receptor genes in Bactrocera minax larvae(Diptera:Tephritidae):Role of BminGR59f in larval growth

Insects employ various types of gustatory receptors(GRs)to identify nutrient-rich food and avoid toxic substances.The larval gustatory system is the critical checkpoint for food acceptance or rejection.As a specialist herbivore,the larvae of Bactrocera minax feed only on unripe citrus fruits.However,how larvae use GRs to check and adapt to the secondary metabolites in unripe citrus fruits remains unknown.In this study,we first performed developmental expression profiles showing that most BminGRs genes were highly expressed in 1st and 2nd instar larvae and that tissue-specific expression indicated high expression of most BminGRs genes in the mouthparts of 2nd instar larvae.Furthermore,we found that silencing BminGR59f by RNA interference(RNAi)affected the growth of 2nd instar B.minax larvae.Hesperidin and naringin were screened as ligands of BminGR59f via RNAi and cell calcium imaging,and the combination of these two flavones increased the body weight of larvae.In summary,we identified a novel gustatory perception pattern in B.minax for detecting hesperidin and naringin,which boosted the growth of B.minax larvae.These results shed light on how specialist herbivores detect and adapt to host metbolites in adverse environments depending on larval GRs.

Ligand dose-dependent activation of signaling pathways through the gustatory receptor NlGr11 linked to feeding efficacy in Nilaparvata lugens

Insects often face both conditions with sufficient nutrients and conditions of undernutrition in the field.Through gustatory receptors,insects sense nutrients and regulate their physiological functions such as feeding and reproduction.However,it remains unclear whether signaling pathways activated by gustatory receptors depend on the concentration of nutrients and whether the difference in signaling pathways directly affects insects’physiological functions.Herein,we found that a sugar gustatory receptor,NlGr11,from the brown planthopper(BPH),Nilaparvata lugens,activated G protein-coupled signaling and ionotropic pathways when bound to high galactose concentration.BPHs subsequently demonstrated longer feeding times,feeding loads,and higher vitellogenin(NlVg)expression than BPHs exposed to high galactose concentrations,which only activated the ionotropic pathway.For the first time,our findings link plant nutrient conditions,signaling pathways activated by nutrients,and their gustatory receptors,and nutrient dose-dependent feeding efficacy and vitellogenin(Vg)expression in an insect.This will help us to better understand the molecular mechanism for insect feeding strategies on plants at different stages of nutritional conditions.

Galactose-N/Gr11 inhibits AMPK phosphorylation byactivating the PI3K-AKT-PKF-ATPsignaling cascade viainsulin receptor and Gβγ

As ligands of the sugar gustatory receptors,sugars have been known to activatethe insulin/insulin-like growth factor signaling pathway;however,the precise pathways thatare activated by the sugar-bound gustatory receptors in insects remain unclear.In this study,we aimed to investigate the signaling cascades activated by NlGr11,a sugar gustatory re-ceptor in the brown planthopper Nilaparvata lugens(Stal),and its ligand.Galactose-boundNGrl1(galactose-NIGr11)activated the-phosphatidylinositol 3-kinase(PI3K)-AKT signaling cascade via insulin receptor(InR)and Gβγin vitro.In addition,galactose-NlGr11inhibited the adenosine monophosphate-activated protein kinase(AMPK)phosphorylationby activating the AKT-phosphofructokinase(PFK)-ATP signaling cascade in vitro.Impor-tantly,the InR-PI3K-AKT-PFK-AKT signaling cascade was activated and the AMPKphosphorylation was inhibited after feeding the brown planthoppers with galactose solu-tion.Collectively,these findings confirm that NIGr1l can inhibit AMPK phosphorylationby activating the PI3K-AKT-PFK-ATP signaling cascades via both InR and GBy whenbound to galactose.Thus,our study provides novel insights into the signaling pathwaysregulated by the sugar gustatory receptors in insects.

A fructose receptor gene influences development and feed intake in Helicoverpa armigera

Gustatory receptors(GRs)are critical for multiple life activities of insects.Owing to the rapid development of genome and transcriptome sequencing,numerous insect GRs have been identified.However,the expression patterns and functions of these receptors are poorly understood.In this study,we analyzed the expression pattern of GRs in Helicoverpa armigera and found that the fructose receptor HarmGR9 was highly expressed in the foregut and abdomen.The function of HarmGR9 was identified using the clustered regularly interspaced short palindromic repeats(CRISPR)/CRISPR-associated protein 9(Cas9)system.Knockout of the HarmGR9 gene shortened the developmental period of the larval stages and increased food consumption in both larvae and adults.This study revealed the tissue distribution of sugar-sense-related receptors in H.armigera and thereby expanded the understanding of insect feeding regulation.

The genome sequence of a spider mite,Tetranychustruncatus, provides insights into interspecific host rangevariation and the genetic basis of adaptation to a low-qualityhost plant

The phytophagous miteTetranychus truncatusis a serious pest in East Asiabut has a relatively narrower host range than the pest miteTetranychus urticae,which canfeed on over 1200 plant species.Here,we generated a high-quality chromosomal levelgenome ofT.truncatusand compared it with that ofT.urticae,with an emphasis on thegenes related to detoxification and chemoreception,to explore the genomic basis under-lying the evolution of host range.We also conducted population genetics analyses(in 86females from 10 populations)and host transfer experiments(in 4 populations)to investi-gate transcription changes following transfer to a low-quality host(Solanum melongena,eggplant),and we established possible connections between fitness on eggplant and genesrelated to detoxification and chemoreception.We found thatT.truncatushas fewer genesrelated to detoxification,transport,and chemoreception thanT.urticae,with a particularlystrong reduction in gustatory receptor(GR)genes.We also found widespread transcrip-tional variation amongT.truncatuspopulations,which varied in fitness on eggplant.Wecharacterized selection on detoxification-related genes throughωvalues and found a nega-tive correlation between expression levels andωvalues.Based on the transcription results,as well as the fitness and genetic differences among populations,we identified genes po-tentially involved in adaptation to eggplant inT.truncatus.Our work provides a genomicresource for this pest mite and new insights into mechanisms underlying the adaptation ofherbivorous mites to host plants.