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.

Identification of a sugar gustatory receptor and its effect on fecundity of the brown planthopper Nilaparvata lugens

In insects, the gustatory system plays a crucial role in multiple physiological behaviors, including feeding, toxin avoidance, courtship, mating and oviposition. Gustatory stimuli from the environment are recognized by gustatory receptors. To date, little is known about the function of gustatory receptors in agricultural pest insects. In this study, we cloned a sugar gustatory receptor gene, N/Gr11, from the brown planthopper (BPH), Nilaparvata lugens (Stal), a serious pest of rice in Asia;we then identified its ligands, namely, fructose, galactose and arabinose, by calcium imaging assay. After injection of N/Gr11 doublestranded RNA, we found that the number of eggs laid by BPH decreased. Moreover, we found that N/Gr11 inhibited the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and promoted the phosphorylation of protein kinase B (AKT). These findings demonstrated that N/Gr11 could accelerate the fecundity of BPH through AMPK- and AKT-mediated signaling pathways. This is the first report to indicate that a gustatory receptor modulates the fecundity of insects and that the receptor could be a potential target for pest control.

FoxO directly regulates the expression of TOR/S6K and vitellogenin to modulate the fecundity of the brown planthopper

As a conserved transcription factor,FoxO plays a crucial role in multiple physiological processes in vivo,including stress resistance,longevity,growth and reproduction.Previous studies on FoxO have focused on human,mouse,Drosophila melanogaster and Caenorhabditis elegans,while there are few reports on agricultural pests and little is known about how FoxO modulates insect fecundity.In Asia,the brown planthopper(BPH)Nilaparvata lugens(St?l)is one of the most serious pests in rice production and high fecundity is the basis of the outbreak of BPH.Here,using the genome-wide ChIP-seq of NlFoxO in BPH,we found that NlFoxO binds to the promoters of ribosomal protein S6 kinase(NlS6K)and serine/threonine-protein kinase mTOR(NlTOR)and increases their expression levels.We also found that NlFoxO directly binds to the exon of vitellogenin(NlVg)and has a specific inhibitory effect on its expression.In addition,the number of eggs laid and their hatching rate decreased significantly after injection of NlFoxO double-stranded RNA into BPH adults.Our findings provide direct evidence that FoxO modulates insect fecundity through binding to the promoters of NlS6K,NlTOR and the exon of NlVg and affecting their gene expression in the Vg network.

Population density modulates insect progenitive plasticity through the regulation of dopamine biosynthesis

Insect fecundity is a quantitative phenotype strongly affected by genotypes and the environment.However,interactions between genotypes and environmental factors in modulating insect fecundity remain largely unknown.This study investigated the im-pact of population density on the fecundity of Nilaparvata lugens(brown planthopper;BPH)carrying homozygous high-(HFG)or low-(LFG)fecundity homozygous geno-types.Under low population densities,the fecundity and population growth rate of both genotypes showed similar increasing trends across generations,while the trends between HFG and LFG under high population densities were opposite.Through a combination of temporal analysis and weighted gene co-expression network analyses on RNA-seq data of HFG and LFG under low and high population densities in the lst,3rd,and 5th gener-ations,we identified 2 gene modules that were associated with these density-dependent progenitive phenotypes.Four pathways related to the neural system were simultaneously enriched by the 2 gene modules.Furthermore,Nlpale,which encodes a tyrosine hydroxy-lase,was identified as a key gene.The RNA interference of this gene and manipulation of its downstream product dopamine significantly affected the basic and density-dependent progenitive phenotypes of BPH.These findings indicated that dopamine biosynthesis is the key regulatory factor that determines fecundity in response to density changes in dif-ferent BPH genotypes.Thus,this study provides insights into the interaction of a typical environmental factor and insect genotype during the process of population regulation.

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.