The Ligands Indentification And The Fuction Analysis Of Sugar Receptor HaLgrl In Helicoverpa Armigera (Hiibner) Larvae

The contents of plant compounds may dermine the feeding of lepidopteran larvae,in which taste play an important role in the process of feeding preferference.Sugars as one of the original energy resources are important feeding phagostimulants of insects.But the mechanism of gustatory perception of larvae is not clear.The cotton bollworm Helicoverpaarmigera is one of the most serious pests in China and also one of the research models of lepidopteran insects.Study on the sugar receptor neurons,the indentification of sugar receptor and the fuction analysis may provide important cue on the guatatory perceptionmechanism of the polyphagous species H.armigera^ and on the evolution between insects and plants.In this study,the electrophysiological responses,sugar receptor,ligands,and the feeding preference of H.armigera larvae were invesitgted by methods of molecular biology,electrophysiology and ehavior bioassay.(1)A segment of gustatory receptor gene was cloned,named Helicoverpa armigera larvae gustatory receptor 1(HaLgrl).The RNAi was conducted by feeding H.armigeralarvae on dsRNA of HaLgrl,with am aim of post-transcriptional gene silencing(PTGS).Then the effects on the electrophysiological response and the feeding preference of larvaewere investigated.(2)The HaLgrl gene can express in different organs of H.armigera in different developmental stages,especially highly expressed in the midgut,the forgut,the sensilla styloconica of mouthpart,and the eggs.The 3rd instar larvae were exposed to artificial dietscontaining Ijig,10|ig,30jxg, 50|j,g dsRNA of HaLgrl,respectively.The relative expression levael of HaLgrl were investigated 24 h,36h,48 h,60h,and 72h after the previous 72 h feeding on 10 p,g dsRNA.Compared to normal larvae,the relateive expression levels of HaLgrl in larvae fed on any dose dsRNA dsRNA were low at any time tested.(3)Results of electrophysiological responses showed that the mean response frequency of the medial seasillum of larvae fed on dsRNA of HaLgrl were significantly lower than that in the control larvae in the response to trehalose,fructose and myo-inositol,while that of the lateral sensillum of larvae fed on dsRNA was more sensitive to glucose compared to the control larvae.(4)By using two-choice leaf-disc bioassay,the normal larvae preferred significantly to feeding on sugar-treated leaf discs.However,the larvae fed on dsRNA of HaLgrl were not siginificantly different in the feeding preferences between sugar-treted leaf-disc and the control leaf-disc.(5)Combined the results of HaLgrl expression,electrophysio logical response and behavior bioassay,the gustatory receptor of HaLgrl had a significant effects on the gustatory response and feeding preference of H.armigera larvae to trehalose.In addition,the receptor is also releted to the perception of fructose,glucose,sucrose and maltose.Therfore,the HaLgrl may be a receptor with a broad spectrum of sugar ligands.