Genetic Trait And Gene Expression Regulation Of The Long-Winged And Short-Winged Morphs In Rice Planthoppers

The wing dimorphism(long-winged morph and short-winged morph)is an important strategy for rice planthoppers to adapt to changing environmental conditions which is affected by both heredity and environment.Since the wing dimorphism directly related to the switch between migratory diffusion and retention reproduction for the rice planthopper,this phenomenon has attracted extensively attention.The switch genes for wing dimorphism and their modes of action have been identified,and the molecular mechanisms of the regulation of the long-winged and short-winged morph of the rice planthopper have been revealed.Previous studies have shown that there is a genetic basis and an environmental induction effect for wing dimorphism of rice planthopper,and there are various genes and environmental conditions involved in wing dimorphism regulation.Thus,it is suggested that the decision of wing type of the rice planthopper may be controlled by an intricate network of genes.To explore the network of heredity-environment factors in wing dimorphism of rice planthopper and the expressin pattern of some related genes in the long-winged and shortwinged strains of rice planthopper,the nearly pure-bred or pure-bred strains of long-winged and short-winged strains of the three rice planthoppers including N.lugens,S.furcifera and L.striatellus were established as experimental material through targeted inbreeding for successive generations.The pure-bred and nearly pure-bred strains were used for explore the hybrid genetic rule of wing dimorphism,the differences in biological and ecological characteristics between long-winged and short-winged stains,the response for environmental conditions of the offspring of pure-bred strains,the transcriptome differences between two strains during development stages and the expression differences of several genes realated to wing dimorphism.The results will provide evidence to determine the complex regulatory approaches of wing dimorphism in rice planthopper.The results are as follows:1.Selection of long-winged and short-winged pure-bred strains of rice planthopperThe long-winged and short-winged strain were established through sibling inbreeding for successive generations under a constant condition using rice seedlings.The screening process shows that the pure-bred long-winged strain with 100%long-winged morphs of L.striatellus were obtained by directional screening of 7 successive generations;the pure-bred short-winged strain of S.furcifera were obtained by directional screening of 12-15 successive generations and the long-winged strain of S.furcifera were obtained by directional screening of 8-13 successive generations;the pure-bred short-winged strain of N.lugens were obtained by directional screening of 14 successive generations and the long-winged strain of N.lugens were obtained by directional screening of 68 successive generations.The wing dimorphism of the rice planthopper showed a significant response to screening under a constant condition.2.The inheritance law of wing form in N.lugens and S.furciferaThe hybridization experiments between long-winged and short-winged strains were carried out in N.lugens and S.furcifera respectively,and the wing form ratio of the hybrid offspring was investigated.The experimental results showed the short-winged morphs rate in the hybrid offspring is between that of their parents.The short-winged morphs rate of the orthogonal progeny and the reciprocal progeny in S.furcifera were about 50%and 25%,respectively.The short-winged morphs rate of the orthogonal progenies of N.lugens was more than 70%,but no progenies were obtained in the two reciprocal experiments.It is suggested that the wing form of the N.lugens and S.furcifera are genetically regulated,and the regulated genes are probably located on the sex chromosome.3.Differences in biological characteristics between long and short winged strains of N.lugens and S.furciferaThe reproduction rate,survival rate,evelopment duration,length of wing bud,nymph weight and sex ratio of the population from the long-and short-winged strains were measured in pure-bred and nearly pure-bred strains of N.lugens and S.furcifera.The results of comparative analysis showed that for N.lugens and S.furcifera there were no significant differences between the two strains in the survival rate of nymphs,sex ratio and fecundity,but there were significant differences in nymph duration and wing bud length.The nymph duration of the short-winged strain of the furcifera was longer than the long-winged strain,while the long-winged strain of the N.lugens was longer than that of the short-winged strain.The length of wing bud of 5th-instar nymphs of short winged individuals from long-winged strains was significantly longer than that of short winged individuals from short-winged strains,but for long winged individuals,there was no significant difference in the length of wing buds in 5th-instar nymph stage.4.Response of pure or near pure stain of N.lugens to environmental factorsLong-winged and short-winged pure-bred strain or near pure-bred strain were reared with different nymph densities on rice at seedling,tillering and yellow maturity stages or artificial diets with controlled amino acid content,and the proportion of individuals with two wing forms was statistically analyzed.The results showed,the wing form of the progenies of the long-winged and shor-winged strain was not affected by nymph density in N.lugens and S.furcifera,the wing form of female individuals was not affected by the growth period of rice,but the wing form of male individuals was affected,the ratio of long winged male individuals raised on rice at yellow ripeness stage was higher.The wing form of the progenies of the long-winged strain of L.striatellus was not affected by nymph density and rice growth period.The wing form of the progenies of the long-and short-winged strains of N.lugens was not affected by the content of amino acids in the artificial diet.The wing form of shortwinged strain was affected by temperature,but the wing form of long-winged strain was not.The results showed that the pure-bred wing form strains of rice planthopper were not sensitive to the changes of environmental conditions.5.Transcriptome differences between long-winged and short-winged strains of N.lugensThe samples of eggs,3rd-instar nymphs and adutls were collected for transcriptome analysis when the proportion of wing form wing form of the strain was stable.The results showed that there were significant differences in transcriptome between long-winged and short-winged strains of N.lugens in egg,3rd instar nymph and adult stage.A total of 6523 differentially expressed genes were found between the long-winged and short-winged strain at three developmental stages which are mainly involved in regulation of actin cytoskeleton,focal adhesion,tight junction and adherens junction.There were 13606,14706 and 15683 differentially expressed genes among egg stage,3rd instar nymph stage and adult stage,respectively,and these genes mainly involved in insulin signaling pathway,metabolic pathway,amino sugar and nucleotide sugar metabolism and glycolysis/gluconeogenesis pathway.6.The difference of gene expression patterns between long-winged and short-winged strains of N.lugens and S.furciferaThe long-winged and short-winged strains with stable proportion of wing form were used as materials,quantitative PCR was used to determine the relative expression level of the genes related to wing form in different instars or tissues of long-winged and short-winged strains.The results showed that the expression levels of genes related to wing form in N.lugens and S.furcifera were significantly affected by the strain and the age.The relative expression levels of Chico,Akt and tor genes were significantly lower in the long-winged strain than in the short-winged strain at the egg,3rd-instar nymph and adult stages;vitellognin,srf,FOXO and flightin genes were only different in the adult stage;hth,InR1,InR2 and Pten genes were differentially expressed only in the egg stage or the 1st-instar nymph stage.The differences of expression level of these genes were related to the wing dimorphism determination of N.lugens.The expression levels of 10 genes related to wing devepment in S.furcifera were determined,there was no significant difference in distal-less gene between the long-winged and short-winged strain,except that there were significant differences in the expression levels of the other nine genes including apterous,fringe,hth,scalloped,serum response factor,vestigial,wingless,InR1 and InR2 between the long-winged and short-winged strain of at a certain nymph instar and adult stage.These genes were highly expressed in the wing buds of the 5th-instar nymph of the long-winged strain of the S.furcifera.The wing form of rice planthopper was regulated by two types of genes differentially expressed in whole developmental stages and differentially expressed in certain developmental stages.In conclusion,pure-bred wing form strain of the rice planthoppers could be obtained with long-term screening under stable conditions,the pure-bred wing form strains were not sensitive to the change of environmental conditions,and there wing form was determined by genetic factors.There were significant transcriptome differences in the long-winged and short-winged strain of rice planthopper,and there were significant differences in the expression level of wing related genes between the two strains.The expression level of multiple genes in different developmental stages regulated the wing form of rice planthopper.