Comparison of the signaling pathways of wing dimorphism regulated by biotic and abiotic stress in the brown planthopper

Wing polymorphism is an evolutionary trait that is widely present in various insects and provides a model system for studying the evolutionary significance of insect dispersal.The brown planthopper(BPH,Nilaparvata lugens)can alter its wing morphs un-der biotic and abiotic stress.However,whether differential signaling pathways are induced by the 2 types of stress remain largely unknown.Here,we screened a number of candidate genes through weighted gene co-expression network analysis(WGCNA)and found that ornithine decarboxylase(NIODC),a key enzyme in the synthesis of polyamines,was as-sociated with wing differentiation in BPH and mainly responded to abiotic stress stimuli.We analyzed the Kyoto Encyclopedia of Genes and Genomes enrichment pathways of dif-ferentially expressed genes under the 2 stresses by transcriptomic comparison,and found that biotic stress mainly influenced insulin-related signaling pathways while abiotic stress mainly influenced hormone-related pathways.Moreover,we found that insulin receptor 1(NllnRI)may regulate wing differentiation of BPH by responding to both biotic and abiotic stress,but NllnR2 only responded to biotic stress.Similarly,the juvenile hormone epoxide hydrolase associated with juvenile hormone degradation and NIODC may regu-late wing differentiation mainly through abiotic stress.A model based on the genes and stresses to modulate the wing dimorphism of BPH was proposed.These findings present a comprehensive molecular mechanism for wing polymorphism in BPH induced by biotic and abiotic stress.

Relative contribution of genetic and environmental factors to determination of wing morphs of the brown planthopper Nilaparvatalugens

Wing dimorphism is a fascinating feature of the ability of insects to adapt to environments.The brown planthopper(BPH)Nilaparvata lugens,a serious pest of rice,can switch between the long-and short-winged morphs.It has been known that environmental factors can affect the wing morph of BPH.However,it is still unclear whether the effect of environment is dependent on BPH genetic backgrounds or not.In the present study,we established the pure-bred lineages of short-and long-winged BPHs via multigenerational selection,and we found that survival and fecundity were similar between these 2 lineages.Wing morphs of the pure-bred lineages were almost fully dependent on genetics,but independent of the environmental factors,nymphal density and rice plant stage,2 key factors affecting BPH wing morphs.In the unselected BPH population,short-and longwinged morphs were produced depending on those 2 environmental factors,indicating the contribution of environment to wing morph.In the wing-selected lineages,4 developmental regulated genes of wing,NllnRI,NllnR2,NIAkt,and NIFoxo were expressed stably in the short-winged adults,but almost silenced in the long-winged adults.However,all these genes were expressed normally with a similar level in both the short-and long-winged adults in an unselected population except NlFoxo.The pure-bred lineages of long-and short-winged morphs exhibited different expression patterns of wing development-regulated genes,suggesting the genetic determination of wing morphs.Effects of environmental factors on wing morphs occurred only in the genetic mix population.

Molecular characterization, tissue and developmental expression profiles of cryptochrome genes in wing dimorphic brown planthoppers, Nilaparvata lugens

Cryptochromes （CRYs） are blue and UV light photoreceptors, known to play key roles in circadian rhythms and in the light-dependent magnetosensitivity of insects. Two novel cryptochrome genes were cloned from the brown planthopper, and were given the designations of Nlcryl and Nlcry2, with the accession numbers KM108578 and KM108579 in GenBank. The complementary DNA sequences ofNlcryl andNlcry2 are 1935 bp and 2463 bp in length, and they contain an open reading frame of 1629 bp and 1872 bp, encoding amino acids of 542 and 623, with a predicted molecular weight of 62.53 kDa and 70.60 kDa, respectively. Well-conserved motifs such as DNA-photolyase and FAD-binding-7 domains were observed in Nlcry1 and Nlcry2. Phylogenetic analysis demonstrated the proteins of Nlcry1 and Nlcry2 to be clustered into the insect＇s cryptochrome 1 and cryptochrome 2, respectively. Quantitative polymerase chain reaction showed that the daily oscillations of messenger RNA （mRNA） expression in the head of the brown planthopper were mild for Nlcryl, and modest for Nlcry2. Throughout all developmental stages, Nlcryl and Nlcry2 exhibited extreme fluctuations and distinctive expression profiles. Cryptochrome mRNA expression peaked immediately after adult emergence and then decreased subsequently. The tissue expression profiles of newly emerged brown planthopper adults showed higher expression levels of CRYs in the head than in the thorax or abdomen, as well as significantly higher levels of CRYs in the heads of the macropterous strain than in the heads of the brachypterous strain. Taken together, the results of our study suggest that the two cryptochrome genes characterized in the brown planthopper might be associated with developmental physiology and migration.

Morph-specific differences in metabolism related to flight in the wing-dimorphic Aphis gossypii

The cotton aphid, Aphis gossypii Glover, is a wing-dimorphic species, which causes globally important agricultural losses. In this present study, we compared the biochemical basis of wing polymorphism in A. gossypii with respect to trade-off of energy resources, including glycogen, trehalose, lipids （total lipid, triglyceride and phospholipid）, free fatty acids, and soluble protein between dispersal and reproduction morphs during the wing-bud nymph and adulthood. Total lipid, triglyceride and free fatty acids were significantly higher in winged versus wingless morphs at 12 h of adulthood, the period during which alates are able to fly. By contrast, the wingless morph contained more glycogen than the winged morph from the 4th nymphal stage to adulthood. Trehalose content in the wingless morph was also higher than that in the winged morph during the 3rd and 4th nymphal stages, but vice versa at 12 h of adulthood. Finally, soluble protein content increased from nymphs to adults and was higher during adulthood in aptera versus alate. Whole-body water content in 12-h adults was significantly higher in apterae than that in alatae. These results indicate significant physiological differences between morphs related to specialization for flight.