Molecular Mechanism Of The Win Dimorphism Of The Brown Planthopper, Nilaparvata Lugens

Under various environmental conditions, species with the same genotype may show significant differences on external morphology and internal tissue structure. This kind of deveopmental plasticity is also a critical survival strategy for insect adaption to the environment during evolution, such as the wing dimorphism of brown planthopper (BPH, Nilaparvata lugens). The long winged morph (macroptery) has the ability to fly, and is benefitcial for population diffusion, while the short winged morph (brachyptery) is beneficial for population growth with loss of flying ability. Though the insect wing polymorphism has been extensively studied for more than half a century in certain species, including aphids, planthoppers and crikets, the molecular mechanism of this phenomenon remains unclear, In this study supported by genome and transcriptome data, we used BPH as a model organism to explore the molecular mechanism of insect wing dimorphism. The mainly results are as follows:1. Analysis of the BPH genome sequence, and genes related to wing dimorphism. We assembled a size of1.14gigabase draft BPH genome, with a scaffold N50of356.6kbp and a contig N50of24.2kbp, and predicted27,571protein-coding genes. Furthermore, we analyzed genes related to wing dimorphism, including nutrional signaling pathways, juvenile hormone synthesis pathway, wing development network, migration and circadian clock. As the results, TOR signling pathway plays key roles in fertility and hormone synthesis regulation. Two insuling receptor homologous were found in BPH genome. Wing development network is conserved in this species, and differentially expressed between two wing morphs. The genes related to migration and circadian clock are also conserved and may play roles in time compensation and orientation during migration. DNA methylation also involves in differentiations between long winged morphs and short winged morphs.2. Analysis of the BPH transcriptome, and comparison of the expression profiles between long winged and short winged morphs. Illumina sequencing produced 85,526unigenes. We compared the expression profiles between brachypterous female adults and macropterous female adults, revealing differentially expressed genes related to wing dimorphism. In the comparison between macropterous and brachypterous, genes related to muscle composition, energy metabolism and reproduction showed the most difference. Meanwhile, the wing dimorphism related genes identified in genome were comfirmed to be expressed genes in transcriptome analysis, and8of these genes showed differentially changes in the comparison of two wing morphs. Our results provide valuable transcriptional information for BPH study.3. The molecular mechanism of BPH wing dimorphism. We showed that the two BPH insulin receptors,NlInR1and NlnR2, play opposing roles in controlling long wing versus short wing development by regulating the activity of the forkhead transcription factor NlFOXO. NlnR1, via the phosphoinositol3-kinase (MPI3K)-protein kinase B (NlAkt) signaling cascade, leads to the short winged morph if inactivated. NlInR2, by contrast, functions as a negative regulator of the NlInR1-NlPI3K-NlAkt pathway. Thus, suppression of NlInR2results in the long winged morph. A brain-secreted ligand, NlILP3, initiates the insulin signaling activity that triggers development of long winged morphs. Further analysis using whitebacked planthopper and small brown planthopper showed that above regulatory pathway is a common mechanism adopted by the planthopper family. Our findings provide the first evidence of a molecular basis for the regulation of wing polyphenism in insects.4. Comparison of genes of the flight related muslces between the long winged and short winged morphs and analysis of key genes. Combined the comparisons of transcriptome and proteome, we detected a set of significantly differential expression genes between the two winged morphs, such as flightin and TpnC4. The flightin gene played key roles in maintaining indirect flight muscle structure and function exportation. Interestingly, as this gene was conserved in Pancrustacea, it provides clues as to how insects with flying apparatuses evolved from Pancrustacean ancients, and deepens our understanding of muscle differentiation in the wing dimorphism species.