Insulin Signaling Pathway IS Involved In Regulating Wing Polyphenism Of Pea Aphid

Aphids, which belongs to Hemiptera, live by feeding on phloem sap. Photoperiod could affect the reproductive mode of aphids. Sexual reproduction occurs when the days grow shorter in the late summer, and eggs are produced by mated female aphids for overwintering.Under long day and warm conditions, the aphid shows wing polyphenism, in which asexual aphids with an identical genetic background can produce winged or wingless progeny. Under favorable conditions, most of the aphids are wingless to focus on reproduction. Under stressful conditions, including poor host nutrition, high population density and predators, the wingless nymphs will develop into winged aphids, or adults will produce winged progeny. Aphids with different wing morphs show a fecundity-dispersal trade-off. The molecular mechanism governing the wing morph has been revealed for the migratory brown planthopper(Nilaparvata lugens); two insulin receptors in the insulin signaling(IS) pathway play a regulatory role in governing wing morph determination.However, very little is known about the molecular mechanism of developmental and physiological changes in nymphs with wing polyphenism.In this study, we compared the transcript levels of genes in the IS pathway between adult pea aphids(Acyrthosiphon pisum Harris) under high-density and low-density conditions, and between third instar wingless aphids and winged aphids. Then we used RNA interference method to identify the function of a candidate gene of IS pathway. The results are as followed:1, Ten insulin-related peptide genes, two insulin receptor genes, one insulin receptor substrate gene and two insulin-degrading enzyme genes were indentified from pea aphid genome data base.2, The expression levels of IS pathway genes showed obvious tissue variability in adult aphids and third instar aphids.3, Only Apirp5, Apinr1 and Apide1 showed obvious expression differences between high-density and low-density adult aphids.4, Several IS pathway genes showed significant expression differences between two wing-morph nymphs, especially in head and thorax.5, All expression differences of IS pathway genes between the two wing-morph nymphs showed the same trend: higher in wingless nymphs than in winged nymphs.6, Third instar nymphs with wing primordia weighed less than wingless nymphs.Embryos in the ovary of the wingless nymphs were significantly larger than those of the winged nymphs. Carbohydrate and protein contents of winged nymphs were significantly higher than those of wingless nymphs.7, Nymphs with RNA interference of Apirp5 had less weight, smaller embryos and higher carbohydrate and protein contents compared to the control group. Comparison between winged and wingless nymphs showed a similar trend. But there was no different on thorax between ds Apirp5 group and control group, so maybe Apirp5 was just related to reproductive development.These results indicate that Apirp5 is involved in embryo development and metabolic regulation in wing dimorphic pea aphid. These results gave further recognition on the roles of IS pathway on phenotypic plasticity in aphids.