Regulating Mechanism Of IRS And PKA Genes In Insulin Signaling Pathway On Active Immunization In The Termite Reticulitermes Chinensis

Insulin regulates metabolic pathways such as glycolysis,glycogenesis,anti-lipolysis,and anti-apoptosis in insects through signal transduction pathways,thereby maintaining glucose homeostasis and lipid homeostasis.In organisms,metabolism is closely related to immunity,but the role of insulin signaling pathway in collective defense like active immunization has not been reported.Our lab found that during the active immunization of termites against entomopathogenic fungus（Metarhizium anisopliae）infestation,selenium,a trace element related to glucose and lipid metabolism,was significantly down-regulated.Further silencing of selenoprotein gene broke the active immunization of termites and significantly up-regulated the expression of several genes related to insulin signaling pathway,so we hypothesized that insulin signaling pathway might be related to active immunization of termites.In order to test this hypothesis,we used RNAi to silence the insulin receptor substrate（IRS）and protein kinase A（PKA）genes in the insulin signaling pathway in the termite Reticulitermes chinensis Snyder.In this study,we analyzed the regulation of these two genes in the process of resistance to M.anisopliae by using the"insect host-pathogenic fungi"system in order to understand the linkage between insulin signaling pathway and termite social immunity.In this study,we found that the expression of IRS gene decreased significantly after three days of dsRNA injection,and the blood glucose and triglyceride contents in the termites increased significantly.Silencing of the IRS gene increased the grooming behavior of nestmates of fungus-contaminated termites,which added the number of M.anisopliae conidia in their gut.Silencing of IRS significantly reduced the antifungal activity of the nestmates of fungus-infected termites and downregulated expression of the two immune genes Gram-negative bacteria binding protein₂（GNBP₂）and Termicin,but upregulated the expression of the apoptotic gene Caspase₈,which in turn significantly reduced the survival rate of the nestmates of fungus-infected termites and ultimately disrupted the mechanism of the active immunization in R.chinensis.After silencing the PKA gene,the blood glucose and triglyceride contents of termites significantly increased,but the cumulative duration of grooming behavior significantly decreased,the antifungal activity decreased,the expression of the three immune genes（GNBP₁,GNBP₂ and Termicin）decreased,the expression of the three apoptosis genes（Caspase₁,Caspase₃ and Caspase₈）increased,and the survival rate of termites decreased.Therefore,we also suggested that PKA gene is also involved in regulating the active immunization process of R.chinensis.In summary,silencing IRS and PKA genes involved in the insulin signaling pathway led to the abnormalities in glucolipid metabolic homeostasis,hygienic behavior and physiological immunity,thus disrupting active immunization in termites.Although IRS and PKA genes have opposite regulatory effects on hygienic behavior,the two genes participated in manipulating active immunization in termites and can be used as potential target genes for the development of termite-biocontrol agents.