Insulin Receptor Substrate is Involved in Regulating Active Immunization of the Subterranean Termite Reticulitermes Chinensis Against Fungal Infections

Insulin receptor substrate (IRS) proteins are key mediators in insulin signaling pathway. In social insect lives, IRS proteins played important roles in caste differentiation and foraging, but its function in disease defenses such as active immuniztion has not been reported yet. We successfully silenced the IRS gene 3 days after dsRNA injection. Silencing IRS gene down-regulated the expression of its downstream genes phosphatidylinositol 3-kinase ( PI3k ) and Akt serine / threonine kinase / protein kinase B ( AKT/PKB ) in the insulin signaling pathway, and reduced the triglyceride content in termites. Then we tested the effect of IRS silencing on behavioral and physiological responses during active immunization in termites. IRS silencing significantly enhanced grooming behaviors of nestmates of fungus-contaminated termites and hence increased the conidial load in the guts of the the nestmates. IRS silencing significantly reduced the antifungal activity of nestmates of fungus-contaminated termites, together with the downregulation of the immune genes Gram-negative bacteria-binding protrin2 ( GNBP2 ) and termicin and upregulation of the apoptotic gene caspase 8 . The above abnormal behavioral and physiological responses significantly decreased the survival rate of ds IRS -injected nestmates of the fungus-contaminated termites. These findings suggest that IRS is involved in regulation of active immunization in termites, providing a better understanding of the link between insulin signaling and social immunity of termites.