The Mechanisms Of Gram-negative Binding Proteins(GNBPs) Involved In The Defense Of The Locust,Locusta Migratoria Manilensis,Against Fungal Infection

Generally,insects lack of acquired immunity,whereas they have effective innate immunity,which may help to restrain or kill the invaded pathogens.The locust,Locusta migratoria manilensis,as one of major agricultural pests and a model organism for physiological and behavioral research in insects,has been caused many attentions.The entomopathogenic fungus Metarhizium acridum is an environmental-friendly biocontrol agent,and has been widely used to suppress agricultural and forestry pests,including the locust.This study will further explore the mechanism of locust against Metarhizium acridum,expecting to provide theoretical and practical supports for the application of M.acridum.The pattern recognition proteins(PRRs)may recognize and bind to the pathogen-associated molecular patterns(PAMPs).The immune system of insects will be activated after such binding,then the invaded pathogenic microorganisms may be killed or removed through their cellular or/and humoral immunity.Gram-negative binding proteins(GNBPs),known as ?-1,3-glucan recognition proteins(?GRPs),can perceive fungal infection and activate immune response.Three GNBPs have been found in Locusta migratoria manilensis,and named them by GNBP1,GNBP2 and GNBP3 respectively.Tissue distribution of GNBPs indicated that GNBP1 and GNBP3 mainly located in the hemocyte,while GNBP2 mainly located in the midgut.We speculated that GNBP1 and GNBP3 might participate in the process of immune recognition,while GNBP2 as a hydrolase which might participate in the digestive process.The results showed that expression of GNBP3 gene was reduced more than 90% at transcriptional level after 24 h with the injection of dsRNA,a similar decrease of GNBP3 protein through immunoblot analysis.Further,the low level of GNBP3 protein resulted in a significant decrease in the activation of the Toll pathway,the activity of phenol oxidase(PO),the number of nodules formation and the ability of resistance to fungi.These results indicated that GNBP3 might resist fungal infection by activating the PO and Toll pathway.After 24 h of the injection of GNBP1 dsRNA,transcription level and protein level of GNBP1 were also effectively reduced.Although the PO activity increased slightly,the capability of resistance to fungi was not affected.In this project,the mechanism of GNBPs involved in the immune response mechanism was investigated.The results may provide base for a further study of insect resistance to pathogenic fungi,and improve the development of new insecticidal pesticides.