Response Of Silkworm Immune Signal Pathway Against BmNPV And BmBDV Infection

Bombyx mori,as an important economic insect,is a good model organism as well which provides a good model for genetics and pathology.The virus infection caused by Bombyx mori nuclear polyhedrosis virus?BmNPV?is a serious threat to the production of sericulture,which accounts for more than 60%of the total silkworm disease.So far,the sericulture is still in the prevention stage.A highly resistant silkworm strain NB was obtained by anti-BmNPV screening of 344 kinds of silkworm strains,followed by hybridization and backcross with susceptible strain 306,the near isogenic lines Huaba_BC8C8 of 306 strain was constructed being the resistant strain.A series of researches of screening the resistance genes have been conducted at the DNA,RNA and protein levels,but no genes with significant resistance function were obtained.In addition,the Bombyx mori bidensovirus?BmBDV?,the only species of virus of Bidnaviridae,has been identified as the representative specie of the Bidensovirus,which is highly typical.In this study,BmNPV virus was used to infect silkworms,and the transcriptional level of immune signal pathway components in susceptible and resistant strains was detected by real-time PCR.The differences in the expression patterns between the susceptible and the resistant strain were analyzed in order to filter out the pathway elements in the immune signaling pathway hoping to clarify the resistance mechanism of the resistant silkworm strain to the BmNPV infection.Meanwhile,we explored whether there are some similar rules when another DNA virus BmBDV infected Bombyx mori.After analyzing the gene sequence of selected pathway element that may have anti-BmNPV function from different strains of silkworm,we made further effort to identify and evaluate its anti-BmNPV function at the cellular level.The main results are as follows:1.After BmNPV infected silkworms,12 Toll signal pathway related signal factors,6 Imd signal pathway related signal factors and 7 Jak-STAT signal pathway related signal factors were detected by qPCR.It was found that BmNPV infection could activate the immune response of the Toll pathway and Jak-STAT pathway in the silkworm,and the expression of suppressor of cytokine signaling gene BmSocs 2 in the resistant silkworm strain NB and the near isogenic line Huaba_BC8C8 was significantly higher than that of the susceptible strain 306.2.When BmBDV infected silkworm,after detecting 12 Toll signal pathway related signal factors,6 Imd signal pathway related signal factors and 7 Jak-STAT signal pathway related signal factors with the similar method mentioned above,some similarities were found.BmBDV infection could lead to the activation of Toll pathway and Jak-STAT pathway in silkworm as well,and BmSocs 2 is highly expressed in the BmBDV resistant strain silkworm Huaba_BC7.3.The gene of silkworm BmSocs 2 was cloned from the BmNPV susceptible silkworm strain 306,the resistant silkworm strain NB and Huaba_BC8 to investigate whether the cause of the differential expression was due to the difference in the gene sequence between the different silkworm strains.It was found that the sequence of BmSocs 2 gene was consistent in three silkworm strains.When compared with the published BmSocs 2 gene in the silkworm strain Dazao,8 base sequences were found to be mutated,but their amino acid sequences were identical.After bioinformatics analysis,it was found that BmSocs 2 protein has the SH2 domain that is responsible for the signal transduction and the SOCS box acting as a bridge between specific substrate-binding domains and more generic proteins,and there were several potential phosphorylation sites.All these results indicate that the BmSocs 2 gene may conservative and played an important signal transduction role in the Jak-STAT signaling pathway.4.The recombinant eukaryotic expression plasmid containing BmSocs 2 gene was constructed to transfect the silkworm ovarian cell BmN.Through the over expression experiment in vitro,it was studied whether BmSocs 2 have the anti-BmNPV function.The results showed that BmSocs 2 did play an important role in resistance to the BmNPV infection at the cellular level.