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Published on: January 12, 2017
The hemolymph melanization response is related to defence against the AcMNPV infection in Bombyx mori
Tao Li1,2, Xueyang Wang1,3, Sheng Qin1,3
1Jiangsu Key Laboratory of Sericultural Biology and Biotechnology, School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu, China.
Abstract:
Melanization is mediated by the prophenoloxidase (proPO) activation cascade and plays an important role in the arthropods immune system. Previously, we found that the hemolymph of the p50 strain does not perform melanization after infection with Autographa californica multiple nucleopolyhedrovirus (AcMNPV). However, this mechanism is still unclear. In this study, the underlying mechanism of the inhibition of hemolymph melanization was investigated by analysing the AcMNPV-susceptible or -resistant silkworm strains after inoculation with AcMNPV. The results showed that the level of hemolymph melanization was higher in resistant strain C108 than in susceptible strain p50 at the late stage (72 to 120 h postinoculation). The PO activity decreased significantly at the late stage of infection (72 to 120 hpi), and the expression of BmPPO1 and BmPPO2 was downregulated in p50. However, the PO activity increased in the resistant strain C108, while the expression level of BmPPO1 and BmPPO2 displayed no significant changes. The expression of the BmPPAE gene was upregulated in two strains during viral infection. In addition, the hemolymph melanization can weaken the viral activity in vitro. Our results suggested that the silkworm hemolymph melanization response is related to defence against the AcMNPV infection.
Insights
Silkworm immune defense involves melanization, a process regulated by the prophenoloxidase (proPO) cascade. This study reveals how Autographa californica multiple nucleopolyhedrovirus (AcMNPV) affects melanization in susceptible and resistant silkworm strains.
Area of Science:
- * Insect immunology
- * Biochemistry
- * Molecular biology
Background:
- * Melanization, crucial for arthropod immunity, is mediated by the prophenoloxidase (proPO) activation cascade.
- * Previous studies indicated a lack of melanization in the p50 silkworm strain upon Autographa californica multiple nucleopolyhedrovirus (AcMNPV) infection, but the mechanism remained unclear.
- * Understanding this immune evasion strategy is vital for insect disease management.
Purpose of the Study:
- * To elucidate the mechanism behind AcMNPV's inhibition of hemolymph melanization in silkworms.
- * To compare the melanization response in AcMNPV-susceptible (p50) and resistant (C108) silkworm strains.
- * To investigate the role of proPO system genes in AcMNPV infection.
Main Methods:
- * Analysis of hemolymph melanization levels in silkworm strains post-AcMNPV inoculation.
- * Measurement of prophenoloxidase (PO) activity in hemolymph.
- * Quantitative analysis of BmPPO1, BmPPO2, and BmPPAE gene expression using RT-qPCR.
- * In vitro assessment of viral activity in the presence of hemolymph melanization.
Main Results:
- * Resistant C108 strain exhibited higher hemolymph melanization than susceptible p50 strain at late infection stages (72–120 hpi).
- * PO activity decreased in p50 but increased in C108; BmPPO1 and BmPPO2 expression was downregulated in p50 but unchanged in C108.
- * BmPPAE gene expression was upregulated in both strains during infection, and melanization reduced viral activity in vitro.
Conclusions:
- * Silkworm hemolymph melanization is a key defense mechanism against AcMNPV infection.
- * AcMNPV employs strategies to inhibit melanization in susceptible strains, likely involving downregulation of proPO system components.
- * The differential regulation of the proPO system in resistant strains highlights its importance in antiviral immunity.
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