Abstract: 【Aim】 To study the function of two key components Dicer-1 and Argonaute-1 (Ago-1) of microRNA (miRNA) pathway in Acyrthosiphon pisum in defense against bacteria and fungi and to strengthen the knowledge of A. pisum immune system. 【Methods】 qRT-PCR was used to detect the expression levels of Dicer-1 and Ago-1 in A. pisum adults infected with the bacteria Staphylococcus aureus andEscherichiacoli, andthefungusBeauveriabassiana, respectively. After Dicer-1 and Ago-1 of A. pisum adults were silenced by RNAi through injection method followed by infection of S. aureus, E. coli and B. bassiana, the proliferation of the bacteria and the fungus and the survival rate of A. pisum adults were examined. 【Results】 The expression levels of Dicer-1 and Ago-1 in A. pisum adults injected by S. aureus, E. coli and B. bassiana were up-regulated as compared to those in the control group (treated with 0.85% NaCl solution). After RNAi of Dicer-1, the colony-forming unit (CFU) in A. pisum adults at 36 h post infection with S. aureus significantly increased as compared to that in the control group (injected with dsLTA), but there was no significant difference in the survival rate at 7 d after infection between the Dicer-1-silenced group and the control group. After RNAi of Dicer-1, the CFUs in A. pisum adults at 12 and 24 h post infection of E. coli significantly increased, but the survival rate at 7 d post infection significantly decreased, as compared with those in the control group. At 6 d after infection of B. bassiana, the fungal spores in the Dicer-1silenced group significantly increased, but their survival rate at 7 d post infection significantly decreased, as compared with those in the control group. When Ago-1 was knocked down by RNAi, the CFUs in A. pisum adults at 36 h after infection by S. aureus and 24 h after infection by E. coli were significantly higher than those in the control group, respectively, and the survival rate of A. pisum adults infected by S. aureus at 7 d post infection decreased significantly as compared with that in the control group, while the survival rate of adults at 7 d post infection by E. coli had no significant change. At 6 d after infection with B. bassiana, the Ago-1-silenced A. pisum adults bore a significantly larger amount of fungal spores than the control group, but had significantly decreased survival rate at 7 d post infection as compared with the control group. 【Conclusion】 Two crucial elements Dicer-1 and Ago-1 in mRNA pathway are involved in the immune defense of A. pisum against bacteria and fungi, particularly against bacteria.

Key words: Acyrthosiphon pisum, miRNA pathway, Dice-1, Argonaute-1, RNA interference