Abstract: Total RNA was isolated from the fully resistant silkworm (Bombyx mori) strain Qiufeng against BmDNV-Z, the highly susceptible silkworm strain Huaba and near-isogenic line BC₈ which was bred by using Qiufeng to cross with Huaba followed by successive backcrossing to Huaba till the eighth generation, respectively, and then subjected to fluorescent differential display reverse transcription PCR (DDRT-PCR). A full-length cDNA of B. mori carboxylesterase was obtained. Its expression in the midgut of the susceptible strain and the resistant strain against BmDNV-Z was analyzed by real-time fluorescence quantitative PCR at 12 h, 36 h and 72 h after administration with BmDNV-Z. The results showed that: (1) cDNA quantity of carboxylesterase in the midguts of the resistant strains reached the peak 12 h after infection. The cDNA quantity in the resistant strains BC₈ and Qiufeng were 17.714 and 3.602 times respectively that in the susceptible strain Huaba. (2) Within the same strain, there existed a remarkable difference in the detected carboxylesterase cDNA quantity at 12 h between the infected group and the control group. The expression in the resistant strains BC₈and Qiufeng were 15.08 and 3.39 times respectively that of the control group. On the other hand, the expression of carboxylesterase was quite low in the susceptible strain Huaba of both the infected group and the control group. (3) The expression of carboxylesterase varied at different time after infection. Expression in the resistant strains BC₈ and Qiufeng reached its peaks 12 h after infection, remarkably higher than those at 36 h and 72 h. There was no significant difference of the expression in the susceptible strain Huaba infected for 12 h, 36 h and 72 h. The results suggested that the expression of carboxylesterase in B. mori might be related to its resistance against DNV.

Key words: Bombyx mori, carboxylesterase gene, differential expression, near-isogenic line, RT-PCR