Abstract: We developed a method of RNA interference based on bacterially expressed dsRNA in the silkworm, Bombyx mori. By inserting the target, FTZ-F1 gene fragment, between the two convergent T7 polymerase promoters in opposite orientation in L4440 dsRNA expression vector, the recombinant plasmid was formed. Then the recombinant plasmid was transformed into Escherichia coli HT115, an RNase-III deficient strain. dsRNA was extracted from the E. coli HT115 after being treated with isopropyl-β-D-thio-galactopyranoside (IPTG). RNAi treatment was performed by injecting the extracted dsRNA (25 μg) into body cavity of silkworm at the 7th day of 5th instar. The RNAi of FTZ-F1 gene resulted in 85% of the insects with delay of pupal metamorphosis and disablement in pupa formation. Real-time quantitative PCR analysis revealed that the expression of FTZF1 gene was specially inhibited after the insects were treated with dsRNA of FTZ-F1 gene. The results suggest that the bacterially expressed dsRNA has potential to be used in silkworm functional genome analysis in an economical and efficient way.

Key words: Bombyx mori, RNA interference, dsRNA, L4440 plasmid, HT115 Escherichia coli strain, metamorphosis