Comparison of factors that may affect the inhibitory efficacy of transgenic RNAi targeting of baculoviral genes in silkworm, Bombyx mori.

Bombyx mori nucleopolyhedrovirus (BmNPV) is the primary pathogen affecting B. mori. This virus could be combated via RNAi of BmNPV genes in transgenic silkworm. However, several factors may affect the resistance of transgenic RNAi silkworm, such as the connection pattern of gene fragments and spacers ("head to head" or "tail to tail"), and the selection of promoters and target genes. In this study, we constructed several transgenic RNAi vectors using different phase genes (ie-1, helicase, gp64, and vp39) and promoters (BmNPV IE1 promoter (IE1P), IE1P combined with hr3 enhancer of BmNPV, and B. mori A4 promoter (A4P)). Transgenic lines were generated via embryo microinjection using a practical silkworm strain. We analyzed the anti-BmNPV ability, virus gene mRNA level, and BmNPV content of these transgenic larvae. The results showed that "head to head" was better than "tail to tail," IE1P combined with hr3 was better than IE1P and A4P, and an immediate early gene was the best target for RNAi.