Modulation of NPV gene expression pattern and retention of RNAi- based antiviral activity in inbred transgenic silkworm

Infections due to Bombyx mori nucleopolyhedro virus ( Bm NPV) in commercially important silkworm, Bombyx mori L. (Lepidoptera: Bombycidae) causes up to 50% loss to silk production in India. Increased resistance to NPV through introduction of double stranded RNA transgenes against multiple NPV genes is reported in B. mori . However, stability of the RNAi - mediated antiviral activity has not been determined after several generations of inbred transgenic B. mori . Hence, we examined the NPV multiplication rate and induction of the disease symptoms in NPV- infected transgenic and non-transgenic silkworm after 35 generations. Significantly higher multiplication rate of NPV supported by higher copy number of gp-41 gene was observed in non- transgenic larvae as compared to transgenic larvae. Expression of NPV genes, ie-1, lef1 and p74 enhanced significantly in non-transgenic larva as compared to transgenic larva after NPV infection. Strong positive correlation was observed in the expression pattern of NPV genes in transgenic larvae which was absent in non-transgenic larvae. This indicated co-regulation of NPV gene expression in the presence of transgenes.