Bombyx mori nucleopolyhedrovirus (BmNPV) that infects the silkworm, B. mori, accounts for .50% of silk cocoon crop losses globally. We speculated that simultaneous targeting of several BmNPV essential genes in transgenic silkworm would elicit a stable defense against the virus. We introduced into the silkworm germline the vectors carrying short sequences of four essential BmNPV genes in tandem, either in sense or antisense or in inverted-repeat arrangement. The transgenic silkworms carrying the inverted repeat-containing transgene showed stable protection against high doses of baculovirus infection. Further, the antiviral trait was incorporated to a commercially productive silkworm strain highly susceptible to BmNPV. This led to combining the high-yielding cocoon and silk traits of the parental commercial strain and a very high level of refractoriness (.75% survival rate as compared to ,15% in nontransgenic lines) to baculovirus infection conferred by the transgene. We also observed impaired infectivity of the occlusion bodies derived from the transgenic lines as compared to the wild-type ones. Currently, large-scale exploitation of these transgenic lines is underway to bring about economic transformation of sericulture. R NA interference (RNAi) is a mechanism by which cells silence the expression of foreign genes. This process often provides an adaptive innate immunity against viruses where double-stranded RNAs encoded by the viruses during infection act as pathogen trigger after they are taken up by the cellular RNAi machinery (Wang et al. 2006). Alternatively, this natural defense mechanism is exploited as an antiviral therapy via the artificial inhibition of the expression of essential viral genes (Leonard and Schaffer 2006). Multiple protocols of delivery of dsRNA or of constructs encoding dsRNAs in the organism are currently under assay to combat infections of various viruses. The efficiency of the assays is still challenged by the delicate setting of the proper dosage of the RNAi, the relative longevity of the effect, the occurrence of RNAi driven toxicity, and the virus-intrinsic susceptibility. A few attempts have been made in animal and plant models where the antiviral trait was installed by transgenesis to confer stable protection to the transformed individuals and to their progeny. Successes have been reached in plants ( Bucher et al. 2006;Bonfim et al. 2007;Zhang 2010) but, to our knowledge, no case has yet been reported in animals showing a stable and robust protection against a virus after a RNAi-aided antiviral trait was introduced through germline transformation.The baculovirus, Bombyx mori nucleopolyhedrovirus (BmNPV), is a major pathogen that affects silkworm rearings and hampers silk cocoon production in Asia. In India alone .50% of silk cocoon crop losses are attributed to baculovirus infection (Khurad et al. 2006). Effective treatment against the virus has been elusive due to its sturdy nature and the lack of control strategies. Interestingly, the biology of the virus is reasonably...

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Short RNAs of 21 or 22 nucleotides have been shown to mediate RNA interference. Significance and context RNA interference (RNAi) by double-stranded RNA (dsRNA) is a powerful method for preventing the expression of a particular gene. But how does dsRNA target mRNA for destruction? Using a Drosophila in vitro system, Elbashir et al. have now analyzed the molecular mechanism of RNAi and find that the dsRNA is processed into fragments of 21 or 22 nucleotides, which are the mediators of RNA. The requirement for RNA fragments of this length prevents the undesired activation of RNAi by short intramolecular base-paired structures of cellular RNAs.