Non-target Host Immune Gene Modulation in Transgenic Silkworm Bombyx mori Endowed with RNAi Silence BmNPV Genes

Aim: To reveal differential expression of host- response genes activated after nuclear polyhedro virus infection in transgenic silkworm Bombyx mori larva and to show an influence of ‘BmNPV transgenes’ on expression pattern of host- response genes.

Study Design: Relative expression profile of immune genes was analysed after BmNPV infection in transgenic and non-transgenic larvae by real-time PCR.

Place and Duration of Study: Genomics Division, Seribiotech Research Laboratory, Bangalore, India; 2014 January – 2016 December.

Methodology: Expression of immune genes encoding components of Toll and melanisation pathways was analysed in third instar larvae of transgenic B. mori line mff118B by quantitative PCR at 0, 6, 9 and 24 h after BmNPV infection and compared with infected non-transgenic larvae. A significant difference in relative expression was analyzed by Students't – test or ANOVA and correlation in expression pattern, by linear regression in the probability distribution of Y as a function of X, at significance level P < 0.05.

Results: In transgenic larvae, survival rate after NPV infection was up to 70% compared to 30% in non-transgenic larvae. Immune genes encoding NF-kappa B inhibition factor, Cactus, NF kappa B transcription factors, Dorsal and Relish, Toll- activating cytokine Spätzle, melanization pathway components, prophenol oxidase activating enzyme and prophenol oxidase1 showed significantly lower expression in BmNPV infected- transgenic larva whereas enhanced expression in infected non-transgenic larvae. In infected transgenic larvae, selected gene pairs Cactus – Dorsal, Cactus – Relish, Spatzle - Dorsal, Spatzle - Cactus, Relish – Dorsal showed positively correlated expression whereas the correlation derailed in infected non-transgenic larvae.

Conclusion: RNA interference-mediated inhibition of BmNPV multiplication was engineered previously in B. mori. In infected transgenic silkworm, NPV multiplication rate is low and host-response genes showed low expression level. Under the influence of transgenes, host response genes showed correlated expression thus transgenes preserve specific host- gene interactions after NPV infection. Notably influence of ‘BmNPV transgenes' on expression of host response gene is a crucial revelation in the field of transgenesis to develop better antiviral resistance in silkworms.