Paralogous gene conversion, allelic divergence of attacin genes and its expression profile in response to BmNPV infection in silkworm Bombyx mori

Abstract

The genomic organization, structure and polymorphism of attacin gene within the mulberry
silkworm Bombyx mori strains have been analyzed. Genomic contig (AADK01007556) of B. mori attacin gene contains locus with two transcribed basic attacin genes, which were designated as attacin I and attacin II. Survey of the naturally occurring genetic variation in different strains of silkworm B. mori at the promoter and coding regions of two attacin genes revealed high levels of silent nucleotide variations (1- 4 % per nucleotide heterozygosity) without polymorphism at the amino acid level (nonSynonymous substitution). We also investigated variations in gene expression of attacin I and attacin II in silkworm B. mori infected with nucleopolyhedrovirus (BmNPV). Two B. mori strains, Sarupat, CSR-2 which were resistant and susceptible to BmNPV infection respectively were used in this study. Expression profiles of B. mori genes were analyzed using microarray technique and results revealed that the immune response genes including attacin were selectively up regulated in virus invaded midguts of both races. Microarray data and real-time qPCR results revealed that attacin I gene was significantly up-regulated in the midgut of Sarupat following BmNPV infection, indicating its specific role in the anti-viral response. Our results imply that these up-regulated attacin genes were not only involved in anti-bacterial mechanism, but are also involved in B. mori immune response against BmNPV infection.