Decrease in the expression level of the gene encoding the putative Bombyx mori bidensovirus receptor during virus infection.

Bombyx mori bidensovirus (BmBDV) is a pathogen that replicates only in the midgut columnar cells of silkworms, causing fatal disease. Resistance to BmBDV, which does not depend on the viral dose, is determined by a single gene, nsd-2 (resistance gene). Previously, we identified nsd-2 by positional cloning using B. mori genome information and found that this gene encodes a putative amino acid transporter that may function as a receptor for BmBDV. In this study, to understand the relationship between BmBDV and the putative virus receptor, we performed expression analysis of + (allele of nsd-2; susceptibility gene) after virus infection. Quantitative RT-PCR analysis using total RNA isolated from the midgut of an uninfected and a virus-infected silkworm revealed no change in the expression levels of + in the uninfected silkworm, whereas the expression levels of + drastically decreased in the virus-infected silkworm. Moreover, comparison of the expression pattern between the BmBDV-derived transcript and + revealed that the expression level of + decreased with an increase in the virus-derived transcript. In addition, expression analysis of 26 genes encoding other transporters in the midgut demonstrated that the expression levels of three other genes also decreased similarly to the decrease of the expression levels of + after virus infection. Thus, our results suggest that some transporters, including +, are affected by BmBDV infection.