Non-susceptibility genes to Bombyx densovirus type 1, Nid-1 and nsd-1, affect distinct steps of the viral infection pathway.

In the silkworm Bombyx mori, densovirus type 1 (BmDNV-1) replicates only in the midgut and causes fatal disease. Resistance to BmDNV-1 is determined by two genes, nsd-1 and Nid-1, respectively. Neither of them has been identified yet. We investigated the viral transcript by RT-PCR in inoculated silkworms carrying different sets of nsd-1 and Nid-1 genotype. BmDNV-1 transcript was not detected in nsd-1-carrying strains irrespective of existence of Nid-1 but clearly detected in strains carrying Nid-1 without nsd-1. The result suggests that nsd-1 blocks early step of infection. On the other hand, Nid-1 does not block cell and nucleus entry and viral transcription in nuclei but blocks later step in the viral infection cycle.