Multi-targets cleavage of BmNPV genome through genome-wide repeat sequence using CRISPR/Cas9 antiviral system.

The escalating severity of Bombyx mori nuclear polyhedrosis virus (BmNPV) infections poses significant challenges to the silkworm industry, especially when massive production shifts occur from the eastern regions to western regions with lower labor costs. Education and experience levels are different and disease control is badly needed. To solve the problems, we have developed an innovative CRISPR/Cas9 system specifically targeting BmNPV to enhance viral resistance. For the system, we selected BmNPV genes linked to virus replication and proliferation as targets, designing 2 sites for each gene. Mutating the target sequence renders the system incapable of efficiently cleaving the virus genome, hence decreasing cleavage efficiency. We conducted a search for "NGG" or "CCN" target sequences in the BmNPV genome, excluding non-recurring and potential targets in the B. mori genome. We successfully identified 2 distinct target sequences in the BmNPV genome-one being repeated 12 times and the other three times. These sequences lead to fragmentation of virus genome into multiple large segments that are difficult to repair. Transgenic silkworms demonstrate robust resistance to viruses, significantly boosting their survival rates compared with wild-type silkworms under various virus infection concentrations. Our system efficiently targets dozens of viral genomes with just 2 sequences, minimizing transposable elements while ensuring cutting effectiveness. This marks a pioneering advancement by using repetitive elements within the virus genome for targeted CRISPR cleavage, aiming for antiviral effects through genome fragmentation rather than disrupting essential viral genes. Our research introduces innovative concepts to CRISPR antiviral investigations and shows promise for the practical application of gene editing in industrial silkworm strains.