Construction and application of an HSP70 promoter-inducible genome editing system in transgenic silkworm to induce resistance to Nosema bombycis.

The microsporidian Nosema bombycis is an obligate intracellular parasitic fungus that causes devastating disease in sericulture. To date, no efficient biotechnological method to inhibit the proliferation of microspores has been established. Here, we developed a powerful genetic engineering technique involving microsporidia-inducible genome editing in transgenic silkworm that confers resistance to N. bombycis. This system includes an HSP70 promoter-induced expression of the Cas9 protein line and a target BmATAD3A gene line. The double-positive HSP70-Cas9(+)×sgATAD3A(+) lines were obtained by hybridization and activation of the CRISPR/Cas9 system under the condition of microsporidia infection, although it is silenced in uninfected individuals. Genome editing analysis showed that the system could efficiently edit the BmATAD3A gene and induce large deletions. It is notable that the HSP70-induced system could effectively improve the survival rate of transgenic silkworm after microsporidia infection and inhibit the expression of key microsporidia genes. Moreover, no significant developmental differences between the transgenic silkworms infected with microsporidia and normal individuals were observed. In this study, we effectively inhibited microsporidia proliferation in transgenic individuals through disruptive techniques, thereby providing a method for microsporidia treatment and prevention, paving the way for economically advantageous insect breeding.