Construction of microsporidia-inducible GAL4/UAS-RTA system to generate resistance to Nosema bombycis in Bombyx mori.

The presence of microsporidian infections in the animal industry could result in substantial economic losses. Nosema bombycis, as the first identified species of microsporidia, poses a significant threat to the silkworm industry. Currently, there is no strain of silkworm with obvious resistance that can inhibit the proliferation of N. bombycis in silkworm rearing. In this study, we developed a microsporidia-inducible GAL4/UAS-RTA (Ricin toxin A chain) system in silkworms that confers resistance against N. bombycis. This system utilizes the microsporidia-inducible promoters of BmUGT2 and BmUGT3 genes (PUGT2 and PUGT3) to drive the expression of GAL4 gene, while RTA is driven by a UAS cis-acting element. We generated hybrid silkworms through crosses between GAL4 transgenic silkworms (PUGT2-GAL4 or PUGT3-GAL4) and UAS-RTA transgenic silkworms. Under normal conditions, these hybrid lines exhibited unaltered fundamental economic characteristics compared to wild-type silkworms. However, when exposed to N. bombycis infection, they displayed significantly enhanced resistance against microsporidia. Our research successfully demonstrated mitigation of microsporidia proliferation in transgenic individuals using the microsporidia-inducible GAL4/UAS-RTA system in silkworms. This approach not only provides a novel strategy for developing resistant strains against microsporidia but also serves as an important reference for genetically enhancing resistance against intracellular pathogens in other economically significant insects.