Transgenic overexpression of bmo-miR-6498-5p increases resistance to <i>Nosema bombycis</i> in the silkworm, <i>Bombyx mori</i>

Microsporidia are unfriendly microorganisms, and their infections cause considerable damage to economically or environmentally important insects like silkworms and honeybees. Thus, the identification of measures to improve host resistance to microsporidia infections is critically needed. Here, an overexpressed miR-6498-5p transgenic silkworm line was constructed. Importantly, the survival rates and median lethal doses of the transgenic line were clearly higher after infection with <i>Nosema bombycis</i>. H&E staining and RT-qPCR analyses revealed an inhibitory effect on the proliferation of <i>N. bombycis</i> in the transgenic larvae. Metabolomics analysis further revealed the presence of 56 differential metabolites between the two lines. KEGG analysis of these 56 metabolites found that they were involved in various amino acid and vitamin metabolism pathways. Notably, VB6 metabolism was enriched among the metabolites, and the pathway was well known for its involvement in the synthesis, interconversion, and degradation of amino acids. These suggest that miR-6498-5p modifies parasitic environments to inhibit the proliferation of <i>N. bombycis</i> by affecting the host amino acid metabolism. These results demonstrate the potential of microRNAs as biomolecules that can promote resistance to microsporidia and provide new insights and a new approach to generate microsporidia-resistant biological materials.IMPORTANCEMicrosporidia have an extremely wide host range and are capable of infecting a wide variety of insects and vertebrates, including humans, and their lethality to multiple species often poses significant environmental management challenge. Here, we successfully constructed a microsporidium-resistant line in the silkworm, based on the overexpression of miR-6498-5p. Our results strongly support the hypothesis that miR-6498-5p efficiently suppresses the proliferation of <i>Nosema bombycis</i> by regulating the host VB6 metabolism, a key pathway for enzymes involved in amino acid transport and protein metabolism. Our study provides new insights for understanding host anti-pathogen defenses toward microsporidia.