The unique transmembrane protein NbTMP2 (NBO_555g0004) of Nosema bombycis contributes to host infection

Abstract

Nosema bombycis is one of the earliest discovered microsporidia and can infect silkworms through both horizontal and transovarial transmission, posing a significant threat to the sericulture industry. Microsporidia can form mature dormant spores with a thick proteinaceous and chitin-rich wall that shields them from environmental stress, leading to difficulties in prevention and control. However, the intracellular proliferative phase is a particularly active life stage for the pathogen. At this stage, the plasma membrane of pathogen is exposed to the cytoplasm of the host cells without the protection of the spore walls, which make it an ideal phase for intervention. In this study, based on transcriptomic data, we identified that a transmembrane protein of N. bombycis, NbTMP2 (NBO_555g0004), was highly expressed after infection with microsporidia. Sequence analysis of the cloned NbTMP2 gene revealed that the protein consists of 253 amino acids, including a signal peptide and a transmembrane domain. Indirect immunofluorescence analysis (IFA) showed that NbTMP2 is localized to the plasma membrane. Furthermore, IFA, RT-qPCR, and western blotting indicated that NbTMP2 is expressed at all developmental stages, with a significant upregulation during the early proliferative phase of N. bombycis. The interference of NbTMP2 confirmed that downregulation of NbTMP2 expression significantly inhibit the proliferation of N. bombycis. In conclusion, NbTMP2 is a membrane protein that plays a role during the development of N. bombycis. This study provides a potential target for inhibiting the proliferation of N. bombycis and lays a foundation for future research on breeding N. bombycis-resistant silkworms.