Nbseptin2 Expression Pattern and Its Interaction with NbPTP1 during Microsporidia Nosema bombycis Polar Tube Extrusion

Nosema bombycis (Nb) is a deadly species of microsporidia capable of causing pebrine, leading to heavy losses in sericulture. Germination is an important biological event in the invasion process of microsporidia. Septins, a family of membrane-associated proteins, play a critical role in tissue invasion and have been recognized as a virulence factor in numerous pathogens. Previous work in our laboratory has shown that Nosema bombycis septin2 (Nbseptin2) interacts with subtilisin-like protease 2 (NbSLP2). Herein, we found that Nbseptin2 was mainly associated with the plasma membrane in spores. Following spore germination, Nbseptin2 was found to co-localize with polar tube protein 1 (NbPTP1) at the polar cap and proximal zone of the polar tube. Co-immunoprecipitation and yeast two-hybrid analysis further confirmed that Nbseptin2 interacted with NbPTP1. The translocation and interaction of Nbseptin2 in the spores suggest that Nbseptin2 may play a significant role in microsporidia polar tube extrusion process. Our findings improve understanding of the mechanisms underlying microsporidia germination.