Actin-mediated transovarial transmission of a yeastlike symbiont in the brown planthopper.

The brown planthopper Nilaparvata lugens (Hemiptera, Delphacidae) harbors an obligate endosymbiont called the yeastlike symbiont (YLS) in their abdominal fat body. YLS, a filamentous ascomycete belonging to the family Clavicipitaceae, does not spend any part of its life cycle outside the planthopper's body. The YLS is transferred to the next generation via transovarial transmission; it enters the epithelial plug at the posterior end of the host female's ovariole and is transferred to her offspring. In the present study, microscopic examination revealed that actin filaments play an important role in the transmission of YLS. An irregular cell protrusion on the surface of the epithelial plug facilitated the uptake of the YLS, which was then incorporated into the epithelial plug cell. Actin assembly apparently produces the protrusion and actin appears to participate in almost every stage of the process, from the entry of the YLS into the epithelial plug to its delivery to the oocyte. The epithelial plug employs a recognition system for YLS, which drastically changes the cell surface structure to enable the YLS to enter the ovariole.