Rickettsia symbionts favor whitefly ovary development by promoting germ cell mitosis

BACKGROUND Maternally inherited symbionts can impact the reproduction of their host insects in various ways. The ovary is critical for the successful reproduction of female insects. Such symbionts have strong ovary tropism. Intracellular symbionts depend on host cells for replication and transmission. However, the cellular mechanisms by which symbionts impact insect reproduction through affecting ovary development have seldom been investigated. Our previous work has shown that the facultative symbiont Rickettsia can be vertically transmitted through eggs in the whitefly Bemisia tabaci and Rickettsia increases female fecundity. This study is aimed to explore the cellular mechanisms of Rickettsia symbionts affecting the whitefly fecundity. RESULTS We found that Rickettsia symbionts are highly concentrated in the tropharium of whitefly ovarioles. We demonstrated that Rickettsia increases whitefly fecundity by promoting ovary development. Moreover, Rickettsia enhances the expression of cell division genes ( Cyclin B1 and CDK1 ) and germ cell mitosis. Furthermore, Cyclin B1 and CDK1 gene silencing or CDK1 inhibitor treatment reduced the germ cell mitosis, delayed ovary development and decreased whitefly fecundity. CONCLUSION Overall, we revealed that Rickettsia promotes ovary development by regulating germ cell mitosis, which enhances whitefly fecundity. These findings suggest that regulating the host cell cycle by the symbiont is important for the maintenance of the intracellular symbiosis. This study provides new insights into the cellular mechanism of symbionts regulating host reproduction. Our study also provides excellent genetic targets for insect control.