Biogenesis and discharge of the rhoptries: Key organelles for entry and hijack of host cells by the Apicomplexa

Rhoptries are specialized secretory organelles found in the Apicomplexa phylum, playing a central role in the establishment of parasitism. The rhoptry content includes membranous as well as proteinaceous materials that are discharged into the host cell in a regulated fashion during parasite entry. A set of rhoptry neck proteins form a RON complex that critically participates in the moving junction formation during invasion. Some of the rhoptry bulb proteins are associated with the membranous materials and contribute to the formation of the parasitophorous vacuole membrane while others are targeted into the host cell including the nucleus to subvert cellular functions. Here, we review the recent studies on Toxoplasma and Plasmodium parasites that shed light on the key steps leading to rhoptry biogenesis, trafficking, and discharge. Rhoptries are specialized secretory organelles of the obligate intracellular Apicomplexan parasites that secrete their content inside the host cell. Rhoptry proteins play a major role during parasite invasion by forming the moving junction and also contribute to the formation of the parasitophorous vacuole and to the subversion of host cellular function. Here we highlight the recent advances made regarding the rhoptry biogenesis, trafficking and secretion and discuss the remaining questions that require further investigations.