Plasmodium parasites must invade erythrocytes in order to cause the disease malaria.
The invasion process involves the coordinated secretion of parasite proteins from apical
organelles that include the rhoptries. The rhoptry is comprised of two compartments, the neck
and the bulb. Rhoptry neck proteins are involved in host cell adhesion and formation of the
tight junction that forms between the invading parasite and erythrocyte, whereas the role of
rhoptry bulb proteins remains ill-defined due to the lack of functional studies. In this study,
we show that the rhoptry associated protein (RAP) complex is not required for rhoptry
morphology or erythrocyte invasion. Instead, post-invasion when the parasite is bounded by a
parasitophorous vacuolar membrane (PVM), the RAP complex facilitates the survival of the
parasite in its new intracellular environment. Consequently, conditional knockdown of
members of the RAP complex leads to altered PVM structure, delayed intra-erythrocytic
growth and reduced parasitaemias in infected mice. This study provides evidence that rhoptry
bulb proteins localising to the parasite-host cell interface are not simply by-products of the
invasion process but contribute to the growth of Plasmodium in vivo.
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