The Plasmodium GRASP Homolog Modulates Liver Stage Development, Subsequent Blood Infection and Virulence in Mice

Conserved across eukaryotic cells, Golgi reassembly and stacking proteins (GRASPs) are peripheral proteins that hold the flat cisternal membranes of the Golgi apparatus into stacks and that also play a role in a process of unconventional protein secretion involving the autophagy machinery. The Golgi in Plasmodium malaria parasites is composed of unstacked cisternae that contain a single GRASP homolog. We previously showed that the initial development of Plasmodium berghei in hepatocytes involves the clearance of micronemes through their sequestration into PbATG8-positive autophagosomes that fuse with the parasite plasma membrane. Here, we examine the involvement of PbGRASP in microneme elimination and extend our studies to assess the importance of GRASP for parasite development in the mammalian host and mosquito vector. GRASP associates with PbATG8 autophagosomes containing micronemes, though PbGRASP-KO parasites can expel micronemes. PbGRASP-KO parasites have no discernable phenotype during mosquito stage development or asexual blood stage growth. PbGRASP-KO liver stages form small schizonts at mid-infection, and then growth resumes. PbGRASP-KO hepatic merozoites egress from the mouse liver and induce higher parasitemia but display delayed and reduced cerebral malaria symptoms. These observations point to a regulatory role for GRASP in controlling parasite proliferation and virulence in mammalian hosts.