Plasmodium protein kinase 2 is required for ookinete-to-oocyst transition and parasite transmission

Plasmodium parasites rely on diverse protein kinases to regulate critical processes, yet many remain uncharacterised. Protein kinase 2 (PK2) is required for asexual blood-stage proliferation and merozoite invasion, but its role in sexual stages and transmission is unknown. Here, using live-cell and super-resolution imaging, ultrastructural analysis, functional phenotyping, and quantitative phosphoproteomics, we define the role of PK2 in Plasmodium berghei transmission. PK2 was expressed in merozoites, ookinetes, and sporozoites: the three invasive forms of the parasite. Conditional depletion of PK2 impaired ookinete motility, disrupted apical microneme positioning, abolished oocyst formation, and prevented mosquito-to-host transmission. Direct haemocoel injection of mutant ookinetes failed to restore sporozoite production, demonstrating an additional requirement for PK2 downstream of midgut traversal. Although global protein abundance was largely preserved, phosphoproteomic profiling identified altered phosphorylation of proteins associated with cytoskeletal organisation, host-cell interaction, midgut invasion, and gene regulation. These findings highlight PK2's critical role across multiple invasive stages, advancing understanding of malaria parasite transmission and identifying putative PK2-regulated pathways as potential targets for transmission-blocking interventions.