<i>Plasmodium berghei</i> IMC1j interacts with δ-tubulin to orchestrate subpellicular microtubule organization in ookinetes

Apicomplexan parasites possess specialized structures for cell invasion and replication, notably the inner membrane complex (IMC) and the subpellicular microtubules (SPMTs) situated beneath it. SPMTs are thought to interact with proteins embedded in or associated with the IMC. The cytosolic side of the IMC contains a network of proteins known as alveolins. This study focuses on a specific alveolar protein, <i>Plasmodium berghei</i> IMC1j (PbIMC1j). We found that PbIMC1j undergoes palmitoylation and is predominantly expressed in ookinetes. Gene knockout analysis revealed that the absence of PbIMC1j leads to defects in parasite asexual stage fitness and virulence, alters ookinete morphology, and impairs motility and/or infectivity in both ookinetes and sporozoites. Deletion analyses indicated that the C-terminal region containing the coiled-coil (CC) domain is required for proper targeting to and function within the IMC. Immunoprecipitation analysis of PbIMC1j demonstrated the role of the IMCp domain in mediating interactions with and stabilizing the expression of the IMC protein ISC1 and the SPMTs component δ-tubulin (TubD). In ookinetes devoid of TubD, the SPMTs were disorganized, mirroring the defects observed during the zygote-to-ookinete transition in the PbIMC1j-deficient strains. Overall, our study highlights the importance of the PbIMC1j protein in parasite fitness, SPMT organization, and ookinete motility mediated through its IMCp and CC domains.IMPORTANCEMalaria parasites depend on an inner membrane complex (IMC) and subpellicular microtubules (SPMTs) to maintain their shape, motility, and ability to replicate. This study demonstrates that knocking out or disrupting the PbIMC1j protein adversely affects asexual stage fitness, virulence, and the morphology of ookinetes, while also decreasing the motility of ookinetes in <i>P. berghei</i>. Furthermore, PbIMC1j interacts and stabilizes the proteins ISC1 and δ-tubulin, underscoring its role in regulating the IMC and SPMTs.