DCX enables branching of subpellicular microtubules in Plasmodium falciparum gametocytes and is required for mosquito colonisation

Plasmodium falciparum, the causative agent of malaria, relies on specialised tubulin-based cytoskeletal structures to support its parasitic lifestyle. These include the conoid required for parasite motility and host-cell invasion, as well as subpellicular microtubules (SPMTs) that support parasite shape and rigidity. Here, we investigate the function of the doublecortin-domain protein DCX, a microtubule-binding protein previously associated with the Plasmodium conoid. We first show that, in P. falciparum, DCX is not expressed in the merozoite stage and is not required for the invasion of human erythrocytes. By contrast, DCX is expressed in ookinetes, the motile stage responsible for infecting the mosquito vector, where it associates with conoid tubulin fibres, consistent with a role in stabilising the conoid architecture. Unexpectedly, we find that DCX is required for P. falciparum transmission to the mosquito independently of conoid function. We further link this requirement to the distinctive organisation of SPMTs in P. falciparum gametocytes, which display an unusual branching architecture comprising multiple microtubules of 15 to 18 protofilaments. Deletion of DCX leads to a reduction in SPMT branching and is associated with higher protofilament numbers, revealing a previously unrecognised role for DCX in shaping the ultrastructure of SPMTs in P. falciparum gametocytes. Altogether, our findings uncover the repurposing of DCX across distinct microtubule systems in transmission stages and identify DCX as a key factor mediating microtubule branching and stabilisation in SPMTs required for efficient mosquito transmission.