A basal body microtubule singlet-to-doublet transition in Plasmodium male gametogenesis.

Axoneme assembly constitutes a pivotal process in male gametogenesis of Plasmodium. Plasmodium possesses a unique nuclear envelope-anchored basal body that templates axoneme assembly, distinct from the basal body that templates the axoneme of cilia or flagella to protrude from the cell surface. In the canonical basal body, the microtubule (MT) triplet extends and forms the axonemal MT doublet. However, this characteristic MT triplet has not been detected in Plasmodium. Indeed, the MT organization and the mechanism underlying the axonemal MT doublet assembly remain elusive in Plasmodium. Here we utilize high-resolution imaging methods including iterative ultrastructure expansion microscopy (iU-ExM) and cryo-electron tomography (cryo-ET) to resolve the native MT organization in the basal body of male gametes from the rodent malaria parasite P. yoelii. The parasite exhibits an MT singlet-to-doublet transition, distinct from the canonical MT triplet-to-doublet transition. Furthermore, we reveal that δ-Tubulin and ε-Tubulin are expressed in male gametocytes and regulate axoneme formation during male gametogenesis. δ-Tubulin is localized at the proximal end of the MT B-tubule and modulates B-tubule assembly of MT doublet. Our work provides the native architecture of MT singlet-to-doublet transition and reveals the key role of δ-Tubulin and ε-Tubulin in MT singlet-to-doublet transition in the basal body of Plasmodium.