Discussion

The flagellar pocket (FP) of Leishmania is an essential conduit through which the cell interacts with its extracellular environment and is likely to be critical for pathogenicity. In Leishmania promastigotes the flagellum is often described as “free”, extending from the FP at the cell anterior; yet these parasites have homologs of many flagellum attachment zone (FAZ) proteins, which in trypanosomes are used to attach the flagellum laterally to the cell body. We have previously shown by electron tomography and endogenous gene tagging that Leishmania have a FAZ structure, which is intrinsically linked to the morphogenesis of the FP, implicating the FAZ in Leishmania pathogenicity. Here, using specific FAZ gene knockout cells we investigated the function of the FAZ in Leishmania. LmFAZ5 knockout causes a reduction in the length of the FAZ structure and a concomitant reduction in cell body length and volume. Electron microscopy shows the disruption of the FAZ structure leads to a loss of attachment between the flagellum and the cell body resulting in changes to the shape and size of the flagellar pocket and neck region. These data show that the FAZ in Leishmania is critical for determining cell shape and size and crucially for maintaining the shape of the FP and neck regions, potentially impacting on cell infectivity.