Apicomplexans are obligate intracellular parasites that
invade the host cell in an active process that relies on
unique secretory organelles (micronemes, rhoptries and
dense granules) localized at the apical tip of these highly
polarized eukaryotes. In order for the contents of these
specialized organelles to reach their final destination,
these proteins are sorted post-Golgi and it has been
speculated that they pass through endosomal-like
compartments (ELCs), where they undergo maturation.
Here, we characterize a Toxoplasma gondii homologue
of Syntaxin 6 (TgStx6), a well-established marker for
the early endosomes and trans Golgi network (TGN) in
diverse eukaryotes. Indeed, TgStx6 appears to have a
role in the retrograde transport between ELCs, the TGN
and the Golgi, because overexpression of TgStx6 results
in the development of abnormally shaped parasites
with expanded ELCs, a fragmented Golgi and a defect
in inner membrane complex maturation. Interestingly,
other organelles such as the micronemes, rhoptries and
the apicoplast are not affected, establishing the TGN
as a major sorting compartment where several transport
pathways intersect. It therefore appears thatToxoplasma
has retained a plant-like secretory pathway