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Zhu et al., 2000a
). Moreover, all attempts to detect this organelle in
eugregarines, early branching apicomplexans with huge cells associated with
the invertebrate hosts, also failed (
Toso and Omoto, 2007
). According to
molecular phylogeny (
Carreno et al., 1999; Zhu et al., 2000b
) and some
morphological synapomorphies (
Valigurov´ et al., 2007
), both above-
mentioned groups seem to be closely related. We suppose that these
apicomplexans lost their plastid shortly after its acquisition, before the organ-
elle became firmly established and indispensable for the parasite's survival
(
Oborn´k et al., 2009
).
Still, the apicoplast has been found in the most species-rich and wide-
spread groups of apicomplexan parasites, such as Coccidia, Piroplasmida,
and Haemosporidia (
Lim and McFadden, 2010; Oborn
´
k et al., 2009
). In
the best studied
Plasmodium falciparum
, this relic plastid was shown to be
essential for the cell, its disruption leading to the so-called delayed death
effect (
Fichera et al., 1995; He et al., 2001; Pfefferkorn et al., 1992;
Ramya et al., 2007
). The apicoplast therefore represents a new promising
target, even a proverbial Achilles' heel of these pathogens (
Jomaa et al.,
1999; McFadden and Roos, 1999; Soldati, 1999; Wiesner and Jomaa,
2007; Wiesner et al., 2008
). The discovery of this organelle led to the
groundbreaking suggestion that these heterotrophic parasites had evolved
from a phototrophic ancestor, particularly, an alga hosting a complex plastid
(
McFadden et al., 1996
). Although the apicoplast apparently lost the main
plastid function and is thus not photosynthetic anymore, several likely essen-
tial metabolic pathways still take place in this organelle, such as the heme
biosynthesis (
Koˇen´ et al., 2011
, 2013;
van Dooren et al., 2012; Wilson,
2002; Williams and Keeling, 2003
), fatty acid synthesis (
Goodman and
McFadden, 2008
), or nonmevalonate isoprenoid synthetic route (
Jomaa
et al., 1999
; reviewed by
Ralph et al., 2004
). It has been proposed that par-
ticularly the heme (tetrapyrrole) biosynthetic pathway plays an important
role in the plastid losses, which are known to occur frequently, especially
during the evolution of alveolates and stramenopiles (
Barbrook et al.,
2006; Ko
ˇ
en´ et al., 2011, 2012; Ko
ˇ
en´ and Oborn
´
k, 2011
). As a matter
of fact, substantial attention has been paid to the heme pathway when
searching for a suitable antimalarial drug target (
Seeber and Soldati-Favre,
2010; van Dooren et al., 2012
). However, it has been shown recently by
an elegant chemical rescue of
Plasmodium
freed of the apicoplast that for
its erythrocytic (
bloodstreams) stages, the only truly essential compound
produced by the apicoplast is isopentenyl pyrophosphate, a product of the
nonmevalonate isoprenoid pathway (
Yeh and DeRisi, 2011
).
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