basal ring of apical complex

GO:0020032 · Cytoskeleton · Other · Proposed

An electron dense ring at the most posterior position of the apical complex, from which the subpellicular microtubules originate; formed during an invasive life cycle stage of an apicomplexan parasite. [GO:0020032]

Synonyms: lower polar ring of apical complex; posterior polar ring of apical complex

Part of: apical complex (GO:0020007)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Taxonomic distribution

NCBITaxon:5811 Toxoplasma gondii — COMMON: Toxoplasma tachyzoites have a lower polar ring at the origin of the subpellicular microtubules. The conoid extends and retracts relative to this ring. [DOI:10.1371/journal.ppat.0020013]

Canonical examples

NCBITaxon:5811 Toxoplasma gondii — Apicomplexan model in which the conoid fibers, polar rings, intraconoid microtubules and subpellicular microtubules of the apical complex were resolved as distinct cytoskeletal elements. [DOI:10.1371/journal.ppat.0020013]

Functions

subpellicular microtubule origin — The basal ring of the apical complex marks the origin of the subpellicular microtubules; it is distinct from the preconoidal rings at the conoid tip.
- GO:0020032 Gene Ontology defines the basal ring of the apical complex by the origin of the subpellicular microtubules.
- DOI:10.1371/journal.ppat.0020013 Hu et al. 2006 distinguish the polar ring from which the 22 subpellicular microtubules originate from the distal preconoidal rings.

Mechanism graphs

The lower polar ring marks the origin of subpellicular microtubules (ASSEMBLY)

The lower polar ring marks the origin of Toxoplasma subpellicular microtubules. Its posterior position relative to the conoid is shown for the extruded conoid, not asserted for every conoid state.

Subject	Predicate	Object	Evidence
basal ring of apical complex	is part of	apical complex	`GO:0020007` Gene Ontology places the basal ring of the apical complex under the apical-complex cellular-component term.
basal ring of apical complex	is posterior to	conoid	`DOI:10.1083/jcb.200112086` Figure 1 and Results distinguish the moving anterior ring/conoid from the lower polar ring during extension and retraction. `DOI:10.1371/journal.ppat.0020013` Introduction and Figure 1 distinguish the distal preconoidal rings from the SPMT-origin polar ring.
subpellicular microtubule	originates from	basal ring of apical complex	`GO:0020032` Gene Ontology defines the basal ring by the origin of the subpellicular microtubules.

Discussions

CURATION_TODO (OPEN): Resolve exact basal-ring resident proteins and their source-neutral family groundings. This first basal-ring record captures the GO-delimited lower polar ring and its subpellicular-microtubule origin topology. It leaves protein components out until direct evidence places candidate proteins in the mature basal ring and an exact taxon-neutral family scope can be reviewed.
INTERPRETATION (RESOLVED): Keep the basal or posterior polar ring distinct from the anterior polar ring of the apical complex. GO:0020032 denotes the lower/posterior/preconoidal ring from which subpellicular microtubules originate, whereas GO:0020031 denotes the anterior polar ring from which conoid fibers originate. The two terms therefore represent adjacent but separate apical-complex rings.
INTERPRETATION (RESOLVED): Separate the GO synonym conflict from the demonstrated basal-ring anatomy. The original discussion faithfully recorded a GO:0020032 exact synonym, preconoidal ring of apical complex. Hu 2006 instead places preconoidal rings at the distal conoid tip and the SPMT-origin polar ring at the base. Hu 2002 distinguishes the moving anterior ring/conoid from the lower ring. Thus the GO synonym conflicts with the primary anatomy and cannot establish biological equivalence.

Evidence

GO:0020032 Gene Ontology cellular-component term for the basal ring of the apical complex.
GO:0020007 Gene Ontology models the basal ring of the apical complex as part of the apicomplexan apical complex.
DOI:10.1371/journal.ppat.0020013 Hu et al. 2006, Cytoskeletal Components of an Invasion Machine--the Apical Complex of Toxoplasma gondii, PLOS Pathogens.
DOI:10.1083/jcb.200112086 Hu, Roos and Murray 2002, A novel polymer of tubulin forms the conoid of Toxoplasma gondii. Figure 1 supports state-dependent conoid/ring topology.

Curation history

2026-10-02T14:24:21Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-02T14:25:23Z codex · EXPANDED_RECORD — Added exact GO basal-ring synonyms, GO apical-complex parthood, Toxoplasma gondii scope, Hu 2006 and GO evidence, a nonmechanistic basal-ring topology graph, and curation discussions for unresolved constituents and the anterior/posterior polar-ring boundary.
2026-10-11T19:53:32Z codex · ADDRESS_SAVED_REVIEW — Addressed #2247: Separated the active basal-ring topology from preconoidal-ring synonym conflation and qualified conoid-relative position for extrusion. The GO/source conflict and original rationale remain explicit.

Source: data/structures/cytoskeleton/basal_ring_of_apical_complex.yaml