eyespot apparatus

GO:1990413 · Membrane organelle · Other · Proposed

A small pigmented organelle used in single-celled organisms to detect light. [GO:1990413]

Synonyms: eyespot; stigma

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
eyespot carotenoid pigments	Small molecule	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Carotenoid pigments concentrated in reflective granule layers that shade eyespot photoreceptors from light condensed through the cell body. `DOI:10.1093/genetics/153.2.721` Lamb et al. 1999 described reflective carotenoid pigment layers beneath the Chlamydomonas plasma-membrane photoreceptor region. `DOI:10.1073/pnas.1525538113` Ueki et al. 2016 tested how eyespot carotenoid layers shield Chlamydomonas photoreceptors.
eyespot channelrhodopsin photoreceptors	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Light-gated rhodopsin photoreceptors positioned at the eyespot to initiate phototaxis signaling. `DOI:10.1083/jcb.201009131` Mittelmeier et al. 2011 followed Chlamydomonas ChR1 localization at the eyespot photoreceptor patch. `DOI:10.1038/srep34646` Awasthi et al. 2016 followed bacterial-type rhodopsin trafficking into the Chlamydomonas eyespot and flagella.

Taxonomic distribution

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: This green alga was the source for purified eyespot fractions used in proteomic analysis of the eyespot apparatus. [DOI:10.1105/tpc.106.041749]

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model in which eyespot-assembly mutants defined loci required for pigmented eyespot formation and placement. [DOI:10.1093/genetics/153.2.721]

Functions

directional light detection for phototaxis — The eyespot apparatus uses carotenoid layers to shade photoreceptors so a motile cell can infer the direction of incident light.
- DOI:10.1073/pnas.1525538113 Ueki et al. 2016 showed that Chlamydomonas eyespot pigment layers determine the phototactic sign by shielding photoreceptors from light condensed through the cell body.

Mechanism graphs

Carotenoid layers shade channelrhodopsins for directional phototaxis (FUNCTION)

The Chlamydomonas eyespot concentrates carotenoid pigments in reflective granule layers with a localized channelrhodopsin photoreceptor patch so the cell can sense the direction of incident light.

Subject	Predicate	Object	Evidence
eyespot carotenoid pigments	concentrated in	eyespot apparatus	`DOI:10.1093/genetics/153.2.721` Lamb et al. 1999 described the pigment layers of the Chlamydomonas eyespot.
eyespot channelrhodopsin photoreceptors	localize to	eyespot apparatus	`DOI:10.1083/jcb.201009131` Mittelmeier et al. 2011 tracked ChR1 photoreceptor localization in wild-type and multieyed Chlamydomonas cells.
eyespot carotenoid pigments	shield	eyespot channelrhodopsin photoreceptors	`DOI:10.1073/pnas.1525538113` Ueki et al. 2016 tested carotenoid-layer shielding during Chlamydomonas phototaxis.
eyespot apparatus	supports	directional light detection	`DOI:10.1073/pnas.1525538113` Ueki et al. 2016 linked eyespot shielding to correct phototactic sign in Chlamydomonas reinhardtii.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings and component boundaries for Chlamydomonas channelrhodopsins, carotenoid pigment chemistry and additional eyespot-proteome candidates. The first eyespot-apparatus pass records only two reviewed label-only Chlamydomonas component cohorts. The purified eyespot proteome identified many additional protein candidates, but their exact family groundings and mature-organelle membership need curator review before expansion.

Evidence

GO:1990413 Gene Ontology cellular-component term for eyespot apparatus.
DOI:10.1093/genetics/153.2.721 Lamb et al. 1999, Eyespot-Assembly Mutants in Chlamydomonas reinhardtii, Genetics.
DOI:10.1105/tpc.106.041749 Schmidt et al. 2006, Proteomic Analysis of the Eyespot of Chlamydomonas reinhardtii Provides Novel Insights into Its Components and Tactic Movements, The Plant Cell.
DOI:10.1083/jcb.201009131 Mittelmeier et al. 2011, Asymmetric properties of the Chlamydomonas reinhardtii cytoskeleton direct rhodopsin photoreceptor localization, Journal of Cell Biology.
DOI:10.1038/srep34646 Awasthi et al. 2016, The trafficking of bacterial type rhodopsins into the Chlamydomonas eyespot and flagella is IFT mediated, Scientific Reports.
DOI:10.1073/pnas.1525538113 Ueki et al. 2016, Eyespot-dependent determination of the phototactic sign in Chlamydomonas reinhardtii, Proceedings of the National Academy of Sciences.

Curation history

2026-09-11T14:23:03Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T14:23:45Z codex · EXPANDED_RECORD — Added eyespot synonyms, Chlamydomonas channelrhodopsin and carotenoid-granule components, Chlamydomonas scope, a directional phototaxis function, DOI evidence, a nonmechanistic pigment-shielding graph, and a component-boundary grounding TODO.
2026-09-11T14:28:40Z codex · ADDRESS_REVIEW — Resolved #497 by narrowing the pigment component to a small-molecule carotenoid cohort, resolved #498 by adding plural channelrhodopsin evidence, and resolved #499 by keeping Ueki-backed function text focused on carotenoid-layer shielding.

Source: data/structures/membrane_organelle/eyespot_apparatus.yaml