chloroplast nucleoid

GO:0042644 · Nucleoid · Subcellular region · Proposed

The region of a chloroplast to which the DNA is confined. [GO:0042644]

Part of: chloroplast stroma (GO:0009570)

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
chloroplast DNA	Dna	part of	Reviewed label only (reviewed name; no accession asserted)			ESSENTIAL	Plastid genome DNA compacted with proteins into discrete nucleoids inside the chloroplast stroma. `DOI:10.1093/gbe/evv233` Kobayashi et al. 2015 describe chloroplast DNA as compacted into chloroplast nucleoids. `DOI:10.1093/mp/ssp083` Karcher et al. 2009 assayed Chlamydomonas chloroplast DNA organization as HLP-containing nucleoids.
chloroplast nucleoid HU-like proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	HU-like DNA-binding proteins, represented by Chlamydomonas HLP, that associate with chloroplast nucleoids and support their organization. `DOI:10.1093/mp/ssp083` Karcher et al. 2009 showed that the Chlamydomonas HLP protein targets to chloroplasts, associates with nucleoids, and is required for nucleoid organization and genome maintenance.

Taxonomic distribution

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: Chloroplast nucleoids and the nucleoid-associated HLP protein have been characterized in the Chlamydomonas chloroplast. [DOI:10.1093/mp/ssp083]

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model in which HLP knockdown connected a chloroplast-targeted, HU-like protein to chloroplast nucleoid organization and genome maintenance. [DOI:10.1093/mp/ssp083]

Functions

chloroplast genome organization — The chloroplast nucleoid confines, compacts and organizes chloroplast DNA within the chloroplast stroma.
- GO:0042644 GO defines the chloroplast nucleoid as the chloroplast region to which DNA is confined.
- DOI:10.1093/mp/ssp083 Karcher et al. 2009 linked Chlamydomonas HLP to chloroplast nucleoid organization and genome maintenance.

Mechanism graphs

HLP helps organize Chlamydomonas chloroplast DNA nucleoids (FUNCTION)

HU-like DNA-binding proteins represented by Chlamydomonas HLP associate with chloroplast nucleoids and support cpDNA packaging and genome maintenance.

Subject	Predicate	Object	Evidence
chloroplast nucleoid HU-like proteins	associates with	chloroplast nucleoid	`DOI:10.1093/mp/ssp083` Karcher et al. 2009 localized HLP to Chlamydomonas chloroplasts and nucleoids.
chloroplast DNA	compacts into	chloroplast nucleoid	`DOI:10.1093/gbe/evv233` Kobayashi et al. 2015 describe chloroplast DNA compaction into nucleoprotein complexes called chloroplast nucleoids.
chloroplast nucleoid HU-like proteins	supports	chloroplast genome organization	`DOI:10.1093/mp/ssp083` Karcher et al. 2009 connected RNAi knockdown of HLP with defective Chlamydomonas chloroplast nucleoid organization and genome maintenance.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings for chloroplast DNA and chloroplast nucleoid-associated protein families before expanding this record beyond HLP. The chloroplast nucleoid is a DNA-protein structure with multiple nucleoid-associated proteins, but this first record only curates a reviewed-label-only HU-like component represented by Chlamydomonas HLP and avoids guessing Sequence Ontology or protein-family CURIEs.

Evidence

GO:0042644 Gene Ontology cellular-component term for chloroplast nucleoid.
DOI:10.1093/mp/ssp083 Karcher et al. 2009, The Chlamydomonas Chloroplast HLP Protein Is Required for Nucleoid Organization and Genome Maintenance, Molecular Plant.
DOI:10.1093/gbe/evv233 Kobayashi et al. 2015, Eukaryotic Components Remodeled Chloroplast Nucleoid Organization during the Green Plant Evolution, Genome Biology and Evolution.

Curation history

2026-09-12T11:16:04Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-12T11:16:45Z codex · EXPANDED_RECORD — Moved the GO:0042644 scaffold into the nucleoid category; added plastid nucleoid parentage and chloroplast-stroma parthood; curated chloroplast DNA and HLP components; added Chlamydomonas taxonomic scope, a genome organization function, core literature evidence, a nonmechanistic HLP organization graph, and a component-grounding TODO.
2026-09-12T11:24:56Z codex · ADDRESS_REVIEW — Resolved #637 by removing the unqualified HLP gene symbol from the source-neutral HU-like protein component, and resolved #638 by repointing the Karcher HLP perturbation edge from the generic chloroplast nucleoid node to the HLP component.

Source: data/structures/nucleoid/chloroplast_nucleoid.yaml