ciliary rootlet

GO:0035253 · Cytoskeleton · Other · Proposed

A cytoskeleton-like structure, originating from the basal body at the proximal end of a cilium, and extending proximally toward the cell nucleus. Rootlets are typically 80-100 nm in diameter and contain cross striae distributed at regular intervals of approximately 55-70 nm. [GO:0035253]

Synonyms: cilial rootlet; cilium rootlet; flagellar root; striated rootlet

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
SF-assemblin homologs	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Segmented coiled-coil proteins that polymerize into the 2-nm filaments of striated ciliary and flagellar rootlets in microbial eukaryotes. `DOI:10.1083/jcb.121.4.837` Weber et al. 1993 identified SF-assemblin as the structural protein of 2-nm filaments from striated microtubule-associated fibers of algal flagellar roots. `DOI:10.1186/s13630-019-0062-y` Nabi et al. 2019 found SF-Assemblin homologs in Paramecium ciliary striated rootlets.

Taxonomic distribution

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: Chlamydomonas reinhardtii carries SF-assemblin-positive noncontractile striated roots in its flagellar basal apparatus. [DOI:10.1242/jcs.115.7.1511]
NCBITaxon:5888 Paramecium tetraurelia — COMMON: Paramecium tetraurelia basal bodies carry striated ciliary rootlets containing SF-Assemblin homologs. [DOI:10.1186/s13630-019-0062-y]

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model in which SF-assemblin was tagged, depleted and localized to noncontractile striated roots in the flagellar basal apparatus. [DOI:10.1242/jcs.115.7.1511]
NCBITaxon:5888 Paramecium tetraurelia — Ciliate model in which SF-Assemblin paralogs and structural groups were linked to ciliary striated rootlet organization by RNAi. [DOI:10.1186/s13630-019-0062-y]

Mechanism graphs

SF-assemblin homologs build striated ciliary rootlets (FUNCTION)

In microbial eukaryotes, segmented coiled-coil SF-assemblin homologs assemble into striated ciliary or flagellar rootlets that originate at ciliary basal bodies.

Subject	Predicate	Object	Evidence
SF-assemblin homologs	polymerize into	ciliary rootlet	`DOI:10.1083/jcb.121.4.837` Weber et al. 1993 identified SF-assemblin as the structural protein of 2-nm filaments from algal flagellar-root fibers. `DOI:10.1242/jcs.115.7.1511` Lechtreck et al. 2002 observed SFA-GFP assembling into striated fibers in Chlamydomonas transformants.
ciliary rootlet	originates at	ciliary basal body	`GO:0035253` GO defines the ciliary rootlet as a cytoskeleton-like structure originating from the ciliary basal body.
ciliary rootlet	supports	flagellar assembly	`DOI:10.1242/jcs.115.7.1511` Lechtreck et al. 2002 reduced SF-assemblin and observed defects in flagellar assembly.

Discussions

CURATION_TODO (OPEN): Resolve exact InterPro, Pfam or NCBIfam grounding for microbial eukaryotic SF-assemblin homologs that build striated ciliary rootlets. SF-assemblin homologs are established constituents of green-algal and ciliate striated rootlets, but this pass did not verify one family accession that exactly covers those rootlet proteins without pulling in unrelated coiled-coil proteins.
CURATION_TODO (OPEN): Decide whether algal rhizoplasts, Paramecium transverse, post-ciliary and striated rootlets, and metazoan rootletin-based rootlets need subtype records. The GO term names the broad ciliary rootlet class, while microbial eukaryotes carry lineage-specific rootlet arrays whose geometry and molecular paralogs differ.

Evidence

GO:0035253 Gene Ontology cellular-component term for the ciliary rootlet.
DOI:10.1083/jcb.115.3.705 Lechtreck and Melkonian 1991 identified assemblin as a 34-kDa structural protein that forms paracrystalline 2-nm filaments in striated microtubule-associated fibers.
DOI:10.1083/jcb.121.4.837 Weber et al. 1993, SF-assemblin, the structural protein of the 2-nm filaments from striated microtubule associated fibers of algal flagellar roots, forms a segmented coiled coil.
DOI:10.1242/jcs.115.7.1511 Lechtreck, Rostmann and Grunow 2002 analyzed Chlamydomonas SF-assemblin by GFP tagging and antisense constructs.
DOI:10.1186/s13630-019-0062-y Nabi et al. 2019 linked Paramecium SF-Assemblin genes to ciliary striated rootlets and surface organization.

Curation history

2026-09-22T09:45:34Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-22T09:46:40Z codex · EXPANDED_RECORD — Added GO synonyms, an SF-assemblin homolog component, Chlamydomonas and Paramecium scope, DOI evidence, a nonmechanistic ciliary-rootlet topology graph, and TODOs for SF-assemblin grounding and rootlet subtype boundaries.

Source: data/structures/cytoskeleton/ciliary_rootlet.yaml