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Retron system

traitmech:000235 · CLASS · PROPOSED

A phage defense system in which an organism possesses a retron locus encoding a reverse transcriptase, an msr/msd non-coding RNA that yields multicopy single-stranded DNA, and an associated effector whose activation can inhibit bacteriophage propagation through abortive infection.

Trait evidence (8)

  • DOI:10.1016/j.cell.2020.09.065
    We report that retrons function as anti-phage defense systems

    Millman et al. support retrons as experimentally observed antiphage defense systems rather than only retroelement sequence features.

  • DOI:10.1016/j.cell.2020.09.065
    The defensive unit is composed of three components: the RT, the ncRNA, and an effector protein

    Millman et al. support defining the broad record around a reverse transcriptase, non-coding RNA, and associated effector rather than a bare reverse-transcriptase gene.

  • DOI:10.1016/j.cell.2020.09.065
    We examined multiple retron systems and show that they confer defense against a broad range of phages via abortive infection

    Millman et al. support treating Retron system as a family of organism-level antiphage traits, with abortive infection as a shared defense output.

  • DOI:10.1016/j.cell.2020.09.065
    retrons, functioning together with their associated effector genes, form anti-phage defense systems

    Millman et al. connect associated effector genes to Retron antiphage function.

  • DOI:10.1038/s41586-022-05091-4
    RcaT is neutralized by the reverse transcriptase–msDNA antitoxin complex, and becomes active upon perturbation of msDNA biosynthesis

    Bobonis et al. support an RcaT-containing Retron-Sen2 example in which the reverse-transcriptase-msDNA complex controls effector activity.

  • DOI:10.1038/s41586-022-05091-4
    we identified multiple trigger and blocker proteins of phage origin

    Bobonis et al. support phage-encoded trigger and blocker logic for the characterized Retron-Sen2 RcaT system.

  • DOI:10.1038/s41586-022-05091-4
    phage-related triggers directly modify the msDNA, thereby activating RcaT and inhibiting bacterial growth

    Bobonis et al. connect phage-triggered msDNA modification to RcaT activation in Retron-Sen2 without making that trigger universal across all retrons.

  • DOI:10.1038/s41586-022-05091-4
    retron toxin–antitoxin systems act as abortive infection anti-phage defence systems

    Bobonis et al. support retron toxin-antitoxin systems as abortive-infection antiphage systems.

Retrons couple msDNA complexes to effector activation

Evidence-backed process sketch linking a complete retron locus to RT/ncRNA-dependent msDNA biosynthesis, control of associated effectors, abortive-infection outputs, and inhibition of phage growth.

NONMECHANISTIC · The graph stays at the retron family level and uses the Ec48 RecBCD-guarding and Retron-Sen2 RcaT mechanisms as characterized examples without asserting one universal effector fold, phage trigger, direct msDNA-modification event, guarded host target, or Retron-Septu release architecture across all retron antiphage loci.

Retrons couple msDNA complexes to effector activation Interactive directed graph showing evidence-backed causal relationships for Retron system.

Edge evidence

  • retron locus contributes to retron msDNA biosynthesis RO:0002326

    Retron loci encode the reverse transcriptase and non-coding RNA components that biosynthesize msDNA.

    • DOI:10.1016/j.cell.2020.09.065 Retrons encode a non-coding RNA (ncRNA) and a reverse transcriptase (RT) Millman et al. describe the RT and ncRNA parts of the retron msDNA-biosynthesis module.
  • retron locus contributes to RT-msDNA effector control RO:0002326

    Complete retron defensive units include an associated effector coupled to the RT/ncRNA core.

    • DOI:10.1016/j.cell.2020.09.065 The defensive unit is composed of three components: the RT, the ncRNA, and an effector protein Millman et al. support the effector as a required part of a complete retron defensive unit.
  • retron msDNA biosynthesis contributes to RT-msDNA effector control RO:0002326

    The reverse-transcriptase-msDNA complex can control associated retron effector activity.

    • DOI:10.1038/s41586-022-05091-4 RcaT is neutralized by the reverse transcriptase–msDNA antitoxin complex, and becomes active upon perturbation of msDNA biosynthesis Bobonis et al. connect msDNA biosynthesis and the RT-msDNA complex to RcaT toxin control in Retron-Sen2.
  • RT-msDNA effector control contributes to effector-dependent abortive infection RO:0002326

    Phage-triggered perturbation of retron effector control can activate an associated effector.

    • DOI:10.1038/s41586-022-05091-4 phage-related triggers directly modify the msDNA, thereby activating RcaT and inhibiting bacterial growth Bobonis et al. support phage-triggered activation of the RcaT effector in Retron-Sen2.
  • effector-dependent abortive infection mitigates phage growth METPO:2007407

    Retron effector activation can block phage amplification through abortive infection.

    • DOI:10.1016/j.cell.2020.09.065 We examined multiple retron systems and show that they confer defense against a broad range of phages via abortive infection Millman et al. link multiple retron systems to broad antiphage defense by abortive infection.
  • effector-dependent abortive infection confers Retron system METPO:2007700

    Associated effector activity realizes the Retron system defense phenotype.

    • DOI:10.1016/j.cell.2020.09.065 retrons, functioning together with their associated effector genes, form anti-phage defense systems Millman et al. support complete retron systems in which the retron and associated effector genes together confer defense.
  • Retron system is a phage defense system rdfs:subClassOf

    Retron system possession is a phage-defense-system trait.

    • DOI:10.1016/j.cell.2020.09.065 We report that retrons function as anti-phage defense systems Millman et al. support Retron system as a child of phage defense system.

Provenance

Identifier source
TraitMech local identifier
Definition source
DOI:10.1016/j.cell.2020.09.065

Parent traits (1)

kg-microbe context

No kg-microbe node embedding matched this record in the 2026-04-25 deepwalk.

Canonical examples (1)

Organisms cited as exemplars of this trait. Taxon ids are NCBITaxon and link out to the NCBI record.

  • Escherichia coli NCBITaxon:562 DOI:10.1016/j.cell.2020.09.065 Millman et al. cloned E. coli Ec48 and Ec73 retrons with their predicted effector genes into E. coli MG1655 and showed that both engineered E. coli systems had broad antiphage activity that depended on reverse-transcriptase catalytic-site residues.

Discussions and Knowledge Gaps (1)

Open questions attached to this trait. Seeded by just knowledge-gap-scan and curated; see the corpus-wide index.

Resolve retron effector, phage-trigger, and hybrid-system diversity before minting narrower Retron-Sen2, Ec48, or Retron-Septu mechanism children.

KNOWLEDGE GAP OPEN retron-effector-trigger-gap · raised by codex · 2026-09-15

Not yet attached to a section of this record — a curator sets attaches_to (e.g. causal_graphs#some_edge) so the gap shows beside the mechanism it concerns.

Millman et al. support multiple RT/ncRNA/effector retron systems as abortive-infection antiphage systems, and Bobonis et al. resolve the Retron-Sen2 RcaT example in which a reverse-transcriptase-msDNA antitoxin complex responds to phage-triggered msDNA modification. The first TraitRecord therefore stays at the broad retron-system level until separate subtype review resolves which effectors, guarded host targets, phage triggers, direct-msDNA modification steps, and Septu-coupled architectures apply across each retron family.

Curation history

  1. · MINTED_TRAITMECH_ID · codex

    Minted Retron system as a DOI-backed GENOMICS TraitRecord under the phage defense system parent after an ignored-and-hidden duplicate review found no exact live TraitMech, METPO, or prior proposal record; the replacement placeholder is reserved in proposals/metpo_traitmech_v112.