Tripartite toxin-antitoxin systems: expanding the paradigm of molecular interplay and antiphage defense.

Tripartite toxin-antitoxin systems expand canonical two-gene TA modules by adding a third component, increasing functional diversity and regulatory potential for stress responses and antiphage defense.

• Why it matters: Canonical TA systems do not capture how TA modules diversify to regulate stress and counter phage infection, leaving the mechanisms and activation pathways of tripartite variants unclear.
• What they did: This review compares tripartite TA architectures—TA-chaperone (TAC), TA-regulator (TAR), dual-antitoxin, and dual-toxin—against bipartite systems, summarizing neutralizing mechanisms and phage-triggered activation pathways.
• The result: Tripartite TAs show greater regulatory capacity and modularity, illuminating evolutionary trajectories and coevolutionary dynamics among TA systems, host bacteria, and phages.

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