Reverse transcribed ssDNA derepresses translation of a retron antiviral protein.

Reverse transcribed ssDNA from retrons derepresses toxin translation, enabling bacterial defense against phages without detectable msDNA in the absence of infection.

• Why it matters: Understanding bacterial immune mechanisms is crucial for developing phage resistance strategies and insights into non-canonical retron functions. This work addresses the gap in knowledge about retrons that do not produce detectable msDNA yet still confer defense.
• What they did: The authors studied Retron-Vpa2 from V. parahaemolyticus, identifying a structured hybrid RNA (hyRNA) transcript containing the reverse transcription template and toxin gene, and demonstrated that phage infection induces msDNA accumulation which triggers toxin expression via RNase H cleavage.
• The result: This mechanism suggests that phage-induced msDNA hybridization to hyRNA derepresses toxin translation, revealing a novel retron-based defense pathway that operates independently of detectable msDNA in uninfected cells.