Bacterial Retrons Function In Anti-Phage Defense.

Authors :: Millman A
Bernheim A
Stokar-Avihail A
Fedorenko T
Voichek M
Leavitt A
Oppenheimer-Shaanan Y
Sorek R
Source :: Cell [Cell] 2020 Dec 10; Vol. 183 (6), pp. 1551-1561.e12. Date of Electronic Publication: 2020 Nov 05.
Publication Year :: 2020
Abstract: Retrons are bacterial genetic elements comprised of a reverse transcriptase (RT) and a non-coding RNA (ncRNA). The RT uses the ncRNA as template, generating a chimeric RNA/DNA molecule in which the RNA and DNA components are covalently linked. Although retrons were discovered three decades ago, their function remained unknown. We report that retrons function as anti-phage defense systems. The defensive unit is composed of three components: the RT, the ncRNA, and an effector protein. We examined multiple retron systems and show that they confer defense against a broad range of phages via abortive infection. Focusing on retron Ec48, we show evidence that it "guards" RecBCD, a complex with central anti-phage functions in bacteria. Inhibition of RecBCD by phage proteins activates the retron, leading to abortive infection and cell death. Thus, the Ec48 retron forms a second line of defense that is triggered if the first lines of defense have collapsed.<br />Competing Interests: Declaration of Interests R.S. is a scientific cofounder and consultant of BiomX Ltd., Pantheon Ltd., and EcoPhage.<br /> (Copyright © 2020 Elsevier Inc. All rights reserved.)