Synechococcus Elongatus Argonaute Reduces Natural Transformation Efficiency and Provides Immunity Against Exogenous Plasmids.

The cyanobacterium Synechococcus elongatus PCC 7942 produces an active prokaryotic Argonaute nuclease, SeAgo, whose function is unknown. Here, we show that SeAgo reduces natural transformation and prevents the maintenance of RSF1010 replicons in S. elongatus. In addition, a Cas4-like nuclease and two other proteins, UvrD and RecJcy (cyanobacterial lineage), were found to reduce the transfer or maintenance of RSF1010 replicons. Like other prokaryotic Argonautes, our results indicate that SeAgo provides defense against invading DNA. An S. elongatus ago deletion strain shares the same morphology, growth rate, and circadian gene expression as the wild type, has higher transformation efficiency, and enables the use of RSF1010-based plasmids for genetic engineering.