mGem: Toxins from killer plasmids as a universal killing system in the fungal kingdom

Killer plasmids are cytosolic linear dsDNA plasmids found in many species of Saccharomycotina, the budding yeasts. They encode toxins that give their hosts an advantage against competitor yeasts in the environment. They cause cell death in their prey by targeting non-coding RNAs of the translation apparatus, either tRNAs or rRNAs. We recently discovered that similar toxin systems are integrated into the nuclear genomes of many filamentous ascomycetes. Cytosolic linear plasmids similar to killer plasmids are also present in two deeply divergent phyla of terrestrial fungi (Zoopagomycota and Mucoromycota), although they have not yet been shown to have killing activity. It is becoming apparent that plasmid-encoded toxin systems or toxin-like systems are far more widespread than previously considered and have impacted upon fungal biology and evolution for hundreds of millions of years.