Agrobacterium tumefaciens, which is a pathogen of numerous dicot plants, contains a tumor-inducing plasmid (Ti). The Ti plasmid has now been transformed into a cloning vector that can still transport genes of interest into a range of plants while no longer being pathogenic to plants.
The art of delivering genes by pathogens in their eukaryotic host has generated knowledge to transform these tools of pathogens into useful vector:

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