A major challenge in the management of insect-vector borne plant diseases is the in planta delivery of therapeutics to block pathogen infection or insect acquisition and transmission. The ability of Agrobacterium to insert DNA into plant genomes was rapidly adapted to genetic engineering by removing plant growth regulator genes from the Ti plasmid and replacing them with genes that induce desired plant phenotypes and selectable markers, technology which has led to the development of numerous examples of transgenic resistance. However, the transgenic plant adoption in agriculture has been limited. By adding back plant growth regulator genes to a binary transformation vector, we engineered plant cells, referred to here as symbionts (to distinguish from a pathogenic gall), capable of imparting desirable phenotypic traits to plants. We demonstrate symbiont formation with excised and cultured cells cured of Agrobacterium. Thus, symbionts eliminate the risk of environmental release of genetically modified microorganisms. Symbionts enable real-time, in vivo delivery of genetically-encoded molecules to a plant without generation of a transgenic plant. Benefits include: 1) allowing selection of high expression cultured symbiont cells; 2) environmental delivery of only symbiont cells that cannot survive away from plants; thus, mitigating concerns over environmental contamination with modified genetic material; 3) rapid ability to make phenotypic evaluations within two weeks of symbiont formation and 4) production of molecules that can be harvested directly in cell culture or from in planta grown symbionts. Ongoing research is focused on optimizing molecule export from the symbiont into the plant.
