Citrus huanglongbing (HLB), or citrus greening, is caused by a bacterial pathogen (Candidatus Liberibacter asiaticus, CLas) and is considered the most destructive citrus disease worldwide. The disease has affected millions of citrus trees both in Florida and around the world, resulting in billions of dollars in annual production losses. Infection by the CLas disrupts vascular movement, weakens the tree root system, and cause a rapid decline in tree health. Despite extensive research efforts, there are still no effective management tools to cure HLB-positive trees or prevent new infections. Current HLB management strategies include chemical application of insecticides to control the insect vector of the CLas bacterium (the Asian citrus psyllid) and traditional antibiotics that kill the CLas bacterium. Vector control has not been effective and antibiotic use has been complicated because the CLas bacterium resides inside the plant in the vascular system, and it is difficult to get enough antibiotics to penetrate at effective concentrations. We present a novel method of biological molecule delivery method referred to as Symbionts™. In Symbionts™, host cells are modified to divide autonomously using plant growth regulator genes from Agrobacterium tumefaciens and to produce biological molecules that can improve host-plant defenses against CLas. To produce the Symbiont, host cells expressing cargo of interest can either be induced on citrus trees by infection with A. tumefaciens, or cultured symbiont cells can be produced in the lab and transplanted (free of A. tumefaciens).