Plant Immunity–Activating Endophytic Bacteria Induce Dynamic Metabolic Changes in Cultured Plant Cells Without Inhibiting Their Growth

Co-culture of microorganisms with plant cells is a promising approach for inducing gene expression for the synthesis of bioactive compounds in cultured plant cells. However, the use of microorganisms is often difficult because they tend to inhibit the growth of cultured plant cells. In this study, we explored the potential of plant immunity-activating endophytic bacteria for inducing metabolic changes in cultured plant cells. Delftia sp. BR1R-2, originally isolated from a Brassicaceae plant, reportedly activates plant immunity without inhibiting plant growth. Here, we found that strain BR1R-2 had no adverse effects on the growth of tobacco BY-2 cells, even though Escherichia coli, which was examined as a control, markedly inhibited cell growth. In addition, the metabolic profile of BY-2 cells was significantly altered by co-culture with BR1R-2 cells. Strain BR1R-2 induced the expression of defence-related genes and the production of antibacterial compounds in BY-2 cells. Using two wells separated by a 0.6-μm-pore-size filter, we demonstrated that physical contact with strain BR1R-2 was required for the induction of metabolic changes in BY-2 cells. Another plant immunity-activating endophytic bacterium, Pseudomonas sp. RS1P-1, also induced metabolic changes in not only tobacco BY-2 cells but also Arabidopsis T87 cells, without inhibiting their growth. These results indicate that plant immunity-activating endophytic bacteria exhibit great potential for use in altering the metabolic profile of cultured plant cells for the production of valuable phytochemicals.