Resistance to Bacterial Pathogens in Plants

To successfully infect a plant, pathogens must overcome three layers of defense: (1) preformedphysical barriers; (2) a cell-surface-based surveillance system that detects conserved pathogenmolecules and (3) an intracellular surveillance system that detects effector proteins injected into host cells. Bacterial plant pathogens overcome the first layer either by invading through natural openings and wounds, and/or by secreting hydrolytic enzymes that break down surface layers. Bacteria typically overcome the second layer by injecting effectors that interfere with defense signaling. Bacteria overcome the third layer either by modifying or eliminating existing effectors, or by evolving new effectors that suppress defense activation.