17. Pathogens versus Plant Defenses: An Evolutionary Battle
Gregory Martin
Gregory B. Martin, Plant Pathology, and research colleagues at the Boyce Thompson Institute for Plant Research gained insight into how Pseudomonas syringae, a bacterium that infects tomatoes by injecting a protein into the plant’s cells, weakens the plant’s defense system. Resistant plant varieties often become susceptible to pathogens about six years after their release, since pathogens evolve quickly to tear down the plant’s defenses. The researchers showed how a single bacterial protein, AvrPtoB, which P. syringae injects into plant cells with a molecular “syringe,” attacks the plant. The plant’s defense system, in turn, tries to detect the pathogen. As part of its surveillance system, tomatoes carry a protein in their cells called Fen that helps detect P. syringae and trigger an immune response to prevent disease. Some strains of P. syringae have evolved the AvrPtoB protein, which mimics a tomato enzyme known as an E3 ubiquitin ligase that tags proteins to be destroyed. Once injected, AvrPtoB binds to the Fen protein, and the plant’s own system eliminates it, allowing the bacteria to avoid detection as it causes disease. The study provides molecular data on how pathogens develop new ways to spread and attack organisms and the novel defenses organisms create to battle them. Understanding why some plant varieties have more durable disease resistance is important to the development of sustainable agricultural practices.