Bacterium Evolves Stealth Strategy Against Tomatoes

Suppose a species has one defense against bacterial infection, then the bacteria evolve to get around the defense. The host species will succumb to infection until another defense evolves to stop the attack. This is known as an evolutionary arms race — a continuous battle between two organisms to outdo each others tactics. Now, Tracy Rosebrock, a plant pathology student at Boyce Thompson Institute for Plant Research at Cornell University, published molecular data supporting the evolutionary arms race theory.

Tomatoes use a protein called Fen to protect themselves from an infectious bacterium, Pseudomonas syringae. Fen triggers an immune response in the tomatoes as soon as it comes across P. syringae.

Now, some strains of P. syringae produce a protein that acts like a tomato enzyme called E3 ubiquitin ligase. E3 ubiquitin ligase binds to proteins that the tomato plant should destroy. The copycat bacterial protein binds to Fen, causing tomato plant to eliminate Fen from its system. P. syringae evolved an effective way to turn off the tomato plants defensive system. The bacterium avoids detection and infects the plant.

The host resistance mechanism of the tomato against P. syringae and now the blocking of this immune response is now understood at the molecular level.

“Plant breeders often find that five or six years after their release, resistant plant varieties become susceptible because pathogens can evolve very quickly to overcome plant defenses,” notes Gregory Martin, Cornell professor of plant pathology and senior author of the research paper. Agricultural scientists and growers may need to look more often at disease resistance at molecular to mount a successful defense in the ongoing evolutionary arms race.

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