Evolution of defense mechanisms causes shifts of power between predator and prey over time. It is a constant back-and-forth power struggle that will only end when a pathogen “gives up” or when it completely overcomes and wipes out the prey population.
In a recent study published in the journal Cell, a group of researchers have discovered that the Arabidopsis plant took its immune defense to the next level against one of its biggest rivals, the bacterial pathogen Ralstonia solanacearum. This bacterium is an extremely effective pathogen that causes wilting in a number of different plants. It works by injecting an effector named PopP2 into the cell, which targets different transcription factors in the nucleus. Under normal conditions, these specific transcription factors associate with and facilitate the transcription of the gene sequences responsible for generating an immune response. PopP2 binds to these transcription factors and prevents the cell from signaling an immune response against the pathogen. The pathogen is then free to commandeer the host cell.
Sounds like checkmate, right?
It turns out the Arabidopsis plant has a few tricks up its sleeve as well. Researchers have observed that this plant has developed “decoy” receptors that are directly integrated into the DNA. The PopP2 effector binds to this decoy and causes the release of the receptor, which is then free to initiate and sustain a quick and powerful immune response against the pathogen. Since the binding activity of the effector is an intrinsic characteristic (it is its fundamental course of action), this defense mechanism is essentially a trap that the effector has no choice but to fall into every time. A complex (and unlikely) evolution of the PopP2 effector that changes its basic characteristics would be needed to prevent this decoy defense.
Our newfound understanding of this defense mechanism has promising implications for commercial use. Genetic manipulation of plants by inserting such “decoys” into their genomes may provide agriculturists with an extremely effective solution to similar pest problems. Molecular mechanisms can often be applied across a very broad range of organisms. While it is far too soon to tell, the hopeful scientist in me would like to think that this new model of defense might open up the possibility of therapeutic developments in other living beings (like animals and humans) as well.
CNRS (Délégation Paris Michel-Ange). “Arabidopsis uses molecular decoy to trick pathogens.” ScienceDaily. ScienceDaily, 5 June 2015. <www.sciencedaily.com/releases/2015/06/150605182417.htm>.