The immunity paradox: how do plants survive without adaptive immunity?

SUMMARY

Higher plants and mammals exist in similar microbial environments and face similar challenges from microbial pathogens. Both taxonomic groups encode proteins capable of recognizing and triggering responses to pathogens; however, their recognitional capacities differ substantially. The mammalian innate immune system encodes several dozen receptors capable of recognizing a variety of pathogen‐associated molecular patterns and, in addition, has an adaptive immune system with a vast recognitional capacity based on the potential production of up to approximately 10 ¹⁶ –10 ¹⁸ distinct antibodies through somatic recombination in specialized immune cells. By contrast, plants possess only innate immune receptors. The ability of fast‐evolving microbial pathogens to evade the recognitional capabilities of plant innate immune receptors has been clearly demonstrated. Under these circumstances, how do plants, especially species with lifespans of hundreds of years, successfully counteract their populations of rapidly evolving pathogens? Here I discuss the ways that plants navigate their relationship with the microbial world without an adaptive immune system. I suggest that the importance of plant innate immune receptors in resisting infection, though crucial, may often have been overemphasized in the literature. I propose a view of plant immunity which highlights the ability of the plant to suppress, contain and tolerate infections and ways in which this perspective might influence our future actions.