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Plant immune system

Lucija Luskar

Plants do not have immune cells like humans, so they rely on a complex, efficient, and specific defense system against pathogens. The cuticle and epithelium serve as a physical barrier between the plant and the pathogen, providing continuous defense. In case a pathogen breaches the physical barrier, plants have a system that detects pathogens, known as inducible defense.

Plants are capable of detecting molecular patterns of specific pathogens or their effector molecules. Pattern-triggered immunity (PTI) is initiated when plant pattern recognition receptors (PRRs) detect molecular patterns or molecules associated with the pathogen (PAMPs – microbial or pathogen-associated molecular patterns). As a result, there is a synthesis of salicylic acid, jasmonic acid, ethylene, an oxidative burst, production of antimicrobial substances, callose deposition at the plasmodesmata, and reduced substance transfer from the cytosol to the apoplast.

Throughout evolution, pathogens have developed various strategies to evade such defenses. They have devised methods to suppress defense through effector molecules, bypass it with toxic effectors, or degrade the products of defense signals.

In response, plants have developed effector-triggered immunity (ETI), where R proteins play a role. These proteins detect effector molecules or modifications of key plant proteins. As a result, hypersensitive responses occur, manifested as localized programmed cell death, synthesis of salicylic acid, and an oxidative burst that prevents the spread of the pathogen within the plant. In plants, too, there is a constant evolutionary arms race between the host and the pathogen, with the host developing and adapting receptors to recognize pathogens, while the pathogen evolves new strategies to evade the host’s defense mechanisms.


Lucija Luskar, Slovenian Institute for Hop Reserch and Brewing

Mikro+Polo Company Science Promotor 2023