Cross-kingdom mechanisms of trained immunity in plant systemic acquired resistance

Plants face constant microbial threats and have evolved highly effective immune systems characterized by inducible defence mechanisms. On recognizing microbial patterns and/or effectors, plants activate localized pattern-triggered immunity and/or effector-triggered immunity, which culminate in systemic acquired resistance-a broad-spectrum immune response that enhances protection throughout the plant. Systemic acquired resistance shares striking similarities with mammalian trained immunity, particularly in defence priming, which equips organisms with an enhanced capacity to respond to subsequent infections. This Review explores the cross-kingdom similarities between systemic acquired resistance and trained immunity, emphasizing their potential to transform agricultural practices and medical therapies. These insights present innovative opportunities for developing new plant-protection strategies, producing disease-resistant crops and optimizing vaccine approaches, while also highlighting critical knowledge gaps to inspire future research.