In the intricate world of biological defense, plants and animals have evolved sophisticated immune systems that, although separated by vast evolutionary distances, show surprising parallels in how they respond to microbial threats. A groundbreaking review by Conrath, published in Nature Plants (2025), sheds light on these cross-kingdom similarities, focusing on the concept of trained immunity as it manifests in plants through systemic acquired resistance (SAR). This revelation not only bridges fundamental gaps in immunology but also opens transformative avenues in agriculture and medicine alike.
Plants, despite their apparent vulnerability, exhibit a robust immune capacity that is inducible rather than constant. Upon detecting molecules associated with pathogenic microbes, known as pathogen-associated molecular patterns (PAMPs), or specific microbial effectors, plants orchestrate a defense strategy termed pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). These responses are localized initially but culminate in systemic acquired resistance, a whole-plant defensive state that primes the organism for enhanced responsiveness to subsequent infection challenges. This priming is the hallmark of a memory-like immune mechanism traditionally thought absent in plants.
The emerging concept of trained immunity, originally described in mammals, involves epigenetic and metabolic reprogramming of innate immune cells that endows them with a heightened state of readiness after initial exposure to a pathogen. Remarkably, SAR in plants exhibits many analogous features, including long-lasting metabolic changes and chromatin remodeling that enable plants to mount quicker and stronger responses upon re-exposure to pathogens. This cross-kingdom convergence reveals that memory-like innate immune adaptations are more universal than previously recognized.
At a molecular level, SAR relies on mobilization and accumulation of signaling molecules such as salicylic acid, pipecolic acid, and various lipid-derived compounds, which orchestrate systemic signaling networks. These molecules do not merely act locally but induce epigenetic modifications across distal tissues, altering gene expression landscapes to foster a primed immunological state. This systemic signaling ensures that even plant parts distant from the initial infection site become fortified against microbial assault, a concept parallel to trained immunity’s systemic nature in mammals.
Further scrutiny into the chromatin dynamics during SAR reveals a complex interplay of histone modifications, nucleosome repositioning, and DNA methylation changes influencing defense gene accessibility. Similar epigenetic mechanisms underpin mammalian trained immunity, where histone marks such as H3K4me3 and H3K27ac remodel the chromatin environment to sustain an enhanced innate immune profile. Such conserved epigenetic strategies across kingdoms underscore the evolutionary utility of modifying genome architecture in immune memory.
In addition to epigenetic reprogramming, metabolic shifts are pivotal during SAR. Plants redirect metabolic flux towards the biosynthesis of phenolic compounds, amino acid derivatives, and antimicrobial secondary metabolites that bolster defense capacity. This metabolic rewiring mirrors observations in mammalian innate immune cells, where glycolytic and mitochondrial reconfigurations fuel trained immunity. Thus, both plants and animals leverage metabolic plasticity as a foundation for immunological memory.
Understanding these shared mechanisms expands the horizon for developing innovative disease management strategies in agriculture. Engineering or breeding crops that capitalize on SAR’s priming potential could result in plants with durable resistance against a broad spectrum of pathogens. Unlike conventional approaches that rely heavily on pesticides or genetically engineered resistance to specific pathogens, enhancing SAR offers a sustainable, holistic method to fortify plant immunity while potentially reducing chemical inputs and environmental impact.
Moreover, the insights gained from comparing plant SAR with mammalian trained immunity have reciprocal benefits for medical science. Vaccinology might draw inspiration from the systemic and epigenetic priming principles observed in plants to devise vaccines or immunotherapies that harness or mimic innate immune memory. Recognizing that complex organisms, regardless of kingdom, have evolved convergent mechanisms to improve immune robustness may revolutionize approaches to infectious disease control.
Despite these promising vistas, significant knowledge gaps remain in fully deciphering the molecular underpinnings, specificity, duration, and trade-offs associated with SAR and trained immunity. For example, how precisely plants discriminate between diverse pathogen signals to tailor SAR, or the potential costs of sustained immune priming on growth and development, require deeper investigation. Similarly, the molecular connectors linking metabolic changes to epigenetic reprogramming in both plants and animals remain incompletely understood.
Future research will need to employ advanced genomic, epigenomic, and metabolomic tools across multiple species to unravel these complexities. High-resolution temporal and spatial analyses of immune priming states can illuminate how memory is encoded, maintained, and erased. Such integrative efforts can lead to the identification of novel biomarkers and targets for manipulating trained immunity or SAR with precision, providing a new frontier in interdisciplinary biology.
This cross-kingdom perspective also calls for greater collaboration between plant scientists and immunologists. Breaking down disciplinary silos can accelerate discoveries that neither field could achieve in isolation. For instance, understanding how plants manage to systemically propagate immune information via mobile signals could inform strategies to enhance systemic innate immune training in humans and animals.
As the world confronts escalating challenges posed by emerging pathogens, climate change, and food security concerns, the significance of durable, broad-spectrum immunity cannot be overstated. The paradigms illuminated by Conrath’s review emphasize that nature’s solutions have often converged on similar principles, despite the vast evolutionary distances separating lineages. Harnessing these conserved mechanisms holds vast potential for sustainable advancements in agriculture and medicine.
In conclusion, systemic acquired resistance in plants and trained immunity in mammals share a deeply conserved repertoire of mechanisms that reshape immune function through priming, epigenetic remodeling, and metabolic reprogramming. This cross-kingdom understanding revolutionizes the concept of immune memory beyond adaptive immunity, highlighting innate immune systems’ dynamic capacities. The implications for disease resistance, crop improvement, vaccine innovation, and fundamental biology are profound, marking an exciting frontier poised to transform multiple scientific landscapes.
The ongoing exploration of these universal immune strategies promises to yield transformative insights and applications, inspirational for researchers, clinicians, and agricultural experts alike. By embracing this integrative view, the next generation of biotechnologies could enhance resilience against infections while promoting health and productivity in both plants and animals, creating a more secure and sustainable future.
Subject of Research: Plant immunity, systemic acquired resistance, trained immunity, cross-kingdom immune mechanisms.
Article Title: Cross-kingdom mechanisms of trained immunity in plant systemic acquired resistance.
Article References:
Conrath, U. Cross-kingdom mechanisms of trained immunity in plant systemic acquired resistance.
Nat. Plants (2025). https://doi.org/10.1038/s41477-025-02119-1
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