Plants Remember Stress Without a Brain: Epigenetic Changes and Soil Legacy

Plants possess the ability to remember stress, a phenomenon that scientists are actively studying to enhance crop resilience amidst climate change. Jurriaan Ton, Professor of Plant Environmental Signalling at the University of Sheffield, notes that plants, since colonizing land 500 million years ago, have developed defense mechanisms, including the capacity to "remember" stressful encounters and use this memory for self-defense. This "immune priming" is akin to how vaccines build human immunity but operates through different mechanisms. Unlike vertebrates with mobile immune systems and memory cells, plants utilize "epigenetic" changes within their cells to store information about past attacks and prime their innate immune system. This allows them to better resist pests and diseases, even if genetically susceptible. Research indicates that repeated exposure to pests or diseases can cause long-lasting epigenetic changes to plant DNA, without altering the underlying sequence. This enables plants to remain in a primed defense state. Immune priming has been observed in various plant species, from short-lived annuals like *Arabidopsis thaliana* [thale cress] to long-living trees like Norway spruce, which can live up to 400 years. While immune priming can reduce growth, the primed memory is reversible and diminishes without ongoing stress. However, strong stress stimuli can lead to lifelong priming, even transmitted to subsequent generations. Plants constantly adjust gene activity to adapt to their environment, with genes being switched off via epigenetic changes, often at transposons (or "jumping genes") – DNA pieces that can move within the genome. Stress can partially "wake them up", driving long-lasting memory. Plants also use their environment to store stress memory. Under attack, they release chemicals from their roots, attracting beneficial microbes that suppress diseases. This "soil legacy" can benefit future plant generations. In species like maize, scientists have identified secondary metabolites driving this external stress memory, with some genes controlling these root chemicals regulated by stress-responsive epigenetic mechanisms. Understanding plant stress memories could transform crop protection, potentially reducing reliance on chemical pesticides and creating crops better equipped to handle environmental stresses. This research offers promising tools for developing more sustainable crop protection schemes.