Stress priming, memory, and signalling in plants.

Plants need to cope with changing environmental conditions, be it variable light or temperature, different availability of water or nutrients, or attack by pathogens or insects. Some of these changing conditions can become stressful and require strong countermeasures to ensure plant survival. Plants have evolved numerous distinct sensing and signalling mechanisms to perceive and respond appropriately to a variety of stresses. Because of the unpredictable nature of numerous stresses, resource-saving stress response mechanisms are inducible and become activated only upon a stress experience. Furthermore, plants have evolved mechanisms by which they can remember past stress events and prime their responses in order to react more rapidly or more strongly to recurrent stress. Research over the last decade has revealed mechanisms of this information storage and retrieval, which include epigenetic regulation, transcriptional priming, primed conformation of proteins, or specific hormonal or metabolic signatures. There is also increasing understanding of the ecological constraints and relevance of stress priming and memory. This special issue presents research articles and reviews addressing various aspects of this exciting and growing field of research. Here, we introduce the topic by referring to the articles published in this issue, and we outline open questions and future directions of research.