Exposed to the elements but unable to move, plants must continuously respond to stressors ranging from temperature and moisture changes to nutrient limitations – and they almost always find a way to cope. According to a new Science Advances review, instead of remembering, plants may have learned “forgetting and resetting” as an evolutionary strategy to combat physical stressors. 

Plants grow in dynamic environments. Sometimes extreme drought or cold can last for weeks, even months, and sometimes, plants living in the understory, for example, might suddenly be exposed to light as the Sun moves through the sky over the course of a day. In other words, variables can be cyclic and predictable, or random and unpredictable. Retaining stressful memories might help prime the plants for stronger or faster responses when the disruptions occur again in the future – and it could lead to acclimation and even adaptation. Most researchers agree that plants possess the capacity for memory and memory dissipation (or forgetfulness), though little is known about these two phenomena. 

To investigate, an Australian National University Canberra team led by Barry Pogson reviewed published studies on plant priming, memory, and epigenetics (since stress-induced modifications to DNA do occur). Memory, they found, is likely a relatively rare event, and the predominant strategy of plants is resetting and recovery. “Stress memories may be maladaptive, hindering recovery and affecting development and potential yield,” the authors write. “In some circumstances, it may be advantageous for plants to learn to forget.” It could help them tolerate unpredictable environmental conditions.

Additionally, the team found that the stress recovery period is a key step that decides whether memories are formed or forgotten. During this period, plants weigh memory formation (and potential acclimation) against the benefits of resetting to an original state. And RNA metabolism plays a key role in this delicate balancing act.