Systemic Integration of Chromatin and Metabolism in Stress Memory: Insights from Grafted Citrus

Plants experience environmental stresses as recurrent rather than isolated events, yet how long-lived grafted perennials retain and use prior stress experience remains poorly understood. Perennial crops provide valuable systems for investigating stress memory across developmental and seasonal timescales, while grafted plants add an additional systemic dimension through interactions between rootstock and scion. Here, we synthesize current evidence for stress memory in grafted perennials, integrating physiological, hormonal, epigenetic, redox, transcriptomic, and metabolomic perspectives, with citrus serving as the principal empirical model. We evaluate how systemic signalling, chromatin-associated regulation, metabolic reprogramming, and developmental continuity may contribute to altered responses during later stress encounters. We further examine evidence that some stress-associated effects can persist in meristem-derived tissues and influence responses of subsequently grafted plants. Importantly, such outcomes are context-dependent and may be adaptive, neutral, or maladaptive depending on genotype, graft combination, and environment. Finally, we identify key conceptual gaps and propose testable predictions concerning memory storage, persistence versus resetting, cross-stress interactions, and the extent to which common principles operate across grafted perennial crops. Resolving these questions may help advance more predictive frameworks for improving resilience in long-lived agricultural systems under climate change.