Plant Stress Biology in a Warming World: Synergies in Abiotic and Biotic Adaptation

Climatic volatility exposes crops to repeated, irregular and often overlapping episodes of heat, drought, salinity and cold, and this pattern of recurrence differs qualitatively from the single severe stress events around which most tolerance breeding has been organised. Plants respond to a first stress episode with molecular changes that persist beyond the recovery period and alter the response to a subsequent episode, a phenomenon described as priming or stress memory. Chromatin modification, nucleosome remodelling, small RNA activity, transcript stability and DNA methylation have all been proposed as carriers of this information, and a further proposal holds that some of it survives meiosis and can therefore be exploited in breeding. This review evaluates the strength, internal consistency and agronomic reach of that proposition. Evidence is organised around five questions: what memory is and how it can be distinguished from continuing physiological adjustment; which molecular carriers are supported by mechanistic rather than correlative evidence; how long memory persists and what causes it to decay; whether stress-induced epigenetic states are transmitted across generations reliably enough to be selected upon; and whether priming and heritable epigenetic variation act synergistically in the field. The evidence is strongest for histone H3 lysine 4 methylation and nucleosome-level chromatin changes as carriers of somatic transcriptional memory in model species, where inducible perturbation experiments have supported causal interpretation. Evidence for stress-induced, environmentally directed and stably heritable DNA methylation change in crops is substantially weaker, and several well-controlled experiments report no consistent methylome response. Field-scale priming benefits in cereals are real but modest, context-dependent and rarely traced to a defined epigenetic mechanism. The synergy proposed between priming and heritable epigenetic variation remains a plausible working model rather than a demonstrated agronomic strategy, and the principal constraint is not conceptual but methodological.