Somatic salt stress memory enhances tolerance in poplar: Insights from integrated transcriptome and physiological analyses

Soil salinization severely restricts the productivity of industrial crops and forest trees, threatening sustainable forestry and biomass production. Enhancing plant salt tolerance is therefore an urgent agricultural and economic imperative. Stress memory, a key adaptive trait developed through repeated stress exposure, can significantly improve plant resilience. However, the molecular mechanisms underlying its formation in trees remain unclear. This study investigated the physiological and transcriptomic responses of Populus yunnanensis to NaCl priming and subsequent recovery. We observed that primed plants exhibited reduced malondialdehyde (MDA) levels and alleviated oxidative damage upon recurrent high salt stress (75 mM NaCl), indicative of an effective somatic (within-generation) salt stress memory. This memory was characterized by enhanced growth traits and the activation of specific early and late transcriptional responses. Key to this adaptation were the stable expression of genes related to plant hormone signal transduction and ion homeostasis (e.g., SOS pathway members), coupled with the sustained induction of genes involved in oxidation-reduction processes. These coordinated transcriptional changes underpinned the maintenance of high antioxidant enzyme activities (SOD, POD) and modulated the accumulation of osmolytes like proline and soluble sugars. Furthermore, co-expression network analysis identified critical hub genes, including transcription factors (TCP, MADS-box, MYB) and epigenetic modifiers, as potential master regulators of this memory state. Our findings elucidate the molecular basis of salt stress memory in poplar, providing valuable genetic targets and insights for breeding improved industrial forest tree varieties with enhanced salinity tolerance.