Drought stress memory enhances the tolerance of alfalfa Medicago sativa L. in response to a subsequent drought: A physiological and omics perspective
Here, we conducted physiological, global DNA methylation, and transcriptome assays on alfalfa (Medicago sativa L.) exposed to recurrent drought stress to investigate stress memory and the response to subsequent drought stress and recovery. Our findings revealed a distinct memory response characterized by significant alterations in DNA cytosine methylation patterns across the genome. Notably, seedlings that underwent drought stress training exhibited enhanced growth and vitality, displaying greener and healthier traits than the control group after rewatering. Increased levels of jasmonic acid and cytokinins in drought stress-trained seedlings underscore the role of phytohormones in drought memory responses. Furthermore, the upregulation of ribulose-1,5-bisphosphate carboxylase/oxygenase, peroxidase, and superoxide dismutase in drought stress-trained alfalfa reinforces the enhanced stress tolerance acquired through drought stress training. A transcriptomic analysis revealed a notable promotion of energy metabolism, photosynthesis, and nitrogen metabolism in alfalfa enabling individuals to endure subsequent drought stress following recurrent drought training. Post-rewatering, alfalfa underwent a metabolic shift from energy metabolism to lipid catabolism to generate energy to cope with drought stress and promote growth. This study provides valuable insights into the mechanisms governing the formation of stress memory in alfalfa exposed to drought, presenting potential strategies for improving plant resilience and productivity in the face of water scarcity induced by climate change.