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 recycle drought stress to investigate stress memory and the response of 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. Jasmonic acid and cytokinin levels were improved in drought stress-trained alfalfa, emphasizing these two hormones play a key role in drought memory responses. Furthermore, the upregulation of RuBisCO, peroxidase, and superoxide dismutase in drought stress-trained alfalfa reinforces the enhanced stress tolerance acquired through drought stress training. Differential DNA methylation during drought training mainly facilitates the selective expression of energy metabolism-related genes. 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 offers valuable understanding into the mechanisms governing the formation of stress memory in alfalfa exposed to drought, presenting potential strategies for improving plant plasticity and productivity under water scarcity induced by climate change.