Synergistic regulation of abiotic stress adaptation by copper miRNAs miR398 and miR408 in melon.

MicroRNAs (miRNAs) in general and miR398 and miR408 in particular have emerged as key regulators of plant adaptation to individual stress, yet their roles regulating the crop response to diverse unfavorable environments remain poorly explored. Here, we report transgenic melon (Cucumis melo) plants overexpressing miR398 and miR408 precursors, two conserved miRNAs involved in copper-related regulatory pathways and associated with stress response. Engineered plants exhibited enhanced vegetative development, including stem elongation, internode formation, root architecture, and leaf production. The significant increased accumulation of well-processed miR398 and miR408, along with the downregulation of their respective targets (Copper/Zinc Superoxide Dismutase and Basic Blue Protein) demonstrates the functional activity of the transgenes. Sequencing analysis revealed a positive correlation in the accumulation of miR398 and miR408, suggesting a coordinated accumulation pattern with interdependent miRNA regulation, potentially independent of conventional transcription factor activity. Transgenic plants showed improved tolerance to drought, salinity, heat, and cold stress, validating the role of miR398 and miR408 as master regulators of abiotic stress resilience in melon. This work highlights the potential of biotechnological strategies based on engineering Cu-related miRNAs to enhance crop performance under different adverse environments, thereby contributing to agricultural sustainability in the face of climate change.