MIR408-encoded peptide, miPEP408, regulates cadmium stress response through sulfur assimilation pathway

Small peptides encoded by pri-miRNAs (miPEPs), have been identified as significant plant growth and development regulators. However, their roles in plant-environment interactions and heavy metal stress response remain largely unexplored. Here, we demonstrate that Arabidopsis MIR408-encoded peptide (miPEP408) plays a significant role in cadmium (Cd) stress response by modulating the sulfur assimilation pathway. Using a combination of exogenous synthetic peptide assays, CRISPR/Cas9-mediated knockout mutants (miPEP408^CR), and overexpression lines (miPEP408OX), we analyzed phenotypic and molecular levels to elucidate the function of miPEP408 under Cd stress. Our results suggest that miPEP408 regulates miR408 expression and its targets in response to Cd exposure. Plants treated with exogenous miPEP408 or overexpressing miPEP408 exhibited reduced glutathione (GSH) levels, suppression of sulfur assimilation pathway genes, and heightened sensitivity to Cd. miPEP408^CR plants showed enhanced GSH levels, upregulation of sulfur assimilation genes, and improved Cd detoxification. Furthermore, miPEP408 influenced the expression of Cd transporters and Cd accumulation in plants. In conclusion, this study establishes miPEP408 as a key regulator of Cd stress response in Arabidopsis, functioning through modulation of the sulfur assimilation pathway and metal transporter gene expression. These findings underscore the indispensable role of miPEPs in enhancing plant resilience to heavy metal stress.