The miPEP408-miR408 module regulates plant susceptibility to Rhizoctonia solani through LAC3-mediated lignin deposition in Arabidopsis.

Plant microRNAs (miRNAs) function as critical regulators of various developmental and physiological processes by downregulating the expression of their target genes. miRNA-encoded peptides (miPEPs) represent an additional regulatory layer by enhancing the transcription of their cognate miRNAs. . Although miPEP408 has been implicated in heavy-metal tolerance through regulation of sulfur assimilation, its role in plant immunity remains unknown. Here, we investigate the role of the miPEP408-miR408-Laccase3 (LAC3) regulatory cascade in defense against the necrotrophic fungus Rhizoctonia solani AG-1A using Arabidopsis thaliana. Providing mechanistic insight, we demonstrate through DNA-protein interaction assays that miPEP408 directly binds the MIR408 promoter, promoting miR408 accumulation and regulating its downstream target, Laccase3 (LAC3). We further show that LAC3 is a key determinant of defense by promoting lignin deposition in the cell wall to restrict pathogen invasion. In-planta bioassays further demonstrate that infection with the necrotrophic fungal pathogen R. solani AG-1A suppresses miPEP408 accumulation, thereby reducing miR408 expression and enhancing LAC3-mediated defense in Arabidopsis thaliana. Consistently, genetic manipulation of miR408 or LAC3 inversely modulates lignin deposition and disease susceptibility. Together, our findings establish the miPEP408-miR408-LAC3 module as a regulator of lignification-mediated cell wall immunity and identify miPEP408 as a promising target for engineering crops with enhanced resistance to biotic stress.