Light-dependent expression and accumulation of miR408-encoded peptide, miPEP408, is regulated by HY5 in Arabidopsis

Recent studies propose that primary transcripts of miRNAs (pri-miRNAs) contain small Open Reading Frames (ORFs) capable of encoding miRNA-encoded peptides (miPEPs). These miPEPs can function as transcriptional regulators for their corresponding pri-miRNAs, ultimately enhancing mature miRNA accumulation. Notably, pri-miR408 encodes the functional peptide miPEP408, regulating expression of miR408 and its target genes, providing plant tolerance to stresses. While miPEPs are crucial regulators, the factors governing them are have not been studied in detail. Here, we explored the light-dependent regulation of miPEP408 in Arabidopsis. Expression analysis during dark-light transitions revealed light-induced transcription and accumulation of the miPEP408. As the promoter of miR408 contains cis-acting elements responsible for binding to the bZIP-type transcription factor ELONGATED HYPOCOTYL5 (HY5), known for light-mediated regulation in plants, we studied its involvement in the regulation of miR408. Analysis of HY5 mutant (hy5-215), complemented line (HY5OX/hy5), and CONSTITUTIVE PHOTOMORPHOGENIC 1 mutant (cop1-4) plants supported HY5's positive regulation of miPEP408. Grafting and GUS assays further suggested the role of HY5 as a shoot-root mobile signal inducing light-dependent miPEP408 expression. This study underscores the regulatory impact of light on small peptides, exemplified by miPEP408, mediated by the key transcription factor HY5.