Primary transcript of miR858 encodes regulatory peptide and controls flavonoid biosynthesis and development in Arabidopsis

MicroRNAs (miRNAs) are processed products of primary miRNAs (pri-miRNAs) and regulate the target gene expression. Though the regulatory roles of the several mature plant miRNAs have been studied in detail, the functions of other regions of the pri-miRNAs are still unrecognized. Recent studies suggest that a few pri-miRNAs may encode small peptides, miRNA-encoded peptides (miPEPs); however, the functions of these peptides have not been studied in detail. We report that the pri-miR858a of Arabidopsis thaliana encodes a small peptide, miPEP858a, which regulates the expression of pri-miR858a and associated target genes. miPEP858a-edited and miPEP858a-overexpressing lines showed altered plant development and accumulated modulated levels of flavonoids due to changes in the expression of genes associated with the phenylpropanoid pathway and auxin signalling. The exogenous treatment of the miPEP858a-edited plants with synthetic miPEP858a complemented the phenotypes and the gene function. This study suggests the importance of miPEP858a in exerting control over plant development and the phenylpropanoid pathway. The primary miR858a transcript encodes a micro-peptide (miPEP) that regulates its own expression. This mechanism regulates the flavonoid biosynthesis pathway. It is the second miPEP functionally characterized in plants.