Emerging of microRNAs as Key Regulators in Plant Secondary Metabolism

microRNAs (miRNAs) are well-known gene regulators of various biological processes in plants. Despite the growing knowledge of the miRNAs as main players in genetic systems, their involvement in regulating plant secondary metabolite (SM) biosynthesis is still poorly understood. In plants, these metabolites provide protection against various types of stresses that arise from unfavorable conditions. These plant-derived compounds are also significantly used in pharmaceuticals, food additives, and fragrances industries. Hence, there is a pressing need to explore how their biosynthetic pathways are being regulated, especially at post-transcriptional level with the involvement of miRNAs. Here, we discuss the recent progress on the post-transcriptional regulation by miRNAs of SMs biosynthetic pathways, namely terpenoids, flavonoids and alkaloids. We also summarize the key points to utilize miRNAs for genetic engineering to manipulate SMs production in plants.