Heterologous expression of Arabidopsis miR858 modulates biosynthesis of secondary metabolites and affects drought tolerance in tobacco

microRNA858 (miR858) is known to regulate the phenylpropanoid pathway, which synthesizes flavonols, anthocyanin, and lignin. Flavonoids represent an important secondary metabolite in plants that play multi-functional roles. Scarcity of water leads to drought, one of the major environmental stress that severely affects crop growth and development. Plants have developed several adaptive mechanisms for the tolerance of stress conditions like drought that includes multiple signal transduction pathways, alteration in expression of several genes, metabolic adjustments, and synthesis of secondary metabolites. In this study, we have shown that heterologous expression of Arabidopsis thaliana miR858a (AtmiR858a) in Nicotiana tabacum modulates the flavonoid content leading to modulated drought stress responses. Overexpression of AtmiR858a in tobacco led to the decreased expression of MYB transcriptional factor, NtMYB12, and associated genes of phenylpropanoid pathway that are involved in the biosynthesis of flavonoids, and plants showed sensitivity towards drought stress. Simultaneously, the expression of target mimic for miR858 (MIMIC858) in tobacco enhanced the expression of NtMYB12 and genes involved in the biosynthesis of flavonoids and conferred tolerance towards drought stress. This study suggests that alteration in the expression of genes associated with the flavonoid biosynthesis through associated miRNAs can modulate secondary metabolite biosynthesis and drought stress responses. Based on the results of this study, we conclude that miR858 can be considered a possible candidate for enhanced flavonoid biosynthesis and drought tolerance in plants.