MicroRNA-mediated regulation of nitrate signaling in crop plants: a focus on rice

Nitrogen is a vital macronutrient essential for plant growth and development. The exogenous application of nitrogenous fertilizers significantly enhances biomass and crop yield. However, excessive use of fertilizers often leads to soil pollution and severe environmental damage. Plants have evolved various strategies to cope with fluctuating environmental nitrate concentrations. In recent years, substantial advances have been made to elucidate the molecular pathways involved in nitrogen uptake, transport, and downstream regulatory mechanisms. Among these, microRNAs, a class of small, regulatory, non-coding RNAs, are promising regulators of nitrate homeostasis in plants. MicroRNAs primarily target transcription factors and regulate their expression; they are implicated in all aspects of plant growth, development, and stress responses. Advances in sequencing techniques have enabled the discovery of various miRNAs and their target mRNAs involved in nitrate-mediated signaling in crop plants. Manipulating miRNA expression is an effective strategy for developing crop plants with improved Nitrogen Use Efficiency (NUE). In this review, we focus on recent progress and challenges related to nitrate-responsive miRNAs and their target genes that regulate nitrate signaling in crop plants, and on harnessing these miRNAs for crop improvement, particularly in rice.