Plant microRNAs: master regulator of gene expression mechanism.

Several signaling molecules critically regulate the physiological responses in plants. Among them, miRNAs, generally 21-24 nucleotides long, are widely distributed in different plant species and play as key signaling intermediates in diverse physiological responses. The mature miRNAs are synthesized from MIR genes by RNA polymerase II and processed by Dicer-like (DCL) protein family members associated with some accessory protein molecules. The processed miRNAs are transported to the cytoplasm from the nucleus by specific group of transporters and incorporated into RNA-induced silencing complex (RISC) for specific mRNA cleavage. MicroRNAs can suppress the diverse gene expression, depending on the sequence complementarity of the target transcript except of its own gene. Besides, miRNAs can modulate the gene expression by DNA methylation and translational inhibition of the target transcript. Different classes of DCLs and Argonaute proteins (AGOs) help the miRNAs-mediated gene silencing mechanism in plants.