Figure 1. Subcellular locations where miRNA biogenesis or activity takes place in plants. A pri-miRNA is processed by a DCL1 complex into a pre-miRNA (arrow 1) and, subsequently, a miRNA:miRNA* duplex (arrow 2). The mature miRNA is loaded into AGO1 and represses target mRNAs through both mRNA cleavage (not diagramed) and translational repression. It is not known whether miRISC is capable of translational repression in the cytosol, but it is likely transported to the rough ER (arrow 3) or P-bodies (arrow 4), both of which are subcellular compartments where translational repression by miRNAs has been implicated to take place. The integral ER membrane protein AMP1 interacts with AGO1 and inhibits the loading of miRNA target mRNAs onto membrane-bound polysomes. How the P-body component and decapping factor VCS mediates the translational repression activity of plant miRNAs is currently unknown. Lipid metabolism (e.g., sterol synthesis), which influences membrane composition or states, also affects miRNA activity via an unknown mechanism. In addition, cytoskeleton (e.g., microtubules) dynamics may influence miRNA activities by affecting the subcellular trafficking of miRISCs.