MicroRNAs (miRNAs) are important for regulating gene expression in muticellular organisms. MiRNA processing is a two-step process. In animal cells, the first step is nuclear and the second step cytoplasmic, whereas in plant cells, both steps occur in the nucleus via the enzyme Dicer-like1 (DCL1)
[1] and
[2] and other proteins including the zinc-finger-domain protein Serrate (SE)
[3] and
[4] and a double-stranded RNA (dsRNA) binding-domain protein, Hyponastic L
eaves1 (HYL1)
[5],
[6] and
[7]. Furthermore, plant miRNAs are methylated by Hua Enhancer (HEN1) at their 3′ ends
[8] and loaded onto Argonaute1 (AGO1)
[9]. However, little is known about the cellular basis of miRNA biogenesis. Using live-cell imaging, we show here that DCL1 and HYL1 colocalize in discrete nuclear bodies in addition to being present in a low-level diffuse nucleoplasmic distribution. These bodies, which we refer to as nuclear dicing bodies (D-bodies), differ from Ca
jal bodies
[10] and
[11]. A mutated DCL1 with impaired function in miRNA processing fails to target to D-bodies, and an introduced primary (pri)-miRNA transcript is recruited to D-bodies. Furthermore, bimolecular fluorescence complementation (BiFC) shows that DCL1, HYL1, and SE interact in D-bodies. On the basis of these data, we propose that D-bodies are crucial for orchestrating pri-miRNA processing and/or storage/assembly of miRNA-processing complexes in the nuclei of plant cells.