Current Biology
Volume 17, Issue 9, 1 May 2007, Pages 818-823
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Identification of Nuclear Dicing Bodies Containing Proteins for MicroRNA Biogenesis in Living Arabidopsis Plants

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Summary

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, 2 and other proteins including the zinc-finger-domain protein Serrate (SE) 3, 4 and a double-stranded RNA (dsRNA) binding-domain protein, Hyponastic Leaves1 (HYL1) 5, 6, 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 Cajal bodies 10, 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.

RNA

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