Identification of Nuclear Dicing Bodies Containing Proteins for MicroRNA Biogenesis in Living Arabidopsis Plants

摘要

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) [, ] and other proteins including the zinc finger domain protein Serrate (SE) [, ] and a double-stranded RNA (DsRNA) binding domain protein Hyponastic Leaves1 (HYL1) [–]. Furthermore, plant miRNAs are methylated by Hua Enhancer (HEN1) at their 3’ ends [] and loaded onto Argonuate1 (AGO1) []. 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 [, ]. A mutated DCL1 with impaired function in miRNA processing fails to target to D-bodies, and an introduced pri-miRNA transcrpt is recruited to D-bodies. Furthermore, bi-molecular fluorescence complementation (BiFC) shows that DCL1, HYL1 and SE interact in D-bodies. Based upon 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.