Han Meng-Hsuan, Goud Saiprasad, Song Liang, Fedoroff Nina
Biology Department and Huck Institutes of Life Sciences, Pennsylvania State University, University Park, PA 16802, USA.
Proc Natl Acad Sci U S A. 2004 Jan 27;101(4):1093-8. doi: 10.1073/pnas.0307969100. Epub 2004 Jan 13.
The Arabidopsis HYL1 gene encodes a nuclear double-stranded RNA-binding protein. A knockout mutation of the hyl1 gene is recessive and pleiotropic, causing developmental abnormalities, increasing sensitivity to abscisic acid, and reducing sensitivity to auxin and cytokinin. We report that levels of several microRNAs (miRNAs; miR159, -167, and -171) are reduced in homozygous mutant plants, and levels of two of three tested target mRNAs are elevated. Conversely, the miRNA levels are elevated in plants expressing a HYL1 cDNA from a strong promoter, and the corresponding target RNAs are reduced. These changes result from alterations in the stability of the target RNAs. However, double-stranded RNA-induced posttranscriptional gene silencing is unaffected by the hyl1 mutation. One-third to one-half of the cellular HYL1 protein is in a macromolecular complex, and a GFP-HYL1 fusion protein is found predominantly in the nucleus, although it is observed in both nucleus and cytoplasm in some cells. Within nuclei, HYL1 is associated with subnuclear bodies and ring-like structures. These observations provide evidence that the HYL1 protein is part of a nuclear macromolecular complex that is involved in miRNA-mediated gene regulation. Because hyl1 mutants show marked abnormalities in hormone responses, these results further suggest that miRNA-mediated changes in mRNA stability play a vital role in plant hormone signaling.
拟南芥HYL1基因编码一种核双链RNA结合蛋白。hyl1基因的敲除突变是隐性且多效性的，会导致发育异常，增加对脱落酸的敏感性，并降低对生长素和细胞分裂素的敏感性。我们报道，在纯合突变体植株中，几种微小RNA（miRNA；miR159、-167和-171）的水平降低，而三个测试靶标mRNA中的两个水平升高。相反，在从强启动子表达HYL1 cDNA的植株中，miRNA水平升高，相应的靶标RNA水平降低。这些变化是由靶标RNA稳定性的改变引起的。然而，双链RNA诱导的转录后基因沉默不受hyl1突变的影响。细胞中三分之一到二分之一的HYL1蛋白存在于大分子复合物中，GFP-HYL1融合蛋白主要存在于细胞核中，尽管在某些细胞的细胞核和细胞质中都能观察到。在细胞核内，HYL1与亚核小体和环状结构相关。这些观察结果提供了证据，表明HYL1蛋白是参与miRNA介导的基因调控的核大分子复合物的一部分。由于hyl1突变体在激素反应中表现出明显异常，这些结果进一步表明，miRNA介导的mRNA稳定性变化在植物激素信号传导中起着至关重要的作用。
