Zahid Kiran, Zhao Jian-Hua, Smith Neil A, Schumann Ulrike, Fang Yuan-Yuan, Dennis Elizabeth S, Zhang Ren, Guo Hui-Shan, Wang Ming-Bo
CSIRO Plant Industry, Canberra, Australian Capital Territory, Australia; School of Biological Sciences, University of Wollongong, Wollongong, New South Wales, Australia.
State Key Laboratory of Plant Genomics and National Center for Plant Gene Research, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
PLoS Genet. 2015 Jan 8;11(1):e1004906. doi: 10.1371/journal.pgen.1004906. eCollection 2015 Jan.
Satellite RNAs (satRNAs) are small noncoding subviral RNA pathogens in plants that depend on helper viruses for replication and spread. Despite many decades of research, the origin of satRNAs remains unknown. In this study we show that a β-glucuronidase (GUS) transgene fused with a Cucumber mosaic virus (CMV) Y satellite RNA (Y-Sat) sequence (35S-GUS:Sat) was transcriptionally repressed in N. tabacum in comparison to a 35S-GUS transgene that did not contain the Y-Sat sequence. This repression was not due to DNA methylation at the 35S promoter, but was associated with specific DNA methylation at the Y-Sat sequence. Both northern blot hybridization and small RNA deep sequencing detected 24-nt siRNAs in wild-type Nicotiana plants with sequence homology to Y-Sat, suggesting that the N. tabacum genome contains Y-Sat-like sequences that give rise to 24-nt sRNAs capable of guiding RNA-directed DNA methylation (RdDM) to the Y-Sat sequence in the 35S-GUS:Sat transgene. Consistent with this, Southern blot hybridization detected multiple DNA bands in Nicotiana plants that had sequence homology to Y-Sat, suggesting that Y-Sat-like sequences exist in the Nicotiana genome as repetitive DNA, a DNA feature associated with 24-nt sRNAs. Our results point to a host genome origin for CMV satRNAs, and suggest novel approach of using small RNA sequences for finding the origin of other satRNAs.
卫星RNA（satRNAs）是植物中的小型非编码亚病毒RNA病原体，其复制和传播依赖于辅助病毒。尽管经过了数十年的研究，satRNAs的起源仍然未知。在本研究中，我们发现与不包含黄瓜花叶病毒（CMV）Y卫星RNA（Y-Sat）序列的35S-GUS转基因相比，与CMV Y卫星RNA序列（35S-GUS:Sat）融合的β-葡萄糖醛酸酶（GUS）转基因在烟草中受到转录抑制。这种抑制不是由于35S启动子处的DNA甲基化，而是与Y-Sat序列处的特异性DNA甲基化有关。Northern印迹杂交和小RNA深度测序均在野生型烟草植株中检测到与Y-Sat具有序列同源性的24核苷酸小干扰RNA（siRNAs），这表明烟草基因组包含Y-Sat样序列，这些序列可产生能够将RNA指导的DNA甲基化（RdDM）导向35S-GUS:Sat转基因中Y-Sat序列的24核苷酸小RNA。与此一致的是，Southern印迹杂交在烟草植株中检测到多个与Y-Sat具有序列同源性的DNA条带，这表明Y-Sat样序列以重复DNA的形式存在于烟草基因组中，这是一种与24核苷酸小RNA相关的DNA特征。我们的结果表明CMV satRNAs起源于宿主基因组，并提出了一种利用小RNA序列寻找其他satRNAs起源的新方法。
