高表達Nt-RDR1基因的植物,，表現(xiàn)出對病毒的高度敏感（病毒熒光增強）,。Nb為野生型植物對照。
RNA沉默途徑（RNAi途徑）和水楊酸抗性途徑（SA途徑）是植物抗病反應調(diào)控系統(tǒng)中兩條非常重要的信號轉(zhuǎn)導通路,。植物中依賴于RNA的RNA聚合酶（RNA-dependent RNA polymerases, RDRs）家族有不同成員各自參與這兩條抗性途徑。其中,，RDR6參與RNAi途徑,，擴增RNAi途徑的關(guān)鍵因子小RNA（siRNA）,，并對抵抗病毒的侵染起關(guān)鍵的作用；而RDR1主要參與SA介導的抗病毒途徑,。
在一種本明煙（Nicotiana benthamiana）煙草中,， RDR1被發(fā)現(xiàn)自然突變成無功能基因。以往假設認為：可能由于本明煙中與SA-途徑相關(guān)的RDR1的突變,，導致本明煙很容易被病毒感染,，使其成為一種可被多種病毒寄生的植物宿主。
近日,，中國科學院微生物研究所植物基因組學國家重點實驗室郭惠珊研究組通過分析與本明煙RDR1高度同源的普通煙草（Nicotiana tabacum）的RDR1（Nt-RDR1）,，發(fā)現(xiàn)Nt-RDR1在本明煙中過表達，非但不能提高本明煙對病毒的抗性,，反而使本明煙對很多病毒出現(xiàn)超感表型,。他們進一步研究發(fā)現(xiàn)，Nt-RDR1蛋白具有RNA沉默抑制子活性,。Nt-RDR1蛋白能抑制RDR6參與的RNAi途徑,，干擾依賴RDR6產(chǎn)生的siRNA的沉默活性。該研究提供證據(jù)表明：RDR1蛋白具有雙功能作用,，一方面,，參與SA抗性途徑，另一方面,，抑制RDR6介導的抗病毒RNAi途徑,。
該項研究揭示了本明煙RDR1自然突變的生物學意義。闡明本明煙RDR1的自然突變可能是植物本身長期面臨廣泛病毒侵染的選擇壓力而發(fā)生的結(jié)果,，通過RDR1的失活突變以激活更強的RDR6介導的抗病毒能力,。該研究為植物抗病途徑在農(nóng)業(yè)抗病毒生產(chǎn)應用上提供了新的證據(jù)。研究論文已在線發(fā)表于2010年4月16日的《植物細胞》（The Plant Cell）上,。（生物谷Bioon.com）
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生物谷推薦原文出處：
Plant Cell doi：10.1105/tpc.109.072058
RNA-Dependent RNA Polymerase 1 from Nicotiana tabacum Suppresses RNA Silencing and Enhances Viral Infection in Nicotiana benthamiana
Xiao-Bao Yinga,b, Li Donga, Hui Zhua,b, Cheng-Guo Duana, Quan-Sheng Dua, Dian-Qiu Lva,c, Yuan-Yuan Fanga, Juan Antonio Garciad, Rong-Xiang Fanga and Hui-Shan Guoa,1
a State Key Laboratory of Plant Genomics and National Center for Plant Gene Research (Beijing), Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China
b Graduate University of Chinese Academy of Sciences, Beijing, 100049, China
c Virus-Free Seedling Institute of Heilongjiang Academy of Agricultural Sciences, Heilongjiang, 150086, Haerbin
d Department of Plant Molecular Genetics, Centro National de Biotecnologia (Consejo Superior de Investigaciones Científicas), Campus Universidad Autonoma de Madrid, 28049 Madrid, Spain
Endogenous eukaryotic RNA-dependent RNA polymerases (RDRs) produce double-stranded RNA intermediates in diverse processes of small RNA synthesis in RNA silencing pathways. RDR6 is required in plants for posttranscriptional gene silencing induced by sense transgenes (S-PTGS) and has an important role in amplification of antiviral silencing. Whereas RDR1 is also involved in antiviral defense in plants, this does not necessarily proceed through triggering silencing. In this study, we show that Nicotiana benthamiana transformed with RDR1 from Nicotiana tabacum (Nt-RDR1 plants) exhibits hypersusceptibility to Plum pox potyvirus and other viruses, resembling RDR6-silenced (RDR6i) N. benthamiana. Analysis of transient induction of RNA silencing in N. benthamiana Nt-RDR1 and RDR6i plants revealed that Nt-RDR1 possesses silencing suppression activity. We found that Nt-RDR1 does not interfere with RDR6-dependent siRNA accumulation but turns out to suppress RDR6-dependent S-PTGS. Our results, together with previously published data, suggest that RDR1 might have a dual role, contributing, on one hand, to salicylic acid–mediated antiviral defense, and suppressing, on the other hand, the RDR6-mediated antiviral RNA silencing. We propose a scenario in which the natural loss-of-function variant of RDR1 in N. benthamiana may be the outcome of selective pressure to maintain a high RDR6-dependent antiviral defense, which would be required to face the hypersensitivity of this plant to a large number of viruses.
