Qu Feng, Ye Xiaohong, Hou Guichuan, Sato Shirley, Clemente Thomas E, Morris T Jack
School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68588-0666, USA.
J Virol. 2005 Dec;79(24):15209-17. doi: 10.1128/JVI.79.24.15209-15217.2005.
SDE1/SGS2/RDR6, a putative RNA-dependent RNA polymerase (RdRP) from Arabidopsis thaliana, has previously been found to be indispensable for maintaining the posttranscriptional silencing of transgenes, but it is seemingly redundant for antiviral defense. To elucidate the antiviral role of this RdRP in a different host plant and to evaluate whether plant growth conditions affect its role, we down-regulated expression of the Nicotiana benthamiana homolog, NbRDR6, and examined the plants for altered susceptibility to various viruses at different growth temperatures. The results we describe here clearly show that plants with reduced expression of NbRDR6 were more susceptible to all viruses tested and that this effect was more pronounced at higher growth temperatures. Diminished expression of NbRDR6 also permitted efficient multiplication of tobacco mosaic virus in the shoot apices, leading to serious disruption with microRNA-mediated developmental regulation. Based on these results, we propose that NbRDR6 participates in the antiviral RNA silencing pathway that is stimulated by rising temperatures but suppressed by virus-encoded silencing suppressors. The relative strengths of these two factors, along with other plant defense components, critically influence the outcome of virus infections.
SDE1/SGS2/RDR6是一种来自拟南芥的假定的RNA依赖性RNA聚合酶(RdRP),此前已发现它对于维持转基因的转录后沉默不可或缺,但它在抗病毒防御方面似乎是冗余的。为了阐明这种RdRP在不同宿主植物中的抗病毒作用,并评估植物生长条件是否会影响其作用,我们下调了本氏烟草同源物NbRDR6的表达,并检测了这些植物在不同生长温度下对各种病毒易感性的变化。我们在此描述的结果清楚地表明,NbRDR6表达降低的植物对所有测试病毒更易感,并且这种效应在较高生长温度下更为明显。NbRDR6表达的降低还使烟草花叶病毒能够在茎尖高效繁殖,导致microRNA介导的发育调控受到严重破坏。基于这些结果,我们提出NbRDR6参与了抗病毒RNA沉默途径,该途径受温度升高刺激,但被病毒编码的沉默抑制子抑制。这两个因素以及其他植物防御成分的相对强度,严重影响病毒感染的结果。