Variability in the level of RNA silencing suppression caused by triple gene block protein 1 (TGBp1) from various potexviruses during infection

RNA silencing is an important defence mechanism against virus infection, and many plant viruses encode RNA silencing suppressors as a counter defence. In this study, we analysed the RNA silencing suppression ability of multiple virus species of the genus Potexvirus. Nicotiana benthamiana plants exhibiting RNA silencing of a green fluorescent protein (GFP) transgene showed reversal of GFP fluorescence when systemically infected with potexviruses. However, the degree of GFP fluorescence varied among potexviruses. Agrobacterium-mediated transient expression assay in N. benthamiana leaves demonstrated that the triple gene block protein 1 (TGBp1) encoded by these potexviruses has drastically different levels of silencing suppressor activity, and these differences were directly related to variations in the silencing suppression ability during virus infection. These results suggest that suppressor activities differ even among homologous proteins encoded by viruses of the same genus, and that TGBp1 contributes to the variation in the level of RNA silencing suppression by potexviruses. Moreover, we investigated the effect of TGBp1 encoded by Plantago asiatica mosaic virus (PlAMV), which exhibited a strong suppressor activity, on the accumulation of microRNA, virus genomic RNA and virus-derived small interfering RNAs.

RNA沉默是抵御病毒感染的一种重要防御机制，许多植物病毒编码RNA沉默抑制子作为一种反防御手段。在本研究中，我们分析了马铃薯X病毒属（Potexvirus）多种病毒的RNA沉默抑制能力。本氏烟（Nicotiana benthamiana）植株在其绿色荧光蛋白（GFP）转基因发生RNA沉默时，当系统感染马铃薯X病毒后会出现GFP荧光的恢复。然而，不同马铃薯X病毒的GFP荧光强度有所不同。在本氏烟叶片中进行的农杆菌介导的瞬时表达实验表明，这些马铃薯X病毒编码的三联基因块蛋白1（TGBp1）具有差异极大的沉默抑制子活性水平，并且这些差异与病毒感染过程中沉默抑制能力的变化直接相关。这些结果表明，即使在同一属病毒编码的同源蛋白之间，抑制子活性也存在差异，并且TGBp1导致了马铃薯X病毒RNA沉默抑制水平的变化。此外，我们研究了具有强抑制子活性的车前草花叶病毒（Plantago asiatica mosaic virus，PlAMV）编码的TGBp1对微小RNA、病毒基因组RNA以及病毒来源的小干扰RNA积累的影响。