Tomato torrado virus (ToTV) is a type member of the Torradovirus genus in the Secoviridae family known to cause severe necrosis in susceptible tomato varieties. ToTV also infects other Solanaceae plants, including Nicotiana benthamiana, where it induces distinctive disease symptoms: plant growth drop with the emergence of spoon-like malformed systemic leaves. Virus-induced post-transcriptional gene silencing (PTGS) is significant among plant defense mechanisms activated upon virus invasion. The PTGS, however, can be counteracted by suppressors of RNA silencing commonly found in viruses, which efficiently disrupt the antiviral defense of their host. Here we addressed a question of PTGS antiviral activity and its suppression in N. benthamiana during ToTV infection – a phenomenon not described for any representative from the Torradovirus genus so far. First, we showed that neither the Vp26 – necrosis-inducing pathogenicity determinant of ToTV nor other structural viral proteins – limited the locally induced PTGS similarly to the p19, a well-characterized potent suppressor of RNA silencing of tombusviruses. Moreover, by employing wild-type and transgenic lines of N. benthamiana with suppressed Dicer-like 2, Dicer-like 4 (DCL2 and DCL4), Argonaute2 (AGO2) and RNA-dependent RNA6 (RDR6) proteins, we proved their involvement in anti-ToTV defense. Additionally, we identified the DCL4 as the major processor of ToTV-derived siRNA. More importantly, our results indicate the essential role of the SGS3/RDR6 pathway in anti-ToTV defense. Finally, we conclude that ToTV might not require a potent RNA silencing suppressor during infection of the model plant N. benthamiana.

中文翻译：

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Dicer 样蛋白 4 和 RNA 依赖性 RNA 聚合酶 6 参与烟草番茄 Torrado 病毒发病机制

番茄托拉多病毒（ToTV）是塞科病毒科托拉多病毒属的一种类型成员，已知会导致易受影响的番茄品种严重坏死。ToTV 还感染其他茄科植物，包括本塞姆氏烟草，它会诱发独特的疾病症状：植物生长下降，出现勺状畸形的全身叶子。病毒诱导的转录后基因沉默（PTGS）在病毒入侵时激活的植物防御机制中具有重要意义。然而，PTGS 可以被病毒中常见的 RNA 沉默抑制因子所抵消，从而有效破坏宿主的抗病毒防御。在这里，我们解决了 ToTV 感染期间本塞姆氏烟草中 PTGS 抗病毒活性及其抑制的问题——迄今为止，托拉多病毒属的任何代表都没有描述过这种现象。首先，我们表明，Vp26（ToTV 的坏死诱导致病性决定因素）和其他结构病毒蛋白都不会限制局部诱导的 PTGS，与 p19 类似，p19 是一种充分表征的烟草病毒 RNA 沉默的有效抑制因子。此外，通过使用具有抑制的 Dicer-like 2、Dicer-like 4（DCL2 和 DCL4）、Argonaute2（AGO2）和 RNA 依赖性 RNA6（RDR6）蛋白的本塞姆氏烟草野生型和转基因品系，我们证明了它们参与反 ToTV 防御。此外，我们确定 DCL4 是 ToTV 衍生 siRNA 的主要处理器。更重要的是，我们的结果表明 SGS3/RDR6 通路在抗 ToTV 防御中的重要作用。最后，我们得出结论，ToTV 在感染模型植物本塞姆氏烟草期间可能不需要有效的 RNA 沉默抑制子。