Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pests, Ministry of Education and College of Plant Protection, Hainan University, Haikou, Hainan, China.
Institute of Tropical Bioscience and Biotechnology, Chinese Academy of Tropical Agricultural Sciences, Haikou, Hainan, China.
J Virol. 2020 Dec 9;95(1). doi: 10.1128/JVI.01414-20.
is the largest family of plant-infecting RNA viruses and includes many agriculturally and economically important viral pathogens. The viruses in the family, known as potyvirids, possess single-stranded, positive-sense RNA genomes with polyprotein processing as a gene expression strategy. The N-terminal regions of potyvirid polyproteins vary greatly in sequence. Previously, we identified a novel virus species within the family, (ANSSV), which was predicted to encode two cysteine proteases, HCPro1 and HCPro2, in tandem at the N-terminal region. Here, we present evidence showing self-cleavage activity of these two proteins and define their -cleavage sites. We demonstrate that HCPro2 is a viral suppressor of RNA silencing (VSR), and both the variable N-terminal and conserved C-terminal (protease domain) moieties have antisilencing activity. Intriguingly, the N-terminal region of HCPro1 also has RNA silencing suppression activity, which is, however, suppressed by its C-terminal protease domain, leading to the functional divergence of HCPro1 and HCPro2 in RNA silencing suppression. Moreover, the deletion of HCPro1 or HCPro2 in a newly created infectious clone abolishes viral infection, and the deletion mutants cannot be rescued by addition of corresponding counterparts of a potyvirus. Altogether, these data suggest that the two closely related leader proteases of ANSSV have evolved differential and essential functions to concertedly maintain viral viability. The represent the largest group of known plant RNA viruses and account for more than half of the viral crop damage worldwide. The leader proteases of viruses within the family vary greatly in size and arrangement and play key roles during the infection. Here, we experimentally demonstrate the presence of a distinct pattern of leader proteases, HCPro1 and HCPro2 in tandem, in a newly identified member within the family. Moreover, HCPro1 and HCPro2, which are closely related and typically characterized with a short size, have evolved contrasting RNA silencing suppression activity and seem to function in a coordinated manner to maintain viral infectivity. Altogether, the new knowledge fills a missing piece in the evolutionary relationship history of potyvirids and improves our understanding of the diversification of potyvirid genomes.
是植物侵染 RNA 病毒中最大的家族，包括许多农业和经济上重要的病毒病原体。该家族中的病毒被称为马铃薯 Y 病毒属，它们具有单链、正链 RNA 基因组，采用多蛋白加工作为基因表达策略。马铃薯 Y 病毒属多蛋白的 N 端区域在序列上差异很大。此前，我们在该家族中鉴定出了一个新的病毒物种，（ANSSV），它被预测在 N 端区域串联编码两个半胱氨酸蛋白酶，HCPro1 和 HCPro2。在这里，我们提供了证据表明这两种蛋白质具有自我切割活性，并定义了它们的 -切割位点。我们证明 HCPro2 是一种病毒 RNA 沉默抑制子（VSR），可变的 N 端和保守的 C 端（蛋白酶结构域）部分都具有抗沉默活性。有趣的是，HCPro1 的 N 端区域也具有 RNA 沉默抑制活性，但被其 C 端蛋白酶结构域抑制，导致 HCPro1 和 HCPro2 在 RNA 沉默抑制中的功能分化。此外，在新创建的传染性克隆中缺失 HCPro1 或 HCPro2 会导致病毒感染的丧失，并且缺失突变体不能通过添加马铃薯 Y 病毒属的相应对应物来挽救。总之，这些数据表明，ANSSV 的两个密切相关的前导蛋白酶已经进化出不同的、必不可少的功能，以协同维持病毒的生存能力。马铃薯 Y 病毒属是已知的最大的植物 RNA 病毒群，占全球病毒作物损害的一半以上。该家族中的病毒前导蛋白酶在大小和排列上差异很大，在感染过程中发挥着关键作用。在这里，我们通过实验证明了在家族中的一个新成员中存在一种独特的串联前导蛋白酶模式，HCPro1 和 HCPro2。此外，HCPro1 和 HCPro2 是密切相关的，通常具有较短的大小，已经进化出不同的 RNA 沉默抑制活性，似乎以协调的方式发挥作用，以维持病毒的感染力。总的来说，新知识填补了马铃薯 Y 病毒属进化关系历史中的一个空缺，提高了我们对马铃薯 Y 病毒属基因组多样化的理解。
