Like other positive-strand RNA viruses, plant potyviruses assemble viral replication complexes (VRCs) on modified cellular membranes. Potyviruses encode two membrane proteins, 6K2 and P3. The former is known to play pivotal roles in the formation of membrane-associated VRCs. However, P3 remains to be one of the least characterized potyviral proteins. The P3 cistron codes for P3 as well as P3N-PIPO which results from RNA polymerase slippage. In this study, we show that the P3N-PIPO of Turnip mosaic virus (TuMV) is required for viral cell-to-cell movement but not for viral replication. We demonstrate that the C-terminal region of P3 (P3C) is indispensable for P3 to form cytoplasmic punctate inclusions and target VRCs. We reveal that TuMV mutants that lack P3C are replication-defective. Taken together, these data suggest that the P3 cistron has two distinct functions: P3N-PIPO as a dedicated movement protein and P3 as an essential component of the VRC.

与其他正链 RNA 病毒一样，植物马铃薯病毒在经过修饰的细胞膜上组装病毒复制复合物 (VRC)。马铃薯Y病毒组编码两种膜蛋白，6K2和P3。已知前者在膜相关 VRC 的形成中发挥关键作用。然而，P3 仍然是特征最少的马铃薯病毒蛋白之一。 P3顺反子编码 P3 以及由 RNA 聚合酶滑移产生的 P3N-PIPO。在这项研究中，我们证明芜菁花叶病毒（TuMV）的 P3N-PIPO 是病毒细胞间移动所必需的，但不是病毒复制所必需的。我们证明 P3 的 C 末端区域 (P3C) 对于 P3 形成细胞质点状包涵体和靶向 VRC 是必不可少的。我们发现缺乏 P3C 的 TuMV 突变体存在复制缺陷。总而言之，这些数据表明P3顺反子具有两种不同的功能：P3N-PIPO 作为专用运动蛋白，P3 作为 VRC 的重要组成部分。