Picorna-like plant viruses are non-enveloped RNA spherical viruses of ~30 nm. Part of the survival of these viruses depends on their capsid being stable enough to harbour the viral genome and yet malleable enough to allow its release. However, molecular mechanisms remain obscure. Here, we report a structure of a picorna-like plant virus, apple latent spherical virus, at 2.87 Å resolution by single-particle cryo-electron microscopy (cryo-EM) with a cold-field emission beam. The cryo-EM map reveals a unique structure composed of three capsid proteins Vp25, Vp20, and Vp24. Strikingly Vp25 has a long N-terminal extension, which substantially stabilises the capsid frame of Vp25 and Vp20 subunits. Cryo-EM images also resolve RNA genome leaking from a pentameric protrusion of Vp24 subunits. The structures and observations suggest that genome release occurs through occasional opening of the Vp24 subunits, possibly suppressed to a low frequency by the rigid frame of the other subunits.

Picorna 样植物病毒是约 30 nm 的无包膜 RNA 球形病毒。这些病毒的存活部分取决于它们的衣壳足够稳定以容纳病毒基因组，并且具有足够的延展性以允许其释放。然而，分子机制仍不清楚。在这里，我们通过具有冷场发射光束的单粒子冷冻电子显微镜 (cryo-EM) 以 2.87 Å 的分辨率报告了一种类似 picorna 的植物病毒，苹果潜伏球形病毒的结构。冷冻电镜图揭示了一种由三种衣壳蛋白 Vp25、Vp20 和 Vp24 组成的独特结构。引人注目的是 Vp25 有一个长的 N 端延伸，它基本上稳定了 Vp25 和 Vp20 亚基的衣壳框架。冷冻电镜图像还解决了从 Vp24 亚基的五聚体突起泄漏的 RNA 基因组。