Viruses on the move | Nature Reviews Microbiology

To complete the infection cycle, positive-strand RNA plant viruses are designed to encode replication proteins and movement proteins to ensure the movement of the viral genome into neighboring cells and through the host's vascular system, silencing suppressors to combat the plant's immune defenses , and capsid proteins for encapsidation of the genomic RNA. However, umbraviruses, which are plant viruses, belong to the family TombusviridaeThey lack capsid proteins or silencing suppressors and have been shown to require a helper virus for successful infection and transmission. Umbravirus-like viruses that lack movement proteins have recently been discovered, and previous reports suggest that these viruses infect plants in the absence of a helper virus. In this new study, Ying, Bera et al. aimed to uncover the mechanisms by which umbravirus-like viruses infect plants and reported that at least some of the viruses encode a putative capsid protein and use a host movement protein for systemic infections.

Next, the authors identified the possible function of the ORF5 protein. Structural analysis revealed that the encoded protein has more similarities to a capsid protein than the 30K class of movement proteins. Consistent with this, the authors showed that CY2-infected plants contained macromolecular assemblies that resembled small virus-like particles (VLPs). Furthermore, these VLPs were associated with ORF5_CY2 and CY2 RNA. In contrast, CY1, which lacks ORF5_CY2It has been shown to interact with the host protein phloem protein 2 (PP2, considered a nonspecific RNA-binding protein), potentially forming protective ribonucleoproteins that could act as infectious particles. Finally, infection of plants in which PP2 had been knocked out with CY1 resulted in a reduction in symptoms. These results suggest that PP2 is important for the systemic movement of CY1 in the host.