Cylindrical Inclusion Protein of Turnip Mosaic Virus Serves as a Docking Point for the Intercellular Movement of Viral Replication Vesicles

Abstract

Plant viruses move from the initially infected cell to adjacent cells through plasmodesmata (PDs). To do so, viruses encode dedicated protein(s) that facilitate this process. How viral proteins act together to support the intercellular movement of viruses is poorly defined. Here, by using an infection-free intercellular vesicle movement assay, we investigate the action of CI (cylindrical inclusion) and P3N-PIPO (amino-terminal half of P3 fused to Pretty Interesting Potyviridae open reading frame), the two PD-localized potyviral proteins encoded by (TuMV), in the intercellular movement of the viral replication vesicles. We provide evidence that CI and P3N-PIPO are sufficient to support the PD targeting and intercellular movement of TuMV replication vesicles induced by 6K2, a viral protein responsible for the generation of replication vesicles. 6K2 interacts with CI but not P3N-PIPO. When this interaction is impaired, the intercellular movement of TuMV replication vesicles is inhibited. Furthermore, in transmission electron microscopy, vesicular structures are observed in connection with the cylindrical inclusion bodies at structurally modified PDs in cells coexpressing 6K2, CI, and P3N-PIPO. CI is directed to PDs through its interaction with P3N-PIPO. We hypothesize that CI serves as a docking point for PD targeting and the intercellular movement of TuMV replication vesicles. This work contributes to a better understanding of the roles of different viral proteins in coordinating the intercellular movement of viral replication vesicles.

A Host ER Fusogen Is Recruited by Turnip Mosaic Virus for Maturation of Viral Replication Vesicles

“…This dual construct expresses both 6K2-mCherry and GFP-HDEL from the infectious TuMV. The construct allows monitoring of the production of 6K2 vesicles in primarily infected cells (indicated by the presence of both GFP-HDEL and 6K2-mCherry) and in secondarily infected cells (indicated by the presence of 6K2-mCherry only; Agbeci et al, 2013;Jiang et al, 2015;Movahed et al, 2017). As indicated in Figure 2, the production of 6K2-mCherry in primary infection foci, as evidence by the production of green and red fluorescence, was first observed in both Col-0 and rhd3-8 plants after 7 dpi (Fig.…”

“…Because knockout of the RHD3 gene leads to the formation of a "cable-like" nonbranched ER network (Chen et al, 2011;Zhang et al, 2013;Feng et al, 2016), it was suggested that the affected ER structure plays a role in the delayed movement of the Tomato spotted wilt tospovirus and its movement protein (Feng et al, 2016). However, it is known that the replication vesicles of TuMV are not only the site of viral replication, but also the vehicle for TuMV intercellular movement (Movahed et al, 2017). It has been suggested that replication incompetent DMVs and MVBs may play an important role in the systemic spread of TuMV (Wan et al, 2015b).…”

“…No interactions were found between PLV-Cub-RHD3 and free NubG (Fig. 5, A and B, row 1), or between PLV-Cub-6K2 and P3N-PIPO-NubG (Movahed et al, 2017;Fig. 5, A and B, row 2).…”

“…The construction of PLV-Cub-RHD3 and NubG-RHD3 was described in Chen et al (2011). The construction of P3N-PIPO was described in Movahed et al (2017).…”

Remorin interacting with PCaP1 impairs Turnip mosaic virus intercellular movement but is antagonised by VPg

“…For the Potyvirus members, accumulating evidence shows that P3N-PIPO functions as a MP to mediate viral cell-to-cell movement (Choi et al, 2005;Chung et al, 2008;Wei et al, 2010b;Wen & Hajimorad, 2010;Vijayapalani et al, 2012;Cui et al, 2017). P3N-PIPO recruits CI to PD (Wei et al, 2010b;Deng et al, 2015;Movahed et al, 2017), while CI serves as a docking point for the intercellular movement of virus replication vesicles (Movahed et al, 2017).…”