TGB2 (green) localizes to membranous caps at the entrance to plasmodesmata, whereas TGB1 (red) is found inside the channels. Dashed lines indicate cell walls.

TGB2 (green) localizes to membranous caps at the entrance to plasmodesmata, whereas TGB1 (red) is found inside the channels. Dashed lines indicate cell walls.

Tilsner et al. describe how three viral proteins combine to help newly synthesized viruses spread to neighboring plant cells.

Plant viruses move between cells through narrow channels in the cell wall called plasmodesmata. Potato virus X, which replicates on the surface of the endoplasmic reticulum (ER), encodes three proteins—TGB1, 2, and 3—that promote the virus’ transport into neighboring cells, but the precise function of each of these “movement proteins” is unclear.

Tilsner et al. found that TGB2 and TGB3 established clusters of ER membranes that capped the entrances to plasmodesmata. These caps appeared to be sites of viral replication because they contained the virus’ RNA polymerase and RNA that was not yet encased by viral coat proteins. In addition, TGB2 and TGB3 recruited TGB1 to plasmodesmata, where it helped insert viral coat proteins into the intercellular channel.

The authors think that newly synthesized viral RNAs are encased by coat proteins and quickly trafficked into neighboring cells. Thus, by compartmentalizing viral replication to plasmodesmata, the movement proteins allow the potato virus to rapidly spread before the plant’s defense mechanisms can shut the pathogen down. Lead author Jens Tilsner now wants to investigate how TGB1 interacts with the viral coat protein in order to insert it into the plasmodesmata channel.

References

References
Tilsner
J.
et al
.
2013
.
J. Cell Biol.
.

Author notes

Text by Ben Short