Plasmodesmata and Long-Distance Virus Movement

Long-distance movement (or systemic movement) of viruses is a term used to refer to the transport of viruses between organs of infected plants via the vascular bundles. For the vast majority of viruses, long-distance movement occurs through sieve elements (SEs). During this process, invading viruses must therefore successfully spread from initially infected cells, enter veins, move through the sieve tubes to distal organs and exit the vasculature in order to propagate in the systemically infected tissues. Insect-transmitted viruses may be deposited directly into SEs by their vectors and so enter the phloem passively in the natural situation. During movement, viruses must circumvent interactions with host factors that may result in plant resistance to movement. As viruses are obligate non-mobile parasites, however, their replication and movement within plants requires interaction with host proteins and subcellular structures such as plasmodesmata. Thus for a successful systemic invasion of the host, viruses must maintain or enhance interactions with host factors that are required for movement through plasmodesmata, while avoiding interactions with host factors that prevent it.