Plant Virus Movement

Abstract

Plant virus movement is the process of the spread of virus genetic material from the initially infected cells to the rest of the plant. There are several distinct stages including intracellular movement from sites of virus replication to plasmodesmata (PD) (plant‐specific intercellular nanopores), cell‐to‐cell trafficking through PD and long‐distance movement between organs through the phloem (the specialized vascular system used by plants for the transport of assimilates and macromolecules). Transport is mediated by virus‐encoded ‘movement’ proteins. Several different types of movement proteins can be distinguished, which share properties such as nucleic acid binding, targeting and dilation of PD, and intercellular movement. These functions can be distributed amongst several movement proteins. Some movement proteins form a hollow tubule through PD which allows the passage of virus particles, but for the majority of viruses, the precise mechanism of transport through PD is still unknown. Key Concepts: Plant viruses need to overcome the barrier of the cell wall to spread from the initially infected cells to the rest of the plant. Local cell‐to‐cell movement occurs through PD which are plant‐specific membrane‐lined nanopores that connect adjoining cells. Long‐distance movement between plant organs occurs through the phloem, one of the two components of the plant's vasculature. Viral cell‐to‐cell movement constitutes an extreme population bottleneck and needs to stay ahead of plant defence signals trafficking through the same channels. Movement is mediated by one or several virus‐encoded movement proteins, which facilitate transport of virus genomes or virus particles between cells. The transported form of the viral genome is usually either a virus particle that can be modified, or a nonvirion ribonucleoprotein complex containing RNA and movement proteins. Local and long‐distance movement forms can be different. Two different movement mechanisms are observed: insertion of a MP‐comprised tubule into PD that forms a conduit for virus particles, or tubule‐less movement by an unknown mechanism. Mechanisms contributing to PD dilation may include breakdown of the polysaccharide callose in the surrounding cell wall and severing of actin filaments. Viruses use elements of the cell's cytoskeleton and/or endomembrane system to get from replication sites to PD, or replication and movement can be spatially linked at PD. Nuclear host factors are required for long‐distance movement of some viruses.

A novel block of plant virus movement genes

“…Studies of plant virus cell-to-cell movement carried out in the last 35 years have revealed several types of viral transport system exhibiting remarkable differences in their gene organization, as well as in the structure and biochemical properties of their encoded movement proteins (MPs), with the movement functions being performed by a single protein or distributed among several MPs (Heinlein, 2015;Lucas, 2006;Tilsner et al, 2014).…”

Identification of Ourmiavirus 30K movement protein amino acid residues involved in symptomatology, viral movement, subcellular localization and tubule formation

“…Successful infection of a plant host by a virus derives from its ability to spread from the initial infection site to distant tissues and organs. This process involves various steps in different cellular compartments: intracellularly from the replication site to the cell periphery, through the cell wall to the adjacent cell, across tissues to the vascular system (usually phloem sieve tubes) and through the conductive elements to distant host tissues, where the virus can initiate systemic infection (Harries and Nelson, 2008;Hull, 2014;Schoelz et al, 2011;Tilsner et al, 2014;Ueki and Citovsky, 2007). In all the intercellular stages, viruses must traverse a substantial barrier that surrounds the host cells: the plant cell wall.…”

Potato Mop-Top Virus Co-Opts the Stress Sensor HIPP26 for Long-Distance Movement

“…These proteins 155 were chosen to represent common types of virus movement proteins (Tilsner et al, 2014; …”