Creating Contacts Between Replication and Movement at Plasmodesmata – A Role for Membrane Contact Sites in Plant Virus Infections?

Abstract

To infect their hosts and cause disease, plant viruses must replicate within cells and move throughout the plant both locally and systemically. RNA virus replication occurs on the surface of various cellular membranes, whose shape and composition become extensively modified in the process. Membrane contact sites (MCS) can mediate nonvesicular lipid-shuttling between different membranes and viruses co-opt components of these structures to make their membrane environment suitable for replication. Whereas animal viruses exit and enter cells when moving throughout their host, the rigid wall of plant cells obstructs this pathway and plant viruses therefore move between cells symplastically through plasmodesmata (PD). PD are membranous channels connecting nearly all plant cells and are now viewed to constitute a specialized type of endoplasmic reticulum (ER)-plasma membrane (PM) MCS themselves. Thus, both replication and movement of plant viruses rely on MCS. However, recent work also suggests that for some viruses, replication and movement are closely coupled at ER-PM MCS at the entrances of PD. Movement-coupled replication at PD may be distinct from the main bulk of replication and virus accumulation, which produces progeny virions for plant-to-plant transmission. Thus, MCS play a central role in plant virus infections, and may provide a link between two essential steps in the viral life cycle, replication and movement. Here, we provide an overview of plant virus-MCS interactions identified to date, and place these in the context of the connection between viral replication and cell-to-cell movement.

Small hydrophobic viral proteins involved in intercellular movement of diverse plant virus genomes

“…These inclusion bodies at structurally modified PDs may serve as docking and conducting structures coordinating different viral proteins in the intercellular movement of viral replication vesicles and virions. In addition, VPg also may positively influence cell-to-cell potyvirus movement inducing proteasome-mediated degradation of plant protein remorin, thus preventing formation of remorin-specific plasma membrane nanodomains, which reduce membrane plasticity, and subsequent PD closure [5] – [7] , [44] , [60] , [86] – [90] .…”

“…As plant cells contain a tough, rigid cell wall, virus cell-to-cell movement occurs through plasmodesmata (PD), the channels in cell walls interconnecting neighboring cells. In the PD pore, the plasma membrane (PM) is continuous between the two cells, and the endoplasmic reticulum (ER) traverses the pore as a tightly appressed tube called the desmotubule [1] – [7] . It has been suggested that filaments composed at least partly from actin are located in the PD cytoplasmic sleeve between PM and desmotubule [3] – [6] .…”

Variability, Functions and Interactions of Plant Virus Movement Proteins: What Do We Know So Far?

“…In this review, we have chosen to bring together recent findings on MPs, interactions that they share and the division of labor that they show with other ancillary proteins required for the intercellular movement of plant viruses. Several other previous in-depth reviews present an exhaustive discussion on various aspects governing the intra-, and intercellular movement of viruses and the reader is guided to these for a more holistic understanding of this topic [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. Additionally, we request readers to go through the reviews [ 5 , 15 , 16 , 17 , 18 ] to get an overview of the historical perspective and earlier findings, specifically on MPs and their interactions.…”

Intercellular movement of plant RNA viruses: Targeting replication complexes to the plasmodesma for both accuracy and efficiency

“…From the perspective of the virus, the specific host factors recruited by viruses for replication or movement are only referred to when necessary. Readers can find information on these topics elsewhere 4,15‐18 …”

“…Readers can find information on these topics elsewhere. 4,[15][16][17][18] 1.1 | 30 K superfamily MPs recruit VRCs to PD for cell-to-cell movement TMV is the type species of the genus Tobamovirus in the family Virgaviridae and is one of the most well-studied plant RNA viruses. Its genome encodes at least four proteins: the 5 0 terminal 126 kilodalton (kDa) protein (126K); a translational read-through product of 183 kDa (183K); a 30 kDa MP; and a 17.6 kDa coat protein (CP).…”