Cell-to-Cell and Phloem-Mediated Transport of Potato Virus X: The Role of Virions

Abstract

Movement-deficient potato virus X (PVX) mutants tagged with the green fluorescent protein were used to investigate the role of the coat protein (CP) and triple gene block (TGB) proteins in virus movement. Mutants lacking either a functional CP or TGB were restricted to single epidermal cells. Microinjection of dextran probes into cells infected with the mutants showed that an increase in the plasmodesmal size exclusion limit was dependent on one or more of the TGB proteins and was independent of CP. Fluorescently labeled CP that was injected into epidermal cells was confined to the injected cells, showing that the CP lacks an intrinsic transport function. In additional experiments, transgenic plants expressing the PVX CP were used as rootstocks and grafted with nontransformed scions. Inoculation of the PVX CP mutants to the transgenic rootstocks resulted in cell-to-cell and systemic movement within the transgenic tissue. Translocation of the CP mutants into sink leaves of the nontransgenic scions was also observed, but infection was restricted to cells close to major veins. These results indicate that the PVX CP is transported through the phloem, unloads into the vascular tissue, and subsequently is transported between cells during the course of infection. Evidence is presented that PVX uses a novel strategy for cell-to-cell movement involving the transport of filamentous virions through plasmodesmata.

Quasispecies nature of Pepino mosaic virus and its evolutionary dynamics

“…Potato virus X (PVX) TGB1 is a multifunctional protein that induces plasmodesmal gating, mediates viral cell-tocell movement, has ATPase and RNA helicase activities, binds viral RNAs, and acts as suppressor of RNA silencing [11]. ORF5 encodes the coat protein (CP) which, in addition to its structural role, is required for cell-to-cell and long distance movement [12]. Finally, two short untranslated sequences flank the coding regions and there is a poly(A) tail at the 3 0 end of the genomic RNA [13].…”

Parallels between nuclear-pore and plasmodesmal trafficking of information molecules

“…However, this may not be the universal form in which infectious material moves from cell to cell. Indeed, some viruses that form long,¯exuous particles may be capable of moving through the PD microchannel, provided the diameter of the particle is on the order of 10 nm (see Santa Cruz et al 1998). If this were the case, the coat protein encoded by these viruses should possess the motifs required to interact with the PD machinery that mediates the general transport of MPs and/or vRNPs.…”

Capsid protein gene and the type of host plant differentially modulate cell-to-cell movement of cowpea chlorotic mottle virus

“…The inclusions observed for CCMV CP:EGFP also appear to be similar in size to the inclusions formed by the potato virus X (PVX) potexvirus CP:GFP fusion [31]. In PVX, CP is required for cell-to-cell movement and it also associates with plasmodesmata [31]. Further investigation of CCMV CP localization at electron microscopic level will be necessary to understand the relationship between CCMV CP and cellular components.…”

“…Such an association could be evolutionarily related to BMV helping CP to act in conjunction with the MP and assist cell-to-cell spread. The inclusions observed for CCMV CP:EGFP also appear to be similar in size to the inclusions formed by the potato virus X (PVX) potexvirus CP:GFP fusion [31]. In PVX, CP is required for cell-to-cell movement and it also associates with plasmodesmata [31].…”