Hitching a Ride on Vesicles: Cauliflower Mosaic Virus Movement Protein Trafficking in the Endomembrane System

Abstract

The transport of a viral genome from cell to cell is enabled by movement proteins (MPs) targeting the cell periphery to mediate the gating of plasmodesmata. Given their essential role in the development of viral infection, understanding the regulation of MPs is of great importance. Here, we show that cauliflower mosaic virus (CaMV) MP contains three tyrosine-based sorting signals that interact with an Arabidopsis (Arabidopsis thaliana) mA-adaptin subunit. Fluorophore-tagged MP is incorporated into vesicles labeled with the endocytic tracer N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide. The presence of at least one of the three endocytosis motifs is essential for internalization of the protein from the plasma membrane to early endosomes, for tubule formation, and for CaMV infection. In addition, we show that MP colocalizes in vesicles with the Rab GTPase AtRAB-F2b, which is resident in prevacuolar late endosomal compartments that deliver proteins to the vacuole for degradation. Altogether, these results demonstrate that CaMV MP traffics in the endocytic pathway and that virus viability depends on functional host endomembranes.

Plant virus replication and movement

“…Mutation of the binding motifs in MP abolished its accumulation in PD and its assembly into tubules but not its targeting to the PM, suggesting a role of endosomal trafficking in a pathway that concentrates MP at PD. The role of endosomal trafficking was confirmed by colocalizing P1 vesicles with the endosomal marker FM6-64 and by inhibition of PD targeting as well as the presence of P1 in FM6-64-tagged vesicles by treatment with Tyrphostin A23, an inhibitor of recognition of Tyr signals by m2 (Carluccio et al, 2014). Tyr-based sorting motifs (YXXΦ) were also found in the TGB3 of PMTV and the MP of GFLV and other nepoviruses (Haupt et al, 2005;Laporte et al, 2003), thus supporting a widespread role of endoscytic retrieval pathways that direct the MPs from the PM to PD.…”

“…Since the formation of the MP tubule inside the PD channel displaces the desmotubule, these viruses cannot rely on the ER for PD targeting. The P1 MP of CaMV failed to target PD and formed typical BFA compartments upon BFA treatment (Carluccio et al, 2014). The compartment contained internalized FM4-64, thus indicating that also downstream endosomal P1 trafficking was affected.…”

Association of the P6 Protein of Cauliflower mosaic virus with Plasmodesmata and Plasmodesmal Proteins

“…Additional studies have shown that the CaMV MP is incorporated into vesicles and is trafficked on the endomembrane system to reach the plasmodesma (Carluccio et al, 2014). These authors suggest that the CaMV MP is recycled in a vesicular transport pathway between plasmodesmata and early endosome compartments.…”

“…These authors suggest that the CaMV MP is recycled in a vesicular transport pathway between plasmodesmata and early endosome compartments. The CaMV MP interacts with mA-Adaptin (Carluccio et al, 2014) and Movement Protein-Interacting7 (Huang et al, 2001), two proteins shown to have a role in vesicular trafficking. Once the MP arrives at plasmodesmata, it interacts with the Plasmodesmata-Localized Protein (PDLP) proteins, which comprise a family of eight proteins associated with plasmodesmata (Amari et al, 2010).…”

Plants, Functions and Processes Adapt to Different Environments

“…Therefore, functional integrity of disturbance caused by an imbalance in absorption of water supply and consumption conditions of drought can be caused not only by disturbances in intensity and water absorption capacity of root system, and hydraulic conductivity of plant. This in turn depends on permeability of cell membrane proteins transporting controlled water activity (aquaporins) and long distance water transport by specialized tissues [24]. Saturation deficit, caused by water stress (drought) advanced hydraulic conductivity results in inhibition of plants with serious consequences on process of water delivery vegetative and generative organs of plant, including apical meristems.…”