Abstract
Cell-to-cell movement of plant viruses occurs via plasmodesmata (PD), organelles that evolved to facilitate intercellular communications. Viral movement proteins (MP) modify PD to allow passage of the virus particles or nucleoproteins. This passage occurs via several distinct mechanisms one of which is MP-dependent formation of the tubules that traverse PD and provide a conduit for virion translocation. The MP of tubule-forming viruses including Grapevine fanleaf virus (GFLV) recruit the plant PD receptors called Plasmodesmata Located Proteins (PDLP) to mediate tubule assembly and virus movement. Here we show that PDLP1 is transported to PD through a specific route within the secretory pathway in a myosin-dependent manner. This transport relies primarily on the class XI myosins XI-K and XI-2. Inactivation of these myosins using dominant negative inhibition results in mislocalization of PDLP and MP and suppression of GFLV movement. We also found that the proper targeting of specific markers of the Golgi apparatus, the plasma membrane, PD, lipid raft subdomains within the plasma membrane, and the tonoplast was not affected by myosin XI-K inhibition. However, the normal tonoplast dynamics required myosin XI-K activity. These results reveal a new pathway of the myosin-dependent protein trafficking to PD that is hijacked by GFLV to promote tubule-guided transport of this virus between plant cells.
Highlights
Plant viruses are intracellular parasites that recruit numerous host factors for their replication and movement within plants
We show that Plasmodesmata Located Proteins (PDLP) targeting to PD depends on the molecular motors myosin XI-K and XI-2
For the PD targeting of Tobacco mosaic virus (TMV) ribonucleoprotein complexes, evidence has been provided for microtubule-dependent [15,16] and actomyosin-dependent [17,18] transport, as well as for diffusion in the endoplasmic reticulum (ER) network [19]
Summary
Plant viruses are intracellular parasites that recruit numerous host factors for their replication and movement within plants. Virus cell-to-cell movement involves transport from replication factories to the cell periphery, passage through plasmodesmata (PD) interconnecting adjacent cells, and long-distance transport via the phloem vasculature [1]. All plant viruses encode one or more specialized movement proteins (MP) facilitating virus transport. The first movement strategy is represented by Tobacco mosaic virus (TMV) MP that directly binds and chaperones viral RNA genome via modified PD [2,3,4]. The second movement strategy involves MP that heavily modify PD structure by forming tubules through which the assembled virions traverse PD [5,6]. The third type of movement strategies is used primarily by the filamentous viruses, which usually require more than one MP and capsid protein for efficient intercellular transport [7]. The longest known filamentous viruses, closteroviruses, have evolved the most complex machinery that includes a virionassociated movement device and a membrane-targeted MP [8]
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