Abstract
The p25 triple gene block protein of Potato virus X (PVX) is multifunctional, participating in viral movement and acting as a suppressor of RNA silencing. The cell-to-cell movement of PVX is known to depend on the suppression function of p25. GFP-fused p25 accumulates in rod-like (RL) structures with intense fluorescence in cells. By monitoring the location of fluorescence at different times, we have now shown that the RL structure is composed of filaments. P25 mutants without the conditional ability to recover movement function could not form RL structures while the mutants that had the ability did form the structure, suggesting that the ability of p25 to form RL structures is necessary for its function in cell-to-cell movement, but not for its suppressor function. Moreover, chemical inhibition of microfilaments in cells destroyed the formation of the complete RL structure. Additionally, TGBp2 and TGBp3 were recruited into the RL structure, suggesting a relationship between the TGBps in virus movement.
Highlights
The genome of Potato virus X (PVX, genus Potexvirus) has five open reading frames, three of which overlap and are termed the triple gene block (TGB)
Formation of p25 Rod-like Structures in Nicotiana benthamiana Cells. It has previously been reported [16] that expressed p25 fused with GFP at its N-terminus (GFP-p25) formed rod-like structures in both PVX-infected and uninfected cells
The structures occurred when GFP fused with p25 at its Cterminus (p25-GFP) was expressed either alone under the control of Cauliflower mosaic virus (CaMV) 35S promoter or from the PVX-Dp25 vector with the duplicated coat protein subgenomic promoter (Fig. 1A and B)
Summary
The genome of Potato virus X (PVX, genus Potexvirus) has five open reading frames, three of which overlap and are termed the triple gene block (TGB). Studies using microinjection and biolistic bombardment have shown that p25 increases the size exclusion limit (SEL) of plasmodesmata (PD) and chaperones viral RNA and coat protein (CP) across PD [1,2,3,4]. A recent article reviewed the movement strategies employed by TGB-encoding viruses and proposed models for viruses in the genera Potexvirus, Hordeivirus, and Pomovirus [9]. In these models, there are roles for the TGB proteins, coat protein and RNAs of the virus and for the microfilaments, endoplasmic reticulum (ER), Golgi and PD of the host cell [9]
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