Turnip Mosaic Virus Components Are Released into the Extracellular Space by Vesicles in Infected Leaves

Area of Science:

• Plant Virology
• Cell Biology
• Molecular Plant-Microbe Interactions

Background:

• Turnip mosaic virus (TuMV) infection involves significant host cell reorganization.
• Viral protein 6K2 is crucial for forming endoplasmic reticulum-derived vesicles that harbor viral replication complexes.
• Previous work indicated viral RNA associates with multivesicular bodies (MVBs).

Purpose of the Study:

• To investigate the role of the plant extracellular space in TuMV infection.
• To characterize the nature and origin of extracellular vesicles during TuMV infection.
• To determine the presence and composition of viral components within extracellular vesicles.

Main Methods:

• Confocal microscopy to track viral protein localization.
• Transmission electron microscopy (TEM) to visualize cellular structures and vesicle release.
• Immunogold labeling for double-stranded RNA detection.
• Focused ion beam-scanning electron microscopy (FIB-SEM) for 3D imaging.
• Proteomic analysis of purified extracellular vesicles.

Main Results:

• The viral protein 6K2 was detected in the extracellular space.
• Proliferation of MVBs and their fusion with the plasma membrane were observed, releasing intraluminal vesicles.
• Extracellular vesicles contained viral RNA, confirmed by immunogold labeling.
• 3D imaging revealed extracellular vesicles within the cell wall.
• Proteomic analysis confirmed the presence of TuMV proteins and host defense proteins in extracellular vesicles from *Nicotiana benthamiana* and *Arabidopsis thaliana*.

Conclusions:

• TuMV infection leads to the release of extracellular vesicles containing viral RNA and proteins.
• The plant extracellular space is implicated in the spread and infection cycle of TuMV.
• Host proteins involved in defense and vesicular transport are associated with these extracellular vesicles, suggesting complex host-pathogen interactions.