ABSTRACT
Tubular structures involved in the cell-to-cell movement of cowpea mosaic virus (CPMV) were partially purified from infected cowpea protoplasts to identify the structural components. A relatively pure fraction could be obtained by differential centrifugation and this was analysed by PAGE and immunoblotting. Besides the movement protein (MP) and capsid proteins (CP) of CPMV, no other major infection-specific proteins could be detected, suggesting that host proteins are not a major structural component of the movement tubule.
Subject(s)
Comovirus/ultrastructure , Plants/virology , Comovirus/chemistry , Viral Structural Proteins/ultrastructureABSTRACT
The structural phenotype of the movement proteins (MPs) of two representatives of the Bromoviridae, alfalfa mosaic virus (AMV) and brome mosaic virus (BMV), was studied in protoplasts. Immunofluorescence microscopy showed that the MPs of these viruses, for which there has been no evidence of a tubule-guided mechanism, assemble into long tubular structures at the surface of the infected protoplast. Electron microscopy and immunogold analysis confirmed the presence of both MP and virus particles in the tubules induced by AMV and BMV. The significance of the tubule-forming properties of these viral MPs is discussed.
Subject(s)
Alfamovirus/physiology , Bromovirus/physiology , Viral Proteins/genetics , Alfamovirus/ultrastructure , Bromovirus/ultrastructure , Fabaceae/ultrastructure , Fabaceae/virology , Fluorescent Antibody Technique , Microscopy, Electron , Microscopy, Immunoelectron , Plant Viral Movement Proteins , Plants, Medicinal , Protoplasts/ultrastructure , Protoplasts/virology , Viral Proteins/metabolismABSTRACT
The movement proteins (MP) of cowpea mosaic virus and cauliflower mosaic virus (CaMV) are associated with tubular structures in vivo which participate in the transmission of virus particles from cell to cell. Both proteins have been expressed in plant protoplasts and insect cells. In all cases, immunofluorescent histochemistry showed that the MPs accumulate intracellularly as tubular extensions projecting from the cell surface. Additionally, electron microscopy revealed intracellular MP aggregates in CaMV MP-expressing cells. The data presented establish common features for the tubule-forming MPs: no other virus gene products are required for tubule formation and unique plant components (e.g. plasmodesmata) are not essential for tubule synthesis.
