Abstract
Secretory proteins and extracellular glycans are transported to the extracellular space during cell growth. These materials are carried in secretory vesicles generated at the trans-Golgi network (TGN). Analysis of the mammalian post-Golgi secretory pathway demonstrated the movement of separated secretory vesicles in the cell. Using secretory carrier membrane protein 2 (SCAMP2) as a marker for secretory vesicles and tobacco (Nicotiana tabacum) BY-2 cell as a model cell, we characterized the transport machinery in plant cells. A combination of analyses, including electron microscopy of quick-frozen cells and four-dimensional analysis of cells expressing fluorescent-tagged SCAMP2, enabled the identification of a clustered structure of secretory vesicles generated from TGN that moves in the cell and eventually fuses with plasma membrane. This structure was termed the secretory vesicle cluster (SVC). The SVC was also found in Arabidopsis thaliana and rice (Oryza sativa) cells and moved to the cell plate in dividing tobacco cells. Thus, the SVC is a motile structure involved in mass transport from the Golgi to the plasma membrane and cell plate in plant cells.
Highlights
The division and expansion of cells requires trafficking of lipids, proteins, and polysaccharides to the plasma membrane (PM) and extracellular space
We propose that the secretory vesicle cluster (SVC) is a mobile compartment containing secretory carrier membrane protein 2 (SCAMP2) that is involved in mass transport from the Golgi apparatus to the cell exterior in plants
Because its fractionation pattern corresponded to localization to the PM and Golgi apparatus, SCAMP2 was chosen for further analysis
Summary
The division and expansion of cells requires trafficking of lipids, proteins, and polysaccharides to the plasma membrane (PM) and extracellular space. These molecules are synthesized and/or modified in the Golgi apparatus and sorted into secretory vesicles at the trans-Golgi network (TGN) for transport to the PM. One function of the plant Golgi apparatus is as the factory for noncellulose extracellular glycans, including hemicellulose and pectin (Cosgrove, 2005). Dividing plant cells need to synthesize large quantities of these glycans and contain several hundred to thousands of Golgi stacks (Nebenfuhr et al, 1999)
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