Membrane protein transport between the endoplasmic reticulum and the Golgi in tobacco leaves is energy dependent but cytoskeleton independent: evidence from selective photobleaching.
The mechanisms that control protein transport between the endoplasmic reticulum (ER) and the Golgi apparatus are poorly characterized in plants. Here, we examine in tobacco leaves the structural relationship between Golgi and ER membranes using electron microscopy and demonstrate that Golgi membranes contain elements that are in close association and/or in direct contact with the ER. We further visualized protein trafficking between the ER and the Golgi using Golgi marker proteins tagged with green fluorescent protein. Using photobleaching techniques, we showed that Golgi membrane markers constitutively cycle to and from the Golgi in an energy-dependent and N-ethylmaleimide-sensitive manner. We found that membrane protein transport toward the Golgi occurs independently of the cytoskeleton and does not require the Golgi to be motile along the surface of the ER. Brefeldin A treatment blocked forward trafficking of Golgi proteins before their redistribution into the ER. Our results indicate that in plant cells, the Golgi apparatus is a dynamic membrane system whose components continuously traffic via membrane trafficking pathways regulated by brefeldin A- and N-ethylmaleimide-sensitive machinery.
Brandizzi
Federica
F
Research School of Biological and Molecular Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, United Kingdom. fbrandizzi@brookes.ac.uk
Snapp
Erik L
EL
Roberts
Alison G
AG
Lippincott-Schwartz
Jennifer
J
Hawes
Chris
C
D001483:Base Sequence; D003599:Cytoskeleton / Q000502:physiology*; D017931:DNA Primers; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D005822:Genetic Vectors; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D049452:Green Fluorescent Proteins; D008027:Light; D008164:Luminescent Proteins / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000378:metabolism / Q000648:ultrastructure; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012231:Rhizobium / Q000235:genetics; D014026:Nicotiana / Q000378:metabolism*
D017931:DNA Primers; D008164:Luminescent Proteins; D008565:Membrane Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins