Identification and localization of a β‐COP‐like protein involved in the morphodynamics of the plant Golgi apparatus

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Abstract
This paper examines the molecular machinery involved in membrane exchange within the plant endomembrane system. A study has been undertaken on β‐COP‐like proteins in plant cells using M3A5, an antibody raised against the conserved sequence of mammalian β‐COP proteins. In mammalian cells, β‐COP proteins are part of a complex named the coatomer, which probably recruits some specific areas of the endomembrane system. Immunofluorescence analyses by confocal laser scanning microscopy showed that β‐COP‐like proteins marked predominantly the plant Golgi apparatus. Other proteins known to be part of a potential machinery for COPI vesicle formation (γ‐COP, β′‐COP and Arf1 proteins) were immunolocalized on the same membraneous structures as β‐COP. Moreover, β‐COP and other COPI antibodies stained the cell plate in dividing cells. It is further shown that, in maize root cells, and in contrast to observations upon mammalian cells, the drug Brefeldin A (BFA) does not induce the release of β‐COP and Arf1 proteins from the Golgi membrane into the cytosol. These data clearly demonstrate that the antibody M3A5 is a valuable marker for studies on trafficking events in plant cells. They also report for the first time the location of COP components in plant tissue at the light level, especially on a model well known for secretion, i.e. the maize root cells. They also suggest that the membrane recruitment machinery may function in a plant‐specific way.