TARGETING OF ACTIVE SIALYLTRANSFERASE TO THE PLANT GOLGI-APPARATUS

Glycosyltransferases in the Golgi apparatus synthesize cell wall polys accharides and elaborate the complex glycans of glycoproteins. To inve stigate the targeting of this type of enzyme to plant Golgi compartmen ts, we generated transgenic Arabidopsis plants expressing alpha-2,6-si alyltransferase, a glycosyltransferase of the mammalian trans-Golgi ci sternae and the trans-Golgi network. Biochemical analysis as well as i mmunolight and immunoelectron microscopy of these plants indicate that the protein is targeted specifically to the Golgi apparatus. Moreover , the protein is predominantly localized to the cisternae and membrane s of the trans side of the organelle. When supplied with the appropria te substrates, the enzyme has significant alpha-2,6-sialyltransferase activity. These results indicate a conservation of glycosyltransferase targeting mechanisms between plant and mammalian cells and also demon strate that glycosyltransferases can be subcompartmentalized to specif ic cisternae of the plant Golgi apparatus.