Specific roles of complex-modified glycoproteins in plants (Glyco)

Basic data for this project

Description

Upon co-translational import into the lumen of the Endoplasmic Reticulum (ER), secreted glycoproteins are not only folded but also become glycosylated ("core" N-glycosylation, „high mannose" glycans). This is in most cases also a pre-requisite for vesicle-mediated protein transport to the Golgi Apparatus. There, „high mannose" glycans accessible at the protein surface are modified to „complex type" glycans, carrying plant-specific (but for mammals immunogenic) β1,2-xylose and "core" α1,3-fucose residues. In Arabidopsis cgl1 („complex glycan" ) mutants that lack glycosyltransferase GnTI (N-Acetylglucosaminyl transferase I), the early enzymatic bloc (i.e. 2nd of 9 steps) in Golgi-confined N-glycan modification surprisingly did not result in obvious obstruction of plant development (von Schaewen et al., 1993). By GnTI-„antisense" suppression we copied this defect in agronomically important potato and tobacco plants (Wenderoth & von Schaewen, 2000), which was tolerated. In cooperation with the group of Prof. Hisashi Koiwa (Texas A&M University, USA), we have used a collection of Arabidopsis KO mutants during the last years to show that besides ER-resident also Golgi-resident N-glycan modification on secreted glycoproteins plays important roles for salt stress tolerance (Kang et al., 2008). Already without stress, certain Arabidopsis mutant combinations affected in both ER- and Golgi-resident glycosylation defects showed subtle root phenotypes (Frank et al., 2008) to severe developmental obstruction (von Schaewen et al., 2008). We currently analyse, if this also occurs by RNAi-mediated suppression of certain steps in Solanaceae, and whether in planta use or prevention of use of single N-glycosylation sites affects stability or subcellular „targeting" of secreted glycoproteins.