Specific roles of complex-modified glycoproteins in plants

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In contrast to the well known functions of glycoprotein modifications in the ER, additional roles of N-glycan diversity acquired in the Golgi are still unclear. Upon salt stress, we assigned a rootgrowth phenotype to complex glycan 1 (cgl1) mutants, which resembles the radial swelling (rsw) phenotype of Arabidopsis mutants that have defects in ER-resident glycosylation or cellulose biosynthesis at the plasma membrane. As one link we identified the β-D-endoglucanase Korrigan. In this new project we propose to examine how glycosylation defects compromize function and/or targeting of secreted glycoproteins, because our preliminary results indicate that also in plants N-glycans can encode targeting information. We found that when the luminal domain is missing (most published studies) or when aberrantly N-glycosylated, some class-II membrane proteins localize differently. By molecular and biochemical means we will examine to what extend number and/or quality of N-glycans are important for intracellular traffic of integral glycoproteins: Moreover, we ultimately attempt to identify corrsponding receptors in the endomembrane system. Our own Y2H screens with cellulose synthase A1 support that upon stress, signals eminate from the cell wall to reprogram nuclear expression. Thus, in the long run, we aim at identifying components involved in TGN/endosome-to-nucleus, and also plasma membrane-to-nucleus communication.