Golgi α1,4-fucosyltransferase of Arabidopsis thaliana partially localizes at the nuclear envelope.

We analyzed plant-derived α1,4-fucosyltransferase ( FucTc) homologs by reporter fusions and focused on representatives of the Brassicaceae and Solanaceae. Arabidopsis thaliana AtFucTc-green fluorescent protein ( GFP) or tomato LeFucTc-GFP restored Lewis-a formation in a fuctc mutant, confirming functionality in the trans-Golgi. AtFucTc-GFP partly accumulated at the nuclear envelope ( NE) not observed for other homologs or truncated AtFucTc lacking the N-terminus or catalytic domain. Analysis of At/ LeFucTc-GFP swap constructs with exchanged cytosolic, transmembrane and stalk ( CTS), or only the CT regions, revealed that sorting information resides in the membrane anchor. Other domains of AtFuctc also contribute, since amino-acid changes in the CT region strongly reduced but did not abolish NE localization. By contrast, two N-terminal GFP copies did, indicating localization at the inner nuclear membrane ( INM). Tunicamycin treatment of AtFucTc-GFP abolished NE localization and enhanced overlap with an endosomal marker, suggesting involvement of N-glycosylation. Yet neither expression in protoplasts of Arabidopsis N-glycosylation mutants nor elimination of the N-glycosylation site in AtFucTc prevented perinuclear accumulation. Disruption of endoplasmic reticulum ( ER)-to-Golgi transport by co-expression of Sar1( H74L) trapped tunicamycin-released AtFucTc-GFP in the ER, however, without NE localization. Since recovery after tunicamycin-washout required de novo-protein synthesis, our analyses suggest that AtFucTc localizes to the NE/ INM due to interaction with an unknown (glyco)protein. [ABSTRACT FROM AUTHOR]