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

• Published in: Traffic (Copenhagen, Denmark) Vol. 18; no. 10; pp. 646 - 657
• Main Authors: Rips, Stephan, Frank, Manuel, Elting, Annegret, Offenborn, Jan Niklas, von Schaewen, Antje
• Format: Journal Article
• Language: English
• Published: Former Munksgaard John Wiley & Sons A/S 01.10.2017
• Subjects: Active Transport, Cell Nucleus; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Endosomes - metabolism; Fucosyltransferases - chemistry; Fucosyltransferases - genetics; Fucosyltransferases - metabolism; glycoprotein modification; Glycosylation; Golgi Apparatus - metabolism; Golgi‐type complex N‐glycans; nuclear envelope; Nuclear Envelope - metabolism; Protein Processing, Post-Translational; Protein Sorting Signals; R-SNARE Proteins - genetics; R-SNARE Proteins - metabolism; α1,4‐fucosyltransferase; Arabidopsis thaliana; nuclear envelope; α1,4-fucosyltransferase; glycoprotein modification; Golgi-type complex N-glycans
• ISSN: 1398-9219; 1600-0854
• DOI: 10.1111/tra.12506

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. The luminal domains of two homologous fucosyltransferases of Arabidopsis thaliana (At) and tomato (Le), usually residing in the trans‐Golgi network (TGN) of higher plant cells, were exchanged to test for involvement of the N‐ and/or C‐terminal domains in partial localization of the AtFucTc enzyme at the nuclear envelope (NE). Our studies show that AtFucTc likely interacts with an unknown (glyco)protein at the NE, which might either reflect chaperone binding (until heteromerization with an unknown partner) or neo‐functionalization within A. thaliana.