Multiple N-Glycans Cooperate in the Subcellular Targeting and Functioning of Arabidopsis KORRIGAN1 |
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Authors: | Stephan Rips Nolan Bentley In Sil Jeong Justin L Welch Antje von Schaewen Hisashi Koiwa |
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Institution: | aInstitut für Biologie und Biotechnologie der Pflanzen, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany;bVegetable and Fruit Improvement Center, Department of Horticultural Sciences, Molecular and Environmental Plant Science Program, Texas A&M University, College Station, Texas 77843-2133 |
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Abstract: | Arabidopsis thaliana KORRIGAN1 (KOR1) is an integral membrane endo-β1,4-glucanase in the trans-Golgi network and plasma membrane that is essential for cellulose biosynthesis. The extracellular domain of KOR1 contains eight N-glycosylation sites, N1 to N8, of which only N3 to N7 are highly conserved. Genetic evidence indicated that cellular defects in attachment and maturation of these N-glycans affect KOR1 function in vivo, whereas the manner by which N-glycans modulate KOR1 function remained obscure. Site-directed mutagenesis analysis of green fluorescent protein (GFP)-KOR1 expressed from its native regulatory sequences established that all eight N-glycosylation sites (N1 to N8) are used in the wild type, whereas stt3a-2 cells could only inefficiently add N-glycans to less conserved sites. GFP-KOR1 variants with a single N-glycan at nonconserved sites were less effective than those with one at a highly conserved site in rescuing the root growth phenotype of rsw2-1 (kor1 allele). When functionally compromised, GFP-KOR1 tended to accumulate at the tonoplast. GFP-KOR1Δall (without any N-glycan) exhibited partial complementation of rsw2-1; however, root growth of this line was still negatively affected by the absence of complex-type N-glycan modifications in the host plants. These results suggest that one or several additional factor(s) carrying complex N-glycans cooperate(s) with KOR1 in trans to grant proper targeting/functioning in plant cells. |
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