title: Glycosylphosphatidylinositol (GPI) Modification Serves as a Primary Plasmodesmal Sorting Signal.
abstract: Plasmodesmata (Pd) are membranous channels that serve as a major conduit for cell-to-cell communication in plants. The Pd-associated β-1,3-glucanase (BG_pap) and CALLOSE BINDING PROTEIN1 (PDCB1) were identified as key regulators of Pd conductivity. Both are predicted glycosylphosphatidylinositol-anchored proteins (GPI-APs) carrying a conserved GPI modification signal. However, the subcellular targeting mechanism of these proteins is unknown, particularly in the context of other GPI-APs not associated with Pd Here, we conducted a comparative analysis of the subcellular targeting of the two Pd-resident and two unrelated non-Pd GPI-APs in Arabidopsis (Arabidopsis thaliana). We show that GPI modification is necessary and sufficient for delivering both BG_pap and PDCB1 to Pd Moreover, the GPI modification signal from both Pd- and non-Pd GPI-APs is able to target a reporter protein to Pd, likely to plasma membrane microdomains enriched at Pd As such, the GPI modification serves as a primary Pd sorting signal in plant cells. Interestingly, the ectodomain, a region that carries the functional domain in GPI-APs, in Pd-resident proteins further enhances Pd accumulation. However, in non-Pd GPI-APs, the ectodomain overrides the Pd targeting function of the GPI signal and determines a specific GPI-dependent non-Pd localization of these proteins at the plasma membrane and cell wall. Domain-swap analysis showed that the non-Pd localization is also dominant over the Pd-enhancing function mediated by a Pd ectodomain. In conclusion, our results indicate that segregation between Pd- and non-Pd GPI-APs occurs prior to Pd targeting, providing, to our knowledge, the first evidence of the mechanism of GPI-AP sorting in plants.
authors: Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel (R.Z., B.L.E.); andDepartment of Biology, Duke University, Durham, North Carolina 27708 (R.Z., X.D.) raul.zavaliev@duke.edu.
authors: Raul
authors: 0000-0001-9438-062X
authors: R
authors: Zavaliev
authors: Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel (R.Z., B.L.E.); andDepartment of Biology, Duke University, Durham, North Carolina 27708 (R.Z., X.D.).
authors: Xinnian
authors: 0000-0002-1120-0951
authors: X
authors: Dong
authors: Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel (R.Z., B.L.E.); andDepartment of Biology, Duke University, Durham, North Carolina 27708 (R.Z., X.D.).
authors: Bernard L
authors: BL
authors: Epel
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D004693:Glucan Endo-1,3-beta-D-Glucosidase / Q000235:genetics / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D015151:Immunoblotting; D058635:Lipid-Linked Proteins / Q000235:genetics / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism; D018613:Microscopy, Confocal; D008954:Models, Biological; D030821:Plants, Genetically Modified; D031425:Plasmodesmata / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D017261:Glycosylphosphatidylinositols; D058635:Lipid-Linked Proteins; D008562:Membrane Glycoproteins; C542004:PDCB1 protein, Arabidopsis; D004693:Glucan Endo-1,3-beta-D-Glucosidase