title: Protein trafficking to the cell wall occurs through mechanisms distinguishable from default sorting in tobacco.
abstract: The secretory pathway in plants involves sustained traffic to the cell wall, as matrix components, polysaccharides and proteins reach the cell wall through the endomembrane system. We studied the secretion pattern of cell-wall proteins in tobacco protoplasts and leaf epidermal cells using fluorescent forms of a pectin methylesterase inhibitor protein (PMEI1) and a polygalacturonase inhibitor protein (PGIP2). The two most representative protein fusions, secGFP-PMEI1 and PGIP2-GFP, reached the cell wall by passing through ER and Golgi stacks but using distinct mechanisms. secGFP-PMEI1 was linked to a glycosylphosphatidylinositol (GPI) anchor and stably accumulated in the cell wall, regulating the activity of the endogenous pectin methylesterases (PMEs) that are constitutively present in this compartment. A mannosamine-induced non-GPI-anchored form of PMEI1 as well as a form (PMEI1-GFP) that was unable to bind membranes failed to reach the cell wall, and accumulated in the Golgi stacks. In contrast, PGIP2-GFP moved as a soluble cargo protein along the secretory pathway, but was not stably retained in the cell wall, due to internalization to an endosomal compartment and eventually the vacuole. Stable localization of PGIP2 in the wall was observed only in the presence of a specific fungal endopolygalacturonase ligand in the cell wall. Both secGFP-PMEI1 and PGIP2-GFP sorting were distinguishable from that of a secreted GFP, suggesting that rigorous and more complex controls than the simple mechanism of bulk flow are the basis of cell-wall growth and differentiation.
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, 73100 Lecce, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: De Caroli
authors.forename: Marcello S
authors.initials: MS
authors.lastname: Lenucci
authors.forename: Gian-Pietro
authors.initials: GP
authors.lastname: Di Sansebastiano
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Dalessandro
authors.forename: Giulia
authors.initials: G
authors.lastname: De Lorenzo
authors.forename: Gabriella
authors.initials: G
authors.lastname: Piro
mesh_terms: D015415:Biomarkers; D002462:Cell Membrane / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D005656:Fungal Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D058851:GPI-Linked Proteins / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D006595:Hexosamines / Q000009:adverse effects / Q000378:metabolism; D009154:Mutation; D010940:Plant Proteins / Q000378:metabolism* / Q000494:pharmacology; D030821:Plants, Genetically Modified; D011096:Polygalacturonase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011485:Protein Binding; D055550:Protein Stability; D021381:Protein Transport; D011523:Protoplasts / Q000378:metabolism; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism / Q000494:pharmacology; D014026:Nicotiana / Q000166:cytology / Q000235:genetics / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D005656:Fungal Proteins; D058851:GPI-Linked Proteins; D006595:Hexosamines; C081479:PGIP protein, plant; D010940:Plant Proteins; D050765:Qa-SNARE Proteins; D011993:Recombinant Fusion Proteins; C008322:mannosamine; D011096:Polygalacturonase