title: Localization of Arabidopsis SYP125 syntaxin in the plasma membrane sub-apical and distal zones of growing pollen tubes.
abstract: Tip growth in pollen tubes occurs by continuous vesicle secretion and delivery of new wall material, but the exact sub-cellular location of endocytic and exocytic domains remains unclear. Here we studied the localization of the Arabidopsis thaliana pollen specific syntaxin SYP125 using GFP-fusion constructs expressed in Nicotiana tobaccum pollen tubes. In agreement with the predicted role for syntaxins, SYP125 was found to be associated with the plasma membrane and apical vesicles in growing cells. At the plasma membrane, SYP125 was asymmetrically localized with a higher labeling 20-35 μm behind the apex, a distribution which is distinct from SYP124, another pollen-specific syntaxin. Competition with a related dominant negative mutant affected the specific distribution of SYP125 but not tip growth. Co-expression of the phosphatidylinositol-4-monophosphate-5-kinase 4 (PIP5K4) or of the small GTPase Rab11 perturbed polarity and the normal distribution of GFP-SYP but did not inhibit the accumulation in vesicles or at the plasma membrane. Taken together, our results corroborates previous observations that in normal growing pollen tubes, the asymmetric distribution of syntaxins helps to define exocytic sub-domains but requires the involvement of additional signaling and functional mechanisms, namely phosphoinositides and small GTPases. The localization of syntaxins at different membrane domains likely depends on the interaction with specific partners not yet identified.
authors.affiliation: Universidade de Lisboa, Faculdade de Ciências de Lisboa, BioFIG, Lisbon, Portugal.
authors.forename: Reiaz
authors.initials: R
authors.lastname: Ul-Rehman
authors.forename: Pedro Angelo
authors.initials: PA
authors.lastname: Silva
authors.forename: Rui
authors.initials: R
authors.lastname: Malhó
mesh_terms: D029681:Arabidopsis Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D016764:Cell Polarity; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D005453:Fluorescence; D049452:Green Fluorescent Proteins / Q000378:metabolism; D030821:Plants, Genetically Modified; D053205:Pollen Tube / Q000166:cytology* / Q000254:growth & development*; D021381:Protein Transport; D050765:Qa-SNARE Proteins / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014026:Nicotiana / Q000166:cytology / Q000235:genetics / Q000254:growth & development*
chemical_list: D029681:Arabidopsis Proteins; D050765:Qa-SNARE Proteins; C568125:SYP125 protein, Arabidopsis; D049452:Green Fluorescent Proteins