title: An extracellular transglutaminase is required for apple pollen tube growth.
abstract: An extracellular form of the calcium-dependent protein-cross-linking enzyme TGase (transglutaminase) was demonstrated to be involved in the apical growth of Malus domestica pollen tube. Apple pollen TGase and its substrates were co-localized within aggregates on the pollen tube surface, as determined by indirect immunofluorescence staining and the in situ cross-linking of fluorescently labelled substrates. TGase-specific inhibitors and an anti-TGase monoclonal antibody blocked pollen tube growth, whereas incorporation of a recombinant fluorescent mammalian TGase substrate (histidine-tagged green fluorescent protein: His6-Xpr-GFP) into the growing tube wall enhanced tube length and germination, consistent with a role of TGase as a modulator of cell wall building and strengthening. The secreted pollen TGase catalysed the cross-linking of both PAs (polyamines) into proteins (released by the pollen tube) and His6-Xpr-GFP into endogenous or exogenously added substrates. A similar distribution of TGase activity was observed in planta on pollen tubes germinating inside the style, consistent with a possible additional role for TGase in the interaction between the pollen tube and the style during fertilization.
authors.affiliation: Dipartimento di Biologia Evoluzionistica Sperimentale, Università degli Studi di Bologna, Via Irnerio 42, 40126 Bologna, Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Di Sandro
authors.forename: Stefano
authors.initials: S
authors.lastname: Del Duca
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Verderio
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Hargreaves
authors.forename: Alessandra
authors.initials: A
authors.lastname: Scarpellini
authors.forename: Giampiero
authors.initials: G
authors.lastname: Cai
authors.forename: Mauro
authors.initials: M
authors.lastname: Cresti
authors.forename: Claudia
authors.initials: C
authors.lastname: Faleri
authors.forename: Rosa Anna
authors.initials: RA
authors.lastname: Iorio
authors.forename: Shigehisa
authors.initials: S
authors.lastname: Hirose
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Furutani
authors.forename: Ian G C
authors.initials: IG
authors.lastname: Coutts
authors.forename: Martin
authors.initials: M
authors.lastname: Griffin
authors.forename: Philip L R
authors.initials: PL
authors.lastname: Bonner
authors.forename: Donatella
authors.initials: D
authors.lastname: Serafini-Fracassini
mesh_terms: D005110:Extracellular Space / Q000201:enzymology; D018525:Germination; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007150:Immunohistochemistry; D027845:Malus / Q000201:enzymology* / Q000254:growth & development; D008954:Models, Biological; D030821:Plants, Genetically Modified; D053205:Pollen Tube / Q000201:enzymology / Q000254:growth & development; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D011503:Transglutaminases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D011503:Transglutaminases