An extracellular transglutaminase is required for apple pollen tube growth.
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.
Di Sandro
Alessia
A
Dipartimento di Biologia Evoluzionistica Sperimentale, Università degli Studi di Bologna, Via Irnerio 42, 40126 Bologna, Italy.
Del Duca
Stefano
S
Verderio
Elisabetta
E
Hargreaves
Alan J
AJ
Scarpellini
Alessandra
A
Cai
Giampiero
G
Cresti
Mauro
M
Faleri
Claudia
C
Iorio
Rosa Anna
RA
Hirose
Shigehisa
S
Furutani
Yutaka
Y
Coutts
Ian G C
IG
Griffin
Martin
M
Bonner
Philip L R
PL
Serafini-Fracassini
Donatella
D
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*
D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D011503:Transglutaminases