The pollen-specific gene Ntp303 encodes a 69-kDa glycoprotein associated with the vegetative membranes and the cell wall

Abstract

The pollen-specific gene Ntp303 belongs to the class of late pollen specific genes. It is first transcribed directly after pollen mitosis. Biochemical properties, appearance and precise location of the NTP303 protein during pollen development and pollen tube growth were studied by amino-acid micro-sequencing, protein gel blotting and immuno-localization. Antisera were raised against recombinant proteins, encoded by sequences of the pollen-specific Ntp303 gene. The antibodies specifically recognized a 69-kDa glycoprotein. Electron-microscopic immuno-localization of the protein revealed the presence of high concentrations of the NTP303 protein at the vegetative plasma membranes that surround the vegetative cell, the generative cell and the sperm cells of pollen and pollen tubes. The generative plasma membranes of the generative cell and the sperm cells were negative. NTP303 protein was also present in the cell walls and in callose plugs. With this method it was shown that the NTP303 protein was already present in mid-bicellular pollen, after the first, asymmetrical pollen mitosis. Possible functions for the NTP303 protein are discussed in relation to its properties and its association with the vegetative plasma membranes.

The ArabidopsisSKU5Gene Encodes an Extracellular Glycosyl Phosphatidylinositol–Anchored Glycoprotein Involved in Directional Root Growth[W]

“…The functions of these proteins are not known. NTP303, which shares 45% amino acid sequence identity with SKU5, was found to localize to the vegetative plasma membranes of pollen and to the cell walls and callose plugs of pollen tubes (Wittink et al, 2000). Tucker and Zhang (1996) reported that a tomato protein (PE3) that shares 50% amino acid sequence identity with SKU5 possessed pectin esterase activity, but subsequently, they were unable to confirm these results (G. Tucker and J. Zhang, personal communication).…”

“…Two SKU5-like proteins from tobacco and tomato (NTP303, which has 45% amino acid sequence identity with SKU5 [Wittink et al, 2000], and PE3, which has 50% identity [Tucker and Zhang, 1996]) have been purified previously and their N-terminal peptides sequenced. Both proteins lacked the predicted N-terminal hydrophobic domain, presumably because they were removed proteolytically.…”

Control of Male Gametophyte Development

“…They identified 20 such cDNAs; almost all were pollen specific, and many corresponded to lowabundance mRNAs. Despite such intricate cDNA selection schemes (Guyon et al, 2000; see also Mu et al, 1994), it has been difficult to identify genes that are transcribed only upon pollen germination or to identify mRNAs that are essentially not translated until after pollen germination (Wittink et al, 2000).…”

Gametophyte interaction and sexual reproduction: how plants make a zygote

“…Besides callose and cellulose, several hidroxyproline-rich glycoproteins (HRGPs) have been reported to be present in the secondary tube wall (Cassab, 1998;Showalter, 2001). Examples of these glycoproteins are the pollen-specific extensin-like protein (Pex1) of maize and the pollen-specific glycoprotein NTP303 of tobacco (Weterings et al, 1992;Rubinstein et al, 1995;Wittink et al, 2000). The presence of a conserved leucine-rich repeat (LRR) in the known Pex proteins strongly suggests that this motif is involved in the binding of a specific ligand during pollen tube growth (Stratford et al, 2001).…”