title: Identification of major proteins in maize egg cells.
abstract: In most flowering plants, the female gametophyte develops in an ovule deeply embedded in the ovary. Through double fertilization, the egg cell fuses with the sperm cell, resulting in a zygote, which develops into the embryo. In the present study, we analyzed egg cell lysates by polyacrylamide gel electrophoresis and subsequent mass spectrometry-based proteomics technology, and identified major protein components expressed in the egg cell. The identified proteins included three cytosolic enzymes of the glycolytic pathway, glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase and triosephosphate isomerase, two mitochondrial proteins, the ATP synthase beta-subunit and an adenine nucleotide transporter, and annexin p35. In addition, expression levels of these proteins in the egg cell were compared with those in the early embryo, the central cell and the suspension cell. Annexin p35 was highly expressed only in the egg cell, and glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase and the adenine nucleotide transporter were expressed at higher levels in egg cells than in central and cultured cells. These results indicate that annexin p35 in the egg cell and zygote is involved in the exocytosis of cell wall materials, which is induced by a fertilization-triggered increase in cytosolic Ca2+ levels, and that the egg cell is rich in an enzyme subset for the energy metabolism.
authors.affiliation: Department of Biological Sciences, Tokyo Metropolitan University, Minami-osawa 1-1, Hachioji, Tokyo, 192-0397 Japan. okamoto-takashi@c.metro-u.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Okamoto
authors.forename: Kanako
authors.initials: K
authors.lastname: Higuchi
authors.forename: Takashi
authors.initials: T
authors.lastname: Shinkawa
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Isobe
authors.forename: Horst
authors.initials: H
authors.lastname: Lörz
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Koshiba
authors.forename: Erhard
authors.initials: E
authors.lastname: Kranz
mesh_terms: D033741:Adenine Nucleotide Translocator 1 / Q000378:metabolism; D017302:Annexins / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002473:Cell Wall / Q000378:metabolism; D025222:Chloroplast Proton-Translocating ATPases / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004734:Energy Metabolism / Q000235:genetics; D005089:Exocytosis / Q000502:physiology; D024602:Glyceraldehyde-3-Phosphate Dehydrogenase (NADP+)(Phosphorylating) / Q000032:analysis / Q000378:metabolism; D005988:Glyceric Acids / Q000378:metabolism; D009865:Oocytes / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism*; D010770:Phosphotransferases / Q000032:analysis / Q000235:genetics; D010940:Plant Proteins / Q000032:analysis* / Q000378:metabolism; D040901:Proteomics / Q000379:methods; D012639:Seeds / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism*; D014305:Triose-Phosphate Isomerase / Q000378:metabolism; D003313:Zea mays / Q000166:cytology / Q000196:embryology / Q000378:metabolism*
chemical_list: D033741:Adenine Nucleotide Translocator 1; D017302:Annexins; D005988:Glyceric Acids; D010940:Plant Proteins; C005156:3-phosphoglycerate; D024602:Glyceraldehyde-3-Phosphate Dehydrogenase (NADP+)(Phosphorylating); D010770:Phosphotransferases; D025222:Chloroplast Proton-Translocating ATPases; D014305:Triose-Phosphate Isomerase