title: Gamete attachment requires GEX2 for successful fertilization in Arabidopsis.
abstract: Fertilization requires recognition, attachment, and membrane fusion between gametes. In metazoans, rapidly evolving surface proteins contribute to gamete recognition and adhesion. Flowering plants evolved a double fertilization process wherein two immotile sperm cells are delivered to female gametes by the pollen tube, guided by elaborate communications between male and female reproductive organs. Once released, the sperm cells contact female gametes directly prior to gamete fusion. It remains unclear whether active gamete recognition and attachment mechanisms are required for double fertilization. Here, we provide functional characterization of Arabidopsis GAMETE EXPRESSED 2 (GEX2), which encodes a sperm-expressed protein of unknown function. GEX2 is localized to the sperm membrane and contains extracellular immunoglobulin-like domains, similar to gamete interaction factors in algae and mammals. Using a new in vivo assay, we demonstrate that GEX2 is required for gamete attachment, in the absence of which double fertilization is compromised. Ka/Ks analyses indicate relatively rapid evolution of GEX2, like other proteins involved in male and female interactions. We conclude that surface proteins involved in gamete attachment and recognition exist in plants with immotile gametes, similar to algae and metazoans. This conservation broadens the repertoire of research for plant reproduction factors to mechanisms demonstrated in animals.
authors.affiliation: Initiative Research Program, Advanced Science Institute, RIKEN, Wako, Saitama 351-0198, Japan. Electronic address: moritoshi@aoni.waseda.jp.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Mori
authors.affiliation: Graduate School of Horticulture, Chiba University, Matsudo, Chiba 271-8510, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Igawa
authors.affiliation: Advanced Molecular Epidemiology Research Institute, Faculty of Medicine, Yamagata University, Yamagata 990-9585, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Tamiya
authors.affiliation: Center for Frontier Research, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Chiyoda, Tokyo 102-0076, Japan.
authors.forename: Shin-Ya
authors.initials: SY
authors.lastname: Miyagishima
authors.affiliation: Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604, Singapore; Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore. Electronic address: fred@tll.org.sg.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Berger
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D005306:Fertilization; D018506:Gene Expression Regulation, Plant; D005854:Germ Cells / Q000378:metabolism*; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D012639:Seeds / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C506408:GEX2 protein, Arabidopsis; D008565:Membrane Proteins