Required for male fertility (PubMed:17079265, PubMed:20333238). Plays a role in pollen tube guidance and successful gamete attachment (PubMed:17079265). Essential for the fusion of gametes during double fertilization, where one male gamete fuses with the egg to produce a zygote, and another male gamete fuses with the central cell to produce the endosperm (PubMed:17079265, PubMed:20333238, PubMed:21209845). Mediates the fusion of cell membranes (PubMed:28137780). Not required for pollen tube outgrowth (PubMed:17079265, PubMed:20333238). Predominantly localized in a perinuclear ring (PubMed:17079265). Redistribution to the cell membrane is mediated by EC1 peptides after their secretion upon sperm arrival (PubMed:23180860). Expressed only in mature pollen, in the two sperm cells. Expressed during pollen development and tube growth. The N-terminal domain (62-541)and the C-terminal domain (583-705) are both required for functional gamete fusion. A positive charge, and not a conserved primary amino acid sequence, is required for a functional C-terminal domain. The N-terminal domain may be involved in interactions with another membrane-bound protein on female gametes, while positively charged C-terminus may function through electrostatic interactions with the sperm plasma membrane. Defective in pollen tube guidance. Prevents gamete interaction and fertilization, resulting in male sterility. HAP2/GCS1 family members mediate membrane fusion between gametes in a broad range of eukaryotes, ranging from algae and higher plants to protozoans and cnidaria, suggesting they are derived from an ancestral gamete fusogen. They function similar to viral fusogens, by inserting part of their extracellular domain into the lipid bilayer of an adjoining cell. Belongs to the HAP2/GCS1 family. A wretched tale - Issue 146 of January 2013