GENERATIVE CELL SPECIFIC 1 is essential for angiosperm fertilization

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Abstract
The double fertilization process in angiosperms is based on the delivery of a pair of sperm cells by the pollen tube (the male gametophyte), which elongates towards an embryo sac (the female gametophyte) enclosing an egg and a central cell. Several studies have described the mechanisms of gametophyte interaction1, and also the fertilization process — from pollination to pollen tube acceptance2,3,4,5. However, the mechanisms of gamete interaction are not fully understood6,7. Cytological studies have shown that male gametes possess distinct cell-surface structures8,9 and genes specific to male gametes have been detected in cDNA libraries10,11,12,13,14. Thus, studies of isolated gametes may offer clues to understanding the sperm–egg interaction. In this study, we identified a novel protein, designated GCS1 (GENERATIVE CELL SPECIFIC 1), using generative cells isolated from Lilium longiflorum pollen. GCS1 possesses a carboxy-terminal transmembrane domain, and homologues are present in various species, including non-angiosperms. Immunological assays indicate that GCS1 is accumulated during late gametogenesis and is localized on the plasma membrane of generative cells. In addition, Arabidopsis thaliana GCS1 mutant gametes fail to fuse, resulting in male sterility and suggesting that GCS1 is a critical fertilization factor in angiosperms.