The sperm cell-surface protein GEX3 coordinates with GEX2 and DMP8/9 to mediate sperm–egg adhesion and fusion in Arabidopsis

Double fertilization in angiosperms, which involves the simultaneous fusion of two sperm cells with the egg cell and central cell, requires precise gamete recognition and membrane fusion mediated by sperm cell-surface proteins. However, the molecular regulation of these interactions remains incompletely understood. Here, we identify GEX3, a sperm-expressed transmembrane protein with an extracellular β-propeller domain, as a critical mediator of gamete adhesion and fusion. Loss of GEX3 disrupts fertilization by impairing sperm attachment to and fusion with female gametes. GEX3 physically and genetically interacts with GEX2 and DMP8/9 to promote egg-cell-triggered trafficking of the fusogen HAP2/GCS1 to the sperm plasma membrane. Our findings establish GEX3 as an important component of the sperm cell-surface machinery that coordinates membrane adhesion and fusion during double fertilization in flowering plants.