GEX3 interacts with GEX2 to function in gamete attachment and plasma membrane fusion in Arabidopsis

Dr. Sheng Zhong published a paper in Plant Communications.

In angiosperms, male-female gamete interaction leads to double fertilization, yet the molecular mechanisms governing gamete interaction remain poorly understood. Through EMS mutagenesis, we identified two Arabidopsis mutants defective in sperm–egg fusion, both harboring mutation site in GAMETE INTERACTION PROTEIN 1 (GIP1)/GAMETE EXPRESSED 3 (GEX3). GIP1/GEX3 encodes a sperm-specific plasma membrane protein and its loss leads to severe fertility defects due to impaired double fertilization. Using a gip1-cr1 cdka;1 double mutant that produces pollen with a single sperm-like cell, we demonstrated that GIP1/GEX3 is required for the preferential fertilization of the egg cell. Further analysis revealed that GIP1/GEX3 functions at two distinct stages: gamete attachment and subsequent plasma membrane fusion. Importantly, we show that GIP1/GEX3 physically interacts with the sperm membrane protein GEX2 to regulate these two critical steps. Our work thus uncovers a key regulatory module mediating gamete attachment and plasma membrane fusion, providing new mechanistic insight into the control of double fertilization in flowering plants.